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Neurological and other complications of Regional Anaesthesia

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Neurological and other complications of Regional Anaesthesia

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Other misc complications include:
•Overwhelming sympathetic block: treat with vasopressors (and fluid)

•Vaso-vagal reactions, profound bradycardia, even asystole: beware spinals in the sitting, awake, anxious, dehydrated young fit male
•Hemi diaphragmatic paresis: occurs in Interscalene BP blocks (100%); Supraclavicular (50%)

•Pneumothorax: eg Brachial plexus*; paravertebral

•Failure / not meeting patient expectations

•Bladder dysfunction: spinals for hip/knees convey 5% catherisation rate

•Delayed diagnosis of compartment syndrome: recent AA standards on prevention and treatment

•Falls / failed mobilisation due to unintentionally long lasting blocks

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Curriculum: Explains clearly to patients the risks and benefits of regional anaesthesia

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Curriculum: Explains clearly to patients the risks and benefits of regional anaesthesia

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As stated before, go with the RCOA patient information leaflets

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“Awake or asleep” to prevent neural damage .....

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“Awake or asleep” to prevent neural damage .....

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•Little convincing evidence either way so controversial

•Awake might be easier to defend

•Shared decision making recommended

•If done awake, record response and initial function*

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Curriculum item: Assesses when a regional technique is not appropriate; Describes the indications and contraindications to regional anaesthetic techniques

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Curriculum item: Assesses when a regional technique is not appropriate; Describes the indications and contraindications to regional anaesthetic techniques

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Two slides summarising the current evidence base

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🤔 When should we use a nerve stimulator?

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🤔 When should we use a nerve stimulator?

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Curriculum item: Performs simple peripheral nerve blocks with ultrasound

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Curriculum item: Performs simple peripheral nerve blocks with ultrasound

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Nerve block definition:

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Nerve block definition - Regional anesthesia Crash course with Dr. Hadzic

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Curriculum: Manages inadequate block in the awake patient and in recovery if used as an adjunct to general anaesthesia

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Curriculum: Manages inadequate block in the awake patient and in recovery if used as an adjunct to general anaesthesia

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AWAC = Anaesthesia without airway control. Something to be wary of ..
Checking and documentation: some medico-legal advice to formally check before starting surgery
Ketamine: small boluses or infusion (eg 2 ml of 50mg/ml Ketamine added to 50 ml 1% Propofol; roughly 2 mg/ml of Ketamine and run as Propofol TCI sedation)

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Curriculum: Performs ultrasound-guided femoral or fascia iliaca blocks independently

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Curriculum: Performs ultrasound-guided femoral or fascia iliaca blocks independently

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Good first video ..

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Ultrasound-Guided Femoral Nerve Block Video - NYSORA

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This video describes in a practical way the steps to perform a femoral nerve block. Includes essential anatomy, reverse ultrasound images and working tips.

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Everything you need for the exam should be in here ...

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Everything you need for the exam should be in here ...

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All the 2021 curriculum items relevant to Regional Anaesthesia are listed in the columns to the right

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For each item, I have suggested a resource

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For each item, I have suggested a resource

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They are all good, or at least reasonable, in my opinion but no doubt there will be even better ones available, if not now then in the future. If you find one that is better then please do let me know.

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Clearly there are a lot of resources. This is because the attempt here is to be comprehensive. Although you might prefer to access each one, most of you will not need to cover them all, so do start with those you think will be most useful for you

There is no expectation that you will have looked at any of these before the session, but if you have time to do so then you might find it useful, again starting with the areas you are least confident on

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Curriculum item: Performs ultrasound-guided brachial plexus blocks (Axillary)

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Curriculum item: Performs ultrasound-guided brachial plexus blocks (Axillary)

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Catherine Vandepitte, Ana M. Lopez, and Hassanin Jalil

FACTS

Indications: elbow, forearm, and hand surgery

Transducer position: short axis to arm, just distal to the pectoralis major insertion

Goal: local anesthetic spread around axillary artery

Local anesthetic: 15-20 mL

GENERAL CONSIDERATIONS

The axillary brachial plexus block is relatively simple to perform and may be associated with a lower risk of complications compared with interscalene (eg, spinal cord or vertebral artery puncture) and supraclavicular brachial plexus blocks (eg, pneumothorax). In clinical scenarios in which access to the upper parts of the brachial plexus is difficult or impossible (eg, local infection, burns, indwelling venous catheters), the ability to anesthetize the plexus at a more distal level may be important. Although individual nerves can usually be identified this is not absolutely necessary because the deposition of local anesthetic around the axillary artery is sufficient for an effective block.

ULTRASOUND ANATOMY

The structures of interest are superficial (1-3 cm below the skin), and the axillary artery is readily identified within a centimeter of the skin surface on the medial aspect of the proximal arm ( Figure 1-A). The artery is accompanied by one or more axillary veins, often located medially to the artery. Importantly, excessive pressure with the transducer during imaging may compress the veins, rendering veins invisible and prone to puncture with the needle. Surrounding the axillary artery, three of the four principal branches of the brachial plexus can be seen: the median (superficial and lateral to the artery), the ulnar (superficial and medial to the artery), and the radial (posterior and lateral or medial to the artery) nerves. The nerves appear as round hyperechoic structures ( Figure 1-B). Several authors have reported the anatomical variations of the nerves relative to the axillary artery; Figure 2 illustrates the most common patterns.

Three muscles surround the neurovascular bundle: the biceps (anterior and superficial), the wedge-shaped coracobrachialis (anterior and deep), and the conjoined tendon of the teres major and latissimus dorsi (medial and posterior). The musculocutaneous nerve is located in the fascial layers between the biceps and coracobrachialis muscles, though its location is variable and can be seen within either muscle. It is usually seen as a hypoechoic flattened oval structure with a bright hyperechoic rim. Moving the transducer proximally and distally along the long axis of the arm, the musculocutaneous nerve appears to move toward or away from the neurovascular bundle in the fascial plane between the two muscles. Variations are determined by the position of the musculocutaneous nerve relative to the median nerve and by the position of the ulnar nerve relative to the axillary vein. For additional information see Functional Regional Anesthesia Anatomy.
From the Compendium of Regional Anesthesia: Cognitive priming for an axillary brachial plexus block.
DISTRIBUTION OF ANESTHESIA

The axillary brachial plexus block (including the musculocutaneous nerve) results in anesthesia of the upper limb from the mid-arm down to and including the hand. Importantly, the block lends its name from the approach and not from the axillary nerve, which itself is not blocked because it departs from the posterior cord more proximally in the axilla. Therefore, the skin over the deltoid muscle is not anesthetized ( Figure 3). With nerve stimulator and landmark-based techniques, the block of the musculocutaneous nerve is often unreliable. However, the musculocutaneous nerve is readily visualized and reliably anesthetized by a separate injection using ultrasound guidance. When required, the medial skin of the upper arm (intercostobrachial nerve, T2) can be blocked by an additional subcutaneous injection just distal to the axilla.

EQUIPMENT

Ultrasound machine with linear transducer (8-14 MHz), sterile sleeve, and gel

Standard nerve block tray

Syringes with local anesthetic (20 mL)

5-cm, 22-gauge, short-bevel, insulated stimulating needle

Peripheral nerve stimulator

Opening injection pressure monitoring system

Sterile gloves

Learn more about Equipment for Peripheral Nerve Blocks

LANDMARKS AND PATIENT POSITIONING

An abduction of the arm to 90 degrees is necessary to allow for transducer placement and needle advancement, ( Figure 4). Care should be taken not to over-abduct the arm, as this may cause patient discomfort as well as traction on the brachial plexus, making it theoretically more vulnerable to injury by needle or injection. The pectoralis major muscle is palpated as it inserts onto the humerus, and the transducer is placed on the skin immediately distal to that point, perpendicular to the axis of the arm. The starting point should have the transducer overlying both the biceps and triceps muscles (ie, on the medial aspect of the arm). Sliding the transducer proximally will bring the axillary artery, the conjoint tendon and the terminal branches of the brachial plexus into view, if not readily apparent.

GOAL

The goal is to deposit local anesthetic around the axillary artery. Typically, two or three injections are required. In addition, an aliquot of local anesthetic should be injected around the musculocutaneous nerve.

TECHNIQUE

The skin is disinfected and the transducer is positioned in the short axis orientation to identify the axillary artery about 1-3 cm from the skin surface. Once the artery is identified, an attempt is made to identify the hyperechoic median, ulnar, and radial nerves ( Figure 5). However, these may not always be well visualized with ultrasound. Frequently present, an acoustic enhancement artifact deep to the artery is often misinterpreted as the radial nerve. Prescanning should also reveal the position of the musculocutaneous nerve, in the plane between the coracobrachialis and biceps muscles or within either of the muscles (a slight proximal-distal movement of the transducer is often required to bring this nerve into view) ( Figure 6).

The needle is inserted in-plane from the anterior aspect and directed toward the posterior aspect of the axillary artery (Figure 7). Because nerves and vessels are positioned closely together in the neurovascular bundle by adjacent musculature, advancement of the needle may require careful hydrodissection with a small amount of local anesthetic or other injectates. This technique involves the injection of 0.5-2 mL, indicating the plane in which the needle tip is located. The needle is then carefully advanced stepwise few millimeters at a time. The use of nerve stimulation is recommended to decrease the risk of needle-nerve injury during needle advancement. Local anesthetic should be deposited posterior to the artery first, to avoid displacing the structures of interest deeper and obscuring the nerves, which may occur if injections for the median or ulnar nerves are carried out first.

The posteriorly located radial nerve is often visualized more clearly once surrounded by local anesthetic. Once 5-7 mL has been administered, the needle is withdrawn almost to the level of the skin, redirected toward the median and ulnar nerves, and a further 7-10 mL is injected in these areas to complete the spread around the nerves. The described sequence of injection is demonstrated in Figure 8.

An alternative, perivascular approach is to simply inject local anesthetic deep to the artery, at the 6 o'clock position, instead of targeting the three nerves individually. This technique may shorten the duration of the block procedure, but also delay onset time, resulting in no difference in total time from skin puncture to the onset of the surgical block. The last step in the procedure, the needle is withdrawn and redirected toward the musculocutaneous nerve. Once adjacent to the nerve (stimulation will result in elbow flexion), 5-7 mL of local anesthetic is deposited. Occasionally, the musculocutaneous nerve will lie in close proximity to the median nerve, rendering a separate injection unnecessary. In an adult patient, 20 mL of local anesthetic is usually adequate for successful block, although successful blocks have been described with smaller volumes. Adequate spread within the axillary brachial plexus sheath is necessary for success but infrequently seen with a single injection. This is accomplished with two to three redirections and injections of 5-7 mL are usually necessary for a reliable block, as well as a separate injection to block the musculocutaneous nerve.

TIPS

Frequent aspiration and slow administration of local anesthetic are critical for decreasing the risk of intravascular injection. Cases of systemic toxicity have been reported after apparently straightforward ultrasound-guided axillary brachial plexus blocks.

If no spread is seen on the ultrasound image despite local anesthetic injection, the tip of the needle may be located in a vein. If this occurs, injection should be halted immediately and the needle is withdrawn slightly. Pressure on the transducer should be eased before reassessing the ultrasound image for the presence of vascular structures.

Anatomic variations in the position of the musculocutaneous nerve have been described. In 16% of cases, the musculocutaneous nerve splits off of the median nerve distally to the axilla. In this case, a separate injection is not needed to block the musculocutaneous nerve as it will be blocked by the local anesthetic injected around the median nerve.

CONTINUOUS ULTRASOUND-GUIDED AXILLARY BLOCK

The indwelling axillary catheter is a useful technique for analgesia and sympathetic block. The goal of the continuous axillary block is to place the catheter within the vicinity of the branches of the brachial plexus (ie, within the "sheath" of the brachial plexus). The procedure is similar to that previously described in Ultrasound-Guided Interscalene Brachial Plexus. The needle is typically inserted in-plane from the anterior to posterior direction, just as in the single-injection technique). After an initial injection of local anesthetic to confirm proper needle tip position posterior to the axillary artery, the catheter is inserted 3-5 cm beyond the needle tip. Injection is then repeated through the catheter to document adequate spread of local anesthetic, wrapping the axillary artery. Alternatively, the axillary artery can be visualized in the longitudinal view with the catheter being inserted in the longitudinal plane alongside the axillary artery. The longitudinal approach requires a significantly greater degree of ultrasonographic skill; no data suggesting that one approach is more effective than the other currently exist.

Continue reading: Axillary Brachial Plexus Block - Landmarks and Nerve Stimulator Technique

Supplementary video related to this block can be found at Ultrasound-Guided Axillary Brachial Plexus Block Video
This text was a sample of content from the Compendium of Regional Anesthesia on the NYSORA LMS.
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Additional Reading

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Strub B, Sonderegger J, Von Campe A, Grünert J, Osterwalder JJ: What benefits does ultrasound-guided axillary block for brachial plexus anaesthesia offer over the conventional blind approach in hand surgery? J Hand Surg Eur Vol 2011;36:778-786.

Sultan SF, Iohom G, Saunders J, Shorten G: A clinical assessment tool for ultrasound-guided axillary brachial plexus block. Acta Anaesthesiol Scand 2012;56:616-623.

Takeda A, Ferraro LH, Rezende AH, Sadatsune EJ, Falcão LF, Tardelli MA: Minimum effective concentration of bupivacaine for axillary brachial plexus block guided by ultrasound. Braz J Anesthesiol 2015;65:163-169.

Tedore TR, YaDeau JT, Maalouf DB, et al: Comparison of the transarterial axillary block and the ultrasound-guided infraclavicular block for upper extremity surgery: a prospective randomized trial. Reg Anesth Pain Med 2009;34:361-365.

Tran DQ, Clemente A, Tran DQ, Finlayson RJ: A comparison between ultrasound-guided infraclavicular block using the "double bubble" sign and neurostimulation-guided axillary block. Anesth Analg 2008;107: 1075-1078.

Tran DQ, Pham K, Dugani S, Finlayson RJ: A prospective, randomized comparison between double-, triple-, and quadruple-injection ultrasound-guided axillary brachial plexus block. Reg Anesth Pain Med 2012;37: 248-253.

Tran DQ, Russo G, Muñoz L, Zaouter C, Finlayson RJ: A prospective, randomized comparison between ultrasound-guided supraclavicular, infraclavicular, and axillary brachial plexus blocks. Reg Anesth Pain Med 2009;34:366-371.

Veneziano GC, Rao VK, Orebaugh SL: Recognition of local anesthetic maldistribution in axillary brachial plexus block guided by ultrasound and nerve stimulation. J Clin Anesth 2012;24:141-144.

Wong DM, Gledhill S, Thomas R, Barrington MJ: Sonographic location of the radial nerve confirmed by nerve stimulation during axillary brachial plexus block. Reg Anesth Pain Med 2009;34:503-507.

Wong MH, George A, Varma M: Ultrasound-guided perivascular axillary brachial plexus block: not so simple. Reg Anesth Pain Med 2013;38:167.

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Zetlaoui PJ, Labbe JP, Benhamou D: Ultrasound guidance for axillary plexus block does not prevent intravascular injection. Anesthesiology 2008;108:761.

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Ultrasound-Guided Axillary Brachial Plexus Block - NYSORA

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Catherine Vandepitte, Ana M. Lopez, and Hassanin Jalil Indications: elbow, forearm, and hand surgery Transducer position: short axis to arm, just distal to the pectoralis major insertion Goal: local anesthetic spread around axillary artery Local anesthetic: 15-20 mL The axillary brachial plexus block is relatively simple to perform and may be associated with a lower risk of complications compared with interscalene (eg, spinal cord or vertebral artery puncture) and supraclavicular brachial plexus blocks (eg, pneumothorax).

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Curriculum item: Performs ultrasound-guided brachial plexus blocks (ISBP)

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Curriculum item: Performs ultrasound-guided brachial plexus blocks (ISBP)

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Philippe E. Gautier, Catherine Vandepitte, and Jeff Gadsden

FACTS

Indications: Shoulder and upper arm surgery, surgery of the clavicle (combined with cervical plexus nerve block)

Transducer position: Transverse on the neck, 3-4 cm superior to the clavicle, over the external jugular vein

Goal: Local anesthetic spread around superior and middle trunks of brachial plexus, between the anterior and middle scalene muscles

Local anesthetic: 7-15 mL

GENERAL CONSIDERATIONS

US guidance allows for visualization of the spread of the local anesthetic and additional injections around the brachial plexus if needed to ensure an adequate spread of local anesthetic, improving nerve block success. The ability to visualize local anesthetic spread and to inject multiple aliquots also allows for a reduction in the volume of local anesthetic required to accomplish the nerve block.

ULTRASOUND ANATOMY

The brachial plexus at the interscalene level is seen lateral to the carotid artery and internal jugular vein, between the anterior and middle scalene muscles ( Figures 1 and 2).

The prevertebral fascia, superficial cervical plexus, and sternocleidomastoid muscle are seen superficial to the plexus. The transducer is moved in the proximal-distal direction until two or more of the brachial plexus elements are seen in the space between the scalene muscles. Depending on the depth of field selected and the level at which scanning is performed, the first rib and/or the apex of the lung may be seen. The brachial plexus is typically visualized at a depth of 1-3 cm.
From the Compendium of Regional Anesthesia: Cognitive priming for an interscalene brachial plexus block.
block DISTRIBUTION

The interscalene approach to brachial plexus block results in reliable anesthesia of the shoulder and upper arm ( Figure 3). The supraclavicular branches of the cervical plexus, supplying the skin over the acromion and clavicle, are also blocked due to the proximal and superficial spread of local anesthetic. The inferior trunk (C8-T1) is usually spared unless the injection occurs at a more distal level of the brachial plexus.

EQUIPMENT

The equipment needed for an interscalene brachial plexus nerve block includes the following:

Ultrasound machine with a linear transducer (8-14 MHz), sterile sleeve, and gel

Standard nerve block tray

A 20-mL syringe containing the local anesthetic

A 5-cm, 22-gauge, short-bevel, insulated stimulating needle

Peripheral nerve stimulator

Opening injection pressure monitoring system

Sterile gloves

Learn more about Equipment for Peripheral Nerve Blocks

LANDMARKS AND PATIENT POSITIONING

Any position that allows for comfortable placement of the ultrasound transducer and needle advancement is appropriate. The nerve block is typically performed with the patient in a supine, beach chair, or semi-lateral decubitus position, with the patient's head facing away from the side to be blocked ( Figure 4). The latter position may prove more ergonomic, especially during an in-plane approach from the lateral side, in which the needle enters the skin at the posterolateral aspect of the neck. A slight elevation of the head of the bed is often more comfortable for the patient and allows for better drainage and less prominence of the neck veins. The patient should be asked to reach for the ipsilateral knee in order to lower the shoulder and provide more space for the nerve block performance.

Knowledge of the underlying anatomy and the position of the brachial plexus is important to facilitate recognition of the ultrasound anatomy. Scanning usually begins just below the level of the cricoid cartilage and medial to the sternocleidomastoid muscle with the goal of identifying the carotid artery.

GOAL

The goal of this nerve block is to place the needle in the tissue space between the anterior and middle scalene muscles and inject local anesthetic until the spread around the brachial plexus is documented by ultrasound. The volume of the local anesthetic and the number of needle insertions are determined during the procedure and depending on the adequacy of the observed spread of local anesthetic.

TECHNIQUE

With the patient in the proper position, the skin is disinfected and the transducer is positioned in the transverse plane to identify the carotid artery ( Figure 5-A). Once the artery has been identified, the transducer is moved slightly laterally across the neck. The goal is to identify the anterior and middle scalene muscles and the elements of the brachial plexus that is located between them. It is recommended to use the color Doppler to identify vascular structures and avoid them. The needle is then inserted in-plane toward the brachial plexus, typically in a lateral-to-medial direction ( Figure 6), although a medial-to-lateral needle orientation can also be used if there is no room for the former. The needle should always be aimed in between the roots instead of directly at them in order to minimize the risk of accidental nerve injury. As the needle passes through the prevertebral fascia, a certain "pop" is often appreciated. When nerve stimulation is used (0.5 mA, 0.1 msec), the entrance of the needle in the interscalene groove is often associated with a motor response of the shoulder, arm, or forearm as another confirmation of proper needle placement. After careful aspiration to rule out intravascular needle placement, 1-2 mL of local anesthetic is injected to verify proper needle placement ( Figure 7-A). It is necessary to ensure that high resistance to injection is absent to decrease the risk of intrafascicular injection. Injection of several milliliters of local anesthetic often displaces the brachial plexus away from the needle. Additional advancement of the needle 1-2 mm toward the brachial plexus may be beneficial to ensure the proper spread of the local anesthetic ( Figure 7-B). When injection of the local anesthetic does not appear to result in a spread around the brachial plexus, additional needle repositioning and injections may be necessary.

NYSORA TIPS

* When visualization of the brachial plexus between the scalene muscles proves difficult, a "traceback" technique can be used. The transducer is lowered to the supraclavicular fossa. At this position, the brachial plexus is identified posterior and superficial to the subclavian artery ( Figure 5-B). From here, the brachial plexus is traced cranially to the desired level.

TIPS

* It is not necessary to elicit a motor response to nerve stimulation; however, when it occurs at intensities < 0.5 mA, the needle should be slightly withdrawn before injecting as it may be intraneural.
* The neck is a highly vascular area, and care must be exercised to avoid needle placement or injection into the vascular structures. Of particular importance is to avoid the vertebral artery and branches of the thyrocervical trunk: the inferior thyroid artery, suprascapular artery, and transverse cervical artery. Use color Doppler imaging at least once before inserting the needle to locate any vessel that might be in the path of the needle. Anatomical variations are common.
* Never inject against high resistance because such resistance may indicate needle-nerve contact or an intrafascicular injection. A high opening injection pressure (> 15 psi) is always present with needle-root contact. Thus, a seemingly extraneural injection may, in fact, be subepineural. An intraneural injection may spread proximally into the spinal canal.
* One useful maneuver to ensure injection into the proper compartment, after injecting 5-7 mL, is to trace the plexus down to the supraclavicular fossa (while keeping the needle steady to avoid injury). If the injection is performed inside the brachial plexus "sheath," the correct spread can be seen very clearly (see Figure 8-A). The probe can then be moved back until the needle is visualized in order to complete the injection. If the brachial plexus appears unchanged in the supraclavicular area, one must question whether the injection was done outside the correct compartment (see Figure 8-B).
* The lateral-to-medial insertion is often chosen to prevent injury to the phrenic nerve, which is typically located anteriorly to the anterior scalene, although one should be aware that the dorsal scapular nerve and the long thoracic nerve usually course through the middle scalene and could potentially be injured as well ( Figure 9).
* It is common for C6 and C7 to split proximally. It is prudent to avoid injecting between the nerves coming from a single root, as this may result in an intraneural injection. Instead, it is safer to inject between C5 and C6, superficial to C5, or deep to C6 ( Figure 10).
* Another relatively common anatomical variation involves the C5 root traveling through the anterior scalene for part of its course ( Figure 11). To nerve block this anatomical variant, the root should be traced distally until it enters the interscalene groove.
* Multiple injections are best avoided as they are not usually needed to successfully nerve block the brachial plexus and may carry higher risk of nerve injury.
* In an adult patient, 7-15 mL of local anesthetic is usually adequate for a successful and rapid onset of block. Smaller volumes of local anesthetic may also be effective;12,13 however, the rate of success of smaller volumes in everyday clinical practice may be inferior to those reported in meticulously conducted clinical trials.

