Modified Mallampati Test and Thyromental Distance as a Predictor of Difficult Laryngoscopy in Thai Patients
Wichai Ittichaikulthol MD*, Suwanna Chanpradub MD*, Sakda Amnoundetchakorn MD*, Niramon Arayajarernwong MD*, Napasawat Pawaropart MD*, Wilailux Wongkum BN*
Affiliation : * Department of Anesthesiology, Ramathibodi Hospital, Bangkok, Thailand
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: 1,888 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 1,050 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 1,803 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.
Keywords : Modified Mallampati test, Thyromental distance, Difficult laryngoscopy
