Comparison of cricoid and subcricoid transverse diameter of trachea to determine correct size of endotracheal tube in pediatric population: An observational study

Background: Choosing correct endotracheal (ET) tube size in pediatric population is often difficult based on conventional formulas based on age, weight, height, finger diameter, etc. Recently, ultrasonography (USG) has emerged as a noninvasive bedside tool to determine the airway diameter precisely. However, there is conflict regarding the predict efficacy between the glottic, cricoid, and subcricoid diameters. Aims and Objectives: This observational study analyzed the predictive efficacy between the USG-based cricoid diameter, subcricoid diameter, and age-based Motoyama formula. Materials and Methods: The study recruited 90 children, aged 2–12 years, posted for elective surgery requiring general anesthesia. After induction of anesthesia and muscle relaxation, the cricoid and subcricoid transverse diameter was measured using USG. ET tube size was selected based on the equal or the nearest lower value of cricoid diameter. Comparisons were done between ET tube size estimated by USG measurement of cricoid diameter, subcricoid diameter, age-based Motoyama formula, and the ET tube finally passed. Results: The present study finds that the US-guided cricoid diameter bears the highest correlation (r=0.973) with the ET tube finally passed, closely followed by the US-guided subcricoid diameter (r=0.963). In contrast, the correlation coefficient for age-based formula is 0.749 which reflects weaker predictability of age-based formula. Conclusion: The present study indicates that US-guided cricoid diameter can act as a reliable method to ascertain the proper size of ET tube, closely followed by US-guided subcricoid diameter over the traditional age-based formula.