Paediatric ETT Size Formula — FRCA Final MCQ

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EasyPaediatric AnaesthesiaPaediatric ETT Size FormulaFRCA Final

A 3-year-old child (14 kg) is induced with sevoflurane for adenotonsillectomy. After IV access is secured, the child receives atracurium 7 mg (0.5 mg/kg) for intubation. The correct ETT size for this child using the age-based formula is:

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Correct answer: B — 3.5 uncuffed

For children over 1 year, the ETT size formula is: Uncuffed = (age/4) + 4; Cuffed = (age/4) + 3.5. For a 3-year-old: uncuffed = (3/4) + 4 = 4.75 (round to 4.5 or 5.0); cuffed = (3/4) + 3.5 = 4.25 (round to 4.0). Current practice increasingly favours cuffed tubes even in children (APA/DAS guidelines) as they: reduce the need for tube changes, provide a more reliable seal for capnography, reduce anaesthetic gas pollution, and allow accurate tidal volume delivery. Cuff pressure should be maintained <20 cmH2O.

Reference: APA/DAS – 2015 – Paediatric airway guidelines; RCOA – 2023 – Paediatric module