A 3-week-old firstborn male infant presents with 1 week of non-bilious projectile vomiting after feeds. He is hungry immediately after vomiting. Examination shows mild dehydration and an olive-shaped mass in the right upper quadrant. Blood gases show pH 7.52, bicarbonate 34 mEq/L, serum chloride 88 mEq/L, serum potassium 3.1 mEq/L. What is the correct pre-operative electrolyte management?

• A Emergency surgery without fluid correction as obstruction is complete
• B IV sodium bicarbonate to prevent worsening alkalosis during surgery
• C Immediate oral rehydration with ORS and electrolytes
• D Correct hypochloremic metabolic alkalosis and hypokalemia with IV 0.9% NaCl + KCl; surgery only when electrolytes and hydration are corrected ✓

Explanation

Hypertrophic pyloric stenosis causes repeated loss of hydrochloric acid from the stomach, resulting in hypochloremic hypokalemic metabolic alkalosis — the hallmark metabolic derangement. Pre-operative resuscitation with IV 0.9% NaCl (with KCl supplementation after urine output is confirmed) is mandatory to correct the alkalosis and electrolyte disturbances BEFORE surgery. The classic threshold for safe Ramstedt pyloromyotomy requires: serum Cl >100 mEq/L, bicarbonate <30 mEq/L, and K >3.5 mEq/L. This may take 24–48 hours of IV fluid therapy. Proceeding directly to surgery risks anesthetic complications from alkalosis (hypoventilation, electrolyte shifts). Sodium bicarbonate would worsen alkalosis. ORS cannot correct severe metabolic derangements in a vomiting infant.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.