Before We Start
What's physically happening, and who's typically affected
Pyloric stenosis involves hypertrophy (thickening) of the pylorus — the muscular valve between the stomach and small intestine — causing progressive obstruction of the gastric outlet. It classically presents between 2 and 6 weeks of age, and is most common in first-born males, though it can occur in any infant.
💡 The Defining Clinical Picture
Projectile (forceful, non-bilious) vomiting after EVERY feeding, combined with a child who remains hungry and feeds eagerly right afterward — this combination of "vomits everything, then wants to eat again immediately" is the classic, recognizable presentation.
Mnemonic
Presentation, diagnosis, and the metabolic complication
Classic Signs
Projectile vomiting, visible peristaltic waves, olive-shaped mass
Beyond the projectile, non-bilious vomiting itself, visible peristaltic waves may be seen across the abdomen, and a firm, movable, olive-shaped mass is often palpable in the right upper quadrant — a specific, distinctive physical exam finding.
Metabolic Alkalosis
Hypochloremic — losing HCl through vomiting
Repeated vomiting of stomach contents causes significant loss of hydrochloric acid (HCl), which drives the blood pH upward (alkalosis) while chloride and potassium levels drop. This specific electrolyte pattern — metabolic alkalosis with low chloride and low potassium — is a direct, predictable consequence of the vomiting pattern itself.
💊 The chain of logic worth internalizing: vomiting → loss of stomach acid (HCl) → rising pH (alkalosis) + falling chloride and potassium. Understanding this mechanism, rather than just memorizing "metabolic alkalosis happens," makes the lab pattern much easier to predict and recall.
Diagnosis and Treatment
Ultrasound confirms; IV fluids correct electrolytes FIRST, then surgery
Ultrasound is the diagnostic imaging of choice. Critically, IV fluids are given to correct the metabolic alkalosis BEFORE proceeding to surgery — operating on a child with significant electrolyte imbalance carries its own risks, so correction comes first. The definitive treatment is a pyloromyotomy (Ramstedt procedure), a surgical procedure with an excellent prognosis.
Post-Operative Care
Small, frequent feedings starting 4-6 hours after surgery
Feeding resumes relatively quickly after surgery, but in a careful, graduated way — small, frequent feedings rather than a return to a normal feeding volume and schedule immediately.
🏥 Clinical Scenario — Recognizing the Classic Presentation and Correct Treatment Sequence
A 4-week-old, first-born male, presents with forceful, non-bilious vomiting after every feeding for the past several days. The infant appears hungry immediately after vomiting and wants to feed again. On exam, a small olive-shaped mass is palpated in the right upper quadrant.
Recognize the Classic Presentation
Age (4 weeks), sex (male), the specific vomiting pattern (projectile, non-bilious, immediately hungry again), and the olive-shaped RUQ mass together form the classic pyloric stenosis presentation. This combination of findings is specific enough that pyloric stenosis should be strongly suspected even before imaging confirms it.
Anticipate the Metabolic Picture
Given the vomiting pattern, the nurse anticipates lab findings consistent with hypochloremic metabolic alkalosis — elevated pH, low chloride, low potassium — and ensures these are checked. Anticipating this pattern, rather than being surprised by the lab results, reflects understanding of the underlying mechanism (vomiting → HCl loss → alkalosis).
Sequence the Treatment Correctly
The nurse understands that IV fluids to correct the metabolic alkalosis come FIRST, before the infant proceeds to surgical pyloromyotomy — not the other way around. Rushing to surgery before correcting a significant electrolyte imbalance would add unnecessary risk to the procedure.
📌 NCLEX Application
Pyloric stenosis questions test both presentation recognition and treatment sequencing:
Presentation recognition: "A 5-week-old presents with projectile vomiting after every feed and remains hungry afterward. What condition is most consistent with this presentation?" → Pyloric stenosis.
Lab pattern: "What acid-base and electrolyte pattern would be expected in an infant with pyloric stenosis and significant vomiting?" → Hypochloremic metabolic alkalosis, with low potassium.
Treatment sequencing: "What must occur before surgical correction of pyloric stenosis?" → Correction of the metabolic alkalosis with IV fluids.
⚠️ The Trap — Rushing to Surgery Before Correcting the Metabolic Alkalosis
Given that pyloric stenosis has an excellent surgical prognosis and a clear surgical fix, there can be a temptation to move quickly toward the operating room. But proceeding to surgery before correcting significant metabolic alkalosis and electrolyte imbalances adds real anesthesia and surgical risk.
The safeguard: Always ensure electrolyte correction with IV fluids happens first, with surgery following once the infant's metabolic status has been stabilized.
✓ Quick Self-Test
Answer before checking:
1. At what age does pyloric stenosis classically present, and in which population is it most common?
2. What is the classic vomiting pattern, and what physical exam finding often accompanies it?
3. What specific metabolic and electrolyte pattern results from the vomiting, and why?
4. What must happen before surgical pyloromyotomy?
Answers:
1. 2–6 weeks of age; most common in first-born males.
2. Projectile, non-bilious vomiting after every feeding with the infant remaining hungry; an olive-shaped mass palpable in the right upper quadrant.
3. Hypochloremic metabolic alkalosis with low potassium — from loss of hydrochloric acid (HCl) through repeated vomiting.
4. Correction of the metabolic alkalosis with IV fluids.