Question

A patient is started on nitroprusside, and his oxygen saturation by pulse oximetry decreases to 90%. Arterial blood gases are drawn, which show a PaO2 of 60 mm Hg and an arterial oxygen saturation (SaO2) of 90%. What is the mechanism for this change?

A. Methemoglobinemia
B. Intrapulmonary shunt
C. Thiocyanate toxicity
D. Coronary artery steal

Answer 1

The mechanism for the decrease in oxygen saturation is intrapulmonary shunt.

Step-by-step explanation:

The mechanism for the decrease in oxygen saturation by pulse oximetry and the decrease in arterial oxygen saturation (SaO2) in this patient is Intrapulmonary shunt.

An intrapulmonary shunt occurs when blood bypasses the normal process of gas exchange in the lungs and mixes with unoxygenated blood, resulting in decreased oxygenation. This can be caused by factors such as lung collapse, pneumonia, or pulmonary embolism.

In this case, the decrease in oxygen saturation is due to blood shunting past the alveoli without adequate oxygenation, leading to lower oxygen levels in the arterial blood.