Towards personalised paediatric airway management: Ultrasound-derived cricoid and radial epiphyseal diameters outperform age-based formulae in cuffed endotracheal tube size prediction

Background Selecting the appropriately sized endotracheal tube (ETT) remains a persistent challenge in paediatric anaesthesia. Age-based formulae do not account for individual anatomical variability, contributing to tube mismatch and necessitating exchange. We evaluated whether pre-intubation ultrasound-derived transverse cricoid diameter (TCD) and distal radial epiphyseal diameter (RED) more accurately predict best-fit cuffed ETT size than age-based formulae. Methods In this prospective observational study, 105 patients aged 1–12 years scheduled for elective surgery requiring cuffed endotracheal intubation were enrolled consecutively. Initial ETT size was selected by an age-based formula; TCD and RED were measured by a blinded observer after induction and neuromuscular blockade, during bag-mask ventilation prior to intubation. Best-fit ETT was defined as the tube producing an audible tracheal air leak at 10–20 cmH 2 O with the cuff deflated. Spearman correlation, linear regression, and Bland–Altman analysis assessed the strength of association and clinical interchangeability. Results TCD achieved the highest predictive accuracy (92.4%, 95% CI 85.7–96.1%), followed by RED (91.4%, 95% CI 84.5–95.4%), both significantly outperforming the age-based formula (73.3%, 95% CI 64.2–80.9%; TCD vs formula: p = 0.003; RED vs formula: p < 0.001; Bonferroni-corrected McNemar’s test; TCD vs RED: p = 1.000). TCD and RED demonstrated a strong correlation with the best-fit ETT outer diameter (r = 0.98; 95% CI, 0.97–0.99; p < 0.001 for both), with narrow limits of agreement (LoA): TCD, −0.33 to +0.27 mm; RED, −0.37 to +0.34 mm. The age-based formula showed a lower correlation with the best-fit ETT inner diameter (r = 0.96, 95% CI 0.93–0.97, p < 0.001), with a wider LoA (−0.54 to +0.52 mm). First-attempt intubation success was 88.6%; both measurements were acquired in under 40 seconds. Conclusion TCD and RED offer accurate, patient-specific ETT size prediction, substantially outperforming age-based formulae. TCD provides the greatest precision; RED is a practical alternative when subglottic ultrasonography is not feasible. Routine pre-intubation airway ultrasound represents a feasible, clinically meaningful step towards personalised paediatric airway management. Clinical Trial Registration CTRI/2025/03/083632 dated 28th March 2025