Evaluation of ultrasound guided measurement of subglottic diameter for determination of appropriately sized uncuffed flexometallic tube in pediatric patients

INTRODUCTION: Airway management in infants and children poses significant challenges for anaesthetists, paediatricians, and intensivists, and the selection of an appropriately sized endotracheal tube (ETT) is a crucial component. The aim of the study is to evaluate the usefulness of ultrasound-guided (USG) measurement of subglottic diameter for the determination of an appropriately sized uncuffed flexometallic tube in paediatric patients. MATERIALS AND METHODS: This prospective observational study included 62 patients. A USG probe was placed midline on the anterior neck with maximal head extension. After visualising the vocal cords, the probe was moved caudally to identify the cricoid arch. The transverse air column diameter at the lower border of the cricoid, measured at the end of the injection, was recorded as the subglottic diameter. As this measurement corresponds to the outer diameter (OD), uncuffed flexometallic tube with the matching OD was selected. The age-based predicted tube size was calculated using the modified Cole formula: ID (mm) = 0.25 × age (years) + 4. RESULTS: USG accurately predicted the size of the ETT in 55 patients (88.7%); it underestimated the size in 5 and overestimated in 2. The age-based formula was correct in 40 patients (64.5%) of the cases, underestimating in 10 and overestimating in 12. USG demonstrated significantly higher accuracy (p=0.001). The scatterplot shows a strong and significant correlation between tube sizes predicted by the age-based formula and the USG, with the trendline and 95% confidence band indicating agreement (intraclass correlation coefficient = 0.81, p<0.001). CONCLUSIONS: The study concluded that ultrasound-guided measurement of subglottic diameter is a highly accurate and statistically significant method to predict the appropriate size of uncuffed endotracheal tubes compared to the agebased formula.