A 4-week-old male infant presents with non-bilious projectile vomiting. Examination reveals a palpable olive-shaped mass in the epigastrium. ABG shows pH 7.55, Na+ 128 mEq/L, K+ 2.9 mEq/L, Cl- 82 mEq/L. Prior to Ramstedt's pyloromyotomy, which fluid and electrolyte correction is most appropriate?

• A Immediate surgery; metabolic derangement can be corrected intraoperatively
• B IV 5% dextrose with sodium bicarbonate to correct alkalosis
• C Nasogastric tube aspiration alone is sufficient preoperative preparation
• D IV 0.9% NaCl with 20 mEq/L KCl until chloride > 100 mEq/L and pH < 7.45, then surgery ✓

Explanation

Hypertrophic pyloric stenosis causes hypochloremic hypokalemic metabolic alkalosis from loss of HCl-rich gastric secretions. This is a medical emergency for resuscitation, not a surgical emergency. Ramstedt's pyloromyotomy should be delayed until the metabolic derangement is corrected — ideally until serum chloride > 100 mEq/L, sodium > 132 mEq/L, and blood pH < 7.45. Normal saline (0.9% NaCl) with potassium chloride supplementation corrects the chloride deficit; bicarb infusion would worsen alkalosis. The uncorrected alkalosis increases the risk of post-operative apnea in young infants and complicates anaesthetic management.

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

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Written and medically reviewed by the StethoPrep medical team.