Modified Mallampati test, thyromental distance and inter-incisor gap are the best predictors of difficult laryngoscopy in West Africans

Abstract

Purpose: To determine the ability to predict difficult visualization of the larynx (DVL) from the following preoperative airway predictive indices, in isolation and combination: modified Mallampati test (MMT), thyromental distance (TMD), sternomental distance (SMD), horizontal length of the mandible (HLM) and inter-incisor gap (IIG).

Methods: Three hundred and eighty consecutive patients undergoing general anesthesia were evaluated using the MMT, TMD, SMD, HLM and IIG and the cut-off points for the airway predictors were Mallampati III and IV; < or = 6.5 cm, < or = 13.5 cm, < or = 9.0 cm and < or = 4.0 cm respectively. During direct laryngoscopy, the laryngeal view was graded using the Cormack and Lehane (CL) classification. CL grades III and IV were considered difficult visualization. Sensitivity, specificity and positive predictive value for each airway predictor in isolation and in combination were determined. Logistic regression analysis was used to determine independent predictors of DVL.

Results: Difficulty to visualize the larynx was found in 13 (3.4%) patients. The sensitivity, specificity and the positive predictive value for the five airway predictors were: MMT (61.5%; 98.4%; 57.1%), TMD (15.4%; 98.1%; 22.2%), SMD (0%; 100%; 0%), HLM (30.8%, 76.0%; 4.3%) and IIG (30.8%; 97.3%; 28.6%). The best combination of predictors was MMT/TMD/IIG with a sensitivity, specificity and positive predictive value of 84.6%; 94.6%; 35.5% respectively. Logistic regression analysis showed that weight, MMT, IIG and TMD were independent predictors of DVL.

Conclusion: MMT, TMD and IIG appear to provide the optimal combination in prediction of DVL in a West African population.