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Anaphylaxis is a potentially serious life-threatening allergic reaction to a usually harmless substance that the body mistakes to be harmful (allergen)

Immediate immune and inflammatory response that occurs within seconds or minutes

When an allergen is introduced to the body, the immune system releases a large amount of histamine which results in sudden drop in blood pressure, difficulty breathing due to narrowed airways, skin rash and other possible symtpoms

Rogers, J. (2019). McCance & Huether’s Pathophysiology (9th ed.). Elsevier Health Sciences (US). https://pageburstls.elsevier.com/books/9780323789905

Mayo Clinic. (2021). Anaphylaxis.

https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468

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Risk factors for anaphylaxis include:

previous anaphylactic reaction-future reactions can be more severe than the first reaction

allergies

asthma

family history of anaphylaxis

Other health conditions: heart disease or mastocytosis (irregular accumulation of a certain type of white blood cells-mast cells)

Gotter, A. (2019). Anaphylactic shock: what you need to know. Healthline. https://www.healthline.com/health/anaphylactic-shock

Mayo Clinic. (2021). Anaphylaxis.

https://www.mayoclinic.org/diseases-conditions/anaphylaxis/symptoms-causes/syc-20351468

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Cellular Pathophysiology of Type I Hypersensitivity: Anaphylaxis 

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Cellular Pathophysiology of Type I Hypersensitivity: Anaphylaxis 

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Begins with sensitization: an individual's initial exposure to an allergen.

Form immunologic memory of allergen

An anaphylactic response occurs during re-exposure to the same allergen.

Immune response: IgE antibodies bind to mast cells and basophils.

Mast cell: inflammatory cascade; degranulation

IgE antibodies signal the mast cells to degranulate and release mediators.

Histamine

Sources:

Abbas, M., Akel, H., & Moussa, M. (2023, January). Type I hypersensitivity reaction - statpearls - NCBI bookshelf. National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK560561/

Rogers, J. (2019). McCance & Huether's Pathophysiology (9th ed.). Elsevier Health Sciences (US). https://pageburstls.elsevier.com/books/9780323789905

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Immediate response: Type I Hypersensitivity Reaction

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Skin:

Manifestation: pruritus (itchy skin), tingling, warmth, hives

Rationale: Histamine and chemical mediators irritate sensory nerves

Respiratory:

Manifestation: Difficulty with breathing, cough, wheezing, chest pain/tightness

Rationale: Chemical mediators cause contraction of smooth muscles in bronchioles, edema, and increased secretions, leading to narrowing of the airways & lack of oxygen

Cardiovascular:

Manifestation: Decreased blood pressure, weak pulse

Rationale: Chemical mediators cause general vasodilation, with rapid, weak pulse, perhaps irregular, leading to low blood pressure; sympathetic nervous system responds by increasing rate

Central Nervous System:

Manifestation: Anxiety and fear (early); weakness, dizziness, and loss of consciousness

Rationale: Early, sympathetic response; later, lack of oxygen to the brain because of low blood pressure and respiratory obstruction

Gastrointestinal:

Manifestation: Nausea, Vomiting

Rationale: Histamines released to fight off allergies can cause inflammation and irritation in the stomach tissues, leading to uneasiness and nausea

Sources:
Anaphylaxis. Allergy & Asthma Network. (2023, June 27). https://allergyasthmanetwork.org/anaphylaxis/

Poziomkowska-Gęsicka I, Kurek M. Clinical Manifestations and Causes of Anaphylaxis. Analysis of 382 Cases from the Anaphylaxis Registry in West Pomerania Province in Poland. Int J Environ Res Public Health. 2020 Apr 17;17(8):2787. doi: 10.3390/ijerph17082787. PMID: 32316622; PMCID: PMC7215547.

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Type I hypersensitivity is characterized by the immunoglobulin E (IgE)–mediated release of histamine and other mediators from mast cells and basophils.

This reaction is always rapid, occurring within minutes of exposure to an antigen. Anaphylaxis symptoms usually occur within minutes of exposure to an allergen.

Anaphylaxis conforms to this traditional definition as it is "involves the release of numerous chemical mediators from the degranulation of basophils and mast cells after re-exposure to a specific antigen(Mclendon & Sternard, 2023)."

Thus, anaphylaxis is complication of type 1 hypersensitivity in its most extreme form.

Sources:

McLendon K, Sternard BT. Anaphylaxis. [Updated 2023 Jan 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482124/

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Treatment:

Immediate and necessary-Epinephrine (adrenaline) acts as a vasoconstrictor (narrows blood vessels)

Intravenous

Intramuscular

Adjunct therepay:

Bronchiodilators (relaxes airway),

H1 and H2 receptor blockers,

IV corticosteroids

IV fluids, O₂ supplementation

Critical care

Intubation

Osmosis from Elsevier. (2023). Notes: Type 1 hypersensitivity reactions. https://www.osmosis.org/notes/Type_I_hypersensitivity_reactions

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1. To self-administer epinephrine, remove the autoinjector from its carrying tube

2. Next, grasp the unit with the black tip (injecting end) pointed downward. Form a fist around the device, and remove the gray safety release cap.

3. Hold the black tip near the outer thigh and swing and jab firmly into the outer thigh at a 90-degree angle until a click is heard.

4. Hold the device firmly in place for about 10 seconds, remove the device, and massage the site for about 10 seconds.

Source:
How to use EpiPen®. How to Use EpiPen® | Epipen.ca. (n.d.). https://www.epipen.ca/how-to-use-epipen

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Best Epi-Pen Tutorial (Anaphylaxis / Anaphylactic Shock Treatment) | First Aid Training

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Image from: Anaphylaxis: Video, Anatomy, Definition & Function - Osmosis Google Images 

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Tissue/Organ Level Pathophysiology of Type I Hypersensitivity: Anaphylaxis

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Tissue/Organ Level Pathophysiology of Type I Hypersensitivity: Anaphylaxis

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​​Histamine released from mast cells binds to H1 receptors on various target cells.

GI tract

Skin

Respiratory tract

Mast cells are sensitive to the effects of histamine released from them

Inflammatory response

Vascular Effects: histamine causes vasodilation and increased vascular permeability.

Respiratory Effects: histamine causes bronchoconstriction

Skin Effects: histamine causes itching and hives (urticaria) in the skin.

Gastrointestinal Effects: histamine can increase the permeability of blood vessels, leading to localized swelling and inflammation.

stimulate nerve endings causing abdominal cramps and discomfort.

affect smooth muscle of the GI tract

Systemic: affecting multiple tissues and organs; septic shock

Sources:
Abbas, M., Akel, H., & Moussa, M. (2023, January). Type I hypersensitivity reaction - statpearls - NCBI bookshelf. National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK560561/

Rogers, J. (2019). McCance & Huether's Pathophysiology (9th ed.). Elsevier Health Sciences (US). https://pageburstls.elsevier.com/books/9780323789905

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Most common allergens are caused by environmental allergens such as pollen, insect stings, nuts, medications.

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Creative Med Dose. (2023). Type I hypersensitivity: immediate. https://creativemeddoses.com/topics-list/type-1-hypersensitivity-immediate/