Neck circumference to Thyromental Distance ratio: A new predictor of difficult intubation

Abstract

Introduction: Anaesthesiologists should have the ability to recognize the risk of difficult endotracheal intubation even in patients who have apparently normal airways. Though there is no one best test for preoperative prediction of difficult airway, ongoing research takes place to device an easy bedside test that is highly specific and sensitive. In this study we evaluate the ability of the parameter “Ratio of Neck circumference to Thyromental Distance (RNCTMD)” for predicting ease or difficulty in intubation.
Materials and Methods: An Observational study done prospectively in 100 patients of ASA grade I and II. They were assessed and graded for Ratio of Neck Circumference to thyromental distance (RNCTMD), Thyromental distance (TMD), Neck circumference (NC), Modified mallampatti test(MMT), Inter incisor gap(IIG), Hyomental Distance (HMD), Sternomental Distance (SMD), Body Mass Index(BMI) using standard techniques and correlated with Intubation difficulty scale(IDS).
Results: RNCTMD showed high sensitivity and NPV, IIG with high specificity and PPV. RNCTMD with a p value of 0.000 has been found to have higher statistical significance. ROC curve in this study for RNCTMD showed that cut off 4.85cm can predict difficulty in intubation more accurately.
Conclusion: Ratio of neck circumference to thyromental distance is found to be a better predictor of difficulty intubation compared to the other independent airway assessment parameters.