Modified Mallampati test and thyromental distance as a predictor of difficult laryngoscopy in Thai patients.

BACKGROUND Preoperative evaluation of anatomical landmarks and clinical factors are important in the detection of patients at risk for difficult laryngoscopy. The modified Mallampati test (MMT) and thyromental distance (TMD) are commonly used for this purpose but there are controversies regarding their accuracy. OBJECTIVE The objective of the present study was to evaluate the accuracy of MMT and TMD in the prediction of difficult laryngoscopy in Thai patients. MATERIAL AND METHOD 1888 consecutive patients undergoing general anesthesia requiring endotracheal intubation were evaluated preoperatively using the MMT and TMD. The cut-off points for the difficult airway predictors were: Mallampati 3, 4 and TMD less than 6 cm. During direct laryngoscopy, the laryngeal view was graded using the Cormack and Lehane (CL) classification. CL grades III and IV were considered difficult laryngoscopy. Sensitivity and specificity for each airway predictor in isolation and in combination were determined. RESULTS The present study found Mallampati grade I 1050 patients (55.6%), grade II 730 patients (38.7%), grade III 104 patients (5.5%), grade IV 4 pateints (0.2%) and TMD less than 6 cm 85 patients (4.5%), TMD more than 6 cm 1803 patients (95.5%). Difficult laryngoscopy occurred in 60 patients (3.2%). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the two airway predictors were: MMT 41.7%, 95.5%, 23.1% and 98.0% and TMD 23.3%, 96.1%, 16.5% and 97.4% respectively. The combination of two predictors with a sensitivity, specificity PPV and NPV were 55.0%, 92.3%, 19.1% and 98.4%. CONCLUSION MMT TMD and their combination are good predictors of difficult laryngoscopy in a Thai population.