Clinical Study On Intraoperative Transcranial Facial Nerve Moter-evoked Potential Monitoring Under Partial Neuromuscular Blockade

Clinical study on intraoperative transcranial facial nerve moter-evoked potential monitoring under partial neuromuscular blockadeBackground:With the development in intraoperative monitoring and microscopic techniques, the incident rate of iatrogenic facial paresis or paralysis after acoustic neuroma sugery is becoming smaller. But it still remains a significant clinical problem. Transcranial facial nerve motor-evoked potential (FNMEP) monitoring is a non-invasive technique, which can induce the compound muscle action potential (CMAP) from target muscles including orbicularis oculi and oris muscles when the stimulation is given through scalp electrodes placed at the area corresponding to the cortex that control the facial muscles. This kind of effective and innovational technique can help surgeons to detect and stop the damage to the facial nerve as soon as possible to avoid permanent harm during the operation. However, body movement induced by electricity stimulation can interfere with micro-surgical manipulation. Till now, there is no research in the field of intraoperative facial never motor-evoked potential monitoring under partial neuromuscular blockade.Objective:To investigate the possibility of facial nerve motor-evoked potential monitoring under partial neuromuscular blockade and to decide the level of muscle relaxation which is the most suitable for the intraoperative monitoring to avoid micro-surgical interruption.7This research also focuses on the relativity between decreased amplitude of FNMEP and facial nerve function postoperatively.Methods:Part1:30 patients undergoing elective sugery under general aneasthesia were randomly selected. Through comparison of FNMEP amplitude between different levels of muscle relaxation, a best suitable patial neuromuscular blockade degree is acquired. Part 2:30 patients undergoing acoustic tumor surgery during September 2009 to February 2010 in Huashan Hospital. Randomly 15 of which received no muscle relaxant during the surgery(group NM) while the rest 15 received partial neuromuscular blockade (group M) of T1 among 30-40% according to the result of the first part of the study. Their facial nerve function were judged pre and postoperatively according to the House Brackman grading system. During the entire period of the surgery, they all received FNMEP monitoring.The interruption to the operation (interoperative stimulation movement scale), the satisfaction of surgeons and the relationship between postoperative facial nerve dysfunction and the final to baseline FNMEP amplitude ratio were all studied and analyzed. All the patients received facial nerve function rejudgement on the first day,the seventh day and 2 weeks after the surgery.Results:Part 1:We got satisfactory monitoring results from every sample and the datas were collected and analyzed using analystic software SPSS 17. Under single twitch pattern of TOF-WATCH(?), 30%-40% muscle relaxation is best suitable for FNMEP monitoring. And there is no side effects of FNMEP monitoring detected in and after the sugery. Part 2:These two groups have no statistic difference in average data such age,gender or the sizes of acoustic tumors. The average monitoring time for both of the groups is 6 hours(4.5h-7.5h). Under the degree of 30%-40% muscle relaxation and no muscle relation, intraoperative FNMEP monitoring are both accessible and useful to predict facial nerve dysfunction in and after the operation. There are cases that the patients'FNMEP amplitude decreased more than half of the baseline amplitude and in these cases, surgeons were reminded of the situation. After they stopped the procedure they were performing, the amplitude recovered more or less. The stimulation related movement scale which is introduced in this research shows the no-muscle relaxation group have a higher degree of movement with a median score of 3 that means the stimulation can cause obvious movement and the operation is interrupted. On the other hand, the partial muscle relaxation group has a median score of 1 that means no noticeable movement. There's significant differences between two groups.(p<0.05). The relativity beween the postoperative House Brackman grade and the ratio between Postoperative FNMEP amplitude to preoperative FNMEP amplitude is testified according to the Spearman correlation. In the NM group, r=-0.941, p<0.05 while in the N group,r=-0.928,p<0.05。The ratio between postoperative FNMEP amplitude to preoperative FNMEP amplitude over 50% infers iatrogenic facial nerve damage. Its sensitivity is 90% and specificity is 91%.Conclusion:Intraoperative transcranial facial nerve motor evoked potential monitoring during patial neuromuscular blockade is feasible and 30%-40% neuromusclar blockade under single twitch pattern is the most suitable for the monitoring as it can decrease the movement of patients and minimize the interference to the surgury induced by electricity stimulation to the most extent when the stimulation is performed. There is no significant difference between two groups in the abilities of predicting the outcome of facial nerve postoperatively (p>0.05).