The Effectiveness Of Ultrasound Measurement Of Upper Airway Anatomical Parameters In Predicting Difficult Airway

Objective:To explore the value of distance from skin to hyoid bone(DSH),distance from skin to epiglottis(DSE),distance from skin to vocal cords(DSV),width of tongue and thickness of tongue measured by ultrasonography in predicting difficult laryngoscope and difficult tracheal intubation,and compare the sonographic parameters in order to determine which one has better performance.Methods:Patients aged 18-80 y with ASA I-III were selected in this study who underwent elective surgery and required tracheal intubation from December 2019 to October 2020.The following information was obtained the day before operation: sex,age,height,weight,body mass index(BMI),modified Mallampati test(MMT),inter-incisor distance(IID),thyromental distance(TMD),the upper lip bite test(ULBT),thyromental height(TMH).Ultrasound measurements were performed before induction of anesthesia,patients were positioned in supine position to obtain DSH、DSE、DSV、width of tongue and thickness of tongue.These parameters were obtained by the same anesthesiologist.After anesthesia laryngoscope exposure and tracheal intubation were done by the same senior doctor who did not participate in the data analysis,and the Cormack-Lehane(C-L)laryngoscopic grade was noted.The relationships between DSE,DSH,DSV,width of tongue,thickness of tongue and difficulty in laryngoscope exposure and tracheal intubation were analyzed.The Receiver operating characteristic curve(ROC)and Youden index were used to determine the criteria for independent predictors to predict difficult tracheal intubation or difficult laryngoscopy.The accuracy、sensitivity、specificity、positive predictive value and negative predictive value of all indicators were calculated according to the critical value.Results:A total of 420 patients were selected in this study.Of these,6 were excluded from the study because of the loss of incisors,6 were subsequently excluded due to a not achievable ultrasonographic visualization of the vocal cords,8 were excluded from the study due to the loss of ultrasonic measurement data.Accordingly,400 patients completed the study,208 males and 192 females.53 cases(13.25%)experienced difficulty laryngoscope,33 cases(8.25%)experienced difficult tracheal intubation and no intubation failure occurred.According to the Cormack-Lehane grade during direct larygnoscopy and the difficulty of tracheal intubation,the patients were divided into DL group:difficult laryngoscope exposure group;NDL group:non-difficult laryngoscope exposure group;DI group:difficult tracheal intubation group;NDI group: non-difficult tracheal intubation group.(1)The body weight and BMI in DL group were higher than those in NDL group(P<0.05);The body weight and BMI in DI group were higher than those in NDI group(P<0.05);There was no significant difference in sex,age and height between DL group and NDL group,DI group and NDI group(P>0.05).(2)DSE、DSH、DSV、width of tongue and thickness of tongue measured by ultrasound were all related to difficult laryngoscope exposure and difficult tracheal intubation(P<0.05).(3)The area under the curve(AUC)results of indicators to predict difficult laryngoscope exposure were BMI(0.712),MMT(0.698),ULBT(0.536),TMD(0.572),TMH(0.744),IID(0.639),DSE(0.837),DSH(0.661),DSV(0.716),width of tongue(0.739),thickness of tongue(0.773);The area under the curve(AUC)results of parameters to predict difficult tracheal intubation were BMI(0.757),MMT(0.701),ULBT(0.525),TMD(0.607),TMH(0.797),IID(0.663),DSE(0.890),DSH(0.755),DSV(0.766),width of tongue(0.763),thickness of tongue(0.800).(4)When DSE>1.795 cm 、 DSH>0.885 cm 、 DSV>0.745 cm and width of tongue>4.355 cm,the first indicator excelled in accuracy in predicting difficult laryngoscope exposure(P<0.05);statically significant difference was found in accuracy of predicting difficult tracheal intubation when DSE>1.835cm、DSH>0.885cm、DSV>0.755 cm,width of tongue>4.345 cm and thickness of tongue>5.495(P<0.05).Conclusion:DSH、DSE、DSV、width of tongue and thickness of tongue measured by ultrasound can predict the difficult airway effectively;DSE>1.795 cm can predict difficult laryngoscope exposure,DSE>1.835 cm can predict difficult tracheal intubation;compared with other ultrasound parameters,DSE is more valuable in predicting difficult airway.