The Evaluation of Thyromental Height Test as a Single, Accurate Predictor of Difficult Laryngoscopy

Thyromental Height Test is a relatively new, easy method considered as a more accurate predictor of difficult laryngoscopy than existing methods. The aim of this study was to evaluate its accuracy in predicting difficult laryngoscopy as compared to commonly used methods.

This hospital based, cross-sectional, observational study was conducted on 246 patients scheduled for surgery under general anesthesia with endotracheal intubation. Airway assessment was done during pre-anesthetic assessment by Thyromental Height Test, Modified Mallampati Test, Thyromental Distance and Sternomental Distance measurements and predicted as 'difficult' or 'easy' laryngoscopy based on accepted cut-off values. Direct laryngoscopic view was assessed after administration of general anesthesia by a laryngoscopist unaware of the pre-anesthetic assessments and recorded as 'actual' difficult or easy laryngoscopy based on Cormack-Lehane grades. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of each clinical test were determined.

Thyromental Height Test had the highest sensitivity (71.42%) and negative predictive value (98.9% respectively) but lowest accuracy (77.2%). Maximum specificity was observed with Thyromental Distance and Sternomental Distance (97.49% each). Thyromental Distance had the highest positive predictive value (25%) and accuracy (95.52%).

Thyromental Height Test, with its high sensitivity, is a useful predictor of difficult laryngoscopy. However, due a high number of false positives and relatively low accuracy, it cannot be considered as a sole, reliable and accurate predictor of difficult laryngoscopy.