What is the emergency department workup for a 9-month-old infant presenting with projectile vomiting?

Emergency Department Workup for a 9-Month-Old with Projectile Vomiting

The emergency department workup for a 9-month-old infant with projectile vomiting should prioritize abdominal ultrasound as the first-line imaging study to evaluate for hypertrophic pyloric stenosis (HPS) and other obstructive causes, while simultaneously assessing for dehydration and red flag signs. 1

Initial Assessment

Immediate Evaluation

• Assess airway, breathing, and circulation
• Evaluate hydration status (skin turgor, mucous membranes, fontanelle, urine output)
• Check vital signs (heart rate, respiratory rate, blood pressure, temperature)
• Assess weight compared to previous measurements

Critical Red Flags Requiring Urgent Attention 1, 2

• Bilious vomiting (surgical emergency - consider malrotation with volvulus)
• Hematemesis or blood in stool
• Altered mental status or lethargy
• Abdominal distension or tenderness
• Severe dehydration
• Respiratory distress during episodes
• Inconsolable crying or excessive irritability
• Bent-over posture

Diagnostic Workup Algorithm

Step 1: Focused History

• Timing and pattern of vomiting (projectile vs. non-projectile)
• Bilious vs. non-bilious vomit
• Feeding history and recent changes
• Associated symptoms (fever, diarrhea, constipation, irritability)
• Weight gain/loss pattern
• Family history of similar conditions

Step 2: Physical Examination

• Complete abdominal examination (looking for masses, especially "olive-shaped" mass in right upper quadrant suggestive of pyloric stenosis)
• Neurological assessment (fontanelle, level of consciousness)
• Signs of dehydration or electrolyte imbalances
• Assessment for other sources of infection (otitis media, pneumonia)

Step 3: Laboratory Studies 3, 2

• Serum electrolytes and blood gases (to assess for metabolic alkalosis typical in pyloric stenosis)
• Complete blood count (to evaluate for infection)
• Renal and liver function tests
• Urinalysis (to assess hydration status and rule out urinary tract infection)
• Blood glucose (to rule out hypoglycemia)

Step 4: Imaging Studies 3, 1

1. Abdominal ultrasound - First-line imaging for suspected pyloric stenosis
2. Abdominal radiograph - If ultrasound is unavailable or inconclusive, to evaluate for obstruction patterns
3. Upper GI series - If bilious vomiting is present (to evaluate for malrotation with volvulus)
4. Head CT or ultrasound - If neurological symptoms are present or increased intracranial pressure is suspected

Differential Diagnosis

Common Causes in 9-Month-Olds 3, 1, 4

• Gastroesophageal reflux disease (GERD)
• Cow's milk protein allergy
• Viral gastroenteritis
• Pyloric stenosis (less common at 9 months but still possible) 4
• Intestinal obstruction (intussusception, foreign body)
• Malrotation with or without volvulus
• Gastric volvulus
• Neurological causes (increased intracranial pressure)
• Systemic infection

Management Considerations

Immediate Interventions

• IV fluid resuscitation if dehydrated
• Nasogastric tube decompression if bilious vomiting or significant abdominal distension 2
• NPO (nothing by mouth) status until surgical causes ruled out

Medication Considerations

• Ondansetron (0.15 mg/kg IV or 0.2 mg/kg oral; maximum 4 mg) may be considered for persistent vomiting once surgical causes are ruled out 2
• Avoid routine use of medications for presumed GERD without confirming diagnosis 1

Common Pitfalls to Avoid 1

• Misdiagnosing pyloric stenosis as simple reflux, delaying appropriate surgical intervention
• Failing to recognize bilious vomiting as a surgical emergency
• Confusing physiological gastroesophageal reflux with cow's milk protein allergy
• Relying solely on clinical examination without appropriate imaging
• Overlooking non-GI causes of vomiting (neurological, metabolic, infectious)
• Discharging patients without ensuring adequate hydration and ability to tolerate feeds

By following this systematic approach, clinicians can efficiently evaluate and manage a 9-month-old infant presenting with projectile vomiting in the emergency department, ensuring that potentially life-threatening conditions are promptly identified and treated.