UPPER LIP BITE TEST : A NOVEL TEST OF PREDICTING DIFFICULTY IN INTUBATION

BACKGROUND: Although there are many preoperative tests to predict difficult airway, they are far from being ideal i. e. easy to perform, highly sensitive and specific, having high positive predictive value with few false positive predictions. AIMS: to elucidate the role of upper lip bite test (ULBT) with other prevailing tests, hyomental/thyrosternal distance ((HMD/ TSD), and mandible length (ML) in predicting difficulty in endotracheal intubation. MATERIAL AND METHOD: 300 patients meeting inclusion criteria, aged 21-60 yrs. having ASA I and II status, posted for elective surgery under general anesthesia with endotracheal intubation were enrolled in this study. Preoperatively anesthesiologist not involved in intubation evaluated and assessed the ULBT class and obtained measurements of HMD, TSD, ML. Laryngoscopy was assesed by anesthesiologist blinded to the measurements and was graded according to Cormack and Lahane’s Grading system. ULBT of class III, HMD<3.5cms, TSD<6.5cms and ML <9cms were considered as markers of a potentially difficult intubation. STATISTICAL ANALYSIS: Data was analysed using kappa agreement and sensitivity, specificity, positive predictive value, negative predictive value with their 95% confidence interval was calculated. RESULTS: The negative predictive value (NPV) and positive predictive value (PPV) of ULBT were 100% and 92. 2% respectively. These corresponding figures for HMD, ML, and TSD were 57.14, 0, 81.82 and 87, 71, 86.39, 89.27 respectively. Specificities for ULBT, HMD, ML, TSD were 45, 10, 0, 22.5% respectively. Sensitivity for ULBT, HMD, ML, TSD was 100, 98.85, 99.23, 97.69 respectively. ULBT showed greatest agreement with laryngoscopic grading (kappa=. 59 with p-value <0.0001). An agreement between HMD, ML, TSD and laryngoscopic grading which was comparatively weaker also existed (0.14, 0.31, -0.04, respectively.) CONCLUSION: The high specificity, NPV, PPV, and accuracy of ULBT as revealed in this study could be a good rationale for its application in the prediction of difficulty or easiness in intubation. The quantitative parameters, ML and HMD, had a slight and fair agreement with kappa coefficient. Hence, either of them can be useful in combination with a qualitative parameter, ULBT, so as to get acceptable and dependable result as it enhances its potential value in being diagnostic in airway assessment.