Comparison of Thyromental Height Test With Ratio of Height to Thyromental Distance, Thyromental Distance, and Modified Mallampati Test in Predicting Difficult Laryngoscopy: A Prospective Observational Study.

A prospective observational single- blinded, comparative study was conducted to evaluate the accuracy of the TMHT in predicting difcult laryngoscopy, compared with the other established bedside airway parameters like Modied Mallampati Test (MMT), Thyro-Mental Distance (TMD) and Ratio of Height to Thyromental Distance (RHTMD). A total of 150 patients of American Society of Anesthesiologists (ASA) physical status I & II, aged between 18-60 years, BMI < 30 kg/m2 scheduled for elective surgery under general anesthesia (GA) with endotracheal intubation, were enrolled in the study. The airway assessment tests TMHT, TMD, RHTMD and MMT were performed in the preoperative holding area. A standard GA protocol was followed in all cases. In this study, we have considered CL Grade IIb III and IV as difcult laryngoscopy. 45 out of 150 cases were intubated with optimum external laryngeal manipulation/ backward upward rightward pressure/with the help of gum elastic bougie, within 15 seconds of intubation time. Video laryngoscope was used in 2 out of 25 cases of difcult laryngoscopy which had signicantly low TMHT (36mm and 38mm), low TMD (5cm and 5.6cm) and belonged to MMT class IV. In our study, the TMHT demonstrated the highest sensitivity of 72%, specicity of 100%, positive predictive value (PPV) of 100%, and accuracy of 95% compared to TMD, RHTMD and MMT, thus indicating that TMHT is the best predictor of difcult laryngoscopy. RHTMD showed low sensitivity of 47% and high NPV of 95%. From the receiver operating characteristic curve (ROC), the area under the curve (AUC) for TMHT was calculated to be 0.99 which indicates that this has highest predictive value compared to other airway assessment tests.