What is the evaluation and management of projectile vomiting in a 5-week-old infant?

Evaluation of Projectile Vomiting in a 5-Week-Old Infant

Projectile vomiting in a 5-week-old infant requires prompt evaluation for hypertrophic pyloric stenosis (HPS) as the most likely diagnosis, with abdominal ultrasound being the first-line imaging study of choice. 1

Initial Clinical Assessment

When evaluating projectile vomiting in a 5-week-old infant, focus on:

• Vomiting characteristics:

  • Forceful/projectile nature (distance vomitus travels)
  • Non-bilious vs. bilious (bilious suggests obstruction distal to ampulla of Vater)
  • Timing in relation to feeds
  • Frequency and progression

• Associated symptoms:

  • Weight loss or poor weight gain
  • Dehydration signs
  • Lethargy or irritability
  • Abdominal distension
  • Presence of blood in vomitus or stool

• Physical examination:

  • Palpation for the classic "olive" mass in the right upper quadrant (hypertrophied pyloric muscle)
  • Visible peristaltic waves across the abdomen
  • Hydration status assessment
  • Abdominal distension or tenderness

Diagnostic Algorithm

1. Abdominal ultrasound: First-line imaging study for suspected HPS

   • High sensitivity and specificity for diagnosing pyloric stenosis
   • No radiation exposure
   • Can visualize hypertrophied pyloric muscle

2. If ultrasound is inconclusive or unavailable:

   • Abdominal radiograph to evaluate for obstruction patterns
   • Upper GI series if diagnosis remains unclear

3. If bilious vomiting is present:

   • Urgent evaluation for malrotation with or without volvulus
   • Upper GI series becomes the priority imaging study

Differential Diagnosis

1. Hypertrophic pyloric stenosis (HPS):

   • Most common surgical cause of non-bilious projectile vomiting in infants 2
   • Typically presents between 2-8 weeks of age
   • Progressive worsening of symptoms

2. Gastroesophageal reflux disease (GERD):

   • Common in infants but rarely causes true projectile vomiting 3
   • Usually improves with conservative measures

3. Cow's milk protein allergy:

   • Can mimic or coexist with GERD 3
   • May present with vomiting, irritability, and poor weight gain

4. Malrotation with or without volvulus:

   • Medical emergency if present
   • Usually presents with bilious vomiting 1

5. Other less common causes:

   • Pylorospasm
   • Gastric volvulus
   • Metabolic disorders
   • Increased intracranial pressure

Management Based on Diagnosis

For Hypertrophic Pyloric Stenosis:

• Surgical consultation for pyloromyotomy
• Correction of fluid and electrolyte abnormalities before surgery
• Post-operative monitoring for return of normal gastric emptying 4

For Gastroesophageal Reflux:

• Conservative management first:
  • Smaller, more frequent feedings
  • Upright positioning for 20-30 minutes after feeding
  • Avoid car seats or semi-reclined positions after feeding 3
  • Thickened feeds may be considered

For Cow's Milk Protein Allergy:

• For breastfed infants: Maternal elimination diet removing milk and eggs 3
• For formula-fed infants: Switch to extensively hydrolyzed formula or amino acid-based formula 3

Red Flags Requiring Immediate Attention

• Bilious vomiting
• Hematemesis or blood in stool
• Severe dehydration
• Lethargy or altered mental status
• Abdominal distension or tenderness
• Respiratory distress or cyanosis during episodes

Common Pitfalls to Avoid

1. Misdiagnosing HPS as simple reflux, delaying appropriate surgical intervention
2. Confusing physiological GER with cow's milk protein allergy 3
3. Failing to recognize bilious vomiting as a surgical emergency
4. Relying solely on clinical examination without appropriate imaging
5. Overuse of medications for presumed GERD without confirming diagnosis

Projectile vomiting in a 5-week-old infant is not normal and warrants thorough evaluation, with hypertrophic pyloric stenosis being the most concerning diagnosis that needs to be ruled out promptly.