Background:Unpredictable difficult laryngoscopy (DL) remains a challenge for anesthesiologists,especially when difficult ventilation occurs during standard laryngoscopy.Accurate airway assessment should always be performed,but the common airway assessment methods only perform superficial screening.Thus,the deep laryngopharyngeal anatomy may not be evaluated.Ultrasound-based airway assessment has been recently proposed as a useful,simple,and non-invasive bedside tool as an adjunct to clinical methods,which may facilitate identification of DL.The present study aimed to determine the correlation between ultrasound-measured indicators and DL.Methods:Patients undergoing elective surgery under general anesthesia with tracheal intubation were enrolled.Ultrasonic airway assessments were performed before anesthesia induction.Ultrasound diagnostic indicators included the thickness and width of the base of the tongue,the angle between the epiglottis and glottis,the length of the thyrohyoid membrane,and the thickness of the lateral pharyngeal wall.A score of ≥3 in the Modified Cormack-Lehane Scoring System was used as a standard of DL and was also applied to divide patients into DL and non-DL groups.The area under the receiver operating characteristic (ROC) curve was used to evaluate the diagnostic ability of various diagnostic indicators.Results:A total of 499 patients were enrolled into non-DL and DL groups comprising 452 (452/499,90.6％) and 47 (47/499,9.4％)patients,respectively.One ultrasonic diagnoses indicator correlated with DL,namely,the angle between the epiglottis and glottis.When the angle between the epiglottis and glottis was 50°,the area under the ROC curve was maximum (0.902),and the best sensitivity (81％) and specificity (89％) were achieved.Conclusions:Airway ultrasounds should be considered to identify DL.The ultrasonic angle measured between the epiglottis and glottis is highly associated with DL,which may occur when the angle is less than 50°.