Evaluation of neck-circumference-thyromental-distance ratio as a predictor of difficult intubation: A prospective, observational study

Background and Aims: Preoperative identification of difficult airway and subsequent planning is of utmost importance for a patient's safety. Previous studies have identified the ratio of the neck circumference (NC) to the thyromental distance (TMD); NC/TMD as a reliable predictor of difficult intubation in obese patients. But there is a lack of studies evaluating the NC/TMD in non-obese patients. Therefore, the aim of this study was to compare the NC/TMD as a predictor of difficult intubation in both obese and non-obese patients. Methods: A prospective, observational study was conducted after obtaining institutional ethics committee clearance and written and informed consent from each patient. One hundred adult patients undergoing elective surgeries under general anaesthesia with orotracheal intubation were included in this study. Difficulty in intubation was assessed using the Intubation Difficulty Scale. The NC/TMD was calculated and the predictive accuracy of NC/TMD and other established parameters in obese and non-obese patients were compared. Results: Univariate logistic regression analysis showed that gender, weight, body mass index, inter-incisor gap, Mallampati classification, NC, TMD, sternomental distance, and NC/TMD had a significant association with difficult intubation. NC/TMD has a higher sensitivity, specificity, and positive and negative predictive value with better predictability in comparison to other parameters. Conclusion: The NC/TMD is a reliable and better predictor of difficult intubation in both obese and non-obese patients in comparison to NC, TMD, and sternomental distance alone.