A 6-week-old boy is brought in with a damp bib and a kitchen towel that has become a permanent accessory. His mother says the spit-up has gone from “a little milk” to forceful gushes across the crib, and today he looks strangely eager to feed again after each episode. On exam, he’s alert but thin, with a dry mouth and an empty diaper that hasn’t been changed since dawn. You can almost feel the diagnosis in the story, but the next move still matters.

— What’s your move? Read on.

Before you read
  • What single bedside decision determines whether this child needs immediate resuscitation before imaging?
  • What electrolyte pattern should make you think of a surgically correctable cause?

When to Think of It

Age 2–8 weeks, progressive projectile nonbilious vomiting, hungry after emesis, weight loss or poor gain, dehydration, visible gastric peristalsis, or an olive in the epigastrium/RUQ. Think of it in any infant who vomits forcefully but does not have bile.

Sick or Not Sick

The fork is unstable dehydrated infant vs. stable infant with suspected gastric outlet obstruction. If shocky, lethargic, or unable to tolerate oral intake, resuscitate first; if stable, confirm diagnosis and involve surgery.

The First Fifteen Minutes

  • Signs of dehydration/hypovolemia → isotonic fluid bolus 20 mL/kg IV/IO (normal saline or lactated Ringer’s), repeat as needed, because it restores intravascular volume before any procedure.
  • Hypoglycemia or poor feeding → D10W 2 mL/kg IV if glucose is low, because infants have limited glycogen reserve and can crash quickly.
  • Persistent vomiting → NPO + nasogastric tube decompression if significant gastric distention, because it reduces aspiration risk and ongoing losses.
  • Pain/agitation → acetaminophen 15 mg/kg PO/PR if needed, because comfort matters while avoiding respiratory depression.
  • Electrolyte derangement on labs (esp. hypochloremic metabolic alkalosis) → IV chloride-containing fluids and potassium once urine output is confirmed, because correction of alkalosis and hypokalemia is required before anesthesia.

Definitive Care & Disposition

Obtain ultrasound to confirm pyloric muscle thickening/elongation; if equivocal and suspicion remains high, repeat imaging or upper GI per local pathway. Definitive treatment is pyloromyotomy after electrolyte/volume correction. Admit to pediatrics/surgery; most need inpatient correction of dehydration and pre-op optimization, then postoperative feeding advancement.

How This One Kills

The killer mistake is calling it reflux and sending home a dehydrated infant with progressive gastric outlet obstruction. The infant doesn’t die from the olive — they die from missed fluid depletion, alkalosis, and aspiration or delayed surgery.
The Differential — What Else Looks Like This
  • Physiologic reflux — small effortless spit-ups without dehydration or weight loss; confusing it delays surgery in a worsening obstruction.
  • Gastroenteritis — diarrhea, sick contacts, fever, and diffuse illness point away; confusing it can miss a surgical lesion.
  • Malrotation/Midgut volvulus — bilious emesis is the discriminator; confusing it with pyloric stenosis can miss bowel ischemia.
  • Intussusception — episodic pain, currant jelly stool, and older infant age are clues; confusing it can delay reduction and worsen ischemia.

The Second-Day Story

Premature infants and babies early in the course may have less classic projectile vomiting and more nonspecific feeding intolerance or poor weight gain. Some present mainly with dehydration and metabolic alkalosis, with the vomiting story downplayed by caregivers. In a partially treated infant, the abdomen may be deceptively benign. The key is to keep pyloric stenosis on the list for any young infant with persistent nonbilious emesis and failure to thrive, even when the story is muddy.
Back to Our Patient
Back to our patient: the 6-week-old with forceful nonbilious vomiting, dry mouth, and an empty diaper fits infantile hypertrophic pyloric stenosis. He is dehydrated but not yet crashing, so the first step is Recognize the obstructive vomiting pattern, Risk Stratify for volume depletion and electrolyte disturbance, and in the First Fifteen Minutes give isotonic fluid resuscitation, check glucose and electrolytes, keep him NPO, and decompress if distended. Once stabilized, ultrasound confirms the diagnosis and pediatric surgery is consulted for pyloromyotomy; he is admitted for correction of alkalosis and pre-op optimization.
Patient Presentation to Attending
How you’d present this patient on the floor — tight, pertinent positives and negatives, no rambling
“6-week-old previously healthy boy with progressively worsening nonbilious projectile vomiting and poor weight gain. Mom says he feeds eagerly but then forcefully spits up shortly after every feed; no bilious emesis, no fever, no diarrhea, and no sick contacts. On exam he looks mildly dehydrated with dry mucosa and decreased urine output, abdomen is soft with no distention and possibly a small epigastric fullness. Glucose is pending, electrolytes are being sent, and I’m concerned for hypertrophic pyloric stenosis. I’ve made him NPO, started a 20 mL/kg isotonic fluid bolus, and will get pyloric ultrasound and surgery involved once he’s resuscitated.”

Study Directive

  • Draw the pathway from gastric outlet obstruction → vomiting → chloride loss → metabolic alkalosis from memory.
  • Practice a 30-second oral differentiation of pyloric stenosis vs reflux vs malrotation vs intussusception.
  • Memorize the initial resuscitation order: NPO, glucose check, isotonic bolus, electrolytes, ultrasound, surgery.
  • Review ultrasound criteria for pyloric stenosis in your local reference and note what to do if the study is equivocal.

Recent Literature