Step 1

Physiology 5

A 57-year-old man is transported to the emergency department by emergency medical services. The patient is unconscious and was emergently intubated in the field. The patient has a past medical history of major depressive disorder and post-traumatic stress disorder (PTSD). The patient wife reports he is an avid hobbyist and likes to rebuild engines on classic cars. Family history is unremarkable. The patient’s wife found her husband down when she returned home from work. She states that he was working on a car with several gas space heaters running. Vital signs are temperature is 37° C (98.6° F), blood pressure 78/57 mmHg, pulse 130 beats/minu, and respirations 33/min. The patient is 5’11 in and weighs 201 pounds. Arterial blood gas analysis is notable for a pH of 7.32, PCO2 of 33 mmHg, PO2 of 380 mmHg, bicarbonate of 16 mE1/L, and a carboxyhemoglobin level of 22.0% and is improving on continued oxygen therapy.

Which of the following forms of gas exchange governs the most likely etiology of this patient’s condition?

  • A) Diffusion-limited gas exchange
  • B) Early capillary perfusion-limited gas exchange
  • C) End capillary perfusion-limited gas exchange
  • D) Mixed diffusion-limited and perfusion-limited gas exchange
  • E) Normal gas exchange


Philip Khoury


Dr. Ted O'Connell

Last updated

Oct 24, 2023

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