PHRENIC NERVE block

Phrenic nerve block is common following ISB and may compromise respiratory function in patients with pre-existing pulmonary pathology. Four main strategies14 can be used in such patients to provide analgesia after shoulder surgery while avoiding phrenic block: (1) decreasing local anesthetic volume; (2) performing the ISB more caudad in the neck, around C7; (3) using a supraclavicular nerve block; and (4) using a suprascapular nerve block (possibly in association with an axillary nerve block). The phrenic nerve lies just superficially to the interscalene groove at the level of the cricoid cartilage and courses caudad and anteriorly and distally along the superficial aspect of the anterior scalene muscle along the neck. The use of a low volume of local anesthetic (eg, 5 mL) reduces the incidence of phrenic nerve block but may also reduce the duration of analgesia and possibly decreases the success rate. Higher volumes (10 mL) injected at the level of the cricoid would cause phrenic nerve block.

The function of the phrenic nerve can be assessed using ultrasound in M-mode during which a low-frequency curvilinear probe is positioned under the rib cage on the anterior axillary line to evaluate the hemidiaphragm motion ( Figure 12). Of note, some authors have recommended using a combination of suprascapular nerve and axillary nerve block to provide postoperative analgesia with minimal motor block distal to the shoulder with a lower risk of phrenic nerve block and other complications of interscalene nerve block. The targeted nerves are small and may prove difficult to find in obese patient. Moreover, these nerve blocks will not provide surgical anesthesia. Another issue that must be considered is persistent phrenic nerve palsy. There is little agreement as to what causes persistent phrenic nerve palsy, but it seems to be at least in part related to inflammation and nerve entrapment rather than direct needle trauma. A contribution of cervical spine disease has been suggested. Other factors may be involved, as most patients in published series have been male, overweight or obese, and middle-aged.

CONTINUOUS ULTRASOUND-GUIDED INTERSCALENE NERVE BLOCK

The goal of the continuous interscalene nerve block is to place the catheter in the vicinity of the elements of the brachial plexus between the scalene muscles. The procedure consists of: (1) needle placement; (2) LA injection to assure the proper needle tip position and "open up the space" for catheter (3) catheter advancement; (4) Injection through the catheter while monitoring on US to verify its therapeutic position and (5) securing the catheter. For the first two phases of the procedure, ultrasound can be used to ensure accuracy. The needle is typically inserted in plane from the lateral-to-medial direction and underneath the prevertebral fascia to enter the interscalene space ( Figure 13), although other needle orientations, such as out-of-plane or aiming caudad, may also be used. Proper needle placement can also be confirmed by obtaining a motor response of the deltoid muscle, arm, or forearm (0.5 mA, 0.1 msec), at which point 4-5 mL of local anesthetic can be injected. This small dose of local anesthetic serves to ensure adequate distribution of local anesthetic as well as to make the advancement of the catheter more comfortable to the patient. This first phase of the procedure does not significantly differ from the single-injection technique.

The second phase of the procedure involves maintaining the needle in the proper position and inserting the catheter 2-3 cm into the interscalene space within the vicinity of the brachial plexus ( Figure 14). Catheter insertion can be accomplished by a single operator or with an assistant. Proper catheter location can be confirmed either by visualizing the course of the catheter or by an injection of local anesthetic through the catheter. When this proves difficult, an alternative is to inject a small amount of air (1 mL) to confirm the catheter tip location. The catheter is secured either by taping to the skin with or without tunneling. Some clinicians prefer one over the other. However, the decision about which method to use can be based on patient age, duration of catheter therapy, and/or anatomy. Tunneling may be preferred in older patients with obesity or sagging skin over the neck or when a longer duration of catheter infusion is expected. Two main disadvantages of tunneling are the risk of catheter dislodgement during tunneling and the potential for scar formation. A number of catheter-securing devices are available to help stabilize the catheter. For additional information see Continuous Peripheral Nerve Blocks: Local Anesthetic Solutions and Infusion Strategies.

TIPS

* Both stimulating and nonstimulating catheters can be used. Because motor response on catheter stimulation may be absent even with ideal catheter placement, the use of stimulating catheters may lead to unnecessary needle and catheter manipulation to obtain evoked motor responses.
* The catheter-over-needle technique has recently been reintroduced as an alternative to accomplishing continuous interscalene block.

To learn more about the Interscalene Nerve Block, see Interscalene Brachial Plexus Block - Landmarks and Nerve Stimulator Technique.

Supplementary video related to this nerve block can be found at Ultrasound-Guided Interscalene Brachial Plexus Nerve Block and Reverse Anatomy Video.
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Additional Reading

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Vandepitte C, Gautier P, Xu D, Salviz EA, Hadzic A: Effective volume of
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Tsui BC, Lou L: Learning the "traceback" approach for interscalene nerve block. Anaesthesia 2014;69:83-85.

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Orebaugh SL, McFadden K, Skorupan H, Bigeleisen PE: Subepineurial injection in ultrasound-guided interscalene needle tip placement. Reg Anesth Pain Med 2010;35:450-454.

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Thomas SE, Winchester JB, Hickman G, DeBusk E: A confirmed case of injury to the long thoracic nerve following a posterior approach to an interscalene nerve block. Reg Anesth Pain Med 2013;38:370.

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Gautier P, Vandepitte C, Ramquet C, DeCoopman M, Xu D, Hadzic A: The minimum effective anesthetic volume of 0.75% ropivacaine in ultrasound-guided interscalene brachial plexus nerve block. Anesth Analg 2011;113:951-955.

Falcão LF, Perez MV, de Castro I, Yamashita AM, Tardelli MA, Amaral JL: Minimum effective volume of 0.5% bupivacaine with epinephrine in ultrasound-guided interscalene brachial plexus nerve block. Br J Anaesth 2013; 110:450-455.

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Single-Injection Ultrasound-Guided Interscalene Nerve Block

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Falcão LF, Perez MV, de Castro I, Yamashita AM, Tardelli MA, Amaral JL: Minimum effective volume of 0.5% bupivacaine with epinephrine in ultrasound-guided interscalene brachial plexus nerve block. Br J Anaesth 2013;110:450-455.

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Continuous Ultrasound-Guided Interscalene Nerve Block

Antonakakis JG, Sites BD, Shiffrin J: Ultrasound-guided posterior approach for the placement of a continuous interscalene catheter. Reg Anesth Pain Med 2009;34:64-68.
Fredrickson MJ, Ball CM, Dalgleish AJ: Analgesic effectiveness of a continuous versus single-injection interscalene nerve block for minor arthroscopic shoulder surgery. Reg Anesth Pain Med 2010;35:28-33.

Fredrickson MJ, Price DJ: Analgesic effectiveness of ropivacaine 0.2% vs 0.4% via an ultrasound-guided C5-6 root/superior trunk perineural ambulatory catheter. Br J Anaesth 2009;103:434-439.

Fredrickson MJ, Ball CM, Dalgleish AJ: Posterior versus anterolateral approach interscalene catheter placement: a prospective randomized trial. Reg Anesth Pain Med 2011;36:125-133.

Fredrickson MJ, Ball CM, Dalgleish AJ, Stewart AW, Short TG: A prospective randomized comparison of ultrasound and neurostimulation as needle end points for interscalene catheter placement. Anesth Analg 2009;108:1695-1700.

Mariano ER, Afra R, Loland VJ, et al: Continuous interscalene brachial plexus nerve block via an ultrasound-guided posterior approach: a randomized, triplemasked, placebo-controlled study. Anesth Analg 2009;108:1688-1694.

Mariano ER, Loland VJ, Ilfeld BM: Interscalene perineural catheter placement using an ultrasound-guided posterior approach. Reg Anesth Pain Med 2009;34:60-63.

Shin HJ, Ahn JH, Jung HI, et al: Feasibility of ultrasound-guided posterior approach for interscalene catheter placement during arthroscopic shoulder surgery. Korean J Anesthesiol 2011;61:475-481.

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Ultrasound-Guided Interscalene Brachial Plexus Nerve Block - NYSORA

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Philippe E. Gautier, Catherine Vandepitte, and Jeff Gadsden Indications: Shoulder and upper arm surgery, surgery of the clavicle (combined with cervical plexus nerve block) Transducer position: Transverse on the neck, 3-4 cm superior to the clavicle, over the external jugular vein Goal: Local anesthetic spread around superior and middle trunks of brachial plexus, between the anterior and middle scalene muscles Local anesthetic: 7-15 mL US guidance allows for visualization of the spread of the local anesthetic and additional injections around the brachial plexus if needed to ensure an adequate spread of local anesthetic, improving nerve block success.

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They are all good, or at least reasonable, in my opinion but no doubt there will be even better ones available, if not now then in the future.
If you find one that is better then please do let me know.
jonathan.chantler@ouh.nhs.uk

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If one doesn't work, please please let me know!

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If one doesn't work, please please let me know!

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jonathan.chantler@ouh.nhs.uk

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Curriculum: Performs ultrasound-guided fascial plane blocks for the chest or abdominal wall

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Curriculum: Performs ultrasound-guided fascial plane blocks for the chest or abdominal wall

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Good description of TAP blocks but no video
When you can do this block comfortably, practice it with your non dominant hand. Being an ambidextrous needler is an extremely useful skill in regional anaesthesia

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INTRODUCTION

Ultrasound-guided transversus abdominis plane (TAP) nerve block has become a common analgesic method after surgery involving the abdominal wall. Because TAP block is limited to somatic anesthesia of the abdominal wall and highly dependent on interfascial spread, various newer techniques have been proposed to enhance analgesia, either in addition to TAP nerve block or as a single modality. In particular, variants of quadratus lumborum nerve blocks (QLBs) have been proposed as more consistent methods with an aim to accomplish somatic as well as visceral analgesia of the abdomen. The present evidence, mainly case reports, suggests that different variants of QLB have different analgesic effects and mechanisms of action, although this has not been formally validated. In particular, transmuscular QLB and the so-called QLB2 may result in wider and longer sensory block compared to TAP nerve block (T4-L1 for QL nerve block vs. T6-T12 for the TAP nerve blocks) ( Figures 1 and 2). This chapter focuses on underlying principles for TAP block and the newer QLB techniques, with an understanding that the information about the latter is based on sparse evidence of limited quality as outcome-based studies are not yet available.

ANATOMY

The transversus abdominis plane is the fascial plane superficial to the transversus abdominis muscle, the innermost muscular layer of the anterolateral abdominal wall. The upper fibrous anterior part of the muscle lies posterior to the rectus abdominis muscle and reaches the xiphoid process. The posterior aponeuroses of the transversus abdominis and internal oblique muscles fuse and attach to the thoracolumbar fascia (TLF). In the TAP, the intercostal, subcostal, and L1 segmental nerves communicate to form the upper and lower TAP plexuses, which innervate the anterolateral abdominal wall, including the parietal peritoneum. Therefore, TAP block requires anesthesia of the upper (also known as the subcostal or intercostal) TAP plexus, as well as the lower TAP plexus, located in the vicinity of the deep circumflex iliac artery.

The subcostal approach to the TAP nerve block ideally anesthetizes the intercostal nerves T6-T9 between the rectus abdominis sheath and the transversus abdominis muscle. The lateral TAP nerve block in the midaxillary line between the thoracic cage and iliac crest as well as between the internal oblique and transversus abdominis muscles ideally should reach intercostal nerves T10- T11 and the subcostal nerve T12. Of note, the umbilicus is innervated by intercostal nerve T10. The L1 segmental nerves in the TAP are not covered by the lateral TAP nerve block and require an anterior TAP nerve block medial to the anterior superior iliac spine. A posterior approach to nerve block the TAP plexuses via the triangle of Petit has also been described. TAP nerve blocks provide somatic analgesia of the abdominal wall including the parietal peritoneum.

The quadratus lumborum (QL) muscle lies in the posterior abdominal wall dorsolateral to the psoas major muscle ( Figure 3). The QL muscle originates from the posterior part of the iliac crest and the iliolumbar ligament and inserts on the 12th rib and the transverse processes of vertebrae L1-L5. The QL muscle assists in lateral flexion of the lumbar spine.

The thoracolumbar fascia consists of anterior, middle, and posterior layers ( Figure 4). The posterior layer of the TLF forms an attachment to the strong membranous aponeurosis of the latissimus dorsi. The three layers of the TLF are continuous with the fused posterior aponeurosis of the internal oblique and transversus abdominis muscles.

The posterior layer of the TLF covers the superficial side of the erector spinae. In the lumbar region, the posterior layer extends from the spinous processes medially to the lateral margin of the erector spinae, where it fuses with the middle layer of the TLF and forms the so-called lateral raphe, which is a dense connective pillar that extends from the iliac crest to the 12th rib. The deepest lamina of the posterior layer is called the paraspinal retinacular sheath (PRS), which encapsulates the erector spinae muscles. The lateral interfascial triangle (LIFT)s is made by the lateral margin of the erector spinae muscle (base), the PRS with overlying posterior and middle layers of the TLF (sides), and the lateral raphe (apex). The middle layer of the TLF separates the QL and erector spinae muscles. The anterior layer of the TLF covers the anterior aspect of the QL muscle.

The transversalis fascia (TF) invests the parietal subperitoneal areolar tissue in the abdominal cavity. The outer surface of the TF lines the deep side of the transversus abdominis, QL, and psoas major muscles. The TF communicates with the endothoracic fascia posterior to the diaphragm where the TF is thickened as the medial and lateral arcuate ligaments, with possibility of the spread of injectate from the QL and psoas major muscle compartments to the thoracic paravertebral space ( Figure 5). Consequently, when the local anesthetic is injected into the fascial plane between these muscles in the lumbar region, it could spread cranially to the thoracic paravertebral space. The anterior layer of the TLF is fused with the TF. The iliohypogastric, ilioinguinal, and subcostal nerves that cross the QL muscle lie between this muscle and the TF. The four lumbar arteries on each side pass posterior to the psoas major and QL muscles, pierce the aponeurosis of the transversus abdominis muscle, and end up inside the TAP ( Figure 6).

The lower pole of the kidney lies anterior to the QL muscle and can reach the L4 level with deep inspiration. Therefore, this should be checked when performing QL nerve block as the kidney may be separated from the QL muscle only by perinephric fat, the posterior layer of renal fascia, the TF, and the anterior layer of the TLF. In summary, the kidney should always be visualized with QL nerve blocks to avoid kidney injury.

Learn more about Functional Regional Anesthesia Anatomy .

PATIENT POSITIONING AND EQUIPMENT SELECTION

For QL nerve blocks, the lateral decubitus position is preferred over the supine position as it provides better ergonomics and relevant sono-images of the neuraxial structures. A low-frequency (5- to 2-MHz) curved array ultrasound transducer in transverse axis is preferred to visualize the three lateral abdominal wall muscle layers and the QL muscle.

A 22-gauge, short-bevel needle is recommended for the single-injection technique, whereas an 18- to 21-gauge, 10-cm Tuohy needle with extension tubing is used for catheters. A peripheral nerve stimulator may be useful as a warning sign to prevent further needle advancement should the needle be mistakenly placed too deep and next to the lumbar plexus.

Learn more about Equipment for Peripheral Nerve Blocks

SCANNING AND NERVE BLOCK TECHNIQUES

Subcostal TAP Nerve Block

A linear transducer is placed alongside the lower margin of the rib cage as medial and cranial as possible for the subcostal TAP nerve block ( Figure 7a). The rectus abdominis muscle and its posterior rectus sheath are visualized along with the transversus abdominis muscle deep to the posterior rectus sheath.

The target is the fascial plane between the posterior rectus sheath and the transversus abdominis muscle. The needle is inserted above the rectus abdominis close to the midline and advanced from medial to lateral (alternatively, lateral to medial). The endpoint of injection is the spread of local anesthetic between the posterior rectus sheath and the anterior margin of the transversus abdominis muscle. Follow the link to Truncal and Cutaneous Nerve Blocks to learn about how to perform a rectus sheath nerve block.
From the Compendium of Regional Anesthesia: Cognitive priming for a subcostal TAP block.
Lateral TAP Nerve Block

For the lateral TAP nerve block, a linear transducer is placed in the axial plane on the midaxillary line between the subcostal margin and the iliac crest ( Figure 7b). The three layers of abdominal wall muscles are visualized: external and internal oblique as well as the transversus abdominis muscles. The target is the fascial plane between the internal oblique and the transversus abdominis muscles. The needle is inserted in the anterior axillary line, and the needle tip is advanced until it reaches the fascial plane between the internal oblique and transversus abdominis muscles approximately in the midaxillary line.
From the Compendium of Regional Anesthesia: Cognitive priming for a lateral TAP block.
Anterior TAP Nerve Block

A linear transducer is placed medial to the anterior superior iliac spine pointing toward the umbilicus with a caudad tilt for the anterior TAP nerve block ( Figure 7c). The three abdominal wall muscles are visualized (see discussion for the lateral TAP nerve block). The target is the same fascial plane at the level of the deep circumflex iliac artery. The needle is inserted medial to the anterior superior iliac spine. The needle tip is advanced until it is placed between the internal oblique and transversus abdominis muscles adjacent to the deep circumflex iliac artery.

From the Compendium of Regional Anesthesia: Cognitive priming for an anterior TAP block.

Posterior TAP Nerve Block

For the posterior TAP nerve block, the linear transducer is placed in the axial plane in the midaxillary line and moved posteriorly to the most posterior limit of the TAP between the internal oblique and transversus abdominis muscles ( Figure 7d). The target is the most posterior end of the TAP. The needle is inserted in the midaxillary line and advanced posteriorly until it reaches the posterior end of the TAP.

From the Compendium of Regional Anesthesia: Cognitive priming for a posterior TAP block.

Transmuscular QL Nerve Block

A curved array transducer for the transmuscular QL (TQL) nerve block is placed in the axial plane on the patient's flank just cranial to the iliac crest. The "shamrock sign" is visualized: The transverse process of vertebra L4 is the stem, whereas the erector spinae posteriorly, QL laterally, and psoas major anteriorly represent the three leaves of the trefoil. The target for injection is the fascial plane between the QL and psoas major muscles ( Figure 8). The needle is inserted using an in-plane technique from the posterior end of the transducer through the QL muscle ( Figure 9). The injectate should ideally spread from the injection site inside the fascial plane between the QL and psoas major muscles to the thoracic paravertebral space with a goal to accomplish segmental somatic and visceral analgesia from T4 to L1. The needle approaches of the QLBs are shown in Figure 10.

From the Compendium of Regional Anesthesia: Cognitive priming for a transmuscular QL block.

Type 1 QL Nerve Block

For the type 1 QL (QL1) nerve block, a linear transducer is placed in the axial plane in the midaxillary line and moved posteriorly until the posterior aponeurosis of the transversus abdominis muscle becomes visible as a strong specular reflector. The target is just deep to the aponeurosis but superficial to the TF at the lateral margin of the QL muscle. This is just lateral to the pararenal fat compartment. The QL1 nerve block is identical to the fascia transversalis plane nerve block. The needle is inserted from either the anterior or the posterior end of the transducer and advanced until the needle tip just penetrates the posterior aponeurosis of the transversus abdominis muscle. Local anesthetic is injected between the aponeurosis and the TF at the lateral margin of the QL muscle. The main effect is anesthesia of the lateral cutaneous branches of the iliohypogastric, ilioinguinal, and subcostal nerves (T12-L1).

From the Compendium of Regional Anesthesia: Cognitive priming for a QL1 block.

Type 2 QL Nerve Block

In the type 2 QL (QL2) nerve block, a linear transducer is placed in the axial plane in the midaxillary line and moved posteriorly as in the QL1 nerve block, until the LIFT, which encapsulates the paraspinal muscles, becomes visible between the latissimus dorsi and QL muscles.

The target is the deep layer (the PRS) of the middle layer of the TLF. The needle is inserted from the lateral end of the transducer. The needle tip is advanced until it is inside the middle layer of the TLF close to the LIFT. The local anesthetic is injected intrafascially and apparently provides analgesia equivalent to TQL nerve block but with faster onset. The mechanism of action is not well understood.

From the Compendium of Regional Anesthesia: Cognitive priming for a QL2 block.

DOSE AND VOLUME OF LOCAL ANESTHETIC

The TAP nerve blocks as well as the TQL nerve block and QLB1 are "tissue plane" nerve blocks and thus require large volumes of local anesthetic to obtain reliable block. For each of the TAP nerve blocks, a minimum volume of 15 mL is recommended. The local anesthetic dose needs to be considered for the size of the patient to ensure that a maximum safe dose is not exceeded, especially with dual bilateral TAP nerve blocks. The QL region is relatively vascular as the lumbar arteries lie posterior to the muscle. Absorption of the local anesthetic into the circulation depends primarily on the vascularity of the site of deposition. As the QL muscle is well vascularized and a large volume of local anesthetic is needed, the dose should be calculated accurately to prevent high peak plasma concentrations of local anesthetics in this type of nerve block.

For additional information follow the link to Clinical Pharmacology of Local Anesthetics

INDICATIONS

Most of the indications for QL nerve blocks are based on case reports and clinical anecdotal experience. There are no studies comparing the safety and efficacy of the three types of QL nerve block. Table 1 compares and summarizes the three types of QL nerve blocks.

TABLE 1. Main features of QL nerve blocks.

The various QL nerve blocks share the same indications as of the TAP nerve block. Some examples are as follows:

Large-bowel resection, open/laparoscopic appendectomy, and cholecystectomy

Cesarean section, total abdominal hysterectomy

Open prostatectomy, renal transplant surgery, nephrectomy, abdominoplasty, iliac crest bone graft

Ileostomy

Exploratory laparotomy, bilateral nerve blocks for midline incisions

NYSORA Tips

* Close to the transverse process, the QL muscle appears thin as it is visualized anterior-posterior; visualized from the flank, the muscle looks much broader.
* Use color Doppler before insertion of the needle to detect the lumbar arteries on the posterior aspect of the QL muscle or any other large vessels.
* The QL is identified medial to the transversus abdominis muscle. The latissimus dorsi and erector spinae muscles are superficial and more hyperechoic.

SUMMARY

The various TAP nerve blocks can provide somatic analgesia for abdominal wall surgery. QL nerve blocks can provide somatic as well as visceral analgesia of both the abdominal wall and the lower segments of the thoracic wall and therefore could be a useful analgesic modality for selected abdominal surgeries. QL nerve blocks may provide visceral analgesia due to their paravertebral and possibly epidural spread. The information in this chapter is based on the current knowledge, with an understanding that more specific recommendations are pending a stronger evidence base.

REFERENCES

Carney J, Finnerty O, Rauf J, et al: Studies on the spread of local anaesthetic solution in transversus abdominis plane nerve blocks. Anaesthesia 2011;66:1023-1030.

Elsharkawy H: Quadratus lumborum nerve block with paramedian sagittal oblique (subcostal) approach. Anaesthesia 2016;71:241-242.

Skandalakis JE, Colborn GL, Weidman TA, et al: Skandalakis Surgical Anatomy: The Embryologic and Anatomic Basis of Modern Surgery. Paschalidis Medical, 2004.

Willard FH, Vleeming A, Schuenke MD, Danneels L, Schleip R: The thoracolumbar fascia: Anatomy, function and clinical considerations. J Anat 2012;221:507-536.

