A 34-year-old woman with recurrent vomiting is found to have pH 7.50, PaCO2 46 mmHg, HCO3- 36 mEq/L, Na+ 138, K+ 2.9, Cl- 88 mEq/L. Urine chloride is 12 mmol/L. Which is the correct classification of her metabolic alkalosis?

• A Chloride-responsive alkalosis due to gastric HCl loss; will respond to saline and KCl ✓
• B Chloride-resistant alkalosis; likely primary aldosteronism
• C Chloride-resistant alkalosis due to Bartter syndrome; needs prostaglandin inhibition
• D Mixed respiratory acidosis and metabolic alkalosis; no fluid therapy indicated

Explanation

Vomiting loses gastric hydrochloric acid, generating metabolic alkalosis with volume depletion. The kidney avidly reabsorbs sodium with bicarbonate, so the urine chloride falls below 20 mmol/L, defining a chloride-responsive alkalosis that corrects with isotonic saline plus potassium replacement. In mineralocorticoid excess or Bartter syndrome, volume expansion or tubular salt loss keeps urine chloride above 20 mmol/L, which rules out options B and C.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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