A 5-week-old boy presents with progressive non-bilious vomiting after every feed. He is eager to feed but losing weight. Serum electrolytes show sodium 134 mEq/L, potassium 2.9 mEq/L, chloride 88 mEq/L, bicarbonate 32 mEq/L. Which acid-base disturbance does this pattern represent?

• A Hyperchloremic metabolic acidosis
• B High anion gap metabolic acidosis
• C Mixed respiratory acidosis and metabolic alkalosis
• D Hypochloremic hypokalemic metabolic alkalosis ✓

Explanation

Repeated vomiting of gastric juice causes loss of hydrogen ion and chloride, producing hypochloremic metabolic alkalosis, while urinary potassium losses worsen the hypokalemia. This triad in a hungry, eager-to-feed infant with non-bilious vomiting points to hypertrophic pyloric stenosis. Option A describes the opposite disorder seen in diarrheal losses, where bicarbonate rather than acid is lost in stool.

Reference: Nelson Textbook of Pediatrics, 22nd ed.

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