Ultrasound Versus Age-Based Formula for Predicting Endotracheal Tube Size in Pediatric Patients Undergoing General Anesthesia: A Randomized Comparative Study

Introduction Selection of an appropriately sized endotracheal tube (ETT) in pediatric patients is critical to ensure adequate ventilation and minimize airway-related complications. Age-based formulae are commonly used but often fail to account for inter-individual anatomical variability. Ultrasonographic assessment of the subglottic airway offers a patient-specific alternative that may aid in selecting the optimal ETT size. This study compared ultrasound-guided estimation of ETT size with the age-based formula (internal diameter = age/4 + 3.5) and evaluated their agreement with the clinically optimal ETT size. Methods This prospective, randomized, comparative study was conducted at a tertiary care center and included children aged six months to 12 years undergoing elective surgery under general anesthesia. Participants were randomized to either an ultrasound group or a formula group. In the ultrasound group (Group U), subglottic airway diameter was measured at the cricoid level by ultrasonography, and ETT size was determined by subtracting 0.5 mm from the subglottic diameter. In the formula group (Group F), ETT size was calculated using an age-based formula. The clinically optimal ETT size determined using the leak pressure technique served as the reference standard. Agreement between predicted and used ETT sizes and the requirement for tube exchange were analyzed. Results After exclusions, 137 patients were included in the final statistical analysis (Group F, n = 70; Group U, n = 67). Baseline demographic characteristics were comparable between groups. Ultrasound-guided estimation resulted in a significantly lower incidence of oversized ETT selection (Group U vs F; 8 (11.9%) vs. 20 (28.6%), P = 0.045). The incidence of ETT exchange decreased in the ultrasound group, although this did not reach statistical significance. The Bland-Altman analysis confirmed superior agreement in the ultrasound group, with a smaller mean bias (-0.0448 mm vs. -0.129 mm) and lower percentage error (11.5% vs. 13.4%) compared with the formula group. No airway-related complications were observed in either group. Conclusion Ultrasound-guided measurement of the transverse subglottic diameter is superior to the age-based formula for ETT size selection in children. It provides a patient-specific anatomical assessment that significantly improves prediction accuracy and reduces the risk of oversized ETT selection.