A 3-week-old male infant presents with progressive non-bilious projectile vomiting after each feed for the past 5 days. He is hungry after vomiting. On examination, an olive-shaped mass is palpable in the right epigastrium after a test feed. Bloods show: Na 128, K 3.0, Cl 85, pH 7.52, HCO3 32 mEq/L. Which of the following is the most important pre-operative measure?

• A Emergency pyloromyotomy before fluid correction
• B Correct hypochloraemic hypokalaemic metabolic alkalosis with IV normal saline and potassium before surgery ✓
• C Start oral feeds with diluted formula immediately
• D Administer IV atropine to relax the pylorus

Explanation

Hypertrophic pyloric stenosis causes hypochloraemic, hypokalaemic metabolic alkalosis from loss of gastric HCl. Surgery (Ramstedt pyloromyotomy) is not an emergency; the priority is metabolic resuscitation with IV 0.9% NaCl until urine output is adequate, then adding KCl to replacement fluids until pH, chloride, and electrolytes are corrected. Anaesthesia with alkalosis carries risk of apnoea. Atropine is occasionally used as medical therapy (high-dose oral atropine) but not as pre-operative preparation in acute presentation.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.