Pyloric Stenosis on the NCLEX
Projectile nonbilious vomiting, the olive mass, hypochloremic metabolic alkalosis, and pyloromyotomy care.
Pyloric stenosis is the classic surgical vomiting infant. The exam tests the triad and the electrolyte pattern more than anything else.
Recognize it
Typical age 2-8 weeks, more often firstborn males. Projectile, NONbilious vomiting shortly after feeds. The infant is hungry again right after vomiting - that detail separates it from other causes. Olive-shaped mass in the right upper quadrant, easiest to feel after vomiting. Visible peristaltic waves moving left to right. Weight loss, fewer wet diapers, sunken fontanel as dehydration builds. Diagnosis: ultrasound.
The electrolyte pattern
Vomiting stomach contents loses HCl → hypochloremic, hypokalemic METABOLIC ALKALOSIS. This is the most-tested fact. Contrast with bilious vomiting: bile means obstruction below the pylorus and is a surgical red flag for a different problem. Priority before surgery: correct fluids and electrolytes first. Pyloromyotomy is urgent, not emergent, and anesthesia on an alkalotic dehydrated infant is dangerous.
Post-op care after pyloromyotomy
Feeds restart within hours per protocol: small, frequent feeds, advanced slowly. Some vomiting in the first 24-48 hours is expected from gastric irritation and does not mean failure. Position upright during and after feeds, burp well. Monitor the incision for infection and keep it clean during diaper changes. Prognosis is excellent.
Frequently asked
Bilious or nonbilious vomiting?
Nonbilious. The obstruction is at the pylorus, above the bile duct entry. Bilious vomiting points elsewhere.
Why alkalosis and not acidosis?
The infant vomits hydrochloric acid from the stomach. Losing acid and chloride leaves the blood alkalotic and hypochloremic.
Baby vomits once after surgery. Report it?
Document and continue the feeding plan. Mild vomiting is expected early post-op. Persistent or projectile vomiting is what you report.
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