Prediction of difficult laryngoscopy in indian population: Role of ratio of patient's height to thyromental distance

The ratio of the patient's height to thyromental distance (RHTMD) has been recently proposed to be a superior predictor of difficult laryngoscopy compared to thyromental distance (TMD) in the Caucasian population. This prospective study was conducted to compare the predictive value of RHTMD and TMD to predict difficult laryngoscopy in two hundred adult ASA grade I & II patients requiring general anaesthesia with endotracheal intubation. Preoperative airway assessment was done by TMD measurement and RHTMD calculation in addition to the routinely performed Wilson risk - sum scoring (WS) and modified Mallampati test (MMP). A standardized anaesthetic protocol was followed. Cormack and Lehane grade 3 or 4 laryngoscopic view was defined as difficult laryngoscopy. Data were analyzed using Receiver Operating Characteristic Curve (ROC) and the area under the curve (AUC) for each test was computed. P<0.05 was considered significant. The sensitivity, specificity, positive predictive value and negative predictive value were calculated at the cut-off value of =7 cm and =25 for TMD and RHTMD respectively. The incidence of difficult laryngoscopy was 8.5%. The AUC (confidence interval) were as follows: TMD - 0.295 (0.175 to 0.416) [P=0.005], RHTMD - 0.707 (0.574 to 0.840) [P=0.005], WS - 0.935 (0.856 to 1.014) [P=0.000], MMP - 0.805 (0.687 to 0.924) [P=0.000]. Thus we found that RHTMD has a better predictive value than the TMD in Indian population.