Karmakar MK, Gin T, Ho AMH. Ipsilateral thoracolumbar anaesthesia and paravertebral spread after low thoracic paravertebral injection. Br J Anaesth 2001;87:312-316.

Børglum J, Jensen K, Moriggl B, et al: Ultrasound-guided transmuscular quadratus lumborum block. Br J Anesth 2013.

Hebbard PD: Transversalis fascia plane nerve block, a novel ultrasound-guided abdominal wall nerve block. Can J Anaesth 2009;56:618-620.

Mcdonnell JG, Curley G, Carney J, et al: The analgesic efficacy of transversus abdominis plane block after caesarean delivery: A randomized controlled trial. Anesth Analg 2008;106:186-191.

Carney JJ, Mcdonnell JG, Ochana A, Bhinder R, Laffey JG: The transversus abdominis plane nerve block provides effective postoperative analgesia in patients undergoing total abdominal hysterectomy. Anesth Analg 2008;107:2056-2060.

Kadam VR: Ultrasound-guided quadratus lumborum nerve block as a postoperative analgesic technique for laparotomy. J Anaesthesiol Clin Pharmacol 2013;29:550-552.

Visoiu M, Yakovleva N: Continuous postoperative analgesia via quadratus lumborum nerve block-An alternative to transversus abdominis plane nerve block. Paediatr Anaesth 2013;23:959-961.

Chakraborty A, Goswami J, Patro V: Ultrasound-guided continuous quadratus lumborum block for postoperative analgesia in a pediatric patient. A A Case Rep 2015;4:34-36.

Blanco R, Ansari T, Girgis E. Quadratus lumborum nerve block for postoperative pain after caesarean section: a randomised controlleds trial. Eur J Anaesthesiol. 2015;32:812-818.

Murouchi T, Iwasaki S, Yamakage M. Quadratus Lumborum Nerve Block: Analgesic Effects and Chronological Ropivacaine Concentrations After Laparoscopic Surgery. Reg Anesth Pain Med. 2016;41:146-150.

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Ultrasound-Guided Transversus Abdominis Plane and Quadratus Lumborum Nerve Blocks - NYSORA

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Ultrasound-guided transversus abdominis plane (TAP) and quadratus lumborum (QL) blocks have become a common analgesic method after surgery involving the abdominal wall. This section features the relevant anatomy, indications and technique descriptions to perform an ultrasound-guided TAP and QL plane blocks.

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Curriculum: Performs ultrasound-guided fascial plane blocks for the chest or abdominal wall

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Curriculum: Performs ultrasound-guided fascial plane blocks for the chest or abdominal wall

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Good full description of Erector Spinae Block with good graphics, Duke University

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Regional Anesthesiology and Acute Pain Medicine

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Curriculum: Practices measures to avoid wrong-site blocks

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Curriculum: Practices measures to avoid wrong-site blocks

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You should be comfortable with Prepare Stop Block local protocol, but for the exam check out the national information

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Curriculum: Practices measures to avoid wrong-site blocks

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Curriculum: Practices measures to avoid wrong-site blocks

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... and silent video

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Stop Before You Block Silent Training Video 2021

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Curriculum item: Involves the patient in planning and understanding potential complications of regional Anaesthesia

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Curriculum item: Involves the patient in planning and understanding potential complications of regional Anaesthesia

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Anaesthesia UK : Does regional anaesthesia improve outcome? (frca.co.uk)
https://www.frca.co.uk/article.aspx?articleid=100457

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Considerable research has been carried out over the last 30 years to investigate whether regional anaesthesia improves the quality of postoperative analgesia compared with systemic opioids, and whether it influences the outcome from surgery. Some benefits, such as the quality of postoperative analgesia, are easy to demonstrate but the intuitive belief that regional anaesthesia improves the outcome from surgery is more difficult to prove. Many studies have been inconclusive, with methodological weaknesses making it difficult to compare the results of different studies. Nevertheless, the weight of evidence suggests that regional anaesthesia has the potential to improve outcome from surgery.

It is difficult to isolate the analgesic benefits of regional anaesthesia (compared with systemic opioid-based analgesia) from the anaesthetic benefits (compared with general anaesthesia). Regional anaesthesia is most commonly used for surgery and early postoperative analgesia and most studies do not distinguish between these components. If an epidural injection or a major peripheral nerve block is used as the sole anaesthetic technique or is combined with a light general anaesthetic, the use of intra-operative opioids is unnecessary, or reduced, compared with general anaesthesia alone. The depth of general anaesthesia also differs because of the influence of the local anaesthetic technique. These differences influence the early indicators of recovery such as time to consciousness, the incidence of postoperative nausea and vomiting (PONV), return of full cognitive function, and time to first supplementary analgesic. Therefore, while it is possible to compare improvements in pain scores, other benefits may occur purely as a result of avoiding opioids (Figure 1). The quality of analgesia with regional anaesthesia is significantly better than that with systemic opioids. Central and peripheral nerve blocks can prevent or abolish the neural transmission of nociceptive signals; opioids can only modulate the transmission.
Figure 1

Regional anaesthesia has been used in all three perioperative phases to try to improve postoperative analgesia and influence surgical outcome.

Preoperative: regional anaesthesia has little influence on postoperative outcome though it improves the management of pre-existing pain.

Pre-emptive analgesia is the ability to reduce the severity and duration of postoperative pain by instituting effective analgesia before the onset of the pain. It has been demonstrated in animal models, but does not exist as a clinical entity, based on current understanding. Initial studies suggested that regional anaesthesia and systemic analgesia, administered before surgery, would improve postoperative pain, but this was not borne out in later studies.

Intraoperative: the morbidity and mortality associated with surgery and anaesthesia continue to decrease with advances in techniques. In the absence of avoidable errors, there is little difference in intraoperative risk between regional or general anaesthesia. Serious adverse outcomes from anaesthesia are extremely uncommon (0.1-1.5 deaths directly attributable to anaesthesia per 10,000 procedures). Preoperative fitness, patient age and the surgical procedure remain the most important risk factors for major non-fatal morbidity or mortality.

Postoperative phase: effective, continuous, postoperative analgesia is a worthwhile target for humanitarian reasons and for improving outcome. A large number of publications confirm the advantages of regional anaesthesia (both peripheral and central neural blockade) compared with systemic opioids (Figure 2). Regional anaesthesia may also prevent acute pain becoming chronic. A significant number of patients (about 50% for major breast surgery or thoracotomy) develop chronic pain following surgery owing to neuropathic nerve injury. A study of paravertebral blocks following thoractomy showed a significant reduction in post-thoracotomy pain syndrome. ¹
Figure 2 (click to open larger image)

In the last 30 years, numerous prospective, randomized, controlled trials have compared regional with general anaesthesia and their effects on outcome from surgery. In addition to improved analgesia, continuous lumbar epidural blocks for lower abdominal, pelvic and lower limb surgery significantly modify the surgical stress response, which is responsible for much postoperative morbidity (Figure 3).

The effects of thoracic epidural blockade on the stress response are not so marked because of less complete block of the lumbar autonomic nerve supply to the abdominal viscera and lower limbs. Intravenous patient-controlled analgesia (PCA) and other opioid-based analgesic techniques do not influence outcome from surgery despite satisfactory analgesia and a high degree of patient and staff satisfaction scores.

Regional anaesthesia, using local anaesthetic drugs alone or in combination with low doses of opioid drugs, has significant advantages over epidural or intravenous opioid-based analgesia. ²
Figure 3 (click to open larger image)

A number of clinical benefits can be predicted from the effects that regional anaesthesia has on the stress response. It is easier to investigate the influence of regional anaesthesia on a single variable of the stress response than to investigate its overall influence. Consequently, stronger data are available to show that regional anaesthesia has a beneficial effect on single systems during and after surgery (Figure 4) than for its overall effects on outcome. The influence of regional anaesthesia on cognitive function remains unclear.
Figure 4 (click to open larger image)

It is difficult to measure differences in outcome between regional anaesthesia and general anaesthesia for rare but important variables such as perioperative mortality. A very large sample size is required for prospective randomized trials to demonstrate any significant differences (too large even for multi-centre trials when studying these rare outcome events). Systematic Reviews are a useful method of analysing large numbers of smaller studies to evaluate any potential benefits of regional anaesthesia.

Several important meta-analyses of the effects of regional anaesthesia on outcome from surgery have been published recently. A review of hip fractures showed reduced 1-month mortality in favour of regional anaesthesia plus a reduction in the rate of deep vein thrombosis, ³ confirming earlier work that regional anaesthesia offers an early advantage over general anaesthesia, though this advantage reduces with time. At 3 months, mortality is the same as for general anaesthesia. Patients who had a thoracic epidural infusion for at least 24 hours postoperatively had improved postoperative analgesia and a reduction in postoperative myocardial infarction risk. 4 Jorgensen showed improvements in the return of gastrointestinal function as well as improved pain scores. ⁵ A meta-analysis of the effects of various postoperative analgesic regimens on pulmonary outcome confirmed the benefits of local anaesthetic-based epidural infusions. ² The largest and most significant meta-analysis ⁶ evaluated 144 published papers, involved over 9500 patients, and confirmed several benefits of regional anaesthesia (alone or in combination with general anaesthesia) compared with general anaesthesia alone. There was a reduction in the risk of mortality from all causes after major surgery of 30% in the regional anaesthesia group compared with the general anaesthesia group.

The important question is whether the benefits associated with regional anaesthesia lead directly to measurable clinical improvements such as fewer complications, lower mortality and better outcome from surgery. High quality analgesia is an important achievement but does not improve outcome directly. For example, an epidural infusion for postoperative analgesia following major abdominal surgery produces low pain scores, a shorter duration of ileus, a reduced need for postoperative blood transfusion and results in high levels of patient satisfaction. However, unless efforts are made to use the analgesia and other benefits of the epidural to mobilize the patient and encourage early return to full nutrition, there are no long-lasting benefits once the infusion is discontinued. Traditional surgical postoperative practice such as the routine use of nasogastric tubes, the slow return to enteral nutrition and other fixed determinants of the recovery pathway may also delay recovery and fail to maximize the potential improvements in surgical outcome that regional anaesthesia can offer.

The significant risks associated with spinals, epidurals and major peripheral nerve blocks must be balanced against the potential benefits if the anticipated improvement in outcome for an individual patient is to be realized. The key features of regional anaesthesia (quality of analgesia, avoidance of opioid side-effects and minimizing the impact of the surgical stress response), combined with new surgical techniques and ward routines, make it possible to reduce the incidence and severity of complications (e.g. hypoxaemia, fatigue, weight loss) and delayed recovery, and encourage early nutrition, increased mobility and reduced hospital stay.

1 Richardson J, Sabanathan S, Jones J et al. A prospective randomised trial of preoperative and balanced epidural or paravertebral bupivacaine on postthoracotomy pain, pulmonary function and stress response. Br J Anaesth 1999; 83: 387-392.

2 Ballantyne J C, Carr D B, de Ferranti S et al. The comparative effects of postoperative analgesic therapies on pulmonary outcome: cumulative meta-analysis of randomised controlled trials. Anesth Analg 1998; 86: 598-612.

3 Urwin S C, Parker M J, Griffiths R. General versus regional anaesthesia for hip fracture surgery: a meta-analysis of randomised trials. Br J Anaesth 2000; 84: 450-5. (Also published as a Cochrane Systematic Review.)

4 Beattie W S, Badner N H, Choi P. Epidural analgesia reduces postoperative myocardial infarction: a meta-analysis. Anesth Analg 2001; 93: 853-8.

5 Jorgensen S, Wettersler J, Moiniche S, Dahl J B. Epidural local anaesthetics versus opioid-based analgesic regimens on postoperative gastrointestinal paralysis, PONV and pain after abdominal surgery. Cochrane Database of Systematic Reviews 2000; 4: CD 001893.

6 Rodgers A, Walker N, Schug S. Reduction of postoperative mortality and morbidity with epidural or spinal anaesthesia: results from an overview of randomised trials. BMJ 2000; 321:1493.

7 Does epidural analgesia improve surgical outcome? British Journal of Anaesthesia, 2004, Vol. 92, No. 1 4-6

Kehlet H. Modification of responses to surgery by neural blockade. In: Cousins M, Bridenbaugh P O, eds. Neural blockade in clinical anaesthesia and management of pain. 3rd ed. Lippincott-Raven, 1998, pp. 129-75.

PROSPECT procedure specific postoperative pain management

Copyright © 2004 The Medicine Publishing Company Ltd

ArticleDate:20060618
SiteSection: Article

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Does regional anaesthesia improve outcome?

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Considerable research has been carried out over the last 30 years to investigate whether regional anaesthesia improves the quality of postoperative analgesia compared with systemic opioids, and whether it influences the outcome from surgery. Some benefits, such as the quality of postoperative analgesia, are easy to demonstrate but the intuitive belief that regional anaesthesia improves the outcome from surgery is more difficult to prove.

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Curriculum: Discusses the use of regional anaesthesia in the presence of abnormalities of coagulation

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Curriculum: Discusses the use of regional anaesthesia in the presence of abnormalities of coagulation

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Curriculum: Describes ophthalmic blocks for patients undergoing awake ophthalmic surgery

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Curriculum: Describes ophthalmic blocks for patients undergoing awake ophthalmic surgery

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We don't often talk about it, but avoiding GA in an elderly high risk population who are having the most successful operation in QALY terms (cataract surgery)....? Surely the pinnacle of Regional Anaesthesia

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INTRODUCTION

Ophthalmic surgery is one of the most common surgical procedures requiring anesthesia in developed countries. Ophthalmic anesthesia offers insights into some fundamental principles of good anesthetic practice, especially in the conduct of local and regional nerve blocks.

LOCAL ANESTHESIA IN EYE SURGERY

Clinical strategies to minimize patient movement during eye surgery are essential. Historically, eye surgeons favored general anesthesia (GA), which usually provided akinesia (through neuromuscular block) and low intraocular pressure. However, these conditions are not always achieved under GA. A closed claim analysis by Gild and coworkers found that 30% of eye injury claims associated with anesthesia involved the patient moving during ophthalmic surgery, with most incidents occurring under GA. While perioperative morbidity and mortality rates associated with eye surgery (eg, cataract extraction) are low, patients having cataract surgery tend to be older and to have significant comorbidities. For this reason, systematic preoperative evaluation should be performed to consider whether a patient is eligible for a GA and surgery.
Appropriate anesthetic management contributes to the success or failure of ophthalmic surgery. Quicker patient rehabilitation and fewer complications in this patient population are the main reasons why many ophthalmic surgeons are now choosing local anesthesia (LA) over GA.

Traditionally, the gold standard of eye nerve blocks was retrobulbar anesthesia (RBA), with the surgeon performing the nerve block.
However, advances in technology and surgical technique, particularly in cataract surgery, have led to the replacement of the older wide-incision techniques (eg, extra-capsular cataract extraction) with minimally invasive phacoemulsification (PhE) techniques. Consequently, for new generation of cataract surgeons, total akinesia is no longer necessary for PhE.

NYSORA TIPS

* Twenty-first century innovations and trends have revolutionized eye surgery.
* Local and regional anesthetic techniques has largely replaced general anesthesia.
* Understanding functional anatomy and surgical techniques is essential for selection of regional techniques.
* Sub-Tenon's nerve block is one of the most common choices for anesthesia as it can generally achieve akinesia with the favorable safety profile.
* Topical anesthesia, is increasingly becoming most prevalent for cataract surgery.
* Complications of eye nerve blocks are uncommon but can be life- or sight-threatening, emphasizing the need of adequate training.

Innovation has also broadened the anesthetic options for eye surgery. As the conventional RBA carries a greater risk of complications, less invasive techniques have increasingly been used, with a substantial diversity in practice styles around the world. For instance, one Australian study from 2002 reported that peribulbar nerve block was the most popular among an international sample of ophthalmic surgeons. However, a 2006 survey found that 64% of a sample of UK anesthetists favored the sub-Tenon's technique, and, by 2008, a survey of the British Ophthalmic Anaesthesia Society found that over 87% of anesthesiologist members regularly performed sub-Tenon's nerve blocks.

On the other hand, an annual survey of the American Society of Cataract and Refractive Surgery reported that its members' preference for using topical anesthesia had risen steadily from 11% in 1995 to 76% in 2012. In the same survey, the use of sub-Tenon's nerve blocks appeared to be consistently low over the years (around 1%-3%) despite its growing popularity elsewhere, with the use of retrobulbar and peribulbar nerve blocks seemingly in gradual but sustained decline.
Each anesthetic technique has its strengths and limitations.

Knowledge of the relevant anatomy for the various anesthetic techniques is essential to determine the appropriate nerve block for specific clinical situations and to best avoid life- and sight-threatening complications. In this section, we review the relevant anatomy of the eye, classical needle and non-needle nerve block techniques, and choice of LA and adjuvant agents. With a wider range of options comes a greater burden on the anesthesiologist to discuss individual anesthetic requirements with the surgeon, to be adaptable, and to have excellent communication and team-working skills.

FUNCTIONAL ANATOMY

Orbit

The orbits ( Figures 1 and 2) are two symmetrical bony enclosures in the front of the skull, each containing an eyeball (or globe) and its associated structures. The cavity of each orbit is a truncated pyramid, with a flattened apex posteriorly and a trapezoidal base facing anterolaterally. The medial (nasal) walls of each orbit are parallel to each other, while the lateral (temporal) walls are perpendicular to each other. The volume of each adult orbit is approximately 30 mL.

Globe

The globe ( Figure 3) is suspended in the anterosuperior part of the orbit. It is roughly spherical, its contents contained within three outer layers or tunics:

A fibrous tunic comprising the translucent cornea in front and the opaque sclera peripherally and behind

Deep to the fibrous tunic, a vascular, pigmented tunic comprising the iris and ciliary body in front and the choroid peripherally and behind

Deep to this again, a neural tunic overlying the posterior part of the other two tunics internally, comprising the retina.

The globe has a large posterior segment (comprising the vitreous humor, the retina, the macula, and the root of the optic nerve) and a small convex anterior segment comprising two chambers. The anterior chamber immediately behind the cornea is filled with aqueous humor produced by the ciliary body. The posterior chamber contains the lens. The two chambers are separated by the iris and communicate via the pupil of the eye. Externally, the circumferential junction of cornea and sclera (with its overlying conjunctiva) is called the limbus.
The volume of the globe is approximately 7 mL. The axial (anteroposterior) length of the adult globe is on average about 24 mm; however, this can be considerably longer in myopic individuals (> 26 mm) and shorter in hypermetropia (down to 20 mm). As a rule of thumb, the distance from the front of the globe to its equator is about 12-15 mm, but, where possible, it is better to know the measured axial length of the eye before attempting to inject behind the equator (eg, for patients undergoing cataract surgery, biometric data are routinely found in the surgeon's clinical notes).
The sclera is thinnest at the equator and at the insertion points of the extraocular muscles. However, more myopic eyes (with a longer axial length) have a markedly increased prevalence of posterior staphyloma, an otherwise rare "blow-out" weakness in the fibrous tunic, which poses a major risk for globe perforation with blind needle techniques (see "Complications of Eye Nerve Blocks" later).

Muscles of the Eye

The four rectus and two oblique muscles of the eye insert anteriorly near the equator of the globe (see Figure 3). Posteriorly, they originate together at the apex from the tendinous annulus communis of Zinn. The four rectus muscles, running posteriorly from the equator to the annulus of Zinn, delineate the retrobulbar cone. The optic nerve traverses the cone from the posterior part of the globe and enters the orbit through the annulus of Zinn.

Three Intraorbital Compartments

The globe and muscular retrobulbar cone define the three classical anatomical compartments of the orbital cavity: the intraocular, intraconal, and extraconal (see Figure 2). However the retrobulbar cone is not sealed by any intermuscular membrane, and, in fact, there is free communication between the intraconal and extraconal spaces. Thus, a large-volume peribulbar (extraconal) nerve block can theoretically provide an effective anesthesia and akinesia as a targeted small-volume retrobulbar nerve block.

Innervation of the Orbit

Sensory innervation of the orbit and globe is provided mostly by the frontal and nasociliary branches of the ophthalmic nerve (first branch of the trigeminal nerve, V), which pass through the muscular cone ( Figures 4 and 5), while some of the floor of the orbit is supplied by the infraorbital branch of the maxillary nerve (the second branch of the trigeminal nerve).
The trochlear nerve (IV) provides motor control to the superior oblique muscles, the abducens nerve (VI) to the lateral rectus muscle, and the oculomotor nerve (III) to all other extraocular muscles, including the levator muscle. All except the trochlear nerve pass through the muscular conus.

Anatomical Quadrants of the Globe and Orbit

The sphere of the globe can be divided in the three standard perpendicular anatomical planes into eight "quadrants": anterior superomedial, posterior superomedial, and so on. Looking from the front, the corresponding anterior extraocular quadrants of the orbit are often referred to as the superonasal, suprotemporal, inferonasal, and inferotemporal, where nasal has the same meaning as medial, and temporal has the same meaning as lateral ( Figure 6). The inferotemporal (or inferolateral) space is usually the largest and least vascular and the preferred quadrant of approach for modern retrobulbar and single-shot peribulbar nerve blocks. The inferonasal (or inferomedial) quadrant is most popular for sub-Tenon's nerve blocks. The superonasal (or superomedial) quadrant is quite vascular but contains the anterior ethmoidal nerve, a useful nerve to nerve block for some oculoplastic procedures (see "Oculoplastic Nerve Blocks" below).

Tenon's Capsule and Sub-Tenon's Space

The scleral portion of the globe is surrounded by Tenon's capsule (also known as the fascial sheath of the eyeball), a fibroelastic layer stretching from the corneal limbus anteriorly to the optic nerve posteriorly. Tenon's capsule generally becomes thinner and less adherent to the sclera with age. It delimits a potential space referred to as the episcleral space (sub-Tenon's space), which expands when fluid is injected into it. The conjunctiva overlies the sclera in the anterior part of the eye until it is reflected at the fornices of the eye to continue as the mucosal lining of the underside of the eyelids. Note that Tenon's capsule fuses with the sclera about 2 mm from the limbus.
Where the sclera is visible, the two layers are easier to pick up as one; closer to the fornix, the conjunctivum becomes fleshier and more distinct from the sub-Tenon's layer. This helps identify the ideal breach point for the sub-Tenon's technique (q.v.)

Spread of Local Anesthetic Within the Orbit

Injection of LA solution inside the cone will provide anesthesia and akinesia of the globe and (usually) all extraocular muscles. Only the motor nerve to the orbicularis muscle of the eyelids has an extraorbital course, coming from the superior branch of the facial nerve (VII). Many major structures are located within the muscular conus and are therefore at risk of needle and injection injury. These include the optic nerve with its meningeal coverings, the blood vessels of the orbit, and the nerves supplying the globe. For this reason, some authors advise that introduction of the needle into the muscular cone be avoided and suggest that needle insertion be limited to the extraconal space.

KEY SURGICAL CONSIDERATIONS

It is important to get to know your surgeon. Choosing an appropriate local anesthetic technique requires an understanding not only of surgical procedures but also the surgeon's personal preferences.

Akinesia

The requirement for akinesia varies with the procedure (see below) and the surgeon. With nerve blocks behind the equator of the eye, improving the likelihood of akinesia generally requires more volume, more time, or the addition of hyaluronidase 30 (see "Choice of Local Anesthetic and Adjuvant Agents" below).

