Correlation between ultrasound-guided subglottic diameter and little finger breadth with the outer diameter of the endotracheal tube in paediatric patients – A prospective observational study

Background and Aims: Selection of an appropriate endotracheal tube (ETT) in paediatric patients is a challenging situation. The purpose of this study was to compare whether measurement of subglottic diameter with ultrasound or the age-old little finger width correlates better with the outer diameter (OD) of the ETT used for intubation. Methods: Following approval from the Institutional Ethics board and a written informed consent from parent or guardian, this prospective observational study was carried out on 60 American Society of Anesthesiologists physical status I and II patients aged 6 months–8 years, scheduled for elective surgery under general anaesthesia requiring oral endotracheal intubation. Preoperatively ultrasound-guided subglottic diameter (USGD) and little finger breadth (LFB) measurements were taken. On the day of surgery, intubation was done with an uncuffed ETT, whose OD was noted. The concordance and agreeability between two techniques for estimation of the OD of the ETT were measured by Lin's concordance correlation coefficient. Further, the bias and precision between the techniques and the inter-changeability of the techniques were assessed by using Bland and Altman and Mountain plotting, respectively. Results: Lin's concordance correlation coefficient between USGD and LFB with the OD of the ETT was found to be 0.29 (0.13–0.41) and 0.46 (0.29–0.6), respectively. Conclusion: Overall, neither USGD nor LFB can be used as a reliable tool to predict the OD of the ETT. Registered in Clinical Trial Registry of India. REF/2016/08/011955.