A patient breathing 40% oxygen at sea level has a PaO₂ of 50 mm Hg, a PCO₂ of 30 mm Hg and a PAO₂ -PaO₂ of 250 mm Hg. When the FIO₂ is raised to 0.7, the PaO₂ rises to only 58 mm Hg. Hypoxemia is primarily due to which of the following?

Question

Quizplus · Accepted Answer

A rise in inspired oxygen concentration from 0.4 to 0.7 should have resulted in an increase in the PaO2 to approximately 100 mm Hg. The actual increase to only 58 mm Hg suggests that there is a significant right-to-left shunt, through which venous blood is being shunted into the systemic arterial circulation without first passing through the lungs. Hypoventilation, diffusion abnormalities, or V/Q imbalances would all result in low PaO2 levels that would be expected to improve with an increase in the FIO2.

A Patient Breathing 40% Oxygen at Sea Level Has a PaO2

A Patient Breathing 40% Oxygen at Sea Level Has a PaO₂