Metabolic alkalosis is most commonly seen with which clinical scenario?

• A. Severe diarrhea
• B. Prolonged vomiting
• C. Renal failure
• D. Addison disease

Answer: (B)

Metabolic alkalosis arises when there is a net loss of hydrogen ions or a gain in bicarbonate, often from loss of gastric acid. Prolonged vomiting removes H+ and chloride from the body, leading to a rise in serum bicarbonate. The loss of chloride also impairs the kidney’s ability to excrete bicarbonate, and the accompanying volume depletion from vomiting promotes “contraction alkalosis,” further increasing bicarbonate reabsorption. The body attempts to compensate by reducing ventilation to keep CO2 higher, but this compensation is limited.

That’s why prolonged vomiting is the classic scenario causing metabolic alkalosis. Severe diarrhea tends to cause metabolic acidosis due to bicarbonate loss in stool; renal failure usually leads to acidosis from impaired acid excretion; Addison disease typically presents with metabolic acidosis from aldosterone deficiency.