Comparing Subglottic Ultrasound and Distal Phalanx Width for Pediatric Endotracheal Tube Sizing in a Predominantly School‐Aged Pediatric Cohort: A Prospective Study

BACKGROUND: Accurate endotracheal tube (ETT) sizing is essential in pediatric airway management to optimize ventilation and reduce complications. Traditional methods, including age-based formulas and distal phalanx width (DPW), may lack precision. Subglottic ultrasound (US) has emerged as a promising tool, but its predictive accuracy compared with DPW remains unclear. This study aimed to compare accuracy, agreement, diagnostic performance, and clinical applicability of subglottic US versus DPW for predicting optimal ETT size in children, while recognizing that the enrolled cohort was predominantly school-aged. METHODS: In this prospective observational study, pediatric patients aged 0-12 years undergoing elective or emergency intubation were assessed. Pre-intubation measurements included subglottic transverse airway diameter by ultrasound (ACUSON Juniper, microconvex probe, 5-10 MHz) and DPW by digital calipers. Predicted ETT sizes were compared with the final clinically accepted cuffed ETT inner diameter confirmed by leak testing and cuff pressure optimization. Agreement was evaluated using Bland-Altman analysis and intraclass correlation coefficients, while diagnostic performance was defined a priori as accuracy, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratios, and receiver operating characteristic (ROC) curve analysis. Logistic regression identified predictors of good ETT fit. RESULTS: Among 160 patients, the median age was 8.8 years (IQR 7.0-10.5), indicating predominance of older children. Ultrasound-predicted ETT size showed a stronger correlation with actual size (r = 0.479, p < 0.001) than DPW (r = 0.248, p = 0.002). Ultrasound predictions had narrower Bland-Altman limits of agreement, although ultrasound measurement is operator-dependent. DPW showed poor sensitivity (5.9%) but high specificity (99.3%) for identifying underfit ETTs, with limited overall discrimination (ROC AUC = 0.53). Only subglottic diameter was a significant predictor of good ETT fit. CONCLUSION: Subglottic ultrasound showed better agreement with clinically accepted ETT size than DPW in this predominantly school-aged pediatric cohort. These findings support the potential role of ultrasound as an adjunct to pediatric airway assessment, but conclusions should be interpreted cautiously in infants and younger children because they were under-represented. Standardized measurement protocols and operator training are needed before broad implementation.