Evaluation of ultrasound measured tongue thickness, tongue thickness-thyromental distance ratio, and skin-to-epiglottis distance in predicting unanticipated difficult laryngoscopy.

Abstract

Background and aims: The contemporary literature review suggests upper airway ultrasound can help us to diagnose an unanticipated difficult airway before laryngoscopy. The primary objective of this study was to compare ultrasonography (USG) and clinical airway indices across easy and difficult laryngoscopy groups.

Material and methods: This prospective observational study included 258 patients scheduled to undergo surgery under general anesthesia with endotracheal intubation. Ultrasonographic upper airway parameters, viz., tongue thickness (TT), skin-to-epiglottis distance (DSE), and tongue thickness to thyromental distance ratio (TT/TMD) were measured. Patients were identified as easy or difficult laryngoscopy groups based on their Cormack Lehane (CL) grading.

Results: Out of 258 patients, 20 (7.75%) had difficult laryngoscopy, and 238 (92%) had easy laryngoscopy. The USG measured TT mean, and median values were 6.16 ± 0.39 [6.10] cm in difficult and 5.41 ± 0.36 [5.40] cm in easy laryngoscopy groups. The USG measured mean and median value of DSE were 2.75 ± 0.09 [2.74] in difficult and 2.27 ± 0.23 [2.27] in easy laryngoscopy groups. The ratio of TT/TMD with mean and median values of 0.98 ± 0.07 [0.99] in difficult and 0.84 ± 0.13 [0.82] in easy laryngoscopy. Using the inputs, the diagnostic accuracy of the ultrasound-measured significant variables was calculated in terms of their area under the curve using the receiver operating characteristic curve.

Conclusions: This study revealed a relationship between sonographic measurements like TT, DSE, and TT/TMD ratio for easy and difficult laryngoscopy identification. Including these sonographic parameters and their cut-off values may enhance our ability to predict an unanticipated difficult laryngoscopy.