Ultrasonographic Estimation of Endotracheal Tube Size in Paediatric Patients and its Comparison with Physical Indices Based Formulae: A Prospective Study

Abstract

Choosing the correct Endotracheal Tube (ETT) size is important in paediatric anaesthesia. The subglottic diameter being the narrowest diameter of the paediatric upper airway plays an important role in appropriate ETT size selection. This study was planned to determine the accuracy of Ultrasonography (USG) to assess the appropriate ETT size and compare it with physical indices based formulae. The secondary outcome was to assess the number of times the tube was changed based on air leak test for USG estimated tube size. After ethical committee approval, a prospective clinical observational study for a period of one year was conducted on 75 children (power of study 80%, confidence interval 95%) aged one to 14 years of American Society of Anaesthesiologists Physical Status (ASA) I and II undergoing elective surgery under general anaesthesia with orotracheal intubation. Parental consent was obtained. Pre-anaesthetic ultrasonography was performed on every patient at the subglottic region. The tracheal subglottic diameter was estimated to select the ETT size for cuffed and uncuffed tubes. The size estimated by USG and that based on age and height based formulae were compared with clinically used appropriate tube size. Data analysis was done using IBM Statistical Package for the Social Sciences (SPSS) version 20.0; One-way Analysis of Variance (ANOVA) and t-test for comparison were used. USG predicted the appropriate ETT size (p<0.05) better than physical indices based formulae for cuffed and uncuffed tubes. The age based formula predicted the clinically used ETT size well (p=0.58) and the height based formula did not correlate with clinically used tube size (p=0.0002 - a statistically significant value). Eight patients required change of tube once. Ultrasonographic estimation of subglottic diameter is useful for optimal paediatric ETT size selection. USG is effective in estimating the appropriate sized ETT both for cuffed and uncuffed tubes.