A postoperative patient with prolonged nasogastric drainage has pH 7.51, PaCO2 46 mmHg, HCO3 35 mEq/L. Urine chloride is 9 mEq/L. Which statement is correct?
- A Chloride-resistant alkalosis; treat with acetazolamide
- B Compensated respiratory acidosis; treat by increasing minute ventilation
- C Chloride-responsive alkalosis; treat with isotonic saline and potassium replacement ✓
- D Chloride-resistant alkalosis; suspect primary hyperaldosteronism
Correct answer: C. Chloride-responsive alkalosis; treat with isotonic saline and potassium replacement
Explanation
Loss of gastric acid produces a metabolic alkalosis with volume depletion. The urine chloride separates the two families: below 20 mEq/L indicates chloride-responsive alkalosis from volume contraction, vomiting or diuretics, and it corrects with isotonic saline plus potassium chloride. A value above 20 mEq/L points to mineralocorticoid excess, the chloride-resistant group. Acetazolamide is reserved for saline-refractory cases such as those associated with oedema states.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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