A 52-year-old man with chronic duodenal ulcer disease presents with weeks of progressive vomiting after meals and weight loss. Barium study shows gross gastric dilatation with retained food. Serum electrolytes: sodium 138 mEq/L, potassium 2.8 mEq/L, chloride 88 mEq/L, bicarbonate 38 mEq/L. What acid-base disturbance is expected?

• A Hyperchloremic metabolic acidosis
• B Normal anion gap acidosis with hyperkalemia
• C Respiratory acidosis with compensatory hyperkalemia
• D Hypochloremic hypokalemic metabolic alkalosis ✓

Explanation

Gastric outlet obstruction causes loss of hydrochloric acid in vomitus, producing hypochloremic metabolic alkalosis. Volume depletion drives aldosterone-mediated potassium loss in urine and exchange of hydrogen ions, adding hypokalemia and paradoxical aciduria. The combination of dehydration, alkalosis and hypokalemia also predisposes to tetany. Hyperchloremic acidosis occurs with diarrhoea or pancreatic fistula, which makes option A the distractor students pick when they confuse upper and lower GI fluid losses.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.