Can tongue thickness measured by ultrasonography predict difficult tracheal intubation?

BACKGROUND.: Increased tongue thickness is likely to be associated with difficult airways. However, no methods to evaluate tongue thickness were available. Currently, tongue thickness can be measured by ultrasonography. The present study investigated the predictive value of tongue thickness to predict difficult tracheal intubation. METHODS.: Adult patients undergoing tracheal intubation and general anaesthesia were enrolled in the study. Tongue thickness was assessed using submental ultrasonography in the median sagittal plane before anaesthesia. Airway assessments were conducted. Ratios of tongue thickness to thyromental distance were calculated to investigate the potential predictive value of their combination. The primary outcome was difficult tracheal intubation. A multivariable logistic regression and receiver operating characteristic curve analysis were used. RESULTS.: In total, 2254 patients were analysed. One hundred and forty-two (6.3%) patients experienced difficult laryngoscopy, and 51 (2.3%) patients experienced difficult tracheal intubation. Increased tongue thickness (>6.1 cm) was an independent predictor for difficult tracheal intubation [sensitivity 0.75, 95% confidence interval (CI) 0.60-0.86; specificity 0.72, 95% CI 0.70-0.74]. An area under the curve of 0.78 (95% CI 0.77-0.80) for predicting difficult tracheal intubation was calculated. Increased ratios of tongue thickness to thyromental distance (>0.87) presented a considerable area under the curve (0.86, 95% CI 0.84-0.87), sensitivity (0.84, 95% CI 0.71-0.93), and specificity (0.79, 95% CI 0.77-0.81). CONCLUSIONS.: Tongue thickness measured by ultrasonography and its ratio to thyromental distance present significant capacities to predict difficult tracheal intubation. CLINICAL TRIAL REGISTRATION.: ChiCTR-RCS-14004539.