What is the best course of treatment for a 2-month-old infant with vomiting?

Management of Vomiting in a 2-Month-Old Infant

The first priority is to determine whether the vomiting is bilious or non-bilious, as bilious vomiting is a surgical emergency requiring immediate evaluation with abdominal radiography and surgical consultation. 1, 2

Immediate Clinical Assessment

Perform a focused evaluation to identify red flag symptoms that require urgent intervention:

• Bilious (green) vomiting indicates obstruction distal to the ampulla of Vater and requires immediate surgical evaluation 1, 3, 2
• Projectile vomiting in a 2-month-old raises concern for hypertrophic pyloric stenosis (HPS), which typically presents between 2-8 weeks of age 1
• Blood in vomit or stool suggests mucosal damage and warrants urgent evaluation 1, 3
• Abdominal distension indicates possible obstruction 1, 2
• Altered mental status or bulging fontanelle suggests increased intracranial pressure 2
• Decreased urine output (fewer than 4 wet diapers in 24 hours) indicates significant dehydration 1

Diagnostic Approach Based on Vomiting Characteristics

For Non-Bilious Projectile Vomiting:

• Palpate the right upper quadrant for an "olive" mass, which is pathognomonic for HPS 1
• Order abdominal ultrasound as the initial imaging study if HPS is suspected clinically 1, 2
• If ultrasound confirms HPS, obtain immediate surgical consultation 1

For Bilious Vomiting:

• Obtain abdominal radiography immediately as the first imaging study to identify signs of intestinal obstruction 3, 2
• Follow with upper GI contrast series if obstruction is confirmed, as this has 96% sensitivity for detecting malrotation 3
• Withhold all oral feeds and place nasogastric tube for gastric decompression 1
• Obtain immediate pediatric surgical consultation, as conditions like volvulus can cause intestinal necrosis within hours 3

For Non-Bilious, Non-Projectile Vomiting Without Red Flags:

The most likely diagnosis is viral gastroenteritis or gastroesophageal reflux 1, 4:

• Assess hydration status using capillary refill time and clinical examination 1
• No routine laboratory tests or imaging are needed if the infant appears well-hydrated and is gaining weight appropriately 1, 4

Hydration Management

For Mild Dehydration (3-5% deficit):

• Continue breastfeeding on demand if breastfed—breast milk should never be interrupted 1
• Continue full-strength formula immediately if formula-fed 1
• Administer oral rehydration solution (ORS) in small, frequent volumes (5 mL every minute initially) using a spoon or syringe 1
• Replace each vomiting episode with 10 mL/kg of ORS 1

For Moderate Dehydration (6-9% deficit):

• Administer ORS as primary therapy, which is as effective as IV rehydration for preventing hospitalization 1, 4
• Consider ondansetron (0.2 mg/kg oral, maximum 4 mg) only if persistent vomiting prevents oral intake entirely 1, 5

For Severe Dehydration (≥10% deficit):

• Hospitalize and initiate IV fluid resuscitation 1, 4

Medications and Contraindications

• Antiemetics are generally NOT indicated for routine viral gastroenteritis in infants this young 1
• Ondansetron may be considered only if vomiting is so persistent that it completely prevents oral rehydration 1, 5
• Never use antidiarrheal or antimotility agents, as these can cause serious side effects and are ineffective 1

Follow-Up Instructions

Instruct parents to return immediately if:

• Vomiting becomes projectile or bilious (green) 1
• Fewer than 4 wet diapers in 24 hours 1
• Infant becomes lethargic or difficult to arouse 2
• Regular weight checks are essential—poor weight gain elevates concern from benign reflux to GERD disease and warrants specialist referral 1

Common Pitfalls to Avoid

• Never delay evaluation of bilious vomiting—it is a surgical emergency until proven otherwise 3, 2
• Do not assume all vomiting at this age is benign reflux; HPS peaks at exactly this age (2-8 weeks) and requires surgical intervention 1
• Malrotation with volvulus can present at any age, not just in newborns, so maintain vigilance for any change to bilious vomiting 1
• Do not overlook signs of increased intracranial pressure such as bulging fontanelle 2