A 4-week-old male infant presents with projectile non-bilious vomiting after every feed for the past week. On examination, an olive-shaped mass is palpable in the epigastrium. Abdominal ultrasound shows pyloric muscle thickness of 4.5 mm and pyloric channel length of 18 mm. What are the METABOLIC ABNORMALITIES expected in this condition and what is the definitive treatment?
- A Hyperkalemic metabolic acidosis — correct with IV fluids then Ramstedt pyloromyotomy
- B Hypernatremic dehydration — hydrate then operate urgently within 2 hours
- C Metabolic acidosis from starvation — start feeds and operate emergently
- D Hypokalemic hypochloremic metabolic alkalosis (paradoxical aciduria) — correct metabolic derangement BEFORE surgery, then Ramstedt pyloromyotomy ✓
Explanation
Hypertrophic pyloric stenosis (HPS) causes persistent loss of gastric acid (HCl) through vomiting, leading to hypokalemic, hypochloremic metabolic alkalosis. Paradoxical aciduria occurs when the kidneys preferentially excrete H+ ions to preserve potassium in the face of severe hypokalemia, acidifying the urine despite systemic alkalosis. HPS is NOT a surgical emergency requiring immediate operation — metabolic correction (IV normal saline with KCl supplementation to normalize pH, K+, Cl-) must precede surgery to avoid post-operative apnea from uncorrected alkalosis. Definitive treatment is Ramstedt pyloromyotomy (laparoscopic or open). Ultrasound criteria: muscle thickness ≥4 mm, channel length ≥16 mm confirm diagnosis.
Reference: Ghai Essential Pediatrics, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.