A 5-week-old male infant presents with projectile non-bilious vomiting for 10 days. Serum electrolytes: sodium 133 mEq/L, potassium 2.8 mEq/L, chloride 86 mEq/L, bicarbonate 32 mEq/L, pH 7.52. What is the most important biochemical correction required before pyloromyotomy?

• A Rapid normalization of serum sodium
• B Correction of hypochloremia and hypokalemia ✓
• C Reduction of bicarbonate to normal range with acetazolamide
• D Administration of a colloid bolus to expand volume

Explanation

Infantile hypertrophic pyloric stenosis causes gastric loss of hydrochloric acid, producing hypochloremic hypokalemic metabolic alkalosis. Surgery must wait until chloride is normalized and potassium repleted because alkalosis plus hypoventilatory compensation predisposes to postoperative apnea, especially after general anesthesia. Sodium here is near normal and does not need rapid correction. Acetazolamide is not used to lower bicarbonate acutely, and the primary problem is volume and electrolyte depletion rather than a need for colloid.

Reference: Nelson Textbook of Pediatrics, 21st ed.

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