Ultrasound measurement of subglottic diameter for determination of microcuff endotracheal tube size and intubation outcome in paediatric cases: An observational study

Introduction: One of the biggest achievements of medical science is safe anaesthesia especially for children. Management of airway takes priority over any other intraoperative intervention during anaesthesia .Determination of “best -fit” endotracheal tube (ETT) is important in children to provide optimum ventilation without causing any laryngotracheal morbidity[1-4]. Aim: To investigate the 1st attempt success rate of intubation using best fit Micro cuff ETT ( MCETT) size, determined by ultrasound measured subglottic diameter in paediatric population and to compare the result with age based size table of micro cuff endotracheal tube. Materials and methods: 66 paediatric patients aged between 1‑10 year, undergoing various elective surgeries under general anaesthesia were included in the study .The subglottic airway transverse diameter was measured in the brightness (B) mode using the linear probe (range 6-13 MHz) of the USG device with the child in the supine and neutral head position. Best-fit tube ID is considered as the one with satisfactory air leak at an airway pressure of 15-20cm H2O. 1st attempt success rate of intubation using best fit MCETT size, determined by ultrasound measured subglottic diameter in paediatric population were compared with the result with age based size table of micro cuff endotracheal tube. Results and Conclusion: Comparisons of means of sizes of correct MCETT with age based table and with USG guided method revealed that both methods are good predictors for the correct MCETT size estimation (p-value<0.05). However, size of correct MCETT matched with MCETT size calculated using USG method was in 56 patients (84.8%), whereas the MCETT by age-based table selected the correct tracheal tube size in 42 (63.6%) patients with the difference being statistically significant (p=0.026). Furthermore, reliability agreement calculated by Intraclass correlation coefficient suggested that USG based methods are better than age based formulas in children with k- values of 0.939 and 0.887 respectively. Conclusion: We conclude that ultrasound appears to be a reliable predictor for the assessment of the subglottic diameter of the airway in children to estimate the appropriate size of microcuff endotracheal tube