Paediatric anaesthesia · Core08 / 17
Infantile hypertrophic pyloric stenosis5-week-old boy, 3.6 kg, with 4 days of projectile non-bilious vomiting
Infant physiology: fluid and electrolyte correction first, then infant RSI
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Know this first
- Pyloric stenosis needs medical correction first; surgery can wait.
- Vomiting acid leaves a hypochloraemic, hypokalaemic metabolic alkalosis.
- Severe dehydration: 20 mL/kg 0.9% saline, then dextrose-saline; potassium once urine flows.
- Aspirate the stomach supine and in both lateral positions before induction.
- CSF alkalosis lags behind the blood and drives apnoea after surgery.
The patient
5-week-old boy, 3.6 kg, with 4 days of projectile non-bilious vomiting; pyloric stenosis on ultrasound.
Sunken fontanelle, few wet nappies. Na 132, K 2.9, Cl 84 mmol/L, HCO3 34 mmol/L. Nasogastric tube on free drainage.
Plan: laparoscopic pyloromyotomy once resuscitated.
Vitals: HR 168, BP 70/40, SpO2 99% on air, RR 38, capillary refill 4 s.
The examiner asks
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Consider
What are your considerations?
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- A 5-week-old with pyloric stenosis, dry and alkalotic, for pyloromyotomy once resuscitated. Patient
- At 5 weeks his output depends on heart rate, he loses heat fast and desaturates within seconds.
- Losing gastric acid leaves low chloride and potassium with alkalosis; his chloride of 84 is a big deficit. Disease
- A medical urgency first: no theatre until his fluids and electrolytes are fixed. Stem trigger
- Full stomach despite his nasogastric tube, so aspiration at induction is a real risk. Airway
Prepare
How will you prepare him?
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- Severely dry: 20 mL/kg 0.9% saline now, reassessing his perfusion. Stem trigger
- Then 5% dextrose in 0.45% saline at up to 1.5–2 times maintenance. Disease
- Potassium 10–40 mEq/L added once he passes urine, guided by his results.
- Ready when Na is over 130, K at least 3, and chloride above 85 and rising.
- Also passing 1–2 mL/kg/h of urine, with urine chloride over 20 mEq/L.
- Glucose checked; his fluids contain dextrose throughout.
Plan
How do you anaesthetise him?
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- Atropine 20 mcg/kg IV before his stomach and airway are handled. Airway
- Wide-bore orogastric suction with him on his back, then each side, even with his NG in.
- Rapid sequence: IV induction, then rocuronium 1–1.2 mg/kg or suxamethonium 3 mg/kg.
- Gentle low-pressure mask breaths are fine; infants desaturate fast during apnoea.
- Local anaesthetic at the ports and paracetamol 10 mg/kg IV; opioids avoided for apnoea risk. After surgery
- Extubated fully awake; continuous apnoea monitoring for several hours.
Crisis
At induction, despite aspiration, milky fluid wells into his pharynx; SpO2 94%. What do you do?
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- Regurgitation: head down, suction his pharynx, then secure the airway. Crisis
- Once intubated, suction down the tube on 100% oxygen before ventilating.
- No saline lavage; bronchoscopy only if I suspect particles.
- Proceed if he oxygenates well; chest X-ray and close review afterwards. After surgery
Crisis
In recovery, 40 minutes after extubation, he has a 25-second apnoea; HR 70, SpO2 80%. What do you do?
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- Apnoea with bradycardia: stimulate him, 100% oxygen, bag-mask breaths if he doesn't breathe. Crisis
- PALS: if his rate stays below 60 and he's poorly perfused despite ventilation, start CPR.
- Causes in him: lingering CSF alkalosis, residual drugs, low glucose, cold.
- Glucose now; it can drop 2–3 hours after surgery when infusions stop.
- Apnoea monitoring continues; no unmonitored ward tonight. After surgery
Fatal mistakes
- Theatre before his chloride and potassium are corrected.
- Induction without aspirating his stomach in several positions.
- Routine opioids and an unmonitored ward afterwards.
Checked against: Stoelting 8e · Faust · Miller 10e · AHA and AAP guidelines: pediatric advanced life support (2025)
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