Study On The Protective Effect Of Intraoperative Nerve Monitoring On External Branch Of The Superior Laryngeal Nerve

Objective:To evaluate the protective effect of intraoperative nerve monitoring(IONM)on external branch of the superior laryngeal nerve(EBSLN)in thyroid surgery.Methods:A total of 133 patients undergoing thyroid surgery(98 women,35 men,aged 45.6+ 11.7 years)were randomly divided into two groups.For group 1(n=66 patients,112 nerves),we did not try to identify EBSLN when dissecting the superior pole of the thyroid gland.For patients in group 2(n=67 patients,115 nerves),IONM was used to identify EBSLN during the surgery.Cricothyroid muscle(CTM)tremor and vocal cord electromyography(EMG)signal were utilized to evaluate EBSLN function.Voice Impairment Index-5(VII-5)evaluations was performed before and 1,3,6 months after the surgery for all patients.The injury rate of EBSLN,the recognition rate of IONM to EBSLN and the postoperative voice change were observed.Results:EBSLN injury was detected in nine(13.4%)patients and ten(8.9%)nerves in group 1 and in one(1.5%)patient and one(0.9%)nerve in group 2.Compared with group 1,the rate of nerve injury in group 2 was significantly reduced(patients,p=0.015;EBSLNs,p=0.010).Furthermore,IONM contributed significantly to visual(p<0.001)and functional(p<0.001)nerve identification in group 2.The Ⅶ-5 evaluation showed that patients in group 1 had more voice change at 1,3 and 6 months(p=0.013,p=0.016,p=0.03,respectively)after surgery than those in group 2.Conclusion:In thyroid surgery,the utilization of IONM can help the visual and functional identification of the EBSLN and reduce the injury rate of EBSLN,thus reducing the postoperative voice change of patients,that is,IONM has a protective effect on EBSLN.