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Pyloric Stenosis — RACP Paediatrics MCQ

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EasyGastroenterologyPyloric StenosisRACP Paediatrics

A 6-week-old exclusively breastfed male presents with non-bilious projectile vomiting after every feed for the past week. He is eager to feed and shows signs of dehydration. A palpable 'olive-shaped' mass is felt in the right upper quadrant. Which electrolyte abnormality is most likely?

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Correct answer: D — Hypokalaemic hypochloraemic metabolic alkalosis

Pyloric stenosis causes loss of gastric acid (HCl) through persistent vomiting, leading to a hypokalaemic, hypochloraemic metabolic alkalosis. The kidneys compensate by retaining H+ and excreting K+, worsening the hypokalaemia. Diagnosis is confirmed by ultrasound showing pyloric muscle thickness >3 mm and channel length >15 mm. Treatment is Ramstedt pyloromyotomy after fluid and electrolyte correction.

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