Primary Position Versus "On-Axis" Position

Complete paresis of all extraocular muscles renders the eye in the "primary" or "neutral" position. Usually, this corresponds with the surgeon having the pupil aligned with the axis of the surgical microscope (ie, the surgeon has an ideal "on-axis" view of the operative field). However, in cases of incomplete motor nerve block, or in patients who have significant spinal curvature or who are unable to lie flat, the "resting" position of the blocked eye may not correspond to an on-axis view. For this reason, many surgeons actually prefer to have a fully mobile eye for certain patients or certain procedures (eg, trabeculectomy, pterygium removal) so that they can ask the patient to look at the light of the microscope, thereby bringing the eye "on axis," or to look away, allowing greater access to more peripheral parts of the globe.

The Volume Effect of Injections
Behind the Eye

Any substantial injection (> 3 mL) behind the equator of the eye (a peribulbar, retrobulbar, or posterior sub-Tenon injection) can significantly raise intraocular pressure and push the posterior segment forward, resulting in a crescent-shaped anterior chamber with decreased volume ( Figure 7). This can make surgical conditions more challenging, and while this can mostly be offset by counter-pressure (through gentle digital pressure or application of a weight or balloon), some surgeons prefer techniques that retain a "physiological" anterior segment, and most surgeons prefer techniques that avoid large volumes of injectate (> 10 mL) in the orbit. On the other hand, in patients with significant enophthalmos, bringing the globe forward can improve surgical exposure.

"The Only Eye"

In patients who have vision in only one eye-the eye being operated upon-surgeons and anesthetists alike tend to be risk averse and steer away from sharp needle nerve blocks. Techniques that do not involve loss of vision (ie, topical, subconjunctival, "superficial" sub-Tenon's) may be preferable. Techniques that better guarantee akinesia usually cause temporary loss of vision due to anesthesia of the optic nerve. In day-case settings, it may be preferable to use a shorter-duration LA (eg, lidocaine, articaine) over longer-acting agents.

Cataract Surgery

The minimally invasive PhE technique was popularized in the 1990s. The PhE probe is inserted via a small superior, threeplane (self-sealing) incision. The contents of the posterior chamber are manipulated using a needle-width stay probe inserted laterally. After the posterior chamber is voided and cleaned, a foldable or injectable artificial intraocular lens is inserted via the same incision. Anesthesia of the anterior segment is all that is required. Some surgeons require akinesia; others (notably high-turnover surgeons) do not.

Corneal Surgery

The most common operations on the cornea involve trauma, removal of foreign bodies, conjunctival flap and pterygium surgery, corneal transplant surgery, and, increasingly, keratoprosthesis. For these procedures, anesthesia of the anterior segment is typically all that is required. Most surgeons require akinesia for penetrating corneal surgery (eg, trauma, transplant, prosthetic surgery, re-do procedures), while many do not for pterygium surgery, where the fibrous tunic remains essentially intact. Some surgeons find subconjunctival anesthesia useful for separating the conjunctiva from the sclera in pterygium surgery.

Refractive Surgery

Corneal surface ablation, incisional refractive surgery, and intracorneal ring insertion are usually performed under topical anesthesia. Refractive procedures involving the anterior chamber (eg, phakic intraocular lens insertion) are done in a manner similar to cataract surgery.

Glaucoma Surgery

Glaucoma filtration surgery and trabeculectomy both involve creating a fistula between the anterior chamber and the subconjunctival space. Again, anesthesia of only the anterior segment is needed. Depending on the surgeon, there may or may not be a need for akinesia. Some surgeons do not like the disruption of integrity of the conjunctiva that often accompanies the surgical sub-Tenon's (or "snip") technique, particularly in inexperienced hands. Furthermore, conjunctival hematoma can introduce reticuloendothelial cells that interfere with trabeculectomy flaps; consequently, some glaucoma surgeons prefer peribulbar anesthesia for these procedures. Topical anesthesia (with or without intracameral lidocaine) and subconjunctival anesthesia both avoid the potential effect of volume injections behind or around the orbit on pulsatile ocular blood flow in patients with advanced glaucoma. Paradoxically, nonpenetrative glaucoma surgery (eg, deep sclerotomy), being a longer and more difficult procedure, generally requires a technique that guarantees a longer nerve block with akinesia. Procedures involving aqueous tube shunts can be done under topical anesthesia but tend to be more uncomfortable for the patient.
Cyclophotocoagulation is the circumferential ablation of the ciliary body deep to the limbus. Akinesia is not essential for this procedure but may be preferred by some surgeons; however, good analgesia is essential, as the procedure can be very painful. Subconjunctival anesthesia works but needs time; sub-Tenon's or needle nerve blocks usually provide acceptable anesthesia more quickly.

Oculoplastic Surgery

Procedures of the soft tissues of the eye include correction of eyelid malpositions such as entropion and ectropion, eyelash malpositions (districhiasis), ptosis surgery, eyelid tumor surgery, eyelid reconstruction, blepharoplasty, tear duct surgery, orbital decompression (eg, for Grave's disease), and enucleation and evisceration. While many of these procedures can be performed under local infiltration, specific anesthetic techniques are described later in this chapter.

Extraocular Muscle Surgery

Strabismus surgery is most commonly performed in children under general anesthesia. In adults, squint surgery is usually performed in persons under the age of 30, a group which can often be less than stoic, so again GA is usually preferred. However, this surgery can be performed under regional anesthesia. While akinesia is helpful, the main requirement is for deep anesthesia of the muscle cone, as pulling on extraocular muscles is usually quite painful and can induce an oculocardic reflex. Simple suture adjustments can be done under topical anesthesia.

Vitreoretinal Surgery

Vitrectomy and retinal detachment repairs (including scleral buckling) require both anesthesia of the posterior segment and akinesia of the eye; topical and subconjunctival techniques are inadequate for this. Thus, a sub-Tenon's, retrobulbar, or peribulbar nerve block is more appropriate. Prior buckling surgery is a relative contraindication to any regional technique, as both the buckle and scar tissue around it will hamper the spread of local anesthetic. However, if the position of the buckle is known, a deep sub-Tenon's nerve block may be possible via one of the unaffected quadrants. The "tap-and-inject" treatment for endophthalmitis is usually performed using a retrobulbar or peribulbar nerve block.

Open-Globe Injuries

Patients with a known or suspected open-globe injury are most frequently managed under general anesthesia to avoid the risks of infection, retrobulbar hemorrhage, and raised intraocular pressure, which can cause further damage. There are authors who advocate repair under local anesthesia and sedation, arguing that this method avoids the dilemma of using succinylcholine, which can markedly increase intraocular pressure, in patients with both a penetrating eye injury and a full stomach. Rapid-onset nondepolarizing muscle relaxants (NDMRs), such as rocuronium, and the wider availability of the NDMR reversal agent, sugammadex, have largely mitigated this problem. Nevertheless, recent literature appears to suggest that the risk of vitreous extrusion remains very real, and, perhaps in carefully selected situations, local anesthesia should not be discounted as an alternative in cases of eye trauma.

Ophthalmic Oncology

Most procedures for the removal of eye tumors can be performed under local or general anesthesia, according to surgeon and/or patient preference. However, procedures that require stereotactic immobilization or deliberate hypotension should be performed under general anesthesia.

ANESTHETIC TECHNIQUES

Sub-Tenon's (Episcleral) Nerve Block Common Principles

Sub-Tenon's anesthesia, first described in 1884, places the local anesthetic into the potential space between Tenon's capsule and the sclera ( Figure 8). While this space can theoretically be accessed from any quadrant of the globe, the inferonasal conjunctival fornix is most popular, at approximately the 4:30 (right eye) or 7:30 (left eye) position to avoid encountering the insertions of the medial rectus and inferior oblique muscles at the equator.

Using either a surgical or nonsurgical approach (see below), a purpose-specific needle or cannula is directed posteriorly following the curve of the globe. A superficial or deep injection of LA solution can then be performed. "Superficial" or more anterior injections (immediately beyond the equator) allow the LA to spread circularly around the scleral portion of the globe, ensuring high-quality analgesia of the whole globe with relatively low injection volumes (usually 3-5 mL). Injection of a larger volume (up to 8-11 mL) causes the LA to spread to the extraocular muscle sheaths, ensuring reproducible akinesia.

However, larger volumes often cause chemosis (a subconjunctival spread of LA), which requires compression to resolve, as well as a significant increase in intraocular pressure.

On the other hand, "deep" or posterior injections direct more injectate into the posterior intra- and extraconal spaces and are more likely to achieve anesthesia at lower volumes and without chemosis, without akinesia (2-3 mL) or with full akinesia (3-5 mL). While the "surgical" deep injection technique is currently the most popular, several approaches have been described.
Surgical ("Snip") Technique with a Blunt Cannula
This technique, first proposed as a supplement to (or rescue nerve block from) retrobulbar anesthesia, is probably the most popular variation of the sub-Tenon's approach. After topical anesthesia, the bulbar conjunctiva is grasped with small forceps in the inferonasal quadrant near the fornix. Small scissors are used to create a small opening into the conjunctiva and Tenon's capsule to gain access to the episcleral space. The same scissors are used to blunt-dissect a passage to the posterior sub-Tenon's space. A blunt metal (eg, Stevens) or plastic (eg, Helica) cannula is then inserted into this space to allow for the injection.
Some practitioners opt for a superficial passage and then "hydro-dissect" using the local anesthetic injectate; others (particularly for posterior segment surgery) prefer to probe-dissect as close to the intraconal space as possible using closed scissors. It is also possible, particularly in the elderly, to gently push the cannula posteriorly without dissection. The usual LA injection volume is 3-5 mL. Increasing the injection volume (up to 11 mL) results in an increased likelihood of akinesia but is rarely necessary. The main advantage of this technique is its safety, as it avoids the blind introduction of a sharp needle into the orbit. In 6000 cases, no serious complications were reported, with only a 7% rate of subconjunctival hematoma and a 6% rate of subconjunctival edema. Surgery was canceled because of subconjunctival hematoma in only one patient out of the 6000.

Nonsurgical Technique with a Blunt Cannula
Cutting the conjunctiva can result in long-term scarring and creates a portal for bacteria and occasionally other foreign bodies to enter. With practice, a round-tipped blunt cannula (such as a 21-gauge Eagle Laboratories "Tri-Port" sub-Tenon cannula or even a Stevens cannula) can be introduced through the conjunctiva and Tenon's layers without a prior incision.
This causes less trauma, reduces bleeding, and is preferred particularly where conjunctival damage needs to be minimized (eg, glaucoma surgery).

Nonsurgical Technique with a Sharp Needle
A 25-gauge, 25-mm, short-bevel sharp needle is introduced into the fornix between the semilunaris fold of the conjunctiva and the globe, tangentially to the globe. The needle is shifted slightly medially and advanced posteriorly. After a small loss of resistance (click) at 10-15 mm, LA is injected. Using a large volume with this technique (6-11 mL) results in good globe and eyelid akinesia that is more reproducible than classic peribulbar anesthesia; however, note that these are large volumes compared to other techniques, and, as for all sharp-needle techniques, the risk of needle misplacement and its subsequent complications must always be kept in mind. Nevertheless, this technique is associated with a low risk of complications, and it is simple to learn and use. In a series of 2000 cases, no serious complications occurred.

Improvised Cannula Technique
This historical technique was briefly popular before specialized cannulae became widely available. A short intravenous (IV) cannula (18- or 20-gauge) was typically used to inject low volumes of LA (3-5 mL). It provides good globe analgesia but only partial akinesia of the globe and lids. The injection causes only a minor increase in intraocular pressure, and preoperative compression of the globe is typically unnecessary. However, given that it requires introduction of the cannula by piercing the Tenon's capsule, not unlike the technique of IV cannulation, the risk of needle misplacement has reduced the popularity of this technique.

Limitations of the Sub-Tenon's Technique
The sub-Tenon's technique may not be possible where the conjunctival fornices have been obliterated, such as in chronic ocular pemphigus. It should also be avoided where the sclera is known to be thin or frail (eg, the "blue sclerae" of osteogenesis imperfecta or an anterior staphyloma).
Access may be challenging in patients whose inferonasal space is already scarred by multiple previous nerve blocks or in those with a scleral buckle in place, particularly one that is circumferential. In most of these situations, access is possible via an alternative quadrant (most commonly the inferotemporal). Chronic eye inflammation can cause the conjunctiva to become fleshy and painful to touch and to bleed easily. Access through a pterygium should be avoided for the same reasons.

NYSORA TIPS

The Surgical "Snip" Technique of the Sub-Tenon's Nerve Block According to Guise
* Use half-strength iodine: A substantial body of evidence suggests that this reduces the risk of bacterial endophthalmitis.
* Stay in the "line of longitude" from pole to pole: Keep equally between the medial and inferior recti.
* Keep the Westcott scissors closed: Only one snip at the start is needed.
* Keep the tip of the cannula tight against the sclera: It's easy to overshoot.
* Inject in different directions: Rotating the syringe slightly will aid spread behind the eye.
* Avoid the pterygia: They make access to the sub-Tenon's space more difficult, and they bleed.
* Keep the local anesthetic posterior to the equator: Keep the channel created by the Westcott scissors as narrow as possible to minimize reflux.
* Reduce the rate and force of injection: Too fast and hard is painful for the patient and more likely to cause chemosis.
* Use less than 5mL to minimize chemosis and the increase in intraocular pressure.
* Avoid ocular massage, which can cause dramatic peaks in intraocular pressure and may even cause anterior chamber bleeding. Gentle, steady pressure, if anything, is better.
* Take care with scleral buckles: The inferotemporal quadrant is usually clear, but ask your surgeon. If it is not clear, and you are not comfortable trying a different quadrant, or if you expect or encounter significant scarring, try a different technique.

RETROBULBAR ANESTHESIA

Historically, retrobulbar anesthesia (RBA) was the gold standard for anesthesia of the eye and orbit. This technique generally consists of injecting a small volume of LA solution (3-5 mL) inside the muscular cone (see Figure 3). A facial nerve block is occasionally required to prevent blinking (see "Oculoplastic Nerve Blocks" below). Because of its extraconal motor control, the superior oblique muscle frequently may remain functional, precluding total akinesia of the globe. The main hazard of RBA is the risk of injury to the globe or to one of the anatomical structures in the muscular cone. Near the apex, these structures are packed in a very small space and are fixed by the tendon of Zinn, which prevents them from moving away from a needle.

Classical Technique (Now Obsolete)

In Atkinson's classical 1936 description, the patient is asked to look in the "up-and-in" direction. The needle is introduced through the skin below the inferior lid at the junction between the lateral third and the medial two-thirds of the inferior orbital edge. The needle is directed toward the apex of the orbit (slightly medially and cephalad) and advanced to a depth of 25-35 mm. A volume of 2-4 mL of LA solution is then injected. An additional facial nerve block may be needed to prevent blinking; the technique most frequently used is the Van Lint block (see "Oculoplastic Nerve Blocks").

Modern Techniques

Modern retrobulbar nerve blocks are performed with the eye in the neutral position ( Figure 9). The Atkinson "up-and-in" gaze position was abandoned when Liu et al. and Unsöld et al. warned that it increased the risk of optic nerve injury since this position places the optic nerve near the path of the needle. Moreover, the optic nerve is stretched and can be injured easily by the needle, rather than being pushed aside. Alternative puncture sites and specially designed bent or curved needles have been proposed but have not gained popularity.

RBA: Is There a Future?

Given the versatility and rising popularity of sub-Tenon's Nerve blocks, and given that there is no situation in which a retrobulbar nerve block would be preferred over a peribulbar nerve block, it seems unlikely that retrobulbar nerve blocks will remain part of the repertoire of the modern anesthesiologist.

PERIBULBAR ANESTHESIA

With peribulbar anesthesia (PBA), the needle is introduced into the extraconal space ( Figure 10). The classical technique involves two injections. The first injection is inferior and temporal, the needle being introduced at the same site as for an RBA injection, but with a lesser up-and-in angle.
The second injection is superior and nasal, between the medial third and lateral two-thirds of the orbital roof edge (see Figure 10).
The injected volume of LA (6-12 mL) is larger than that for a retrobulbar injection. This larger volume allows the LA to spread into the whole corpus adiposum of the orbit, including the intraconal space, where the nerves to be blocked are located. Additionally, such a large volume allows for the anterior spread of LA to the lids to provide a nerve block of the orbicularis muscle and to avoid the need for an additional lid nerve block.

Several variations on PBA have been described ( Figure 11). The most common are (1) medial canthus injection, (2) lacrimal caruncle injection and (3) inferior and temporal injections.

Principles of Peribulbar Anesthesia

* Single-injection versus multiple-injection technique: Increasing the injected volume of LA provides sufficient anesthesia. Additional injections are not needed. In addition, anatomic distortion following the first injection may increase the risk of complications associated with consecutive injections. As a rule of thumb, a second injection should be performed only as a supplement when the first injection has failed to provide effective anesthesia.
* Needle insertion sites: Needle insertion through the superior nasal site should be avoided. At this level, the distance between the orbital roof and the globe is reduced, theoretically increasing the risk of globe perforation.
Additionally, the needle may injure the superior oblique muscle. The inferonasal approach or an approach through the medial canthus should be used instead. The needle is introduced at the medial junction of the lids, nasal to the lacrimal caruncle, in a strictly posterior direction to a depth of 15 mm or less. At this level, the space between the orbital wall and the globe is similar in size to that of the inferior and temporal approach and is free of blood vessels. Moreover, myopic staphyloma, an anatomical anomaly that represents a risk factor for perforation, is infrequently encountered on the nasal side of the globe.

* Needle insertion depth: Limit the needle insertion depth to 25 mm. Posterior to the globe, the rectus muscles are in contact with the orbital walls, so that the extraconal space entirely disappears and becomes virtual. Increasing the needle insertion depth would be expected to cause a peribulbar injection to become a retrobulbar injection. Some posterior peribulbar nerve blocks are in fact unintentional retrobulbar injections. This is a plausible explanation for optic nerve injury after an attempted peribulbar injection. Moreover, a long needle fully introduced into the orbit may reach the apex of the orbit, another hazardous area. Inserting the needle to a depth of 40 mm has led to performing the injection directly through the optical foramen in 11% of cases.

* Fine needles (25-gauge) are suggested for reducing pain on needle insertion: The use of short-bevel needles may be safer because they may enhance the tactile perception of resistance during needle insertion (intraneural or intramuscular placement). Indeed, on cadavers, more pressure is required with short-bevel needles to perforate the sclera. Nevertheless, these are only theoretical considerations, since the complication rate with peribulbar nerve blocks is low.
* Use compression to lower intraocular pressure, which increases after injection: Compression has not been shown to enhance the quality of the nerve block. Applying a pressure of 30 mm Hg for 5-10 minutes is usually sufficient.
* In all cases, the spread of LA within the corpus adiposum of the orbit remains somewhat unpredictable, leading to the need for more anesthetic to prevent an imperfect nerve block: Depending on the surgeon's request for akinesia, additional anesthetic is required in up to half of all cases. The poor reproducibility in nerve block efficacy is the main disadvantage of peribulbar anesthesia.

Retrobulbar Versus Peribulbar Versus Sub-Tenon's Nerve Blocks

RBA has been traditionally assumed to be more effective than PBA. However, when a sufficient volume of LA is injected, both nerve blocks appear to have similar success rates. This is explained by the absence of an intermuscular membrane to separate extra- from intraconal compartments, resulting in a favorable spread of LA (see "Functional Anatomy"). Therefore, if the effectiveness is similar, one should prefer to use the technique with a lower risk of complications. Since RBA theoretically carries a higher risk of complications (eg, optic nerve injury, brainstem anesthesia, retrobulbar hemorrhage; see "Complications of Eye Nerve Blocks" below), PBA is deemed preferable to RBA.
However, all other requirements being equal, the sub-Tenon's nerve block offers the best safety profile of the three nerve blocks and can reliably deliver both surgical anesthesia and akinesia if performed by an experienced practitioner with an appropriate volume (with or without adjuvants). However, where chemosis, conjunctival hematoma, or the disruption of the conjunctiva are undesirable, or where the posterior anatomy is seriously abnormal, this technique may not be appropriate.
The diversity of opinion and data suggest, to this author at least, that the individual efficacy of any of these nerve blocks is heavily operator dependent. To a significant extent, the same is true in regard to their safety profiles.

COMPLICATIONS OF EYE NERVE BLOCKS

The primary cause of serious complications is needle misplacement. Although some anatomical features may increase the risk of complications, the main risk factor is inadequate knowledge and limited experience on the part of the operator. However, it should be noted that complications such as retrobulbar hemorrhage and oculocardic reflex may occur with even the most experienced practitioners. Presenting signs, symptoms, and mechanisms of common complications are summarized in Tables 1 and 2.

TABLE 1. Signs, symptoms, and mechanisms of complications of retrobulbar anesthesia.

Complication

Signs and Symptoms

Mechanism of Complication

Globe perforation

Ocular pain, intraocular hemorrhage, restlessness

Direct trauma: myopic eye, posterior staphyloma, repeated
injections

Retrobulbar
hemorrhage

Subconjunctival or eyelid ecchymosis, increasing proptosis pain, and/or increased intraocular pressure

Direct trauma (artery or vein)

Optic nerve damage

Visual loss, possible early optic disc welling, late optic disc pallor

Direct injury to nerve or blood vessels, vascular occlusion

Intra-arterial
injection

Cardiopulmonary arrest, convulsions

Retrograde flow to internal carotid and access to midbrain structures

Optic nerve sheath
injection

Brainstem anesthesia: agitation, ptosis, mydriasis dysphagia, dizziness, confusion, contralateral ophthalmoplegia, loss
of consciousness, respiratory depression/arrest, cardiac
arrest

Subdural or subarachnoid injection

Oculocardiac reflex

Bradycardia, other arrhythmias, asystole

Trigeminal nerve (afferent, arc) to floor of fourth ventricle with efferent arc via vagus nerve

TABLE 2. Other complications of retrobulbar anesthesia.

Chemosis (subconjunctival edema)

Usually of minimal concern; disappears with pressure.

Venous hemorrhage

Usually mild and, while unsightly, is easily controlled.

Arterial hemorrhage

Can be dramatic, causing proptosis, extensive subconjunctival and lid hematoma, and a dramatic increase in intraocular pressure. This is a sight-threatening complication: inform surgeon immediately, as orbital decompression (eg, lateral canthotomy/cantholysis) may be necessary to prevent blindness. Usually causes postponement of surgery.

Globe perforation

Likely more common to occur in long, myopic eyes. A long eye has thinner sclera and may have an irregular outline (staphylomata). The needle should be inserted tangentially to the globe and move freely in the orbital fat without rotating the globe.

Damage to the optic nerve

A result of direct trauma, injection into the nerve sheath, or the ischemic consequences of the pressure on injection.

Decreased visual acuity

Usually resolves with resolution of the block, but beware "wipe-out", especially in patients with advanced glaucoma (see "Choice of Local Anesthetic and Adjuvant Agents").

Myotoxicity

May follow direct injection into a muscle or the use of high concentrations of LA (probably more common than currently recognized; usually resolves during surgical convalescence).

Systemic complications

Subarachnoid injection during retrobulbar block is a possible cause of respiratory arrest.

Grand mal seizures, loss of consciousness, and respiratory depression or cardiac arrest

These complications can result from systemic LA toxicity, injection of LA into the optic nerve sheath (and thence to the brainstem), or retrograde arterial flow.

