A 52-year-old man is brought to the emergency department after being found unresponsive on the street. The patient's medical history is unknown. Temperature is 36.2 C (97.2 F), blood pressure is 108/62 mm Hg, and pulse is 72/min. On physical examination, he is unresponsive to verbal and tactile stimuli but moans to deep sternal rub. An arterial blood gas analysis on room air shows a partial pressure of oxygen of 60 mm Hg. The partial pressure of oxygen in his alveoli is calculated to be 68 mm Hg. Which of the following is the most likely cause of this patient's symptoms?

Question

A 52-year-old man is brought to the emergency department after being found unresponsive on the street.  The patient's medical history is unknown.  Temperature is 36.2 C (97.2 F), blood pressure is 108/62 mm Hg, and pulse is 72/min.  On physical examination, he is unresponsive to verbal and tactile stimuli but moans to deep sternal rub.  An arterial blood gas analysis on room air shows a partial pressure of oxygen of 60 mm Hg.  The partial pressure of oxygen in his alveoli is calculated to be 68 mm Hg.  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

Eductional Objective: There are 5 major causes of hypoxemia (low arterial partial pressure of oxygen [PaO₂]): alveolar hypoventilation, low partial pressure of inspired oxygen, ventilation-perfusion mismatch, diffusion impairment, and right-to-left shunting. The A-a gradient is normal with alveolar hypoventilation and low partial pressure of inspired oxygen, which helps distinguish these causes from other causes of hypoxemia.

A 52-Year-Old Man Is Brought to the Emergency Department After