Analysis Of Absence Of Signal Stimulating Nerve Of Intraoperative Neuromonitoring During Thyroid Surgery

Objective Analyze signal absence of intraoperative neuromonitoring of the recurrent laryngeal nerve (RLN),find out the reason and gather experience.Methods The study was performed from October 2012 till April 2015, including 429 patients underwent thyroidectomy using intraoperative neuromonitoring to search and protect RLN in general surgery department of the Chinese PLA General Hospital. Searching,recognizing and protecting the RLN in thyroid surgery in strict accordance with the international standard of IONM steps; capturing the photo of RLN and EMG while stimulating the nerve; summarizing the possibility of signal absence and clearing the cause of the signal absence to confirm that is anesthesia problems or equipment problems, afterwards shifting accordingly to make the system working normally; determining and analyzing the factors of nerve damage, recording conditions of neurological electromyographic signal recovery, judging the prognosis combine with the result of regularly reviewed postoperative laryngoscope of vocal cord function.Results1. All operations were completed successfully.535 nerves were revealed in 564 nerves with help of IONM.2. 39 cases of absence of signal stimulating nerve happened during operation.(1) 24 cases were resulted from injury of nerve of which 18 cases were traction injury,3 cases were heat injury,3 cases were crush injury.Take action protecting nerve after finding reason of absence of signal, amplitudes of 17 cases got a recovery to more than 90% with a normal sound function.6 cases in left 7 cases got a normal voice in just 2 weeks,the other 1 case got a improvement of vocal cord function by laryngoscopy.All these 7 cases got a recovery of normal vocal cord function 3 months after operation.(2) 6 cases were resulted from anesthesia mis-cooperation of which 4 cases of misuse of nerve muscle blocking agent and 2 cases of malposition of endotracheal tube electrode. We can get normal EMG again after full supersession of nerve muscle blocking agent and adjustment of endotracheal tube electrode.(3) There were 3 cases of monitoring equipment dysfunction leading to absence of signal including 1 case of terminal plate problem,lcase of fuse wire broken and 1 case of malposition of grounding electrode. We can get normal EMG again after reconnection of equipment and change of fuse wire.(4) 3 cases leading to absence of signal were invasion of tumor. Dissociate tumor from nerve and keep integrity of nerve of which 2 cases of function of vocal cord improved slightly and got a recovery to normal level after 6 months. Other 1 case did not get any distinct improvement after 5 month of follow-up.(5) Non recurrent laryngeal nerve were identified in 2 cases as an anatomical variation. More attention was paid to protect it getting a normal EMG before end of operation.(6) 1 case were confirmed vocal cord fixed considered of tumor invasion.it shows that lymph node oppress nerve and remove the oppressed lymph node away from nerve.The EMG got a recovery of 70% of average level,voice improves after operation and vocal cord function were good 2 weeks after operation.Conclusion1. Once absence of signal happens during,it must be done to confirm whether it is caused by malposition of endotracheal tube electrode.misuse of nerve muscle blocking agent,terminal plate problem,fuse wire broken and so on. It is noteworthy that anesthesia cooperation plays an important role in normal work of IONM, so communication before operation is needed.2. Heat injury, traction injury and crush injury are common factors of nerve injury. Heat injury and crush injury make the worst harm to nerve and none satisfied recovery would be found before the end of operation.3. Once absence of signal happens,surgeon should explore injure point according to the recommended method and find reason of injury.If injury can be removed,the measure should be taken as soon as possible or new surgery plan should be made whether a second stage surgery is needed.Surgeon can make a analysis of his own action habits to optimize his surgical skills combined with absence of signal.4. Vagus nerve indirect stimulating method can quickly determine the presence of non recurrent laryngeal nerve, greatly reducing the damage rate and the operation time.5. IONM is just an auxiliary tool for helping surgeon recognize and protect nerve. Comprehensive neck anatomical knowledge, reliable surgical technique, clear and reasonable surgery plan and surgical experience are the basis for the successful completion of the surgery, IONM must be combined with the above factors to make the most use of its technical advantages to protect RLN.