The Feasibility Of Preoperative Airway Ultrasound In Predicting Difficult Laryngoscopy

Objective: With the development and application of visualization technology,ultrasound has become an indispensable part of the work of anesthesiologists.The current predictors of difficult laryngoscopy in clinic mainly depends on traditional indicators such as mouth opening,thyromental distance,modified Mallampati test,but these traditional indicators because of low accuracy,can't intuitive evaluation and individual differences apparent and has large limitations.With the advantages of real-time,intuitive and dynamic observation,ultrasound has an advantage in the evaluation of airway.Therefore,the purpose of this study is to compare the ultrasonography measurements with the traditional indicators,so as to evaluate the accuracy of ultrasound in prediction of the difficult laryngoscopy.Methods: Choose elective general anesthesia patients with endotracheal intubation,age 18-70 y and american society of anesthesiologists physical stasus(ASA)grade I-III.Patients who were refused or not with(such as unable to sit up),the degree of mouth opening <2.5 cm,neck surgery,cervical vertebra and mandible limited activities(such as cervical fracture),incisor missing,airway malformation or had done surgery,the need for a clear airway intubation were excluded from the study.Before induction of anesthesia with the traditional indicators of modified Mallampati test(MMT),thyromental distance(TMD),mouth opening,the upper lip bite test(ULBT),the ratio of height to thyromental distance(RHTMD)and the ultrasonography measurements distance from skin to epiglottis(DSE),distance from skin to hyoid bone(DSH),distance from skin to vocal cords(DSV)and the thickness of geniohyoid(TG)were evaluation.After induction of anesthesia,the same three year old resident who did not participate in data analysis was exposed to laryngoscopy and recorded Cormack-Lehane grading.Results: The study was used to evaluate the patients undergoing elective general anesthesia from July 2017 to November 2017.Screening of 445 patients,including 7 limitation of activity of cervical vertebra,12 missing incisors,8 goiter,18 unclear image caused by glottis larynx,a total of 45 patients were excluded from this experiment.Among the 400 cases of statistical analysis,there were 49 cases of laryngoscope exposure grade III and IV,of which 7 were grade IV,and the incidence of difficult laryngoscopy was 12.25%.There were statistically significant differences in the ASA grade,sex,age,weight and body mass index(BMI)between difficult laryngoscocy and easy laryngoscopy(P<0.05).According to the ROC curve,the area under the curve(AUC)of the traditional indicators is MMT(67.47%),TMD(61.81%),mouth opening(59.92%),ULBT(62.94%)and RHTMD(65.7%)and the AUC of ultrasound measurements is DSV(65.16%),DSH(79.82%),DSE(87.31%)and TG(65.79%).The traditional indicators of the sensitivity,specificity,accuracy,positive predict value and negative predictive value were MMT(40.82%?83.76%?78.5%?25.97%?91.02%)?TMD(53.06%?64.1%?62.75%?17.11%?90.73%)?mouth opening(28.57%?89.17%?80.25%?17.39%?88.42%)?ULBT(91.84%?29.91%?85%?26.09%?88.59%)?RHTMD(69.39%?55.56%?57.25%?17.89%?92.86%).The sensitivity,specificity,accuracy,positive predict value and negative predictive value of ultrasound measurements were DSV(71.43%?53.28%?55.5%?17.59%?93.03%)?DSH(81.63%?65.24%?67.25%?24.69%?96.22%)?DSE(65.31%?93.45%?90%?58.18%?95.07%)and TG(63.27%?63.25%?63.25%?19.38%?92.5%),respectively.The critical values of the traditional indicators are TMD(6 cm),mouth opening(3.5 cm),RHTMD(25.15),MMT(2 grade),ULBT(2 grade),and the critical values of the ultrasound measurements are DSV(5.36 mm),DSH(6.34 mm),DSE(21.07 mm),and TG(6.95 mm).Conclusion: The ultrasound measurements has better sensitivity,specificity,accuracy,positive predictive value and negative predictive value than traditional indicators,and it has a predictive value for the difficult laryngoscopy.When DSE was more than 21.07 mm may appear difficult laryngoscopy,the accuracy can reach 90%;and the negative predictive value was 95.07%,that when DSE<21.07 mm,excluding the possibility of difficult laryngoscopy for patients.