Objective: The present study aimed to demonstrate that selecting the endotracheal tube [ETT] size using ultrasound
measurement of the subglottic diameter is a more reliable method than an age-based formula.

Materials and Methods: Ninety-three patients between l and 6 years old undergoing elective surgery under general anesthesia with endotracheal intubation were randomized into 2 groups. In group F (n = 46), a modified Cole formula was used to select the ETT size, while in group US (n = 47),
ultrasound measurement of the subglottic diameter was used to select the ETT size. The appropriate tube size was clinically determined by leakage at airway pressures of 20 to 25 cmH 0. Both groups underwent measurement of the transverse subglottic diameter in the supine position during apnea and
at inspiratory pressures [IP] of l0 cmH 0 and 20 cmH 0 before intubation to examine the correlation with the outer diameter of the appropriate ETT.

Results: The incidence of appropriate ETT size selection in group US was 37 out of 47 (78.7%), which was significantly higher than that in group F (n = 24/46, 52.2%), (p = 0.00l). A good correlation was found between the ETT size from ultrasound measurement of the transverse subglottic diameter and the outer diameter of the final proper ETT size, with weighted kappa of 0.59+0.06, 0.75+0.06 and 0.70+0.06 at apnea, l0 cmH 0 of IP and 20 cmH 0 of IP, respectively. No complications were reported in either group during the study.

Conclusion: Ultrasound measurement of the subglottic diameter to guide the selection of ETT size yielded the appropriate size more frequently than an age-based formula in anesthetized pediatric patients.

Keywords: Intubation, Endotracheal, Pediatrics, Ultrasonography