Question

An intubated patient receiving 30% oxygen has a SpO₂ of 80% and ETCO₂ of 40 torr. After administration of 50% oxygen for 30 minutes, the respiratory therapist notes that the SpO₂ rises to 98% and the ETCO₂ remains stable at 40 torr. The major cause of hypoxemia in this patient is

A. hypoventilation.
B. shunt.
C. ventilation/perfusion mismatch.
D. increased deadspace.

Answer 1

The major cause of hypoxemia in this patient is a ventilation/perfusion mismatch since the SpO₂ greatly improved with an increase in FiO₂ and the ETCO₂ remained stable, suggesting that increasing the oxygen could augment the deficient gas exchange.

Step-by-step explanation:

The major cause of hypoxemia in a patient whose SpO₂ increases upon raising the FiO₂ (fraction of inspired oxygen) from 30% to 50% and whose ETCO₂ (end-tidal carbon dioxide) remains stable is most likely due to a ventilation/perfusion mismatch. This is evident because if hypoventilation was the cause, the ETCO₂ would be high. In the case of a shunt, increasing the oxygen would not have as pronounced an effect on improving SpO₂, and increased dead space would typically not show an improved SpO₂ solely with increased oxygen since there's no improvement in airflow to alveoli. Since the patient responded well to the increase in FiO₂, it indicates that there is still some perfusion and thus improving the partial pressure of oxygen in the blood can help increase oxygen saturation significantly.