Pulmonary edema

Rare; mechanism is poorly understood.

Reaction to epinephrine

Often inappropriately referred to as "epinephrine toxicity"; in patients with hypertension, angina, or arrhythmias, the amount of epinephrine injected with the LA should be reduced.

Oculocardiac reflex, vasovagal reaction

See text for presentation and management.

Allergic reactions

Extremely rare with amide-type LAs; more common with animal-derived hyaluronidase.

Central Nervous System Complications

Central nervous system eye nerve block complications may occur following a needle nerve block by two different mechanisms:
1. An unintentional intra-arterial injection may reverse the blood flow in the ophthalmic artery up to the anterior cerebral or internal carotid artery,70 so that an injected volume as small as 4 mL may cause seizures. Symptomatic treatment by maintaining a patent airway; providing oxygenation; and abolishing seizure activity with small doses of benzodiazepam, propofol, or a barbiturate is usually adequate and results in a rapid recovery without sequelae.
2. An unintentional subarachnoid injection via puncture of the dura mater sheath of the optic nerve or directly through the optic foramen results in partial or total brainstem anesthesia. Katsev et al. have shown that the apex of the orbit may be reached with a 40-mm needle in up to 11% of patients. Depending on the dose and volume of LA spreading toward the brainstem, subarachnoid injection can lead to bilateral nerve block; cranial nerve palsy with sympathetic activation, confusion, and restlessness; or total spinal anesthesia with tetraparesis, arterial hypotension, bradycardia, and eventually respiratory arrest. Symptomatic treatment (oxygen, vasopressors, and, if required, tracheal intubation and ventilation) should permit complete recovery after the spinal nerve block wears off
(a few hours).
Unintentional globe perforation and rupture is the most devastating complication of eye nerve blocks. It has a poor prognosis, especially when the diagnosis is delayed. The incidence is between 1 in 350 and 7 in 50,000 cases. Main risk factors include inadequate experience of the operator and a highly myopic eye (ie, a long eyeball). In a study of 50,000 cases, Edge and Navon observed that myopic staphyloma was a significant risk factor. This suggests that isolated high myopia may not be a risk factor per se but acts as a confounding factor, as staphyloma seems to occur only in myopic eyes. Vohra and Good observed with B-mode ultrasound that the probability of staphyloma is greater in highly myopic than in slightly myopic eyes. Moreover, staphyloma was more frequently found at the posterior pole of the globe (accounting for perforations after RBA) or in the inferior area of the globe (accounting for perforations after inferior and temporal punctures, both peri and retrobulbar). As a result, at least in myopic patients, and at best in all patients, ultrasound measurement of the axial length of the globe (biometry) should be available. In cases of a highly myopic eye (axial length greater than 26 mm), a needle nerve block can carry an increased risk of globe perforation, and a sub-Tenon's or topical nerve block is preferable. Unusual causes of globe perforation include misplaced infraorbital nerve blocks (see "Oculoplastic Nerve Blocks") and patients sneezing under propofol sedation (see "Sedation").

Extraocular Muscle Injury

Injury to an extraocular muscle may cause diplopia and ptosis. Several mechanisms can be involved, including direct injury by the needle resulting in intramuscular hematoma, high pressure as a result of injection into the muscle sheath, or direct LA myotoxicity.

Direct Extraocular Myotoxicity

It has been known for some time that high concentrations of amide-type local anesthetics, particularly bupivacaine, cause myotoxic changes in skeletal muscle. The extraocular muscles seem particularly susceptible, and numerous case reports of persistent diplopia after cataract surgery have been attributed to this. However, to date, no formal clinical evaluation of skeletal muscle function after eye nerve block has been performed. In monkeys, a 0.75% bupivacaine retrobulbar nerve block typically causes a myopathic response that peaks at 14 days and is largely resolved by 27 days. In rabbits, bupivacaine myotoxicity appears to be concentration dependent, with 0.75% solutions producing extensive and longer-lasting damage, whereas 0.19% produces little sign of short- or longterm damage. Lidocaine solutions containing epinephrine cause substantially more damage to skeletal muscle than does plain lidocaine, both in rats and humans. Indeed in humans, bupivacaine toxicity of eye muscles is deliberately induced to treat strabismus. The injury progresses in three steps: first, the muscle is paralyzed; second, the muscle seems to recover; and third, retractile hyperplasia develops.
Given the case reports and the impressive and consistent pathological evidence across species, and with the many thousands of eye nerve blocks being performed each year, it is surprising that the phenomenon is not more clinically apparent. It has been proposed that postoperative pain may mask myopathic changes and that any eye discomfort or dysfunction is readily attributed to the operation rather than other causes. Furthermore, the animal evidence suggests that in most cases there is likely to be rapid recovery with complete tissue regeneration. In another animal study, skeletal muscle damage induced by femoral nerve block was more severe in younger rats than older rats, so perhaps older humans, too, are less susceptible.
Based on the limited available evidence, it would seem that extraocular myotoxicity is probably a more frequent concomitant of volume nerve blocks behind the equator of the eye that is generally recognized and that it is concentration dependent and more likely to occur with bupivacaine, but that any clinically significant adverse effects in the relevant patient population usually (but not always) resolve completely within the time frame of healing of the operation.

NYSORA TIPS

Retrobulbar Hemorrhage
* Retrobulbar hemorrhage is typically caused by an inadvertent arterial puncture. It may lead to a compressive hematoma, which can threaten retinal perfusion.
* At the time of hemorrhage, it is imperative to have an ophthalmologist present who can monitor intraocular pressure and take the appropriate steps to preserve central retinal artery perfusion. Lack of perfusion for even short periods can lead to permanent, devastating loss of vision.
* Surgical decompression may be required, but in most cases, surgery has only to be postponed.
* Venous puncture may occur after both retrobulbar and peribulbar injection. It leads to non-compressive hematoma, the consequences of which are much less severe so that in most cases surgery can be continued.
* For patients on anticoagulants (including even aspirin and similar medications), consider sub-Tenon's or topical anesthesia to minimize the risk of hemorrhage.

Optic Nerve Trauma

Direct optic nerve trauma by the needle is rare but serious, as it causes blindness. Computed tomography imaging usually shows optic nerve enlargement caused by intraneural hematoma.

Summary

Overall, there is a 1%-3% chance of complications, often necessitating postponement of the planned surgery. Since some complications may be life-threatening if patients are not immediately resuscitated, it is recommended that an anesthesiologist be present to monitor the patient perioperatively.

NYSORA TIPS

Oculocardiac Reflex
* Bradycardia due to a range of stimuli in or around the orbit, such as traction on the extraocular muscles, pressure on the globe, retrobulbar nerve block, ocular trauma or pressure on residual tissues after enucleation.
* Also causes other arrhythmias including ventricular tachycardia and (rarely) asystole.
* The relevant neural pathways are branches of the trigeminal nerve (afferent) and vagus nerve (efferent). While mainly associated with stimulation of the ophthalmic nerve, it can occur with any branch of the trigeminal nerve.
* The incidence is highest in children (up to 90% without pre-treatment with atropine).
* For prophylaxis in children, atropine 0.02 mg/kg or glycopyrrolate 0.01 mg/kg prior to surgery is indicated.
* Intramuscular atropine is not useful due to delayed onset.
* Prophylaxis in adults is not indicated.
* Treatment of bradycardia includes removal of stimulus or asking the surgeon to stop the stimulation, initiation of intravenous anticholinergics (eg atropine 5-10 mcg/kg or glycopyrrolate 2.5-5 mcg/kg), and checking depth of anaesthesia (where GA is used).

TOPICAL ANESTHESIA

Instillation of LA eye drops provides corneal anesthesia, thus allowing for cataract surgery by PhE ( Figure 12). This technique is quick and simple to perform and avoids the potential hazards of needle techniques. It has been suggested that the lack of akinesia and intraocular pressure control, associated with the short duration of this technique, may make surgery hazardous;90 however, this observation does not appear to have dented the growing popularity of the technique. Many US surgeons appear to prefer topical anesthesia for routine PhE in more than 90% of their cases.
Nevertheless, use of topical anesthesia should be limited to uncomplicated procedures performed by experienced surgeons in cooperative patients. In parts of the world where PhE is not technically available, and in some specific indications where PhE is not feasible, total akinesia is still required, and the use of topical anesthesia may be questionable.
As to what patients actually prefer, there are conflicting reports. Boezaart has reported that because anesthesia may be incomplete in topical approaches, patients randomly subjected to one of these techniques for one eye and another technique for the other eye preferred the retrobulbar to the topical technique (71% versus 10%).

Patients consistently report less intraoperative discomfort under retrobulbar or sub-Tenon's anesthesia compared to topical anesthesia. On the other hand, a meta-analysis by Zhao et al. reported that patients overwhelmingly preferred topical anesthesia over needle nerve blocks, citing "fear of needles" as a key reason, despite finding that the same population of patients reported more intraoperative discomfort under topical anesthesia compared to needle nerve blocks. In some experienced hands, no anesthesia at all appears to be as effective as topical anesthesia in selected cases.
An intracameral injection of LA appears to substantially enhance analgesia with a topical approach. This consists of injecting small amounts (0.1 mL) of LA into the anterior chamber at the beginning of or during surgery. Intracameral anesthetic agents must be preservative free. Some concerns have been expressed about the toxicity effects of LA on the corneal endothelium, which is unable to regenerate; however, the safety of intracameral injection now seems well established. Some authors have questioned its analgesic benefit when compared with simple topical anesthesia,and indeed the degree of analgesia does not seem to correlate with intracameral LA concentration. Nevertheless, the combination of topical plus intracameral anesthesia is currently the technique most preferred by US ophthalmic surgeons.
The insertion of sponges soaked in LA into the conjunctival fornices has been proposed. The use of lidocaine jelly instead of eye drops seems to enhance the quality of analgesia of the anterior segment and is becoming very popular for improving patient comfort under topical anesthesia.

Direct Corneal Epithelial Toxicity of Topical Anesthetics

From animal studies, it has been known for some time that repeated applications of virtually all topical anesthetic agents cause some degree of transient corneal epithelial toxicity that is macroscopically apparent, including reversible corneal thickening and opacification. Changes may be evident with even a single topical application, and these may take more than an hour or more to recover. In humans, topical anesthetic abuse is a known cause of severe keratopathy among arc welders and metalworkers, and even in patients who overuse their "comfort drops" after refractive keratectomy.
Transient corneal edema has been noted in patients undergoing cataract surgery under topical ropivacaine or lidocaine. Fernandez et al. reviewed the condition of corneal epithelia by slit-lamp examination the day after cataract surgery under topical levobupivacaine or lidocaine. They found mild epithelial changes in 17-22% of patients and signs of significant epithelial damage (punctate) in 2.4-5.8%, respectively; however, no data were provided on how, when, or whether these changes resolved.
Nevertheless, to date, no cases of severe keratopathy associated with the routine administration of topical anesthesia for eye surgery have been reported. The current relative paucity of hard clinical data may in part explain the diversity of practice across continents, as practitioners may interpret what data there is to affirm their own preferences. Given the growing popularity of the technique (especially in the US), one might assume that, as for extraocular myotoxicity, any clinically significant effect is transient and may be masked by and/or attributed to the effects of surgery during convalescence.

SUBCONJUNCTIVAL ANESTHESIA

Subconjunctival injection of LA, a technique relatively unfamiliar to many anesthesiologists, provides anesthesia of the anterior segment without akinesia. Also known as "perilimbal" anesthesia, it is, in effect, a form of episcleral injection and can also be thought of as a "very anterior" or "very superficial" Sub-tenon's nerve block. This nerve block is useful for cataract, pterygium, and superficial glaucoma surgery. After pretreatment with one drop of topical anesthetic, a fine-bore (27- to 30-gauge) needle is used to lift the superotemporal or inferotemporal conjunctiva at least 5-8 mm from the limbus ( Figure 13). A surgical microscope or loupes can be used to avoid conjunctival vessels and hematoma. Once the needle is under the conjunctiva, 0.5-0.8 mL of local anesthetic solution will cause chemosis, which is dispersed with gentle, constant pressure, either using fingers or a purpose-specific weight or balloon. Hyaluronidase can be added to assist with the spread of solution and dispersal of chemosis. Compared to retrobulbar injection, this technique is less painful and reduces the need for supplemental anesthesia during cataract surgery. Injection at the superotemporal conjunctiva appears to be less painful than injection at the inferotemporal conjunctiva. Subconjunctival injection results in reliable and substantial concentrations of local anesthetic in the aqueous humor.

OCULOPLASTIC NERVE BLOCKS

Many oculoplastic procedures ( Figure 14) can be performed under local anesthetic. However, given the sensitive innervation of the face, these nerve blocks are best performed under some form of transient, deep sedation (eg, a small IV dose of propofol), except in the very stoic patient. Note also that, while targeted block of individual nerves is useful, there is often significant overlap of sensory supply. Depending on the site and extent of the proposed operative wound, more than one type of nerve block may be required, and supplemental local infiltration may be necessary. Most oculoplastic surgeons are quite accustomed to this.

Upper and Lower Lid nerve blocks

Procedures such as upper and lower blepharoplasty and ectropion repair can be performed under gentle subcutaneous local infiltration of the base of the operative lid. Certain procedures require the surgeon to evert the eyelid under deep sedation and infiltrate distal to the semilunar fold.

Facial Nerve Block

Occasionally, a nerve block of the periocular branches of the facial nerve is required to prevent excessive blinking during eye surgery. Classical approaches include the Van Lint and O'Brien techniques; Atkinson has described a modified technique, variants of which are probably most popular today. A bleb of local anesthetic is raised about 2-3 cm lateral to the lateral rim of the orbit at the level of the lateral canthus, which is somewhere between the locations of the more distal Van Lint and the more proximal O'Brien approaches. Two radii of local infiltration are then injected superiorly and inferiorly from this point forming a "V" that catches the fibers of the facial nerve. A total of 5 mL is typically more than sufficient.

Supratrochlear/Supraorbital Nerve Block

Nerve Blocks of the supraorbital and supratrochlear nerves, branches of the ophthalmic nerve, are useful for procedures that involve the upper eyelid area immediately at or above the eyebrow. The supraorbital notch can usually be felt about 2-3 cm from the midline along the medial part of the superior rim of the orbit, usually in line with the patient's pupil. Paresthesia can often be elicited by pressing on this notch. A volume of 2 mL of local anesthetic here should provide some anesthesia to the area immediately around the eyebrow, the upper eyelid, and the lower forehead; however, it is usually also necessary to nerve block the supratrochlear nerve by running a medial band of infiltration (an additional 2-3 mL) from the notch to the midline and approximately 1-2 cm laterally to catch lateral supraorbital fibers that can arise through a separate foramen.

Infraorbital Nerve Block

The infraorbital nerve, a major branch of the maxillary nerve, supplies sensation to the lower eyelid and the floor of the orbit. It emerges onto the face through the infraorbital foramen, which is reliably found just below the inferior orbital rim, in line with both the pupil and the supraorbital notch. A volume of 2-3 mL of local anesthetic at this point is usually more than enough. In the traditional approach to this nerve block, the needle is directed slightly upward to align with the orientation of the infraorbital canal; however, note that at least two cases of inadvertent globe penetration have been reported with this technique.

Nasocilary/Infratrochlear/Anterior Ethmoidal Nerve Block

The nasocilary nerve is a branch of the ophthalmic nerve and supplies, via its intratrochlear and anterior ethmoidal branches, sensation to the medial wall of the orbit, the proximal lacrimal sac, the proximal nasolacrimal duct, the mucosa of the nasal cavity, and much of the skin of the nose. This nerve is blocked via an injection of 2-3 mL of local anesthetic by a vertical insertion of a fine-gauge needle parallel to the medial wall of the orbit approximately in line with the bridge of the nose to a depth of about 25 mm. This corresponds with the foramen through which the anterior ethmoidal nerve exits the orbit. It is important that the needle descend freely to the point of injection, as the orbital wall is thin at this level, and perforation of the ethmoidal and even sphenoidal sinuses is quite possible.

Local Anesthesia for Tear Duct Surgery

Local anesthesia for dacryorhinocystostomy and other procedures involving the lacrimal apparatus is possible using a combination of topical anesthesia of the nasal cavity (for the nasal branches of the anterior and posterior ethmoid, sphenopalatine, and nasopalatine nerves), a nasociliary nerve block, an infraorbital nerve block, and a short band of subcutaneous infiltration along the base of the nose from the level of the medial canthus to the level of the infraorbital foramen.

USE OF EYE NERVE BLOCK FOR POSTOPERATIVE ANALGESIA

Regional anesthesia, especially the sub-Tenon's nerve block, has been proposed as a treatment for postoperative pain.122 However, this is not required for anterior segment surgery, which usually results in minimal or no discomfort postoperatively.

NYSORA TIPS

Postoperative Pain
* Significant pain occurring after cataract surgery is unusual and should raise suspicion for increased intraocular pressure, severe inflammation, or infection; the eye should be examined by an ophthalmologist.
* Postoperative pain is more likely after posterior segment surgery. The use of an indwelling retrobulbar, peribulbar, or sub-Tenon's catheter has been proposed to improve intraoperative anesthesia, prolong postoperative regional analgesia, and treat intractable eye pain.

CHOICE OF LOCAL ANESTHETIC AND ADJUVANT AGENTS

All available LAs have been used for eye nerve block, either alone or as a combination of two agents. The injected LAs used most often are lidocaine, bupivacaine, ropivacaine, mepivacaine, or a combination of two of these. The choice of LAs should be based on the pharmacologic properties and availability of the drugs, with the primary consideration being the requirement for quick onset (lidocaine, mepivacaine), prolonged effect, or postoperative residual nerve block for analgesia (ropivacaine, bupivacaine) or akinesia (higher concentration). Because the amount of LA injected is usually small (3-11 mL), systemic toxicity is not a major concern.
Septocaine (articaine) is a relatively novel amide-type LA, commonly used in dentistry, with an emergent use in eye nerve blocks. It has a faster onset than bupivacaine/lidocaine preparations in peribulbar and sub-Tenon's nerve blocks and, because it appears to diffuse through tissues more readily than other LAs, often results in a denser nerve block. There appears to be no clinical advantage of 4% over 2% articaine, at least in dental anesthesia. Despite concerns about its neurotoxic potential in animal studies, there does not seem to any conclusive evidence that it is more toxic than other high-concentration LAs.
Hyaluronidase is an enzyme that has been widely used to facilitate the spread of local anesthetic through connective tissue, thereby improving both the onset and success rate of regional anesthesia for the eye. Another benefit is a reduced incidence of postoperative strabismus connected with its use, possibly by limiting LA myotoxicity owing to its faster spread.
Some authors are less confident about the real benefit of hyaluronidase in improving akinesia. There are also significant concerns about its allergenic potential; however, these may be due to the impurities intrinsic to traditional animal-derived hyaluronidase; newer human recombinant products have been shown to be not only more potent but also to have higher enzyme purity and to be virtually free of hypersensitivity reactions. It would appear that, as the requirement for akinesia relaxes, adjuvants such as hyaluronidase are becoming less popular. Nevertheless, in situations where akinesia is required, hyaluronidase may still have an important role.
α2-adrenergic agonists are well known to ophthalmologists as topical agents that reduce intraocular pressure in glaucoma.
Clonidine has been shown to enhance intraoperative anesthesia and postoperative analgesia when added to the LA in a range of eye nerve blocks. At a dose of 1 mcg/kg, clonidine does not increase the incidence of systemic adverse events such as hypotension or excessive sedation. Moreover, it may help to prevent intraoperative arterial hypertension and lower intraocular pressure. Dexmedetomidine, a more highly selective α2 agonist, has been used increasingly as an effective adjuvant in peripheral nerve blocks, including the sub-Tenon's nerve block. It has been proposed that the addition of α2 agonists may allow for surgical anesthesia at lower concentrations of LA, thereby limiting
LA-induced myotoxicity. It should be noted that all studies on α2 adjuvants to date have been relatively low-powered, and, while this is a promising area of study, substantially higher sample sizes are required. Epinephrine is sometimes used to increase the duration of eye nerve block. However, the availability of long-acting LAs and the fear of vasospasm with subsequent retinal ischemia have decreased its use. "Wipe-out" (a sudden total sight loss not overtly related to ocular pathology) is a rare but serious risk, particularly in glaucoma patients. LA solutions containing epinephrine have been implicated as a contributing factor.
Alkalinization of local anesthetic solutions has been proposed for decreasing pain during injection and accelerating nerve block onset; however, its efficacy remains unproven. Other adjuvant agents have been proposed but have not gained popularity. Small doses of a muscle relaxant may enhance akinesia, but concern has been expressed about their potential risk for systemic effects.
Opioids do not appear to be more efficient via a regional ophthalmic route than via systemic administration.
Warming the LA may decrease pain on injection and enhance nerve block efficacy, although these benefits do not appear to be clinically relevant.

WHO SHOULD PERFORM EYE NERVE BLOCKS?

Since the 1980s, anesthesiologists have become increasingly involved in eye nerve blocks that previously were performed by surgeons. However, in some countries, anesthesiologists are not available, and surgeons have to manage the nerve block themselves. In other countries, anesthesiologists monitor only the anesthesia care, as the surgeon performs the nerve block. In many developed countries (eg, France and Australia), anesthesiologists are often responsible for administering eye nerve blocks. The same was true in the United Kingdom; however, recent cost constraints have forced managers to reconsider the role of the anesthesiologist in elective ophthalmic procedures that do not require a general anesthetic. There are currently no hard data to support or refute the idea that having the anesthesiologist performing eye nerve blocks, rather than the surgeon, or even having the anesthesiologist in attendance, is safer for this patient population. However, the available literature does suggest that with proper training, anesthesiologists can perform eye nerve blocks with the same degree of safety as in other regional anesthesia techniques. Having one experienced person performing nerve blocks while another operates is more time efficient, and there is a theoretical benefit to having a person skilled in resuscitation present in the unlikely event of a life-threatening complication (which, unsurprisingly, materializes into an actual benefit whenever such a complication occurs).

PERIOPERATIVE MANAGEMENT OF PATIENTS UNDERGOING EYE NERVE BLOCK

Patient Selection and Assessment

Older patients undergoing eye surgery frequently have coexisting diseases such as diabetes mellitus, hypertension, coronary artery disease, or cardiac insufficiency. A preoperative assessment should be routinely done to ensure that coexisting medical conditions are reasonably well controlled. Despite the low morbidity and mortality associated with local ophthalmic anesthesia, patients should be carefully screened for their eligibility for surgery. Patients with severe kyphosis or scoliosis pose obvious practical problems for microscopic surgery. Patients who may not be able to lie flat for the requisite period, due to cardiac or respiratory insufficiency, neurological disease, or dementia, are also challenging. Once draped, patients with profound deafness may be unable to respond to intraoperative commands unless carefully briefed preoperatively.

Briefing Patients

Given the potential problems of excessive sedation (see below), an empathic and interactive preoperative briefing is a useful tool for both reducing anxiety and optimizing cooperation during eye surgery. Patients should be given a clear explanation of what will be done to them, what they are likely to experience, and what they may be asked to do during the operation, in language appropriate to their level of understanding.

Monitoring

Intraoperative monitoring should include basic monitoring (ie, electrocardiogram, pulse oximetry, and automated noninvasive blood pressure measurement). Intravascular access is required for any invasive anesthetic technique.

