A 5-Week-Old With Projectile Vomiting and a Consultant On Call Tomorrow
A 5-week-old boy is brought with 5 days of projectile non-bilious vomiting after feeds. He weighed 3.6 kg at birth and weighs 3.2 kg now. He is alert but sluggish, with a sunken fontanelle and dry mucous membranes. Heart rate 168/min, respiratory rate 44/min, capillary refill 3 seconds. Venous gas: pH 7.56, PCO2 48 mmHg, bicarbonate 40 mmol/L, chloride 84 mmol/L, potassium 2.9 mmol/L, sodium 133 mmol/L. Ultrasound reports a pyloric muscle thickness of 4 mm and a channel length of 17 mm. The parents ask whether the baby can be fed, and whether the operation can wait until the morning when the consultant is available.
1. Explain the acid–base disturbance and write the resuscitation plan, including the endpoint that must be reached before anaesthesia.
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Prolonged vomiting of gastric acid loses hydrogen and chloride, producing a hypochloraemic, hypokalaemic metabolic alkalosis with a compensatory rise in PCO2. The kidney initially excretes bicarbonate, but volume depletion drives aldosterone, causing sodium retention and urinary loss of hydrogen and potassium - the paradoxical aciduria. The elevated bicarbonate also shifts potassium into cells, so the measured potassium understates the total body deficit.
Resuscitation:
- Assess for shock; if present, give 10–20 mL/kg of 0.9% sodium chloride as a bolus.
- Then run isotonic saline with added potassium chloride at maintenance plus replacement; do not give potassium until urine output is established, and never as a bolus.
- Decompress the stomach with a nasogastric tube, keep the baby nil by mouth, and record weights, urine output and electrolytes every 6–12 hours.
- Correct magnesium if low, and treat any hypoglycaemia.
- Avoid bicarbonate and avoid lactate-containing solutions as the primary correction, since chloride is the deficient anion.
Endpoint before anaesthesia: chloride above about 100–106 mmol/L, bicarbonate below about 26–28 mmol/L, potassium above 3.5 mmol/L, adequate urine output, and a clinically rehydrated infant. Operating earlier risks postoperative apnoea and prolonged ventilation in a baby with a compensated alkalosis and depleted potassium.
2. How do you answer the parents about feeding and about waiting until the morning?
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Answer directly and without alarm. The diagnosis is hypertrophic pyloric stenosis, the obstruction is mechanical, and it will not resolve with time or medication - an operation is needed. But it is not an operation that must happen within the next few hours: the danger in this baby is the electrolyte and fluid state, not the pylorus itself. Operating tonight on a chloride of 84 mmol/L with a bicarbonate of 40 would put him at risk of postoperative apnoea and a difficult anaesthetic. The correct plan is 24–48 hours of correction, then a Ramstedt pyloromyotomy, which in most centres is performed by the on-call team including the consultant or a senior trainee with consultant cover.
Explain that he will not be fed during correction, that the nasogastric tube will keep his stomach empty, and that feeds restart within hours after surgery in most protocols.
Add safety-netting: if the vomiting becomes bilious, if he becomes lethargic or febrile, or if the abdomen becomes distended, the diagnosis changes - bilious vomiting in a neonate is malrotation with volvulus until proven otherwise and is a surgical emergency that cannot wait. Document the consent discussion and the plan explicitly.
3. At operation, after splitting the pyloric muscle, the anaesthetist reports a sudden rise in end-tidal CO2 and the field looks bruised. What are you checking for, and what is the postoperative feeding plan?
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The main intraoperative complication of pyloromyotomy is mucosal perforation, usually at the duodenal end, where the muscle is thin and the mucosa bulges. Other possibilities are incomplete myotomy and bleeding from the divided muscle edges.
Checks:
- Inspect the whole length of the myotomy for a visible mucosal tear and for bile staining.
- Perform an air-leak test: occlude the distal duodenum gently and insufflate air through the nasogastric tube while the field is covered in saline, looking for bubbles.
- If a perforation is found, close it with fine absorbable sutures, consider a drain and omental buttress, and keep the baby nil by mouth for longer.
- Confirm the myotomy is complete - the pyloric ring should separate and the mucosa should bulge freely; an incomplete myotomy causes persistent vomiting.
Postoperatively, most protocols start small volumes of feeds after 4–6 hours, advancing as tolerated; vomiting in the first 24–48 hours is common and does not mean failure. If the mucosa was perforated, delay feeds for 24–48 hours and use parenteral fluids. Reassess with electrolytes, and counsel the parents that the prognosis is excellent.