Comparison On Morphology Changes Of Upper Airway Before And After General Anesthesia And Correlation Between This Changes With Difficult Laryngoscope Exposure

ObjectiveAirway management is an important technique for surgery,it’s also a prerequisite for successful treatment and rescue.however,various of causes lead to poor glottic exposure that the difficulties or failures of tracheal intubation will occurrence,which even threaten the patient lives in clinical.Respiratory muscle relaxation after general anesthesia could contribute to morphological changes in the upper airway,which may lead to difficult airway(DA).It has been reported that about 30% of death cases in anesthetic were related to the failure of difficult airway management,and more than 50%of seriously anesthesia-related complications were caused by improperly airway management.However,about 90% of DA could be found by preoperative evaluation.Lots of serious cases proved that DA management was closely related to medical safety.But majority of anesthesiologists were still immature on DA prediction in present.Therefore,it is of great significance that we used portable bedside ultrasound to dynamically detect the changes of upper airway before and after general anesthesia,in order to identify the risk factors of DA and improve the sensitivity and accuracy of assessment DA.Primary purposes: To explore the early prediction of DA.Secondary purposes: To collect the upper airway data before and after general anesthesia by ultrasound;To explore the correlation between changes of upper respiratory tract and DA after induction.MethodsAfter the clinical trial ethics committee review(review number:NO.ZYYECK[2018]041)and pilot experiment for sample calculation,100 eligible subjects with elective surgery under general anesthesia were selected to our study in the first affiliated hospital of Guang Zhou university of Chinese Medicine from march 2018 to October 2019.Inclusion criteria: age 18-70,grade ASA 1-2,no history of difficult airway,no oral and maxillofacial and upper respiratory disorders,no severe liver and kidney dysfunction and complicated with severe cardiopulmonary disease,no abnormal coagulation function;patients were accepted.Exclusion criteria: Patients refuse or mentally abnormal.The first part: observe and measure the morphological changes of the upper airway tract before and after general anesthesia induction.Prior to anesthesia induction,an informed consent was signed and we collected age,sex,ASA grade,weight,height,neck circumference,mouth opening,thyromental distance,Mallampati grade for subjects before anesthesia,after using ultrasound to measure the anatomical parameters of the upper airway,routine anesthesia induction was performed,and ventilation was retained for 5 min by a mask,then remove the mask.ultrasound was used again to measure the upper airway parameters after anaesthesia.Ultrasound parameters included: mandibular condylar mobility,distance from skin to under surface of tongue,thickness of the thickest part of tongue body,hyomental distance,distance from the hyoid bone to the skin(depth of hyoid bone),width of hyoid bone,distance from the skin to under-surface of glottis(depth of glottis),visualization rate of the vocal cords and the depth of the anterior combination of the vocal cords,the inner transverse diameter and depth of the trachea in cricothyroid membrane plane,the isthmus of thyroid plane and the suprasternal plane when patients awake.primary outcomes: Comparison whether there are statistical difference between the above ultrasound parameters by two times,to find out the changes of upper airway after anesthesia;The secondary part: To explore and compare the relationship between commonly used clinical parameters and ultrasound measurements before anesthesia with Comack-Lehane grading.Using direct laryngoscope to observe CL grading after ultrasonic measurement for patients,according to whether the CL grading is greater than or equal to 2b,we divided into the all patients to laryngoscope exposure difficulty group and non-difficulty group.Finally,routine airway management and anesthesia maintenance were performed as well as subsequent surgical procedures.Narcotrend values(maintained in D2)and muscular loose monitoring(TOF values <4%)were recorded during anesthesia,respectively.Respiratory rate,heart rate,blood pressure,SPO2 were kept at normal levels for each patient.Primary outcomes: to analyze whether the variables were different in the difficult laryngoscope exposure group and the non-difficult laryngoscope exposure group.Comparison of the sensitivity and specificity to predicte difficult laryngoscope exposure between ultrasonography measurements group and clinical methods group,and the best prediction method was explored.Results:This study included 104 subjects,the total incidence of DA was 28.85%,of which men accounted for 13.46%,women 15.38%,and there was no statistical difference between the gender groups(P >0.05).In the first part,mandibular condylar mobility,distance from skin to under surface of tongue,thickness of the thickest part of tongue body,hyomental distance,width of hyoid bone,distance from the skin to under-surface of glottis(depth of glottis),The distance between skin and sublingual surface,hyomental distance,distance from the hyoid bone to the skin(depth of hyoid bone)and the depth of the epiglottis were 15.7(13.0-17.8)mm、45.1(42.2-48.1)mm、8.7(6.7-10.4)mm、19.7(16.6-21.9)mm,respectively,which were changed to:17.3(14.5-19.1)mm 、 41.0(38.1-43.2)mm 、 7.1(5.4-8.7)mm 、19.3(16.4-21.4)mm,respectively after anesthesia(P<0.05).It indicates that after muscle relaxation,skin to sublingual surface distance increased,lingual body fall closer to the upper jaw,hyomental distance shortened,hyoid depth became smaller,hyoid bone floating,suggesting that the hyoid bone floating while moving to the chin bone direction after anesthesia,and the may be tongue hindered.But after anesthesia,the hyoid body width,the thickness of the hyoid body and the depth of the anterior vocal cord changes were small,and the difference were no statistically significance(P>0.05).In the second part,the commonly used of clinical prediction parameters in this study included neck circumference,opening mouth,thyromental distance modified Mallapati classification.The sensitivity and specificity were42.86% and 74.70% for mouth open,respectively.Sensitivity and specificity were 75.0% and 73.0% for estimating the risk of difficult airway when neck circumference≥41 cm.Compared with other methods,the modified mallapati classification method has high predictive value,with sensitivity of 60.0%and specificity of 85%.In the third part,the tracheal may become thicker and deeper from the cricothyroid membrne to the thyroid gland and suprasternal fossa.However,the transverse diameter of the trachea decreases obviously from thyroid gland to the suprasternal fossa,and the depth of the trachea may increase gradually due to the increase of the thoracic muscles.ConclusionThe results showed that the depth of hyoid was smaller,hyoid floating and the hyomental distance was shortened.After compare the sensitivity and specificity of predicting difficult laryngoscope exposure between commonly used methods and ultrasound measurements,we found that the distance between skin to epiglottis was a more predictive parameter for difficult laryngoscope exposure evaluation.Finally,the internal diameter of the trachea changes slightly first when the trachea extends from the thyroid isthmus to the suprasternal fossa.