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Pyloric Stenosis Electrolytes — RACP Paediatrics MCQ

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ModerateGastroenterologyPyloric Stenosis ElectrolytesRACP Paediatrics

A 10-month-old presents with non-bilious projectile vomiting that has been worsening over 3 days. He is hungry and wants to feed immediately after vomiting. On examination, you palpate a firm olive-shaped mass in the epigastrium. Blood gas shows a metabolic alkalosis with hypochloraemia. What electrolyte abnormality pattern is characteristic?

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Correct answer: A — Hypochloraemic hypokalaemic metabolic alkalosis

Pyloric stenosis causes loss of gastric acid (HCl), leading to hypochloraemic hypokalaemic metabolic alkalosis. The kidneys initially compensate by retaining Na+ and excreting K+/H+ (paradoxical aciduria). Electrolyte correction is essential before surgical pyloromyotomy.

Reference: RCH Melbourne – 2024 – Clinical Practice Guidelines: Pyloric Stenosis