A 55-year-old man is brought to the emergency department because of sharp chest pain for the past 3 hours. He does not take any medications. He has smoked one pack of cigarettes daily for 35 years. Arterial blood gas analysis shows that the patient's alveolar-arterial gradient (PAO₂ - PaO₂) is markedly increased. Although the patient receives 100% oxygen via a face mask, she has persistent hypoxemia and respiratory distress. Consequently, she is intubated and placed on mechanical ventilation with 100% oxygen and positive end-expiratory pressure (PEEP). Results of arterial oxygen measurements are as follows: The patient's improved oxygenation following PEEP application is most likely due to a decrease in which of the following?

Question

Quizplus · Accepted Answer

Eductional Objective: Severe hypoxemia that does not correct with 100% supplemental oxygen is consistent with a right-to-left shunt.  Intrapulmonary shunt effect occurs when an alveolar filling process (eg, diffuse pulmonary edema) causes poor alveolar ventilation despite continued perfusion; this improves with positive end-expiratory pressure.

A 55-Year-Old Man Is Brought to the Emergency Department Because