Design: multicentre retrospective registry cohort (J-PEDIA), multilevel mixed-effects logistic regression with institutional clustering
Population: 18,835 general anaesthesia induction airway encounters in children under 18 across 12 Japanese tertiary hospitals, June 2022 to February 2025
Primary outcome: airway management-related adverse events, with first-attempt intubation success and desaturation ≥10% as secondary outcomes
Effect: no association with the composite; desaturation adjusted OR 2.12 (95% CI 1.17–3.84) obese and 1.31 (1.05–1.64) underweight; first-attempt success 80.5% vs 89.2%, adjusted OR 0.69 (0.60–0.79) for underweight

Paediatric difficult airway teaching concentrates on the obese child, on the assumption that obesity shortens the safe apnoea time and complicates laryngoscopy. A registry analysis of 18,835 induction encounters across 12 Japanese tertiary hospitals from 2022 to 2025 checked that against outcomes, grouping children by World Health Organization weight-for-age and body mass index-for-age standard deviations.

The composite airway adverse event rate did not differ by weight category at all — 2.0% in normal-weight children, 1.9% obese, 1.6% overweight, 2.8% underweight, with no association surviving adjustment. But the two component outcomes did. Desaturation of 10% or more was more common in both obese children (adjusted odds ratio 2.12, 95% confidence interval 1.17 to 3.84) and underweight children (1.31, 1.05 to 1.64). And first-attempt intubation success was markedly lower in underweight children: 80.5% against 89.2% in normal-weight children, adjusted odds ratio 0.69 (0.60 to 0.79). Obese and overweight children actually had slightly higher first-pass success than normal-weight children.

The practical shift is towards a group that does not attract attention. An underweight child — common in Indian paediatric surgical practice, where undernutrition and chronic disease travel together — is more likely to need a second attempt and more likely to desaturate while you take it. That argues for the most experienced available operator on the first attempt, careful preoxygenation, and apnoeic oxygenation in place before induction rather than after the first failure.

Plot weight-for-age before induction in every child; 'looks small' is not a category.
Put the most experienced available operator on the first attempt in an underweight child.
Use apnoeic oxygenation from the start in both underweight and obese children, not as a rescue.
Preoxygenate deliberately and confirm it, rather than assuming a short apnoea is survivable.
Have the second-attempt plan and equipment out before the first attempt, not after it.

Why it matters

Paediatric airway risk teaching is organised around the obese child, and the underweight child performed worse on both measurable outcomes.

The statistics, in plain English

The headline that weight was not associated with the composite adverse event outcome is misleading on its own: the composite pooled events of different frequency and severity, and the components moved in ways the composite hid. The desaturation estimate for obese children (2.12, 1.17 to 3.84) is based on only 667 obese encounters, which is why the interval is wide; the underweight estimates rest on 2,219 encounters and are correspondingly tighter. All of these are adjusted associations from registry data, so they identify who is at risk rather than what to do about it — and a registry of tertiary difficult-airway practice will not reflect the case mix of a district theatre.