Sedation

Eye surgery (eg, cataract surgery) carries a low risk of perioperative morbidity and mortality. Eye nerve block is associated with lower perioperative morbidity than is general anesthesia used for ophthalmic surgery, provided that heavy sedation is avoided. Anxiety and residual pain frequently occur during eye surgery under LA. Perfect immobility is required, and the presence of drapes over the head increases patient anxiety and impairs access to the airway. The patient should be positioned as comfortably as possible, with sufficient space to allow free breathing. Intraoperative sedation with judicious doses of sedatives may be used to limit anxiety and pain. However, an excess of sedation may lead to restlessness, sleeping, snoring, or respiratory depression, which, in the absence of any airway access, pose a significant intraoperative challenge. Maintenance of meaningful patient contact is of paramount importance to avoid disasters that can occur with disoriented or combative patients while the surgery is underway.
Another interesting and dangerous phenomenon associated with ophthalmic needle nerve blocks performed under propofol sedation is involuntary sneezing, which may occur in up to one-fifth of patients during injection; this reaction is sight-threatening, as it can lead to accidental globe perforation. It is more likely to occur in patients who are male, have a history of photic sneezing (sneezing with sudden exposure to bright light or sunshine), are under deeper sedation, or who are given concurrent midazolam. It does not appear to occur in patients undergoing nerve blocks with remifentanil sedation or with no sedation at all. Awareness of this phenomenon should better prepare operators to withdraw the nerve block needle immediately if a sneeze is imminent and possibly reconsider their current sedation practice. Dexmedetomidine, a highly selective α-agonist, is gaining some popularity as a sedative agent in a range of clinical settings, including eye surgery.

Do Patients Undergoing Eye Nerve Block Need to Fast?

Fasting practices for patients having procedures under topical, local, or regional nerve block have undergone an evolution in recent years. In the complex machine of public-sector medical practice, the well-intentioned and traditional "NPO from midnight" doctrine often leads to patients fasting well in excess of 12 hours. In addition to an increased likelihood of postoperative nausea and vomiting, inappropriately prolonged fasting can cause discomfort and distress, as well as dehydration and metabolic derangements, all of which can make patients (especially children and the elderly) restless and uncooperative. Moreover, while there is an obvious theoretical case for fasting prior to any surgical procedure, there have been no reported cases of aspiration under local anesthesia during cataract operations. The joint view of the learned colleges in the United Kingdom is that fasting is generally not required for patients undergoing eye surgery without sedation. Moreover, at least one experienced ophthalmic center has performed nerve blocks under "judicious doses" (0.5-2 mg) of IV midazolam in over 5000 unfasted patients without untoward incident. Nevertheless, where it is anticipated that deep sedation or general anesthesia, however brief, will be needed either to perform the nerve block or during the operation, then standard preoperative fasting remains a sensible prerequisite, and, where needed, systemic measures should be explored to minimize inappropriately prolonged fasting. Where fasting is not routinely required, a small proportion of problematic patients will present for surgery unfasted but for whom the need for deep sedation becomes obvious once they are in the operating room. Individual institutions need to audit the prevalence of this phenomenon and to make cost and risk-benefit decisions accordingly. A comprehensive and compassionate preoperative patient briefing may have an important role in minimizing this issue.

Is Intravenous Access Required in Patients Undergoing Eye Nerve Block?

In recent years, many centers, particularly those performing office-based eye procedures, have abandoned the traditional requirement of securing IV access for all surgical procedures, provided that procedures are performed under "needleless" anesthesia (ie, topical anesthesia or sub-Tenon's nerve block). According to a joint statement of the Royal College of Anaesthetists and the Royal College of Ophthalmologists in the UK, "Intravenous access ... is essential with peribulbar and retrobulbar nerve blocks and when intraoperative sedation is used" and "recommended for long/complex cases, sub-Tenon's nerve blocks, and patients with poor general health." In relation to this, the author is in agreement with Guise in making the following observations: (1) Sedation may occasionally be required at very short notice by patients even under topical anesthesia, and prior IV access makes timely sedation easier and less stressful; (2) vasovagal and other dysrhythmic reactions, while uncommon, may also occur, in which case IV access already in situ is beneficial for both patient and resuscitator; and (3) it is a prudent clinical precaution, and no real trouble, if a person experienced in IV cannulation (such as an anesthesiologist) is in attendance.

Eye Nerve Blocks and the Anticoagulated Patient

Traditionally, anesthesiologists would often make a formulaic decision whether to perform an ophthalmic regional nerve block (which was usually a retrobulbar or peribulbar nerve block) based on results of a blood-clotting profile and by nominating an arbitrary cut-off point (eg, an international normalized ratio [INR] of 1.5-2.0 or a platelet count of 50-100). Nowadays, however, there is not only a diversity of anticoagulant therapies (several of which defy easy assessment), but also a range of anesthetic management options. Moreover, the risks of discontinuing anticoagulant therapy in some patients may outweigh the risks of perioperative bleeding on full anticoagulation. Consequently, there is no clear algorithm for managing "patients undergoing eye surgery who are on anticoagulants." It is best to make a balanced benefit-versus-risk decision in each case based on a number of fundamental questions:

* Which anticogulant(s) is the patient taking? A variety of agents are now available. While there are established management strategies for drugs such as warfarin and heparin, strategies for others are less straightforward.
Dabigatran, for example, is a novel long-acting oral anticoagulant with no direct antidote. The perioperative management of potential bleeding in patients on this drug is currently a matter of much concern, including those undergoing eye surgery. Since there are currently no data on patients on dabigatran undergoing eye nerve block, including sub-Tenon's nerve block, current recommendations are to withhold the drug for two to five days prior to performing the nerve block and surgery.
* Why is the patient being anticoagulated? Occasionally, patients self-initiate aspirin intake (eg, because they have read about it in a magazine). It is common for patients to be treated with warfarin for acute-onset atrial fibrillation that spontaneously reverts. Such situations make it easier to consider withholding the drug rather than choosing not to perform the nerve block.
* Is the patient in a high-risk group (eg, with a documented history of thromboembolism)? Often, there is not only a clear clinical indication for anticoagulation, but also a clear increased risk if perioperative anticoagulation is not managed correctly, and therefore a greater imperative to use a technique that does not require the patient's anticoagulant therapy to be modified. When in doubt, consult with the medical team that started the patient on anticoagulant therapy.
* What are the relative bleeding risks of the procedure proposed? Here, the team should consider both the surgical and anesthetic procedures. Oculoplastic and glaucoma surgeries tends to carry a higher bleeding risk, whereas most PhE and vitreoretinal procedures can be done on full anticoagulation (however, discuss individual cases with the surgeon, as the decision is ultimately his or hers).
Generally, topical, subconjunctival, and sub-Tenon's nerve blocks are considered low risk, and the limited evidence to date supports going ahead with these techniques without altering the patient's routine anticoagulant therapy. Lowpowered studies suggest that, while minor bleeding complications such as subconjunctival hematoma are more frequent with sub-Tenon's nerve blocks performed in patients on aspirin, warfarin, or clopidogrel, major complications such as sight-threatening bleeding are not. Retrobulbar and peribulbar nerve blocks are considered high risk.
* What are the surgical requirements for anesthesia? Where akinesia is not required for anterior segment surgery, topical or subconjunctival techniques are more attractive. If posterior segment anesthesia and/or akinesia are needed and there are no other contraindications, sub-Tenon's nerve block is now seen to be the safest option.
* Is it an elective case or a true emergency? Where there is time to take a more gradual approach that avoids the use of antidotes and prothrombotic agents, this opportunity should be taken.

Working with High-Volume Surgeons

Running a high-turnover cataract list (20 or more patients a day) safely and efficiently is both a science and an art form requiring not only consummate individual technical skill but also good teamwork and communication skills, as well as attention to ergonomic detail. A good surgeon will include all members of his or her theater team in the planning and execution of the list. The anesthesiologist's role is to support the team both technically and tactfully, monitoring the whole team and signaling when the team should slow down or even stop. Standardization wherever possible-from role allocation and patient trolley positioning to the vocabulary used to describe equipment and procedures-helps to streamline activities and to make deviations from routine more salient. The use of a modified World Health Organization (WHO) surgical safety checklist in a fast-paced eye theater may also help to detect anomalies and reduce errors. Regular feedback and discussion of individual and team performance helps to promote kaizen: the approximation of perfection through small, continuous, incremental improvements over time.

SUMMARY

In developed countries, eye surgery is among the most frequently performed surgical procedures requiring anesthesia.
During the past 20 years, anesthesiologists have assumed a growing role in performing eye nerve blocks. The requirement for a deep anesthetic nerve block with total akinesia has been greatly lessened through the use of PhE for cataract surgery, giving a more prominent role to topical anesthesia.
Needle Nerve blocks carry a low but real risk of serious complications, mainly the result of needle misplacement. Training and practice are required to minimize such problems. The use of the sub-Tenon's nerve block reduces the risks of needle nerve blocks and is now an established and popular technique, although it does not completely prevent complications. The right anesthetic technique is informed by the anesthesiologist's skill, experience, and understanding of the surgical procedure and the individual surgeon's preferences.
Tips from the Compendium of Regional Anesthesia

Perfect immobility is required. Therefore, the patient should be positioned as comfortably as possible, with sufficient space to allow free breathing.

Intraoperative sedation with judicious doses of sedatives may be used to limit anxiety and pain. However, an excess of sedation may lead to restlessness, sleeping, snoring, or respiratory depression, which, in the absence of any airway access, pose a significant intraoperative challenge.

Maintenance of meaningful patient contact is of utmost importance to avoid disasters that can occur with disoriented or combative patients.

Fasting is generally not required for patients undergoing eye surgery without sedation. Nevertheless, standard preoperative fasting remains a prerequisite when it is anticipated that deep sedation or general anesthesia, however brief, will be needed (either to perform the block or during surgery).

Oculoplastic and glaucoma surgeries tend to carry a higher bleeding risk, whereas most phacoemulsification and vitreoretinal procedures can be done on full anticoagulation (however, discuss individual cases with the surgeon).

Topical, subconjunctival, and sub-Tenon's blocks have a low bleeding risk, whereas retrobulbar and peribulbar blocks are considered high-risk.

APPENDIX: THE OCULOCARDIAC REFLEX

The oculocardiac reflex, first described in 1908; is a decrease in heart rate over 20% below baseline values often seen during traction on the extrinsic muscles of the eye, particularly during strabismus surgery. However, it can also occur during the administration of eye nerve blocks, particularly retrobulbar nerve block.
Other triggers include ocular trauma, intraorbital hematoma, acute glaucoma, a sudden increase in intraocular pressure, stretching of the eyelid muscles, and conjunctiva. In unprepared subjects, bradycardia can be quite dramatic, and occasionally leading to asystole in the patient (and tachycardia in the anesthesiologist), which lasts as long as the triggering stimulation is applied. While sinus slowing of the heart is classical, any arrhythmia including ventricular fibrillation may occur.
The reflex is exaggerated in children (in up to 90% without pretreatment) and in the presence of hypoventilation, hypoxemia, and acidosis.
The reflex arc has been well described ( Figure 15), the afferent limb consisting of the long and short branches of the ciliary nerves, the ophthalmic nerve, the geniculate ganglion, and the main sensory nucleus of the trigeminal nerve. Short internuncial fibers then convey the reflex to the efferent limb, consisting of the motor nucleus of the vagus, the vagus nerve, and the cardiac depressor nerve. The oculocardiac reflex is a specific variant of the trigeminocardiac reflex, a wider constellation of brainstem-mediated reactions-bradycardia, sweating, breath holding, yawning, sneezing, and so on-triggered by stimulation of any of the sensory branches of the trigeminal nerve (primarily the ophthalmic nerve).
The best treatment in children is prophylaxis: IV atropine 10-20 mcg/kg or glycopyrrolate 5-10 mcg/kg on induction. Intramuscular agents are less useful due to their delayed onset. Prophylaxis in adults is usually not indicated; however, it is prudent to have an IV anticholinergic predrawn and available.
Acute treatment consists of removing the stimulus: Ask the surgeon to stop whatever they are doing. If the pulse does not improve, give an anticholinergic (eg, IV atropine 5-10 mcg/kg or glycopyrrolate 2.5-5 mcg/kg). Check the depth of anesthesia in cases of GA.

Acknowledgments

The author would like to thank Jacques Ripart, Kenneth Mehbridge, and Robert Della Rocca for their first-edition version of this chapter and without whom this revision would not have been possible. Thanks with deep gratitude also to Keith Allman, Tom Eke, Phil Guise, and Chandra Kumar, all of whom devoted substantial time and effort to offer invaluable suggestions and additional references.

*Sources: Aschner B. Ueber einen bisher noch nicht beschrieben Reflex vom Auge auf kreislauf and Atmung. Verschwinden des Radialpulsen bei Druck aut des auge. Wiener Klinische Wochenschrift 1908;21:1529-1530; Dagnini G. Intemo ad un riflesso provocato in alcuni emiplegici collo stimolo della come e colla pressione sul bulbo oculare. Bull Sci Med 1908;8:380-381.

Continue reading Nerve Blocks of the Face

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Glantz L, Drenger B, Gozal Y: Perioperative myocardial ischemia in cataract surgery patients: General vs local anesthesia. Anesth Analg 2000;91:1415-1419.

Katz J, Feldman MA, Bass EB, et al. Adverse intraoperative medical events and their association with anesthesia management strategies in cataract surgery. Ophthalmology 2001;108:1721-1726.

Abramson DC. Sudden unexpected sneezing during the insertion of peribulbar block under propofol Sedation. Can J Anaesth1995;42(8): 740-3.

Ahn ES, Mills DM, Meyer DR, Stasior GO: Sneezing reflex associated with intravenous sedation and periocular anesthetic injection. Am J Ophthal 2008;146:31-35.

Boezaart AP, Berry RA, Nell MA, van Dyk AL: A comparison of propofol and remifentanil for sedation and limitation of movement during periretrobulbar block. J Clin Anesth 2001;13:422-426.

Morley AM, Jazayeri F, Ali S, Malhotra R: Factors prompting sneezing in intravenously sedated patients receiving local anesthetic injections to the eyelids. Ophthalmology 2010;117:1032-1036.

Schaack E, Diallo B et al. [Inadvertent globe perforation during peribulbar anaesthesia and sedation with propofol]. Ann Fr Anesth Reanim 2006;25(1):43-5.

Steeds C, Mather SJ. Fasting regimens for regional ophthalmic anaesthesia: a survey of members of the British Ophthalmic Anaesthesia Society. Anaesthesia 2001;56:638

Crenshaw JT, Winslow EH: Preoperative fasting: old habits die hard. Am J Nurs 2002;102:36-44.

The Royal College of Anaesthetists. Guidelines for the Provision of Anaesthetic Services. Chapter 13: Guidance on the Provision of Ophthalmic Anaesthesia Services. London, 2015 weblink http://www.rcoa.ac.uk/system/files/GPAS-2015-13-OPHTHAL.pdf accessed 31 August 2016

Royal College of Anaesthetists, Royal College of Ophthalmologists: Local anaesthesia for ophthalmic surgery. Joint guidelines from the Royal College of Anaesthetists and the Royal College of Ophthalmologists. London, 2012. http://www.rcoa.ac.uk/system/files/LA- Ophthalmicsurgery-2012.pdf accessed 31 August 2016

Guise P, personal communication, July 16, 2013.

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Local and Regional Anesthesia for Ophthalmic Surgery - NYSORA

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Ophthalmic surgery is one of the most common surgical procedures requiring anesthesia in developed countries. Ophthalmic anesthesia offers insights into some fundamental principles of good anesthetic practice, especially in the conduct of local and regional nerve blocks. Clinical strategies to minimize patient movement during eye surgery are essential.

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Curriculum: Describes ophthalmic blocks for patients undergoing awake ophthalmic surgery

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Curriculum: Describes ophthalmic blocks for patients undergoing awake ophthalmic surgery

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Short video of sub-Tenon’s block

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Full and exam orientated description of conduct of epidural and subarachnoid blockade

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Anaesthesia UK : Conduct of epidural and subarachnoid blockade

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In 1898, the first subarachnoid blockade in man was performed by Karl August Bier using a cocaine solution. From 1930 to 1950, spinal techniques were used widely for anaesthesia, but subsequently declined in popularity, partly because of the fear of toxicity and partly owing to the improvements in g…

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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ultrasound then spinal in morbidly obese patient

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Difficult Spinal in Obese Patient- Crash course with Dr. Hadzic

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Curriculum: Performs spinal anaesthesia for ASA 1-3 surgical patients independently

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Suggests an approach to a difficult spinal, using needle as the examining tool

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Difficult spinal, needle as the examining tool - Regional anesthesia Crash course with Dr. Hadzic

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I have missed this out as you get a specific session on this in the program, but be aware that a stage 1 curriculum item is:
"Provides epidural or combined spinal-epidural analgesia for labour in the ASA 1-3 obstetric patient, and offers other forms of pain relief when neuraxial analgesia is contraindicated"

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Curriculum: Identifies and initiates initial management of complications of regional anaesthesia including systemic local anaesthetic toxicity, 

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Curriculum: Identifies and initiates initial management of complications of regional anaesthesia including systemic local anaesthetic toxicity, 

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The Association Quick Reference Guides are useful exam reading

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Can be due to spinal dosage; migration (more common with isobaric mixtures); Epidural migration; spinal top up of recent epidural load
Also recognised complications of "peripheral" nerve blocks such as Interscalene Brachial / Lumbar Plexus Blocks (if the injection is within the dural cuff of a nerve root)

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Key points
Headache is a common symptom in the postpartum period.
There are numerous causes of postpartum
headache, some of which can be severely debilitating and require urgent treatment.
All women who experience accidental dural
puncture or postdural puncture headache (PDPH)
should be reviewed by a member of the anaesthetic team.
Other differential diagnoses should be considered
before postdural puncture headache is
diagnosed.
Conservative management of PDPH is frequently
inadequate, and an epidural blood patch is the
most effective treatment.

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Dural puncture headache: more detailed account

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Dural puncture headache: more detailed account

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This is a comprehensive account, but my take home messages are:
•Can have wide differentiation including neurology referral or MRI

•Onset is typically within 2–3 days of the dural puncture, but can occasionally be much sooner or later

•Symptoms are classically a searing frontal or occipital headache, sometimes exacerbated by head movement / upright posture, and relieved by lying down

•Symptoms can, however, be confusingly nebulous eg neck stiffness, nausea, vomiting, hearing loss, tinnitus, vertigo, paraesthesia and visual disturbance.

Therapy:
•Get an expert in, someone who sees them often, normally an obs anaes:

•maximum analgesia, typically paracetamol, an NSAID and a weak opioid.

•Failure of this regimen should prompt consideration of an epidural blood patch.

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Postural headaches following interventions that disrupt meningeal integrity are most commonly labeled postdural puncture headaches (PDPHs). This terminology has been officially adopted in the International Classification of Headache Disorders and is used in this chapter.

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👍A mini lecture on U/S and equipment tips and advice

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👍A mini lecture on U/S and equipment tips and advice

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Advantages
Imaging and artefacts
Needle choice and cautions
Use of nerve stimulators
Test injections

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Curriculum: Discusses drugs and equipment used in regional anaesthesia

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Curriculum: Discusses drugs and equipment used in regional anaesthesia

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Summary of Local Anaesthetic and Additive drugs

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Anaesthesia UK : Local anaesthetic and additive drugs

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Local anaesthetics reversibly block nerve impulses and are the mainstays of regional anaesthesia. Local anaesthetics can be divided into two main groups, esters (e.g. cocaine, procaine, chloroprocaine, tetracaine) and the more commonly used amides (e.g. lidocaine, prilocaine, bupivacaine). The newer…

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Curriculum: Discusses drugs and equipment used in regional anaesthesia, if you prefer a video

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Curriculum: Discusses drugs and equipment used in regional anaesthesia, if you prefer a video

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Video: How to Choose Local Anaesthetics for Nerve Blocks:

Useful summary at 14 mins onwards

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How to Choose Local Anesthetics for Nerve Blocks - Crash course with Dr. Hadzic

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Apart from adrenaline which is pre-mixed, at best modest evidence published for the adjuncts used in practice. NB Caution mixing drugs . Its normally unlicensed practice, and an opportunity for potentially catastrophic drug error.

Dexamethasone 8mg added to brachial plexus blocks “shown” to prolong block significantly. However, likely publication bias and iv dexamethasone has been shown to have similar effects to interscalene administration.

Clonidine: neutral published evidence for peripheral nerve blocks.

Spinal clonidine: less is more. It is likely that the ceiling dose for prolonging the block is less than the ceiling dose for side effects (mainly hypotension). So higher doses cause more side effects than lower doses, without extra benefits. 15-30 mcg intrathecally reasonable practice.

Opioids: more evidence of safety and benefit. Again, less is more. No evidence of one opioid over another for safety, but fentanyl/diamorphine/morphine last 6/12/24 hours respectively. Local practice is preservative free morphine. Again less is more: significant nausea/itching (and presumably respiratory failure) at doses higher than 150mcg, with no apparent increase in analgesic effect. 100-150 mcg intrathecally reasonable practice.

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Curriculum: Discusses the scientific basis of ultrasound and the generation of ultrasound images

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Curriculum: Discusses the scientific basis of ultrasound and the generation of ultrasound images

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INTRODUCTION

Ultrasound application allows for noninvasive visualization of tissue structures. Real-time ultrasound images are integrated images resulting from reflection of organ surfaces and scattering within heterogeneous tissues. Ultrasound scanning is an interactive procedure involving the operator, patient, and ultrasound instruments. Although the physics behind ultrasound generation, propagation, detection, and transformation into practical information is rather complex, its clinical application is much simpler. Because ultrasound imaging has improved tremendously over the last decade, it can provide anesthesiologists opportunity to directly visualize target nerve and relevant anatomical structures. An ultrasound-guided nerve block is a critical growth area for new applications of ultrasound technology and has become an essential part of regional anesthesia. Understanding the basic ultrasound physics presented in this section will be helpful for anesthesiologists to appropriately select the transducer, set the ultrasound system, and then obtain satisfactory imaging.

HISTORY OF ULTRASOUND

In 1880, French physicists Pierre Curie and his elder brother, Paul-Jacques Curie, discovered the piezoelectric effect in certain crystals. Paul Langevin, a student of Pierre Curie, developed piezoelectric materials, which can generate and receive mechanical vibrations with high frequency (therefore ultrasound). During World War I, ultrasound was introduced in the navy as a means to detect enemy submarines. In the medical field, however, ultrasound was initially used for therapeutic rather than diagnostic purposes. In the late 1920s, Paul Langevin discovered that high-power ultrasound could generate heat in bone and disrupt animal tissues. As a result, throughout the early 1950s ultrasound was used to treat patients with Ménière disease, Parkinson disease, and rheumatic arthritis. Diagnostic applications of ultrasound began through the collaboration of physicians and sonar (sound navigation ranging) engineers. In 1942, Karl Dussik, a neuropsychiatrist, and his brother, Friederich Dussik, a physicist, described ultrasound as a medical diagnostic tool to visualize neoplastic tissues in the brain and the cerebral ventricles. However, limitations of ultrasound instrumentation at the time prevented further development of clinical applications until the mid-1960s. The real-time B-scanner was developed in 1965 and was first introduced in obstetrics. In 1976, the first ultrasound machines coupled with Doppler measurements were commercially available. With regard to regional anesthesia, as early as 1978, La Grange and his colleagues were the first anesthesiologists to publish a case series report of ultrasound application for peripheral nerve block. They simply used a Doppler transducer to locate the subclavian artery and performed supraclavicular brachial plexus block in 61 patients ( Figures 1A and 1B). Reportedly, Doppler guidance led to a high block success rate (98%) and absence of complications such as pneumothorax, phrenic nerve palsy, hematoma, convulsion, recurrent laryngeal nerve block, and spinal anesthesia. In 1989, Ting and Sivagnanaratnam reported the use of B-mode ultrasonography to demonstrate the anatomy of the axilla and to observe the spread of local anesthetics during axillary brachial plexus block.

