A patient with COPD has decreased diffusion capacity; which gas exchange abnormality would you expect?

A patient with COPD has decreased diffusion capacity; which gas exchange abnormality would you expect?

• A. Hypoxemia with hypercapnia (low PaO2 and high PaCO2)
• B. Hypoxemia with normal PaCO2
• C. Hypercapnia without hypoxemia
• D. Normal PaO2 and PaCO2

Answer: (A)

Impaired transfer of oxygen from the alveoli to the blood is the key idea. In COPD with reduced diffusion capacity, the alveolar-capillary membrane and capillary bed are damaged or decreased, so less O2 crosses into the blood, causing hypoxemia. At the same time, advanced COPD often involves hypoventilation and airflow obstruction with V/Q mismatch, which can raise the arterial CO2 level. So the typical gas exchange pattern is low PaO2 with elevated PaCO2.

Impaired transfer of oxygen from the alveoli to the blood is the key idea. In COPD with reduced diffusion capacity, the alveolar-capillary membrane and capillary bed are damaged or decreased, so less O2 crosses into the blood, causing hypoxemia. At the same time, advanced COPD often involves hypoventilation and airflow obstruction with V/Q mismatch, which can raise the arterial CO2 level. So the typical gas exchange pattern is low PaO2 with elevated PaCO2.