Question 98

Question:

A 23-year-old man who is planning to climb Mount Kilimanjaro comes to your office and asks you how to prevent altitude sickness. He knows that gradual ascent and prevention of dehydration are important, but wants some pharmacologic help to make sure he does not get sick. You tell him that acetazolamide, a bicarbonate-wasting diuretic, may be useful. What is the mechanism by which acetazolamide decreases tissue hypoxia in a low-oxygen environment?

Correct Answer: B.  Hyperventilation

The question stem tells you that acetazolamide is a bicarbonate-wasting diuretic. This means that bicarbonate is lost in the urine. This results in a metabolic acidosis. One of the physiologic mechanisms of compensating for a metabolic acidosis is hyperventilation (in order “to blow off CO2”). Peripheral chemoreceptors in the carotid and aortic bodies detect the increase in pCO2, and respiration is stimulated, allowing for better ventilation and increased oxygen saturation.