A 45-Year-Old Hospitalized Man Is Evaluated for Shortness of Breath

A 45-year-old hospitalized man is evaluated for shortness of breath and hypoxemia.  The patient was admitted 3 days ago after a motor vehicle collision.  At that time, evaluation revealed a femur fracture but no other injuries, and the patient underwent open reduction and internal fixation of the fracture.  This morning, he suddenly began experiencing shortness of breath and sharp chest pain.  The patient has no significant medical history and has been receiving morphine for pain control.  He has smoked a pack of cigarettes daily for 15 years and drinks alcohol occasionally.  Temperature is 36.1 C (97 F) , blood pressure is 120/70 mm Hg, and pulse is 98/min.  BMI is 42 kg/m².  Chest x-ray is unremarkable, and arterial blood gas analysis on room air shows a pH of 7.51, PaCO₂ of 30 mm Hg, and PaO₂ of 65 mm Hg.  Which of the following is the primary cause of hypoxemia in this patient?

A) Alveolar hypoventilation
B) Decreased blood oxygen-carrying capacity
C) Increased tissue oxygen extraction
D) Primary diffusion impairment
E) Ventilation/perfusion mismatch

Correct Answer:

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