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Respiratory Alkalosis 1

Respiratory alkalosis
physiology

Question

Vignette: A 60-year-old man presents to the emergency department with severe shortness of breath and fatigue. His blood pressure is 130/80 mm Hg, pulse is 100/min, and respiratory rate is 30/min. His arterial blood gas analysis reveals a PaO2 of 55 mm Hg, PaCO2 of 30 mm Hg, and pH of 7.50. Physical examination reveals bilateral crackles at the lung bases and a gallop rhythm. Based on the patient's clinical presentation, which of the following compensatory mechanisms is most likely responsible for the observed pH?

Choices

A) Decreased renal bicarbonate reabsorption

B) Increased renal bicarbonate reabsorption

C) Decreased renal hydrogen ion secretion

D) Increased renal hydrogen ion secretion

E) Decreased respiratory rate

Answer

B) Increased renal bicarbonate reabsorption

Explanation

The patient's clinical presentation is consistent with congestive heart failure (CHF) leading to hypoxemia and respiratory alkalosis due to hyperventilation (elevated respiratory rate, decreased PaCO2, increased pH). In response to respiratory alkalosis, the renal system compensates by decreasing bicarbonate reabsorption, which would result in a decrease in blood bicarbonate levels and a return of the blood pH towards normal. However, this compensation takes several days to occur, and the patient's acute presentation suggests that this process has not yet begun. The most likely explanation for the patient's alkalosis, therefore, is not a compensatory response, but a primary respiratory disorder due to hyperventilation caused by CHF.

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