A 5-week-old male infant presents with non-bilious, projectile vomiting after every feed for 1 week. The vomiting has worsened progressively. The infant is hungry after vomiting. On examination there is visible peristalsis and a palpable olive-shaped mass in the epigastrium. Serum electrolytes show Na 128 mEq/L, K 2.9 mEq/L, Cl 72 mEq/L, bicarbonate 34 mEq/L. Which electrolyte/acid-base pattern and surgical technique are MOST appropriate?
- A Hyperchloremic metabolic acidosis; Swenson pull-through procedure
- B Hypochloremic hypokalemic metabolic alkalosis; Ramstedt pyloromyotomy after correction of alkalosis ✓
- C Hypochloremic metabolic alkalosis; endoscopic balloon dilatation of pylorus
- D Normal acid-base; Ladd procedure for malrotation
Explanation
Hypertrophic pyloric stenosis (HPS) in males 3–6 weeks of age presents with non-bilious projectile vomiting, hungry infant, and palpable 'olive' mass. Repeated vomiting of acid-rich gastric contents causes hypochloremic hypokalemic metabolic alkalosis — the hallmark metabolic abnormality. Surgery (Ramstedt pyloromyotomy — longitudinal division of the hypertrophied pyloric muscle) is curative but must be deferred until the metabolic alkalosis is corrected with IV normal saline + KCl supplementation (target Cl >90 mEq/L, bicarb <30 mEq/L). Operating during significant alkalosis risks postoperative apnea. Ultrasound (pyloric muscle thickness >4 mm, length >16 mm) confirms the diagnosis non-invasively.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.