Causes of hypoxemia

1. Causes of hypoxemia
Examples A-a gradient
Corrects with
supplemental
O2?
Reduced PiO2 High altitude Normal Yes
Hypoventilation CNS depression, morbid obesity Normal Yes
Diffusion limitation Emphysema, ILD Increased Yes
V/Q mismatch* Small PE, lobar pneumonia Increased Yes
Large intrapulmonary shunt Diffuse pulmonary edema Increased No
Large dead-space ventilation
Massive PE, right-to-left
intracardiac shunt
Increased No
*Caused by localized dead-space ventilation and/or intrapulmonary shunting.
A-a gradient = alveolar-arterial oxygen gradient; ILD = interstitial lung disease; PE = pulmonary embolism; PiO2 = partial
pressure of inspired oxygen; V/Q = ventilation/perfusion ratio.