A 3-week-old male infant presents with projectile vomiting after feeds, visible left-to-right gastric peristalsis, and a palpable olive-shaped mass in the right hypochondrium. Ultrasound confirms pyloric muscle thickness of 4.2 mm and pyloric canal length of 19 mm. Which electrolyte abnormality is expected?

• A Hyponatremia, hyperkalaemia, metabolic acidosis
• B Hyponatraemia, hypokalaemia, metabolic acidosis
• C Hypernatraemia, hypochloraemia, metabolic alkalosis
• D Hypokalaemia, hypochloraemia, metabolic alkalosis ✓

Explanation

Hypertrophic pyloric stenosis causes persistent vomiting of gastric contents (HCl), resulting in hypochloraemic, hypokalaemic metabolic alkalosis. The kidneys initially compensate by excreting bicarbonate but later conserve Na+ at the expense of K+ and H+ (paradoxical aciduria). Ultrasound criteria: muscle thickness >3 mm and canal length >14 mm confirm the diagnosis. Surgery (Ramstedt's pyloromyotomy) is performed after electrolyte correction.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.