Prediction of endotracheal tube size in children by predicting subglottic diameter using ultrasonographic measurement versus traditional formulas

BACKGROUND: Paediatric airway assessment remains the most challenging task before the anaesthesiologists. Recent advancement in ultrasonography techniques should now allow for accurate and descriptive evaluation of paediatric airway. To compare calculated external diameters of the endotracheal tube from physical indices of traditional formulas and predetermined by ultrasound. MATERIALS AND METHODS: 100 subjects of either sex between 12-60 months of age, undergoing various elective surgeries under general anaesthesia requiring endotracheal intubation were enrolled in the study. The transverse diameter was measured at the level of cricoids cartilage by ultrasonography. The tracheal tube was considered best fit if air leak was satisfactory at 15-20 cm H(2)O of airway pressure. The obtained values were compared with the values of endotracheal tube size calculated by various age, height, weight based formulas and diameter of right and left little finger. The correlation of size of Endotracheal tube by different modalities was done and Pearson's correlation coefficient was obtained. RESULTS: According to Pearson's correlation there was a moderate correlation of best fit Endotracheal tube with endotracheal tube size by age based formula (r = 0.743), body length based formula (r = 0.683), right little finger based formula (r = 0.587), left little finger based formula (r = 0.587) and multivariate formula (r = 0.741). There was a strong correlation with ultrasonography (r = 0.943). CONCLUSION: Ultrasonography is a reliable method of estimation of subglottic diameter and for prediction of endotracheal tube size in children.