Hypertrophic Pyloric Stenosis

HPS Summary

Key Facts

Age: 3-6 weeks
Male:Female = 4:1
Projectile non-bilious vomiting
Pyloric muscle hypertrophy

Diagnosis

Palpable "olive" mass RUQ
Visible peristalsis
Ultrasound: thickness >4mm
Metabolic alkalosis

Lab Findings

Hypochloremia
Hypokalemia
Metabolic alkalosis
Paradoxical aciduria

Management

Fluid resuscitation first
Correct electrolytes
Pyloromyotomy
Gradual feeding post-op

Differential Dx

Gastroesophageal reflux
Malrotation/volvulus
Gastroenteritis
Pyloric atresia

Overview

Hypertrophic pyloric stenosis is characterized by hypertrophy of the pyloric sphincter causing narrowing of the pyloric canal, leading to projectile non-bilious vomiting in infants aged 3-6 weeks.

Key fact: HPS is 4 times more common in male infants and typically presents between 3-6 weeks of age.

3-6 weeks
Typical onset

4:1 ratio
Male:Female

Projectile
Non-bilious vomiting

Pathophysiology

Pyloric muscle hypertrophy → gastric outlet obstruction
Prolonged vomiting leads to:
- Hypochloremic, hypokalemic metabolic alkalosis
- Hypovolemia → increased aldosterone → paradoxical aciduria
Electrolyte abnormalities correlate with symptom duration

Metabolic Consequences

Initial: Loss of H+ and Cl- in vomitus → metabolic alkalosis
Compensation: Renal HCO3- excretion with Na+ and K+
Late: Volume depletion → aldosterone → paradoxical aciduria

Clinical Features

History

Progressive projectile non-bilious vomiting
Multiple formula changes without improvement
Poor weight gain
Decreased wet nappies (sign of dehydration)
Hungry after vomiting ("hungry vomiter")

Examination

Palpable "olive-shaped" mass in RUQ
Visible peristaltic waves (left to right)
Signs of dehydration:
- Dry mucous membranes
- Sunken fontanelles
- Tachycardia
- Decreased skin turgor

Examination Technique

Palpating the "olive": Use warm hands, empty stomach (NG tube if needed), flex hips and knees, examine from left side. Success rate increases with experience.

Differential Diagnosis

Common

Gastroesophageal reflux
Overfeeding
Gastroenteritis
Food protein intolerance

Serious

Malrotation with volvulus
Pyloric/duodenal atresia
Food allergy
Increased ICP

Red Flags - Exclude Surgical Emergencies

Bilious vomiting: Think malrotation/volvulus until proven otherwise
Abdominal distension: Consider obstruction
Blood in vomit: May indicate serious pathology
Lethargy/irritability: Consider sepsis or metabolic disorders

Investigations

Blood Tests

Electrolytes:
- Hypokalemia
- Hypochloremia
- Metabolic alkalosis
Blood gas analysis
Renal function

Ultrasound

First-line imaging (97-99% sensitive)
Diagnostic criteria:
- Pyloric thickness >4mm
- Pyloric length >17mm
Assess gastric emptying

Other Tests

Abdominal X-ray if obstruction suspected
Upper GI series if US inconclusive
Urinalysis for dehydration assessment

Management

Initial Stabilization

IV fluid resuscitation (0.9% saline)
Correct electrolyte abnormalities:
- Chloride supplementation
- Potassium replacement
NG tube if significant gastric distension
Monitor urine output

Fluid Management Goals

Chloride >100 mmol/L
Bicarbonate <30 mmol/L
Urine output >1-2 mL/kg/hr
Normal mental status

Definitive Treatment

Pyloromyotomy: Extramucosal longitudinal splitting of pyloric muscle
Approaches:
- Open (umbilical or RUQ incision)
- Laparoscopic
Timing: After electrolyte correction (uncorrected alkalosis increases postoperative respiratory depression risk)

Postoperative Care

Gradual reintroduction of feeds (start small, advance slowly)
Monitor for complications:
- Wound infection
- Mucosal perforation
- Incomplete myotomy
- Persistent vomiting
Typical feeding regimen:
- Start with clear fluids 4-6 hours post-op
- Advance to formula/breast milk if tolerated
- Full feeds usually within 24-48 hours

Complications

Preoperative

Severe dehydration
Electrolyte imbalances
Failure to thrive
Aspiration pneumonia

Postoperative

Wound infection
Mucosal perforation (1-3%)
Incomplete myotomy
Incisional hernia
Adhesions