A 40-year-old man with a long history of duodenal ulcer now vomits food ingested 36 hours earlier. Examination shows a succussion splash and visible peristalsis. Serum sodium is 138 mEq/L, potassium 2.8 mEq/L, chloride 86 mEq/L and bicarbonate 38 mEq/L. Which acid-base pattern does this represent?

• A Hyperchloremic normal-anion-gap metabolic acidosis
• B Respiratory acidosis with compensatory metabolic alkalosis
• C Mixed metabolic acidosis and respiratory alkalosis
• D Hypochloremic hypokalemic metabolic alkalosis ✓

Explanation

Gastric outlet obstruction from chronic duodenal ulcer causes repeated loss of gastric hydrochloric acid through vomiting, generating a hypochloremic hypokalemic metabolic alkalosis. Potassium falls further from aldosterone-mediated renal losses and exchange of intracellular potassium for hydrogen ions, which paradoxically produces paradoxical aciduria. Option A is the pattern of diarrhoeal bicarbonate loss, the opposite direction of disturbance.

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

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