A 60-year-old woman with long-standing peptic ulcer disease presents with repeated vomiting of old food. Examination shows succussion splash and visible gastric peristalsis. Serum biochemistry is most likely to show which pattern?

• A Hypochloraemic hypokalaemic metabolic alkalosis ✓
• B Hyperchloraemic metabolic acidosis with normal potassium
• C Hyponatraemic metabolic acidosis with raised urea
• D Normal chloride with respiratory alkalosis

Explanation

Gastric outlet obstruction causes loss of hydrochloric acid through vomiting, producing hypochloraemia and metabolic alkalosis. Secondary hyperaldosteronism from volume depletion drives renal potassium loss and paradoxical aciduria, deepening hypokalaemia. Hyperchloraemic acidosis is seen after diarrhoea or renal tubular losses, and respiratory alkalosis would reflect hyperventilation rather than gastric loss.

Reference: Bailey and Love's Short Practice of Surgery, 27th ed.

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