In 1994, Stephan Kapral and colleagues systematically explored brachial plexus with B-mode ultrasound. Since that time, multiple teams worldwide have worked tirelessly to define and improve the application of ultrasound imaging in regional anesthesia. Ultrasound-guided nerve block is currently used routinely in the practice of regional anesthesia in many centers worldwide.

Here is a summary of ultrasound quick facts:

1880: Pierre and Jacques Curie discovered the piezoelectric effect in crystals.

1915: Ultrasound was used by the navy for detecting submarines.

1920s: Paul Langevin discovered that high-power ultrasound can generate heat in osseous tissues and disrupt animal tissues.

1942: The Dussik brothers described ultrasound use as a diagnostic tool.

1950s: Ultrasound was used to treat patients with Ménière disease, Parkinson disease, and rheumatic arthritis.

1965: The real-time B-scan was developed and was introduced in obstetrics.

1978: La Grange published the first case series of ultrasound application for placement of needles for nerve blocks.

1989: Ting and Sivagnanaratnam used ultrasonography to demonstrate the anatomy of the axilla and to observe the spread of local anesthetics during an axillary block.

1994: Steven Kapral and colleagues explored brachial plexus block using B-mode ultrasound.

Definition of Ultrasound
Sound travels as a mechanical longitudinal wave in which back-and-forth particle motion is parallel to the direction of wave travel. Ultrasound is high-frequency sound and refers to mechanical vibrations above 20 kHz. Human ears can hear sounds with frequencies between 20 Hz and 20 kHz. Elephants can generate and detect sound with frequencies less than 20 Hz for long-distance communication; bats and dolphins produce sounds in the range of 20 to 100 kHz for precise navigation ( Figures 2A and 2B ). Ultrasound frequencies commonly used for medical diagnosis are between 2 and 15 MHz. However, sounds with frequencies above 100 kHz do not occur naturally; only human-developed devices can both generate and detect these frequencies, or ultrasounds.
Piezoelectric Effect
Ultrasound waves can be generated by material with a piezoelectric effect. The piezoelectric effect is a phenomenon exhibited by the generation of an electric charge in response to a mechanical force (squeeze or stretch) applied on certain materials. Conversely, mechanical deformation can be produced when an electric field is applied to such material, also known as the piezoelectric effect ( Figure 3). Both natural and human-made materials, including quartz crystals and ceramic materials, can demonstrate piezoelectric properties. Recently, lead zirconate titanate has been used as piezoelectric material for medical imaging. Lead-free piezoelectric materials are also under development. Individual piezoelectric materials produce a small amount of energy. However, by stacking piezoelectric elements into layers in a transducer, the transducer can convert electric energy into mechanical oscillations more efficiently. These mechanical oscillations are then converted into electric energy.
Ultrasound Terminology
Period is the time for a sound wave to complete one cycle; the period unit of measure is the microsecond (µs). Wavelength is the length of space over which one cycle occurs; it is equal to the travel distance from the beginning to the end of one cycle. Frequency is the number of cycles repeated per second and measured in hertz (Hz). Acoustic velocity is the speed at which a sound wave travels through a medium. It is equal to the frequency times the wavelength. Speed c is determined by the density ρ and stiffness κ of the medium (c = ( κ/ ρ) 1/2). Density is the concentration of a medium. Stiffness is the resistance of a material to compression. Propagation speed increases if the stiffness is increased or the density is decreased.

The average propagation speed in soft tissues is 1540 m/s (ranges from 1400 to 1640 m/s). However, ultrasound cannot penetrate lung or bone tissues. Acoustic impedance z is the degree of difficulty demonstrated by a sound wave being transmitted through a medium; it is equal to density ρ multiplied by acoustic velocity c ( z = ρc). It increases if the propagation speed or the density of the medium is increased. Attenuation coefficient is the parameter used to estimate the decrement of ultrasound amplitude in certain media as a function of ultrasound frequency. The attenuation coefficient increases with increasing frequency; therefore, a practical consequence of attenuation is that the penetration decreases as frequency increases ( Figure 4).

Ultrasound waves have a self-focusing effect, which refers to the natural narrowing of the ultrasound beam at a certain travel distance in the ultrasonic field. It is a transition level between near field and far field. The beam width at the transition level is equal to half the diameter of the transducer. At the distance of two times the near-field length, the beam width reaches the transducer diameter. The self-focusing effect amplifies ultrasound signals by increasing acoustic pressure.

In ultrasound imaging, there are two aspects of spatial resolution: axial and lateral. Axial resolution is the minimum separation of above-below planes along the beam axis. It is determined by spatial pulse length, which is equal to the product of wavelength and the number of cycles within a pulse. It can be presented in the following formula:

Axial resolution = Wavelength λ × Number of cycles per pulse n ÷ 2

The number of cycles within a pulse is determined by the damping characteristics of the transducer. The number of cycles within a pulse is usually set between 2 and 4 by the manufacturer of the ultrasound machines. As an example, if a 2-MHz ultrasound transducer is theoretically used to do the scanning, the axial resolution would be between 0.8 and 1.6 mm, making it impossible to visualize a 21-gauge needle. For constant acoustic velocity, higher-frequency ultrasound can detect smaller objects and provide an image with better resolution. The axial resolution of current ultrasound systems is between 0.05 and 0.5 mm. Figure 5 shows images at different resolutions when a 0.5-mm diameter object is visualized with three different frequency settings.

Lateral resolution is another parameter of sharpness to describe the minimum side-by-side distance between two objects. It is determined by both ultrasound frequency and beam width. The higher frequencies have a narrower focus and provide better axial and lateral resolution. Lateral resolution can also be improved by adjusting focus to reduce the beam width.

Temporal resolution is also important for observing a moving object such as blood vessels and heart. Like a movie or cartoon video, the human eye requires that the image is updated at a rate of approximately 25 times a second or higher for an ultrasound image to appear continuous. However, imaging resolution will be compromised by increasing the frame rate. Optimizing the ratio of resolution to the frame rate is essential for providing the best possible image.

INTERACTIONS OF ULTRASOUND WITH TISSUES

As the ultrasound wave travels through tissues, it is subject to a number of interactions. The most important features are as follows:

When ultrasound encounters boundaries between different media, part of the ultrasound is reflected and the other part is transmitted. The reflected and transmitted directions are given by the reflection angle θr and transmission angle θt, respectively ( Figure 6).

Refection of sound waves is similar to optical reflection. Some of its energy is sent back into the medium from which it came. In a true reflection, the reflection angle θ r must equal the incidence angle θ i. The strength of the reflection from an interface is variable and depends on the difference of impedances between two affinitive media and the incident angle at the boundary. If the media impedances are equal, there is no reflection (no echo). If there is a significant difference between media impedances, there will be nearly complete reflection. For example, an interface between soft tissues and either lung or bone involves a considerable change in acoustic impedance and creates strong echoes. This reflection intensity is also highly angle dependent. In practical terms, it means that the ultrasound transducer must be placed perpendicular to the target nerve to visualize it clearly. A change in sound direction when crossing the boundary between two media is called refraction. If the propagation speed through the second medium is slower than that through the first medium, the refraction angle is smaller than the incident angle. Refraction can cause the artifact that occurs beneath large vessels on the image.

During ultrasound scanning, a coupling medium must be used between the transducer and the skin to displace air from the transducer-skin interface. A variety of gels and oils are applied for this purpose. Moreover, they can act as lubricants, making a smooth scanning performance possible. Most scanned interfaces are somewhat irregular and curved. If the boundary dimensions are significantly less than the wavelength or not smooth, the reflected waves will be diffused.

Scattering is the redirection of sound in any directions by rough surfaces or by heterogeneous media ( Figure 7).

Normally, scattering intensity is much less than mirror-like reflection intensities and is relatively independent of the direction of the incident sound wave; therefore, the visualization of the target nerve is not significantly influenced by another nearby scattering.

Absorption is defined as the direct conversion of the sound energy into heat. In other words, ultrasound scanning generates heat in the tissue. Higher frequencies are absorbed in a greater rate than lower frequencies. However, a higher scanning frequency gives a better axial resolution. If the ultrasound penetration is not sufficient to visualize the structures of interest, a lower frequency is selected to increase the penetration. The use of longer wavelengths (lower frequency) results in lower resolution because the resolution of ultrasound imaging is proportional to the wavelength of the imaging wave. Frequencies between 6 and 12 MHz typically yield adequate resolution for imaging in peripheral nerve block, whereas frequencies between 2 and 5 MHz are usually needed for imaging of neuraxial structures. Frequencies of less than 2 MHz or higher than 15 MHz are rarely used because of insufficient resolution or the insufficient penetration depth in most clinical applications.

ULTRASOUND IMAGE MODES
A-Mode
The A-mode is the oldest ultrasound technique and was invented in 1930. The transducer sends a single pulse of ultrasound into the medium. Consequently, a one-dimensional simplest ultrasound image is created on which a series of vertical peaks is generated after ultrasound beams encounter the boundary of the different tissue. The distance between the echoed spikes ( Figure 8) can be calculated by dividing the speed of ultrasound in the tissue (1540 m/s) by half the elapsed time, but it provides little information on the spatial relationship of imaged structures. Therefore, A-mode ultrasound is not applicable to regional anesthesia.
B-mode
The B-mode is a two-dimensional (2D) image of the area that is simultaneously scanned by a linear array of 100-300 piezoelectric elements rather than a single one as in A-mode ( Figure 9). The amplitude of the echo from a series of A-scans is converted into dots of different brightness in B-mode imaging. The horizontal and vertical directions represent real distances in tissue, whereas the intensity of the grayscale indicates echo strength ( Figure 10). B-mode can provide an image of a cross section through the area of interest, and it is the primary mode currently used in regional anesthesia.
Doppler Mode
The Doppler effect is based on the work of Austrian physicist Johann Christian Doppler. The term describes a change in the frequency or wavelength of a sound wave resulting from relative motion between the sound source and the sound receiver. In other words, at a stationary position, the sound frequency is constant. If the sound source moves toward the sound receiver, the sound waves have to be squeezed, and a higher-pitch sound occurs (positive Doppler shift); if the sound source moves away from the receiver, the sound waves have to be stretched, and the received sound has a lower pitch (negative Doppler shift) ( Figure 11). The magnitude of Doppler shift depends on the incident angle between the directions of emitted ultrasound beam and moving reflectors. With a 90° angle there is no Doppler shift. If the angle is 0° or 180°, the largest Doppler shift can be detected. In medical settings, the Doppler shifts usually fall in the audible range.

Color Doppler produces a color-coded map of Doppler shifts superimposed onto a B-mode ultrasound image. Blood flow direction depends on whether the motion is toward or away from the transducer. Selected by convention, red and blue colors provide information about the direction and velocity of the blood flow. According to the color map (color bar) in the upper left-hand corner of the figure ( Figure 12), the red color on the top of the bar denotes the flow coming toward the ultrasound probe, and the blue color on the bottom of the bar indicates the flow away from the probe.

In ultrasound-guided peripheral nerve blocks, color Doppler mode is used to detect the presence and nature of the blood vessels (artery vs. vein) in the area of interest. When the direction of the ultrasound beam changes, the color of the arterial flow switches from blue to red, or vice versa, depending on the convention used (Figures 13, 14A, 14B, and 14C). Power Doppler is up to five times more sensitive in detecting blood flow than color Doppler, and it is less dependent on the scanning angle. Thus, power Doppler can be used to identify the smaller blood vessels more reliably. The drawback is that power Doppler does not provide any information on the direction and speed of blood flow (Figure 15).
M-Mode
A single beam in an ultrasound scan can be used to produce a picture with a motion signal, where movement of a structure such as a heart valve can be depicted in a wave-like manner. M-mode is used extensively in cardiac and fetal cardiac imaging; however, its present use in regional anesthesia is negligible ( Figure 16).

ULTRASOUND INSTRUMENTS

Ultrasound machines convert the echoes received by the transducer into visible dots, which form the anatomic image on an ultrasound screen. The brightness of each dot corresponds to the echo strength, producing what is known as a grayscale image. Two types of scan transducers are used in regional anesthesia: linear and curved. A linear transducer can produce parallel scan lines and a rectangular display, called a linear scan, whereas a curved transducer yields a curvilinear scan and an arc-shaped image ( Figures 17A and 17B ). In clinical scanning, even a very thin layer of air between the transducer and skin may reflect virtually all the ultrasound, hindering any penetration into the tissue. Therefore, a coupling medium, usually an aqueous gel, is applied between surfaces of the transducer and skin to eliminate the air layer.

The ultrasound machines currently used in regional anesthesia provide a 2D image, or "slice." Machines capable of producing three-dimensional (3D) images have recently been developed. Theoretically, 3D imaging should help in understanding the relationship of anatomic structures and the spread of local anesthetics. There are three major types of 3D ultrasound imaging: (1) Freehand 3D is based on a set of 2D cross-sectional ultrasound images acquired from a sonographer sweeping the transducer over a region of interest ( Figures 18A and 18B). (2) Volume 3D provides 3D volumetric images using a dedicated 3D transducer. The transducer elements automatically sweep through the region of interest during the scanning; the sonographer is not required to perform hand motions ( Figure 18C). (3) Real-time 3D takes multiple images at different angles, allowing the sonographer to see the 3D model moving in real time. However, typical spatial resolution of 3D imaging is about 0.34-0.5 mm. At present, 3D imaging systems still lack the resolution and simplicity of 2D images, so their practical use in regional anesthesia is limited.

TIME-GAIN COMPENSATION

The echoes exhibit a steady decline in amplitude with increasing depth. This occurs for two reasons: First, each successive reflection removes a certain amount of energy from the pulse, decreasing the generation of later echoes. Second, tissue absorbs ultrasound, so there is a steady loss of energy as the ultrasound pulse travels through the tissues. This can be corrected by manipulating time-gain compensation (TGC) and compression functions. Gain is the ratio of output to input electric power; it controls the brightness of the image. The gain is usually measured in decibels (dB). Increasing the gain amplifies not only the returning signals, but also the background noise within the system in the same manner. TGC is a time-dependent amplification. TGC function can be used to increase the amplitude of incoming signals from various tissue depths.

The layout of the TGC controls varies from one machine to another. A popular design is a set of slider knobs. Each knob in the slider set controls the gain for a specific depth, which allows for a well-balanced gain scale on the image ().

Amplification is the conversion of the small voltages received from the transducer into larger ones that are suitable for further processing and storage. There are two amplification processes considered to increase the magnitude of ultrasound echoes: linear and nonlinear amplification. Currently, the ultrasonic imaging system with linear amplifiers is commonly used in medical diagnostic applications. However, the strength of echoes attenuates exponentially as the distance between the transducer and the reflector increases. Ultrasonic imaging instruments equipped with logarithmic amplifiers can display echo signals with a wider dynamic range than a linear amplifier and remarkably improve the sensitivity for a small magnitude of echoes on the screen.

Dynamic range is the range of amplitudes from largest to the smallest echo signals that an ultrasound system can detect. The wider/higher dynamic range presents a larger number of grayscale levels, and it creates a softer image; the image with a narrower/lower dynamic range appears with more contrast ( Figures 20A and 20B). Dynamic range less than 50 dB or greater than 100 dB is probably too low or too high in terms of visualization of peripheral nerve. Compression is the process of decreasing the differences between the smallest and largest echo-voltage amplitudes; the optimal compression is between 2 and 4 for a maximal scale equal to 6.

FOCUSING

As previously discussed, it is common to use electronic means to narrow the width of the beam at some depth and achieve a focusing effect similar to that obtained using a convex lens ( Figure 21). There are two types of focusing: annular and linear. These are illustrated in, respectively.

Adjusting focus improves the spatial resolution on the plane of interest because the beam width is converged. However, the reduction in beam width at the selected depth is achieved at the expense of degradation in beam width at other depths, resulting in poorer images below the focal zone.

BIOEFFECT AND SAFETY

The mechanisms of action by which an ultrasound application could produce a biologic effect can be conceptually categorized into two aspects: heating and mechanical. In reality, these two effects are rarely separable except for extracorporeal lithotripsy, the therapeutic application of mechanical bioeffects alone. The generation of heat increases as ultrasound intensity or frequency is increased. For similar exposure conditions, the expected temperature increase in bone is significantly greater than in soft tissues. In in vivo experiments, high-intensity ultrasound (usually > 2 W/cm ²) is used to evaluate harmful biological effect; it is 5 to 20 times larger than therapeutic intensities (0.08-0.5 W/cm ²) and 8 to 100 times larger than diagnostic intensities (color flow mode 0.25 W/cm ², B-mode scan 0.02 W/cm ²). Reports in animal models (mice and rats) suggest that application of ultrasound may result in a number of undesired effects, such as fetal weight reduction, postpartum mortality, fetal abnormalities, tissue lesions, hind limb paralysis, blood flow stasis, and tumor regression. Other reported undesired effects in mice are abnormalities in B-cell development and ovulatory response and teratogenicity.

In general, adult tissues are more tolerant of rising temperature than fetal and neonatal tissues. A modern ultrasound machine displays two standard indices: thermal and mechanical. The thermal index (TI) is defined as the transducer acoustic output power divided by the estimated power required to raise tissue temperature by 1°C. The mechanical index (MI) is equal to the peak rarefactional pressure divided by the square root of the center frequency of the pulse bandwidth. TI and MI indicate the relative likelihood of thermal and mechanical hazard in vivo, respectively. Either TI or MI greater than 1.0 is hazardous.

The biologic effect due to ultrasound also depends on tissue exposure time. The researchers usually use pregnant mice to expose to ultrasound with a minimum intensity of 1 W/cm ² for 60 to 420 minutes to evaluate the time-dependent adverse events that happen in rodent fetuses. Fortunately, ultrasound-guided nerve block requires the use of only low TI and MI values on the patient for a short period of time. Based on in vitro and in vivo experimental study results to date, there is no evidence that the use of diagnostic ultrasound in routine clinical practice is associated with any biologic risks.

REFERENCES

Curie J, Curie P: Développement par pression de l'é'lectricite polaire dans les cristaux hémièdres à faces inclinées. CR Acad Sci (Paris) 1880;91:294.

Langevin P: French Patent No. 505,703. Filed September 17, 1917. Issued August 5, 1920.

Thompson J: Unrestricted U-boat warfare: The Royal Navy nearly loses the war. In Imperial War Museum Book of the War at Sea 1914-18. Pan Books, 2006, Chapter 10.

Langévin MP: Lés ondes ultrasonores. Rev Gen Elect 1928;23:626.

Ensminger D, Bond LJ: Ultrasonics: Fundamentals, Technologies, and Applications, 3rd ed. Francis Group, 2012.

Dussik KT: On the possibility of using ultrasound waves as a diagnostic aid. Neurol Psychiat 1942;174:153-168.

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Ultrasound application allows for noninvasive visualization of tissue structures. Real-time ultrasound images are integrated images resulting from reflection of organ surfaces and scattering within heterogeneous tissues. Ultrasound scanning is an interactive procedure involving the operator, patient, and ultrasound instruments. Although the physics behind ultrasound generation, propagation, detection, and transformation into practical information is rather complex, its clinical application is much simpler.

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Curriculum: Demonstrates how to achieve an optimal ultrasound image and recognises common ultrasound artefacts

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Curriculum: Demonstrates how to achieve an optimal ultrasound image and recognises common ultrasound artefacts

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NB Use of nerve simulator section

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Steven L. Orebaugh and Kyle R. Kirkham

INTRODUCTION

Ultrasonography (US) as a means to guide peripheral nerve block (PNB) was first explored by anesthesiologists at the University of Vienna in the mid-1990s. Although radiologists had made use of ultrasound technology to guide needles for biopsy, the application of this imaging modality for PNB was novel at that time. The utility of ultrasound to facilitate a range regional anesthesia techniques including brachial plexus and femoral blocks was demonstrated. A decade later, colleagues from the University of Toronto, Canada, began to embrace this technology, further demonstrating its utility and describing in detail the sonoanatomy of the brachial plexus. A number of advances in technology took place in the meantime, including smaller and more mobile ultrasound platforms, improved resolution, and needle recognition software, all cumulatively leading to increased bedside utility of ultrasound by anesthesiologists.

ADVANTAGES OF ULTRASOUND GUIDANCE

The previously used surface anatomy-based techniques, such as nerve stimulation, palpation of landmarks, fascial "clicks," paresthesias, and transarterial approaches, did not allow for the monitoring of the disposition of the local anesthetic injectate. Ultrasound guidance, however, offers a number of important practical advantages for nerve block. Ultrasound allows visualization of the anatomy of the region of interest. This allows more informed guidance for the needle pathway to the target while avoiding structures that might be damaged by the needle. Ultrasound also allows visualization of the needle tip as it is passed through the tissues, confirming alignment with the intended path, again reducing the likelihood of inadvertent needle trauma to unintended structures. Perhaps most important, real-time ultrasound imaging permits continual visualization of local anesthetic solution delivery to ensure proper distribution, with the potential for adjustment of the needle tip position as necessary to optimize local anesthetic distribution.

Introduction of ultrasound guidance in regional anesthesia has led to refinement of many nerve block techniques, expanded use of PNB, and greater acceptance by surgical colleagues and patients.

ULTRASOUND AND SONOANATOMY

Ultrasound-guided PNB may be broken down into two fundamental aspects: imaging structures in the plane of section, including the target nerve, and guiding the needle. Understanding and recognition of three-dimensional anatomic structures on a twodimensional image requires training in the technology and sonoanatomy pattern recognition ( Table 1).

TABLE 1. Optimizing sonoanatomy visualization.

Choose appropriate transducer/frequency
Understand underlying anatomic relationships
Apply varying degree of pressure with transducer
Align transducer with underlying nerve target
Rotate transducer to fine-tune image
Tilt the transducer to optimize image

As anatomic recognition remains essential to placing blocks, even with realtime visual guidance, specialty society guidelines for training residents and fellows continue to stress the importance of anatomical dissection and gross anatomy training as an inherent component of learning ultrasound-guided regional anesthesia (UGRA). In a study conducted over a 1-month regional anesthesia rotation, residents demonstrated markedly improved recognition of relevant structures at the sites of several different PNBs, using ultrasound imaging. In an evaluation of ultrasound-guided interscalene block instruction, residents demonstrated increasing efficiency of sonoanatomy recognition as their experience over the course of the rotation increased.
More innovative methods of training have shown promise as well. Integrating an anatomic program into the software of a bedside ultrasound machine has been shown to improve scores on a written test of anatomy. After exposure to a multimedia anatomy presentation, residents and community anesthesiologists demonstrated increased knowledge of ultrasound anatomy on a posttest, although they were not able to improve scores on a practical examination of sonoanatomy on live models. However, the optimal link between anatomic knowledge and recognition of two-dimensional anatomic patterns on ultrasound has not yet been adequately explored.

