A 6-week-old male infant presents with non-bilious projectile vomiting after every feed since age 3 weeks. He is hungry after vomiting. Examination reveals visible peristaltic waves from left to right in the epigastrium, and an olive-shaped mass palpable to the right of the umbilicus. Serum electrolytes show Na 132 mEq/L, K 2.9 mEq/L, Cl 88 mEq/L, HCO3 32 mEq/L. What is the CORRECT metabolic abnormality and the REASON surgery must not be performed immediately?

• A Metabolic acidosis; surgery must await acid-base correction to prevent respiratory depression
• B Metabolic alkalosis with hypokalemia and hypochloremia; surgery must await electrolyte correction to prevent intraoperative cardiac arrhythmias ✓
• C Metabolic alkalosis; surgery can be performed immediately as the alkalosis corrects spontaneously post-operatively
• D Respiratory alkalosis; surgery is a medical emergency requiring immediate laparotomy without delay

Explanation

Hypertrophic pyloric stenosis (HPS) causes loss of hydrochloric acid from the stomach due to persistent vomiting, resulting in hypochloremic, hypokalemic metabolic alkalosis. The elevated bicarbonate (32 mEq/L), low chloride, and low potassium confirm this. This is NOT a surgical emergency—pyloromyotomy (Ramstedt procedure) is an urgent but not emergent surgery and must be delayed until metabolic correction is achieved. Hypokalemia predisposes to intraoperative cardiac arrhythmias. IV normal saline with potassium chloride supplements over 24–48 hours corrects the electrolyte derangement before surgery.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.