Evaluation of Upper Lip Bite Test and Thyromental Height Test for Prediction of Difficult Laryngoscopy

Abstract

Background and Aims: Unanticipated difficult laryngoscopy (DL) can cause life-threatening complications in the operation theatre, intensive care unit and emergency department. Various screening tests have been developed to predict DL. While modified Mallampati test (MMT) is the most commonly used one, it has poor sensitivity. Upper lip bite test (ULBT) and thyromental height test (TMHT) have been shown to be more reliable in predicting DL. The aim of this study was to compare the three tests and evaluate whether a combination of ULBT and TMHT would show better accuracy in predicting DL. Patients and Methods: A total of 109 adult patients undergoing elective surgery under general anaesthesia with endotracheal intubation were assessed using the MMT, ULBT and TMHT before surgery. The required sample size for the study was calculated using the Fisher Z test. The three tests, and a combination of ULBT with TMHT, were compared for their sensitivity, specificity, positive predictive value, negative predictive value and accuracy in predicting DL. Results: The accuracy of MMT, ULBT, TMHT and ULBT + TMHT in predicting DL was found to be 81.65%, 86.23%, 97.24% and 95.41%, respectively. MMT exhibited the lowest sensitivity and had the highest number of false negatives. TMHT exhibited the best accuracy and sensitivity, with the lowest number of false negatives. A combination of ULBT and TMHT did not improve the PPV in the sample tested. Conclusion: TMHT was found to be the best test for predicting DL, and its combination with ULBT did not improve the accuracy.