Certain basic tenets of optimizing an ultrasound image are applicable to all nerve blocks. For instance, sonography requires an understanding of mechanics and ergonomics. Novices are subject to errors such as probe fatigue, reversing probe orientation, and inadequate equipment preparation. To optimize the ultrasound image, the mnemonic PART (pressure, alignment, rotation, tilting) has been recommended. Pressure is necessary to minimize the distance to the target and compress underlying subcutaneous adipose tissues. Alignment refers to placing the transducer in a position over the extremity (or trunk) at which the underlying nerve is expected to be in the field of view. Rotation allows fine-tuning of the view of the target structure. Tilting helps to bring the face of the probe into a perpendicular arrangement with the underlying target to maximize the number of returning echoes and thus provide the best image ( Figure 1). In-depth discussion on optimizing ultrasound imaging is discussed in " Optimizing an Ultrasound Image ".

NYSORA Tips

To optimize the ultrasound image, the mnemonic PART has been recommended: pressure, alignment, rotation, tilting.

Recognition and understanding of sonoanatomy requires knowledge of the underlying three-dimensional anatomy.

Optimum visualization of the target nerve requires appropriate transducer pressure, alignment with nerve, and rotation and tilting of the probe to fine-tune the image.

OPTIMIZING NERVE AND NEEDLE IMAGING WITH ULTRASOUND-CLINICAL SCENARIOS

Nerve imaging may be performed in either short-axis (probe face perpendicular to axis of nerve) or long-axis (probe face parallel to axis of nerve) position ( Figure 2).

It is frequently easier to recognize the round, often-hyperechoic, neural element with short-axis imaging, especially for a beginner. Because most nerve blocks are conducted in the extremities, this orientation results in a transducer position that is transverse, across the long axis of the arm or leg. In general, understanding the course of the nerves, based on knowledge of gross anatomy, allows one to align and rotate the transducer perpendicular to the course of the nerve subsequently adjusting the tilt as described previously to optimize the image.
Once the nerve and surrounding anatomy are identified, a needle path may be chosen so that it is imaged either in plane (needle parallel to long axis of probe) or out of plane (needle perpendicular to long axis of probe) to the ultrasound beam. While neither method has been shown superior for either block success or patient safety, the preferred approach may vary with anatomic or technical considerations. However, with in-plane imaging, it is possible to maintain an image of the entire needle, including the tip, although it can be challenging to keep the needle entirely in the viewing plane of the transducer. This method is especially beneficial during instruction, as the supervisor has continual visualization of the needle tip as it is advanced through the tissues.
During out-of-plane imaging, the observer is able to see only the cross section of the needle, which appears as a small hyperechoic dot, at any plane along its entire length, so that distinguishing the tip from the shaft is much more difficult.

Guiding the needle tip to the target while maintaining the entire needle in the plane of imaging, however, can be challenging ( Table 2).

TABLE 2. Optimizing needle imaging with ultrasound.

Utilize a shallow angle of approach, if possible
"Heel" the transducer to make the face more parallel to
the needle
Rotate the transducer to ensure the entire needle is seen
Tilt the transducer as necessary
Choose an "echogenic" needle
Apply needle recognition software, if available
"Hydrolocation" may help ascertain needle tip location

Appropriate adjustment of the bed height and ergonomic placement of the ultrasound so that operator's eyes can easily and rapidly shift from the image to the field ( Figure 3), where needle alignment with the long axis of the probe can be ensured, is beneficial. It is surprisingly easy for the transducer to wander away from the plane of the needle while one's vision is fixed on the ultrasound screen. This is more likely if the operator has the probe and needle aligned perpendicular to his or her own axis of viewing, as opposed to aligning the needle and probe with the viewing axis.

In a study of novice medical students learning the basics of UGRA, Speer et al found that the subjects required less time to locate the target, and were better able to keep the needle visualized in plane on the ultrasound image, when eyes, needle, probe, and viewing screen were aligned. Needle guides may also permit improved imaging of the needle during approach to the target, although more work has been done in vascular access. One disadvantage of needle guides is that they restrict needle motion to one plane, which may not be always desirable.
Nerves in short axis have an appearance that is to some extent determined by their proximity to the neuraxis. Although in most areas nerves are round, they may appear fusiform, such as the musculocutaneous nerve in the proximal arm, or ovalshaped, such as the sciatic nerve in the infragluteal region. In close association with the spine, nerves and nerve roots are comprised primarily of neural tissue, with minimal connective tissue. Because neural tissue appears hypoechoic on ultrasound imaging, while the connective tissue between fascicles is hyperechoic, nerves near the neuraxis appear as dark nodules.

As nerves course peripherally, the number of fascicles increases, although they diminish in size, while the amount of connective tissue also increases. These changes lead to an increasingly complex "honeycomb" appearance on ultrasound in short-axis viewing ( Figure 4). Unfortunately, because of the technology limitations of the current ultrasound machines, the number and arrangement of fascicles within a peripheral nerve may not be accurately portrayed.

While different tissues have characteristic appearances on ultrasound, nerve may not be easily be distinguished from tendon when both are viewed in short axis. However, using knowledge of anatomy, the operator can follow the course of the structure caudad-cephalad to determine the nature of the structure imaged. The tendons will eventually disappear into the muscle of origin or insert into bones. A good example is the median nerve at the wrist, where it is difficult to discern the neural structure from the many tendons in the carpal tunnel, versus at the midforearm, where the nerve is much more visually distinct, as it is situated between two layers of muscle, with no surrounding tendons ( Figure 5).
An important aspect of preparing for a block is to obtain the preferred imaging plane while planning the route for needle path. The operator should make certain that no vulnerable structures are in the projected course, such as a blood vessel, the pleura, or sensitive structures such as periosteum.

This process is referred to as a "preblock scan," which can contribute to patient safety and block success. In addition to two-dimensional imaging, the color Doppler setting should be utilized to identify small vessels, which may readily be confused with nerve structures (particularly roots) when viewed in short axis ( Figure 6).

To maintain the view of the needle tip and shaft, several techniques can be used. The more parallel the needle is to the face of the probe, the more echoes are transmitted back to the transducer, resulting in a superior image. This can be accomplished by gently indenting the skin at the needle insertion site or by moving the insertion site further away from the probe, resulting in a less-acute angle of insertion ( Figure 7). The limitation of this approach is that a longer needle may be required, and more tissue is traversed en route to the target.

Another technique, referred to as heeling, involves pressing in on the edge of the transducer opposite the side of needle insertion, which results in a more parallel alignment of the probe face with the needle. In addition, the needle itself may be structurally altered to increase its echogenicity; commercially available versions of these "echogenic needles" usually have been etched on the surface of the shaft with crosshatches to create a greater degree of scatter of the ultrasound beam.

As noted, needle guides may be utilized to improve needle imaging, though at the cost of constraint of movement. Laser guidance systems have also been created to improve alignment, with some success. One novel, alternative method of targeted needle placement and local anesthetic delivery utilizes a GPS guidance system, which may be especially useful when imaging is made difficult by steep needle angles. Proprietary software for needle localization at steep angles makes use of spatial compound imaging, which combines images of different angles of insonation. This results in enhanced needle imaging with both standard and echogenic block needles. Finally, localization of the needle tip may be accomplished with "hydrolocation," in which small volumes of either dextrose solution or local anesthetic are injected to visualize spread within tissues, which typically reveals the position of the needle tip.

NYSORA Tips

* Several different techniques are useful to maintain visualization of the needle with ultrasound imaging, including use of a shallow angle of approach, "heeling" the transducer, commercially available echogenic needles, and physical measures such as rotation and tilting of the transducer.
* In addition, hydrolocation with a small injection of fluid can be utilized to facilitate localization of the needle in difficult situations.
* The needle should be advanced with continuous visualization to avoid injury to anatomic structures.
* A preblock scan, including use of the color Doppler function, helps plan the course of the needle.
* Passage of the needle tip through fascial planes that abut a nerve should be conducted in a tangential fashion to avoid impaling the nerve when the fascia "releases" the needle.

SAFE NEEDLE GUIDANCE WITH ULTRASOUND

In advancing the needle tip toward the targeted nerve with in-plane imaging, one should be cautious and deliberate, attempting to maintain the needle in plane at all times ( Table 3). The in-plane needle tip is characterized by a double-echo return generated from the beveled surface.

TABLE 3. Safety tips during ultrasound-guided nerve blocks.

Perform a "preblock scan" to ascertain anatomy
Utilize the color Doppler setting to identify blood vessels
Do not advance needle if tip is not localized
"Hydrodissection" can be utilized to delineate anatomy
When pushing through fascia toward a nerve, approach
tangentially
Pass through fascia slowly, awaiting a "pop" or sudden
release
Reoptimize image of needle tip after passing through
fascia
When in doubt about needle-nerve interface, gently
move needle to ascertain that the nerve does not
move with it (indicating that tip is embedded within
epineurium)

Ultrasound is reflected from both the superficial and the deep walls of the needle, resulting in a step appearance that can be distinguished from the single return of the needle shaft. A subtle sliding motion of the ultrasound probe can aid in confirming the location of the tip as the beam walks up and down the needle shaft.
Commonly, fascial planes will be encountered that resist advance of the needle. These tough layers of connective tissue may be seen to "tent" as the tip pushes against them, suddenly giving way and snapping back to their original position. This abrupt change may have two consequences: First, the needle may advance quickly and inadvertently beyond the intent of the operator (unless this is anticipated); second, the needle may move out of plane. At this point, the forward motion of the needle should be stopped until the in-plane image is once again optimized. It is common for such fascial planes to lie just superficial or adjacent to the nerve target, as at the interscalene groove, the axillary neurovascular bundle, or the femoral nerve. This motion may actually result in the needle thrusting forward and encountering the nerve if the sudden give of the fascial plane is not anticipated. For this reason, it is recommended to approach nerves tangentially, projecting the advance of the needle so that its tip will lie adjacent to the nerve, but not aiming for its center.
The resistance encountered by these tough facial planes may also inadvertently redirect a needle when approached at a shallow angle. Temporarily steepening the needle angle may permit an easier and more controlled passage. Unfortunately, ultrasound guidance does not always produce clear images that allow one to distinguish the nerve tissue from surrounding tissue. In such situations, as the needle is advanced, "hydrodissection" (deliberate injection of fluid into tissue planes) can be utilized to separate structures, allowing better clarity in imaging, with either dextrose or local anesthetic solution.

In addition, the behavior of tissues can be observed as the needle is advanced to help localize the needle tip in relation to neural tissue.
While it was once held that contacting a nerve with a needle tip would likely result in paresthesia, and, indeed, this was considered an appropriate nerve localization technique, we now know that paresthesia is not consistently elicited with needlenerve contact. This emphasizes the need to accurately localize the needle tip with ultrasound imaging as well as using additional monitoring during PNBs to detect hazardous needle-nerve relationships, such as nerve stimulation and injection pressure monitoring.

NYSORA Tips

Deposition of local anesthetic solution should be optimized by taking advantage of fascial planes or sheaths that can contain or channel the drug around the nerve
and longitudinally along its course.

For nerves without such local fascial containment, the solution should be injected in a circumferential manner to hasten onset of the block.

USE OF PERIPHERAL NERVE STIMULATION WITH ULTRASOUND

The peripheral nerve stimulator (PNS) has been a standard tool in nerve localization during PNBs for several decades, with a high degree of success and low complication rate. However, the widespread adoption of ultrasound imaging has called into question its ongoing role in PNB. Over a decade ago, Perlas et al evaluated the sensitivity of upper extremity peripheral nerves to peripheral nerve stimulation during ultrasound imaging of needle to nerve contact. The authors reported that, despite visualizing the needle tip indenting the surface of the nerve, with the stimulator set to deliver a current of 0.5 mA or less, no motor stimulation occurred over 25% of the time.
Several studies, with a variety of different blocks, have been performed to assess the utility of this localization tool in association with UGRA. Whether for supraclavicular block, for axillary block, or for femoral block authors have shown that addition of the nerve stimulator as a nerve localization tool during ultrasound-guided PNB was not contributory to success.

Moreover, Robards et al found that absence of a motor response to PNS between 0.2 and 0.5 mA during popliteal block did not always exclude placement of the needle within the nerve, and that stimulation might actually lead to unnecessary manipulation of the needle into the nerve.
However, the stimulator may be useful as an adjunct to UGRA for reasons other than ensuring block efficacy. Because it has been well established that a threshold of nerve stimulation lower than 0.2 mA indicates high likelihood of needle tip placement within the nerve, the stimulator may be employed during UGRA as a safety monitor. The nerve stimulator is particularly necessary during US-guided block of the deep nerves, or when the ultrasound image is less precise than desired. In this setting, an evoked motor response could warn against intrafascicular injection of local anesthetic.
Moreover, in some circumstances, it may be desirable to identify different nerves with more precision, as during axillary block, for which the PNS serves to delineate the nerves by their specific motor response to electrical stimulation. There may be, in some anatomic locations, neural structures that can be challenging to identify by visualization alone, whether they are the target of block or one simply wishes to avoid them with the needle; in these cases, a PNS may be invaluable to provide this identification.
Finally, there are nerves that do not lend themselves readily to ultrasound visualization, primarily because of depth or osseous interference with ultrasound transmission. The most common example of this is the posterior approach to the lumbar plexus, in which ultrasound can be used to identify local osseous structures to guide the block, but for which the PNS remains a valuable tool for guidance of the needle tip into proximity with the nerves of the plexus.
Taken overall, a plethora of data indicate that routine use of a nerve stimulator during ultrasound-guided nerve blocks yields clinically relevant safety information that can influence the clinical decision making and positively affect patient safety.
However, the primary purpose of the suggested routine use of nerve stimulation with UGRA is for safety monitoring, rather nerve localization ( Figure 8). In this capacity, the nerve stimulator can be simply set at 0.5 mA (0.1 ms), 2 Hz, without changing the current intensity throughout the procedure.
While the motor response is not sought, occurrence of the motor response should necessitate cessation of the needle advancement and slight withdrawal of the needle as a motor response at this current delivery setting almost always indicates needle-nerve contact or intraneural needle placement.

OPTIMIZING THE DELIVERY OF LOCAL ANESTHETIC NEAR THE TARGET NERVE

After accurate needle placement near the target nerve, and after ascertaining that aspiration is negative for intravascular needle placement, injection of the local anesthetic is made in the tissue plane that contains the nerve(s) to be anesthetized ( Table 4).

TABLE 4. Optimizing local anesthetic deposition.

Inject local anesthetic solution in small aliquots
Observe for pain or high pressure during injection
Make certain that spread of fluid is observed at needle tip
during injection
Aspirate between injections
Be aware of intervening fascial planes that may sequester
or channel the solution
Avoid deposition of local anesthetic into muscle
For solitary nerves in extremities, seek to create a "donut"
or "halo" around nerve
For nerves within a fascial enclosure, seek to "fill" the
fascial confines with solutiona

Brull et al evaluated the long-held notion that the local anesthetic solution should be directed in a circumferential manner around the visible nerve, with change of needle position if necessary, in comparison to simply allowing the solution to accumulate along one aspect of the nerve with one needle position.

They found that the resultant block set up 33% more rapidly with the former than with the latter. While the creation of a "donut" or "halo" around the nerve may be suggested as a general recommendation, some nerves, by virtue of their anatomical situation, may not require such deliberate circumferential placement. This is typically dictated by the location and configuration of overlying or surrounding fascial planes, such as in the interscalene groove and at the femoral triangle. Optimal delivery of local anesthetic around each nerve is described in subsequent specific UGRA sections.
Real-time imaging of local anesthetic injection permits assessment of correct disposition of the fluid. The injection phase should be carried out with small aliquots of local anesthetic (3-5 mL), with a short period allowed to elapse between each, to allow evidence of any symptoms of local anesthetic systemic toxicity (LAST) to be manifest before continuing to administer the drug, as recommended by the American Society of Regional Anesthesia and Pain Medicine (ASRA) guidelines.
In addition, delivery of each aliquot should be preceded by aspiration and should progress with attention to opening injection pressures or complaints of pain or paresthesia in the distribution of the target nerve.
While ultrasound has been shown to produce a lower likelihood of intravascular needle placement, intravascular injection with LAST may still occur. It is thus imperative to be aware of the location of vessels, which have a distending pressure so low that ordinary pressure at the body surface with a transducer obliterates their lumen entirely. Therefore, it is helpful to screen for the presence of vessels using color Doppler during the pre block scan. However, small vessels may be missed, and Doppler function deteriorates at greater depths.
Thus, it is imperative to observe the ultrasound image throughout the injection for evidence of tissue spread by the local anesthetic solution at the tip of the needle. Failure to visualize such spread suggests that the tip of the needle either is out of plane or is in the lumen of a vessel.
Errant needle placement has been described both into vessels and into nerves. Moayeri et al in a cadaver-based study, have shown that ultrasound imaging is sensitive to injection into the peripheral nerve, with as little as 0.5 mL causing visible evidence of nerve distension. Such visualization allows immediate withdrawal of the needle, which may reduce the chance for nerve injury, compared to injection of a large volume of local anesthetic.

CONCLUSION

Ultrasonography has revolutionized the field of regional anesthesia. The effective application of this technology requires understanding of two-dimensional anatomy, optimal imaging of the nerves and anatomical structures, accurate real-time needle guidance, and precise local anesthetic delivery. The combination of these elements ensures that the most benefit can be derived from this powerful imaging modality, ensuring high nerve block success and improved patient safety, particularly with regard to LAST.

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Hanson NA, Auyong DB: Systematic ultrasound identification of the dorsal scapular and long thoracic nerves during interscalene block. Reg Anesth Pain Med 2013;38:54-57.

Karmakar MK, Ho AM, Li X, et al: Ultrasound-guided lumbar plexus block through the acoustic window of the lumbar ultrasound trident. Br J Anaesth 2008;100:533-537.

Gadsden J, Latmore M, Levine DM, Robinson A: High opening injection pressure is associated with needle-nerve and needle-fascia contact during femoral nerve block. Reg Anesth Pain Med 2016;41(1):50-55.

Gadsden JC, Choi JJ, Lin E, Robinson A: Opening injection pressure consistently detects needle-nerve contact during ultrasound-guided interscalene brachial plexus block. Anesthesiology 2014;120(5):1246-1253.

Brull R, MacFarlane AJ, Parrington SJ, et al: Is circumferential injection advantageous for ultrasound-guided popliteal sciatic nerve block? Reg Anesth Pain Med 2011;36:266-270.

Spence BC, Beach ML, Gallagher JD, et al: Ultrasound-guided interscalene blocks: Understanding where to inject the local anesthetic. Anaesthesia 2011;66(6):509-514.

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Abrahams MS, Aziz MF, Fu RF, et al: Ultrasound guidance compared with electrical neurostimulation for peripheral nerve block: A systematic review and meta-analysis of randomized controlled trials. Anaesth 2009;102:408-417.

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Introduction to Ultrasound-Guided Regional Anesthesia - NYSORA

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Ultrasound-guided PNB may be broken down into two fundamental aspects: imaging structures in the plane of section, including the target nerve, and guiding the needle. Understanding and recognition of three-dimensional anatomic structures on a twodimensional image requires training in the technology and sonoanatomy pattern recognition.

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Option A: GA, PCA morphine, admission overnight

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Option A: GA, PCA morphine, admission overnight

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Option B: No GA, Interscalene Brachial Plexus Block, daycase

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Option B: No GA, Interscalene Brachial Plexus Block, daycase

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Option C: GA, Interscalene Brachial Plexus Block, daycase

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Option C: GA, Interscalene Brachial Plexus Block, daycase

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Option A: Block awake under U/S and nerve stimulator

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Option A: Block awake under U/S and nerve stimulator

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Option B: Block asleep under U/S and nerve stimulator

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Option B: Block asleep under U/S and nerve stimulator

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Option C: Don’t mind, let the anaesthetist advise

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Option C: Don’t mind, let the anaesthetist advise

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Curriculum item: Assesses when a regional technique is not appropriate; Describes the indications and contraindications to regional anaesthetic techniques

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Curriculum item: Assesses when a regional technique is not appropriate; Describes the indications and contraindications to regional anaesthetic techniques

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When it comes to talking through pros and cons with a patient in the exam, don't be scared to rely on these RCOA patient information leaflets

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Managing Neurological Complications of Regional Anaesthesia

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Managing Neurological Complications of Regional Anaesthesia

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Have a look at this flowchart, but take homes for me:

•GA is associated with as high or higher rate of neurological symptoms

•neurological symptoms that arise even 2 weeks after a single-shot block should not be dismissed lightly

•Some neurological symptoms after PNB are common (0-2.2% up to 3/12; 0-0.2% up to 12/12)

•Rarely permanent (1:20k-1:5k ie 0.005-0.02%)
If occurs:

•Document Document Document ..

•Urgent imaging (MRI) and neurological referral to exclude treatable leisons (haematoma, abscess)

•Consider Urgent surgery

•Urgent and/or delayed electrophysiological studies (?pre-existing deficit)

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This approach offers a useful window in patients who are unable to position themselves easily or have abnormal anatomy (e.g. kyphoscoliosis). Needle entry is slightly caudal and lateral to the inferior aspect of the spinous process of the chosen interspace. After insertion in a cephalomedial direction, the needle is walked off the lamina until the ligamentum flavum is engaged. Notably, the midline structures of the supraspinous and interspinous ligaments are not involved, and the paraspinous tissue offers little ‘feel’ until this point. The needle on this approach passes through: skin, subcutaneous fat, connective tissue and ligamentum flavum.

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Spinal Tap - Anesthesia: Paramedian Technique - Crash course with Dr. Hadzic

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Growing evidence suggests that ultrasound can be used to identify both vertebral levels and epidural access points more accurately than palpation of surface anatomical landmarks.
A scan before the procedure in patients with known altered anatomy (scoliosis, hyperkyphosis, hyperlordosis) or difficult to palpate landmark anatomy (obesity), improves the technical efficiency of the block and reduces the risk of traumatic or failed insertion.
Ultrasound may also be used to indicate depth of the epidural space. Trial data suggests that obstetric epidural analgesia is more effective when using ultrasound, compared with surface landmark techniques.
Three basic ultrasonographic views can be obtained before needle insertion. These are: ‘paramedian sagittal oblique (interlaminar) view,’ the ‘transverse process view’ and the ‘transverse interlaminar (interspinous) view’. The interlaminar and interspinous views provide an image of the neuraxial structures through acoustic windows.

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🤔What volume should the test injection be?

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🤔What volume should the test injection be?

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Regional Anaesthesia UK is the UK Division of the European Society of Regional Anaesthesia (ESRA)

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👍 Curriculum: Practices measures to avoid wrong-site blocks

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👍 Curriculum: Practices measures to avoid wrong-site blocks

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You should be comfortable with Prepare Stop Block local protocol, but for the exam check out the national information

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Ultrasound-Guided Femoral Nerve Block - Regional anesthesia Crash course with Dr. Hadzic

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Block- good analgesia without systemic effects of opiates
GA- ?position for op precludes awake patient (drapes etc over face/head)

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Not mentioned in the curriculum, but a good video on Ankle Blocks

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Not mentioned in the curriculum, but a good video on Ankle Blocks