COPD (Emphysema) (TU1) by Pauline Wong

1. Brief definition

paulinewong1 — 2023-03-08 00:34:30 UTC

Emphysema is abnormal permanent enlargement of gas-exchange airways (acini) accompanied by destruction of alveolar walls without obvious fibrosis. The major mechanism of airflow limitation in emphysema is loss of elastic recoil. Some degree of emphysema is considered normal in older adults, but results in a slow and predictable decline in lung function with aging.

2. Is it obstructive or restrictive? Why?

paulinewong1 — 2023-03-08 00:34:30 UTC

3. How does the condition effect lung compliance and/or airway resistance?

paulinewong1 — 2023-03-08 00:34:30 UTC

In COPD there is elevated compliance of the lungs due to loss of alveolar and elastic tissue

Airway resistance refers to the resistance encountered by air as it travels through the airways to reach the lungs. In emphysema patients, the damaged air sac walls and enlarged air spaces can also lead to an increase in airway resistance. This can make it more difficult for air to flow through the airways, further reducing the patient's ability to breathe effectively.

4. Explain the role of V/Q mismatch in this condition.

paulinewong1 — 2023-03-08 00:34:30 UTC

Gas exchange doesn’t happen due to -

Shunt: Low alveolar oxygen tension
Dead space: Emphysema destroys alveolar tissue and leads to air trapping and decreased diffusion surface area, thereby increasing dead space volume.

When patients have an area of poorly ventilated alveoli, then they compensate by vasoconstriction. Vasoconstriction causes ventilation/perfusion mismatch.
MANAGEMENT

Uncontrolled O2 – may cause hypercapnic respiratory failure due to:
(1) shunting of blood to low V/Q units -> increasing dead space
(2) loss of hypoxic drive
(3) dissociation of CO2 from Hb (Haldane effect)
(4) anxiolysis and reduction in tachypnoea

from Life in the Fast Lane / COPD

5. How is oxygenation and ventilation affected? Eg. consider O2 content, O2 delivery, alveolar ventilation

paulinewong1 — 2023-03-08 00:34:30 UTC

The principal contributor to hypoxemia in COPD patients is ventilation/perfusion (V/Q) mismatch resulting from progressive airflow limitation and emphysematous destruction of the pulmonary capillary bed.

6. What type of respiratory failure would this condition lead to?

paulinewong1 — 2023-03-08 00:34:30 UTC

COPD is considered type II respiratory failure.
Type II respiratory failure involves low oxygen, with high carbon dioxide (pump failure).

Type 2 Respiratory Failure (hypercapnic): occurs when alveolar ventilation is insufficient to excrete the carbon dioxide being produced. Inadequate ventilation is due to reduced ventilatory effort or inability to overcome increased resistance to ventilation. It affects the lung as a whole, and therefore carbon dioxide accumulates, presenting with PaO2 of <8 kPa (60 mm Hg) or normal, with hypercapnia PaCO2 >6.0kPa (> 50 mm Hg)

8. Clinical manifestations

paulinewong1 — 2023-03-08 00:34:30 UTC

1. productive cough due to increased mucous production in response to inflammation and / or infective process in exacerbations.
2. increasing shortness of breath especially on exertion

3. occasional exacerbations causing worsening symptoms due to infections or non-compliance with medications