Importance of Neck Circumference to Thyromental Distance Ratio: A Preoperative Bedscreening Test Characterizing the Complexity of Endotracheal Intubation in Obese Patients

: This study is performed to assess the ability of an index: the ratio of Neck Circumference/Thyromental Distance (NC/TM), to predict difficult airways in obese patients and to develop a predictor for difficult intubation that is simple and easy to perform with high specificity and sensitivity compared with established indices. METHODS: After receiving ethical approval hospital based observational study was conducted on 50 obese patients aged 18 to 60 years of either sex belonging to ASA grades I and II scheduled under general anaesthesia requiring endotracheal intubation in various operation theatres of Assam Medical College Dibrugarh, preoperatively with the help of performa within time frame of June 2021 to May 2022. Difficult intubation was determined using the Intubation Difficulty Scale (IDS≥5). The NC/TM ratio was calculated and its ability to predict difficult intubation in obese patients was compared with that of established predictors including high BMI, the Mallampati score, the Wilson score, NC, Sternomental Distance(SM), TM, NC/SM and a previous history of difficult intubation. RESULTS:There was positive co-relation (r = 0.282) between NC/TM and IDS Score (p<0.05).It was found that NC/TM test had higher sensitivity 75%, higher positive predictive value 42.85% and moderative to fair specificity 91.30% and negative predictive value 97.67% compared with other established indices.Binary multivariate logistic regression(Forward-Wald) analysis in each patient to determine the independent risk factors for difficult intubation in each group, where we found NC/TM(p=0.002, odds ratio=26.77) to be more statistically significant as an independent risk factor than others. CONCLUSION: There was positive correlation (r = 0.282) between NC/TM and IDS Score (p < 0.05).A NC/TM≥5.0 yielded a moderate-to-fair sensitivity, specificity, and a negative predictive value. Thus we can consider a preoperative value of NC/TM≥5.0 to be a good predictor of difficult intubation in obese patient.