Hypertrophic Pyloric Stenosis
A 5-week-old boy has 10 days of forceful nonbilious vomiting after feeds and has lost 300 g since birth. His heart rate is 172 beats/min, capillary refill 3 seconds, and the fontanelle is sunken. Ultrasound shows pyloric muscle thickness 4.5 mm and channel length 18 mm. Blood gas shows pH 7.52, chloride 88 mmol/L, potassium 3.0 mmol/L, and bicarbonate 34 mmol/L. What is the most appropriate initial step in management?
- A.Keep the infant nil by mouth and observe
- B.Intravenous fluid and electrolyte resuscitationCorrect
- C.Immediate pyloromyotomy in the operating room
- D.Upper gastrointestinal contrast radiography
Explanation
Hypertrophic pyloric stenosis is a medical problem before it is a surgical one, and correction of dehydration and the hypochloremic hypokalemic metabolic alkalosis always precedes the operation. Persistent vomiting of gastric contents loses hydrogen and chloride, and the resulting volume depletion drives renal sodium and bicarbonate retention with paradoxical aciduria as the kidney exchanges hydrogen for sodium despite systemic alkalosis. Operating on an alkalotic infant is dangerous because alkalosis blunts the central respiratory drive and predisposes to postoperative apnea, and hypokalemia raises the risk of arrhythmia. Resuscitation uses isotonic saline boluses followed by dextrose-containing saline with potassium once urine output is established, and surgery proceeds only when chloride exceeds roughly 100 mmol/L, bicarbonate is below about 30 mmol/L, and potassium has normalized, which usually takes 24 to 48 hours. The diagnosis here is already secure on ultrasound, where muscle thickness above 3 mm and channel length above 15 mm are diagnostic, so contrast radiography adds nothing. Keeping the infant nil by mouth is a correct supportive measure but is only part of the plan and by itself does nothing for the profound volume and electrolyte deficits. Pyloromyotomy, whether open or laparoscopic, is curative and feeds usually resume within 6 to 12 hours afterward. Nonbilious vomiting localizes the obstruction proximal to the ampulla of Vater, which is the key discriminator from malrotation with volvulus.
Why each option
- A.
- Withholding feeds is appropriate supportive care but does not correct the dehydration and alkalosis that make anesthesia unsafe.
- B.
- Correct. Fluid and electrolyte correction of hypochloremic hypokalemic alkalosis must precede surgery.
- C.
- Operating before metabolic correction risks postoperative apnea and arrhythmia; pyloromyotomy is never an emergency.
- D.
- The ultrasound findings are already diagnostic, so contrast studies only delay treatment and add radiation.
Reference: Nelson Textbook of Pediatrics, 22nd ed., 2024, Pyloric Stenosis; UpToDate 2025, Infantile hypertrophic pyloric stenosis
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