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Paediatric anaesthesia
A child is not a small adult: double the oxygen consumption, a high and anterior airway and a heart-rate-dependent cardiac output — so the child desaturates faster, coughs and gets laryngospasm more, and bradycardia means hypoxia until proven otherwise.
Why it matters in the exam
The exam asks about tube size and depth, the anatomical differences, treatment of laryngospasm, when to postpone surgery in a child with a cold, fasting before anaesthesia, and maintenance fluids. Questions also cover pyloric stenosis — a medical condition corrected before surgery — apnoea after anaesthesia in an ex-premature infant, and emergence delirium after sevoflurane.
In an infant the larynx is higher (C3–C4), the tongue is large, the epiglottis is long and floppy and the occiput is large — a small roll under the shoulders helps. Oxygen consumption is 6–8 mL/kg/min compared with about 3 in an adult, so apnoea quickly leads to desaturation and bradycardia. The 2016 FDA warning concerns repeated or prolonged anaesthesia (over 3 hours) under the age of 3; studies of a single short anaesthetic have not shown developmental harm.
Preparing the child and the parents matters as much as the drugs: anxiety before anaesthesia is linked to emergence delirium and to later behaviour changes, so an age-appropriate explanation, a parent present at induction and sometimes premedication are used. In many children induction is by inhalation, and the cannula is inserted once the child is asleep. In exam questions every calculation of dose, fluid or tube size starts with weight — and in an emergency it is estimated from age.
Key points
- Double oxygen consumption and heart-rate-dependent output — bradycardia = hypoxia.
- Tube: age/4 + 4 uncuffed, age/4 + 3.5 cuffed; depth age/2 + 12.
- Laryngospasm: oxygen with CPAP, jaw thrust, propofol, then succinylcholine.
- Maintenance fluids 4-2-1, isotonic.
- Pyloric stenosis — correct the alkalosis before surgery.
Summary table
| Issue | Rule | Exam point |
|---|---|---|
| Tube size (over 2 years) | Cuffed: age/4 + 3.5; uncuffed: age/4 + 4 | Oral depth: age/2 + 12 cm |
| Fasting | Clear fluids 1 hour (ESAIC) or 2 hours (ASA); breast milk 4; formula 6 | Long fasting causes dehydration and hypoglycaemia |
| Maintenance fluids | 4-2-1 mL/kg/h by weight | Isotonic fluids — not hypotonic (hyponatraemia) |
| Laryngospasm | 100% oxygen with CPAP, jaw thrust, deepen with propofol, a small dose of succinylcholine | With bradycardia — atropine |
| Pyloric stenosis | Correct the hypochloraemic, hypokalaemic metabolic alkalosis before surgery | Nasogastric tube and gastric emptying before induction |
A free exam question
?כמה זמן תינוק ששתה תחליף חלב צריך לצום לקראת ניתוח אלקטיבי (the question as examined, in Hebrew)
- א. שעתיים
- ב. 4 שעות
- ג. 6 שעות
- ד. 8 שעות
In the full version for subscribers
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Sources
- Miller's Anesthesia, 9th edition (2020) — Pediatric Anesthesia
- ESAIC guideline on pre-operative fasting in children, 2022 — Clear fluids up to 1 hour
- APLS / Advanced Paediatric Life Support, 7th edition (2023) — Equipment and drug calculations
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.