A 3-week-old male infant presents with persistent, non-bilious projectile vomiting after every feed. On examination, a firm olive-shaped mass is palpable in the right upper quadrant. Ultrasound shows pyloric muscle thickness of 4.5 mm and channel length of 19 mm. The metabolic derangement expected and the surgical procedure of choice are:

• A Hyperchloraemic metabolic acidosis; pylorotomy
• B Hypernatraemic dehydration; pyloroplasty
• C Metabolic acidosis; nasogastric drainage alone
• D Hypochloraemic, hypokalaemic metabolic alkalosis; Ramstedt's pyloromyotomy after correction of electrolytes ✓

Explanation

Hypertrophic pyloric stenosis causes loss of gastric hydrochloric acid through repeated vomiting, producing hypochloraemic, hypokalaemic metabolic alkalosis (the classic 'paradoxical aciduria' — the kidney conserves sodium at the expense of H+ when severely volume-depleted). Surgery (Ramstedt's pyloromyotomy) must be deferred until the metabolic derangement is corrected with IV normal saline and potassium.

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.