What is the best course of action for a 5-month-old infant presenting with projectile vomiting?

Projectile Vomiting in a 5-Month-Old Infant

A 5-month-old infant with projectile vomiting requires urgent evaluation for hypertrophic pyloric stenosis (HPS) as the primary concern, with immediate assessment for bilious vomiting or other red flags that would indicate surgical emergency. 1

Immediate Red Flag Assessment

First, determine if this is a surgical emergency by checking for:

• Bilious (green) vomiting - This indicates obstruction distal to the ampulla of Vater and requires immediate surgical consultation and imaging 1, 2
• Blood in vomit or stool - Suggests serious pathology requiring urgent evaluation 1
• Abdominal distension - May indicate intestinal obstruction 1, 2
• Altered mental status or lethargy - Could indicate increased intracranial pressure or severe metabolic derangement 1, 2
• Poor weight gain or weight loss - Suggests chronic pathology 1

Most Likely Diagnosis: Hypertrophic Pyloric Stenosis

At 5 months of age, HPS remains the most common surgical cause of non-bilious projectile vomiting, though it typically presents between 2-8 weeks 1. While less common at this age, it must still be ruled out 3:

• Physical examination: Palpate for the pathognomonic "olive" mass in the right upper quadrant 1, 2
• Ultrasound of the abdomen is the diagnostic modality of choice for suspected HPS 1, 2
• If HPS is confirmed, surgical consultation for pyloromyotomy is required 1

Alternative Diagnoses to Consider

• Malrotation with or without volvulus can present at any age and causes projectile vomiting; this is a surgical emergency 1
• Gastroesophageal reflux disease (GERD) is a non-surgical cause that can present with projectile vomiting 1
• Gastroenteritis is the most common cause of acute vomiting but typically does not present as isolated projectile vomiting 4, 5

Immediate Management Algorithm

If Red Flags Present (Bilious Vomiting, Distension, Altered Mental Status):

• Stop all oral intake immediately 4
• Place nasogastric tube for gastric decompression 4
• Obtain abdominal radiography as initial imaging 2
• Immediate surgical consultation 1, 2
• IV fluid resuscitation for hydration 1

If Non-Bilious Projectile Vomiting Without Red Flags:

• Assess hydration status - Check for signs of dehydration (decreased urine output, dry mucous membranes, sunken fontanelle) 1, 2
• Obtain abdominal ultrasound to evaluate for HPS 1, 2
• Initiate IV fluids if dehydration present or oral intake not tolerated 1
• Withhold feeds temporarily if mechanical obstruction suspected 1

Hydration Management

For infants able to tolerate oral intake:

• Administer oral rehydration solution (ORS) in small, frequent volumes (e.g., 5 mL every minute) using a spoon or syringe 6, 2
• Simultaneous correction of dehydration often lessens vomiting frequency 6
• Continue breastfeeding for breastfed infants 2
• Consider lactose-free formula for formula-fed infants with persistent symptoms 2

Critical Pitfalls to Avoid

• Never dismiss bilious vomiting - This is a surgical emergency until proven otherwise and requires immediate evaluation 2
• Do not assume typical HPS age range - While HPS classically presents at 2-8 weeks, cases have been reported in older infants including at 8 months, sometimes due to extrinsic causes 1, 3
• Do not delay imaging - Ultrasound should be obtained promptly when HPS is suspected 1, 2
• Recognize that projectile vomiting is a red flag symptom requiring thorough evaluation, not just symptomatic management 1

When to Refer for Surgical Consultation

• HPS confirmed or strongly suspected on ultrasound 1
• Any mechanical obstruction identified (malrotation, volvulus) 1
• Bilious vomiting 1, 2
• Abdominal distension with signs of obstruction 1, 2