Evaluation of thyromental height test as a single anatomical measure for prediction of difficult laryngoscopy: a prospective observational study

Background Preoperative airway assessment is essential to predict difficult airway so that adequate planning could be made to secure the airway. Various airway tests have been devised to improve diagnostic accuracy but none of the tests individually have proven to be adequate. Recently, a new airway predictor thyromental height test (TMHT) appears to be a more accurate predictor of difficult laryngoscopy than the existing anatomical measurements. The aim of this study is to evaluate the accuracy of the TMHT and compare it with various screening tests to determine whether TMHT can prove to be a more comprehensive and accurate test for predicting difficult laryngoscopy. Total 150 patients aged > 18 years of either sex with American Society of Anaesthesiologist physical status I-III scheduled for elective surgery under general anaesthesia requiring tracheal intubation were included in this prospective observational study. All patients were subjected to a preoperative airway assessment test including TMHT, modified Mallampati test, upper lip bite test, interincisior gap, thyromental distance and sternomental distance. Intraoperatively direct laryngoscopy was done and the grading of laryngoscopic view was done according to CL.Results The preoperative data and CL grading were used to evaluate the accuracy of TMHT and compared the sensitivity, specificity, positive and negative predictive value with other tests. Twenty six (17.33%) patients had difficult laryngoscopy and 18 patients (12%) required bougie/stylet to facilitate intubation. TMHT had the highest sensitivity (76.92%), specificity (98.38%), PPV (90.90%), NPV (95.31%) and accuracy (94.67%) when compared to other tests.Results The preoperative data and CL grading were used to evaluate the accuracy of TMHT and compared the sensitivity, specificity, positive and negative predictive value with other tests. Twenty six (17.33%) patients had difficult laryngoscopy and 18 patients (12%) required bougie/stylet to facilitate intubation. TMHT had the highest sensitivity (76.92%), specificity (98.38%), PPV (90.90%), NPV (95.31%) and accuracy (94.67%) when compared to other tests.Conclusions TMHT is a simple bedside test with higher sensitivity and specificity for predicting difficult laryngoscopy as compared to other screening tests. Future study should be done to define ethinicity, race, age groups and gender specific cut off values of TMHT for accurate validation of prediction in difficult laryngoscopy.