The Effectiveness of Four Ultrasonographic Parameters as Predictors of Difficult Intubation in Patients without Anticipated Difficult Airway.

Background We evaluated the effectiveness of four upper airway ultrasonographic parameters in predicting difficult intubation (DI). The validity of models based on combined ultrasonography-based parameters was also investigated. Methods In a prospective, observational, double-blinded cohort trial, 1043 ASA-PS I-III patients without anticipated difficult airway, undergoing tracheal intubation under general anesthesia were enrolled. Preoperatively, their tongue thickness (TT), invisibility of hyoid bone (VH), and anterior neck soft tissue thickness from skin to thyrohyoid membrane (ST) and hyoid bone (SH) respectively, were measured under sublingual and submandibular ultrasonographic scans. Based on tracheal intubation, they were categorized as easy intubation (EI) or DI. The logistic regression, youden index, and receiver operator characteristic analysis were used. Results Overall, 985 (94.4%) patients had EI, while 58 (5.6%) encountered DI. The TT, SH, ST and VH had the accuracy of 78.4%, 85.0%, 84.7%, and 84.9%, respectively. The optimal criterion for TT, SH, and ST to predict DI was >5.8cm (sensitivity 84.5%, specificity 78.1%, AUC 0.880), >1.4cm (sensitivity 81%, specificity 85.2%, AUC 0.898), and >2.4 cm (sensitivity 75.9%, specificity 85.2%, AUC 0.885), respectively. VH had a sensitivity and specificity of 72.4% and 85.6% (AUC 0.790), respectively. The AUC of five models (based on combinations of 3 or 4 parameters) ranged from 0.975-0.992. The ST and VH had a significant impact on the individual models. Conclusions The SH had a better accuracy among the four ultrasonographic parameters. Although the individual parameters showed a limited validity, the model including all the four parameters offered better diagnostic profile.