Step I Ddx hypoxemia

[Jenny_94]

I learned that although PaO2 decreases and causes hypoxemia in V/Q mismatch, PaCO2 doesnt increase. This is because the non-affected lung will hyperventilate and send out the CO2. But then why not take in more O2? The non affected lung should take in O2 and send out CO2 but why only the latter?

 

[DandyLion]

Hyperventilation does not lead to compensatory increases in PaO2 because the air in the lungs is already saturated with enough O2 to exceed the carrying capacity of hemoglobin. However, alveolar levels of CO2 drop considerably when hyperventilating creating a greater driving force for offloading of excess PaCO2.