A 55-year-old woman with chronic duodenal ulcer presents with repeated vomiting of old food. She has a succussion splash. Serum sodium 138 mEq/L, potassium 2.8 mEq/L, chloride 88 mEq/L, pH 7.52. What is the characteristic acid-base disturbance?

• A Hypochloraemic hypokalaemic metabolic alkalosis ✓
• B Hyperchloraemic metabolic acidosis
• C Respiratory acidosis with metabolic compensation
• D Mixed metabolic acidosis and alkalosis

Explanation

Gastric outlet obstruction from chronic duodenal ulcer causes loss of hydrochloric acid through vomiting, producing hypochloraemic hypokalaemic metabolic alkalosis. Potassium falls further because of secondary hyperaldosteronism and renal exchange of potassium for hydrogen ions, which also produces paradoxical aciduria. Treatment is nasogastric decompression, correction of chloride and potassium deficits, then endoscopic balloon dilatation or surgery for the obstruction.

Reference: Bailey and Love's Short Practice of Surgery, 28th ed.

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