面神经诱发肌电位反应与神经肌肉阻滞程度的相关性研究.doc

面神经诱发肌电位与外周神经肌阻滞程度的相关性研究复旦大学附属眼耳鼻喉科医院，上海，200031徐静 蔡一榕 陈莲华【摘要】 目的 观察面神经诱发肌电位（Evoked Electromyography, EEMG）与外周神经肌阻滞（Neuromuscular Blockade, NMB）程度之间的相关关系，明确行面神经EEMG监测的手术的最佳NMB范围。方法 40例行鼓室成形术的病人，术前面神经功能正常，术中同步进行面神经EEMG监测和外周NMB程度监测。EEMG监测采用MEDTRONIC XOMED公司的NIMResponse神经监护仪，术中直接电刺激面神经，记录眼轮匝肌、上口轮匝肌和下口轮匝肌的诱发肌电位；外周NMB程度监测采用欧加农公司的TOFWatch SX肌松监测仪，通过表面电极用四个成串刺激(train of four stimulation, TOF )刺激尺神经，以诱发的拇内收肌肌收缩加速度变化来间接反应NMB程度，用1T1（T1为第1个颤搐高度与对照值的百分比）来表示外周NMB程度。常规静吸复合维持全麻，调节罗库溴胺静脉滴注速度至目标肌松程度。手术达面神经时，根据面神经是否暴露将病人分成二组，组A：面神经暴露组,即骨管打开,直接在面神经表面给予刺激；组B：面神经非暴露组,即骨管未打开，在骨管表面间接给予面神经刺激。取梯度神经肌阻滞水平，即NMB分别为0、25%、50、75%、90%、100%时，观察面神经EEMG刺激阈值和固定刺激下EEMG反应振幅。每例病人从最小刺激电流0.1mA起，逐渐增加电流强度至出现EEMG反应时，该电流强度为EEMG刺激阈值，为避免强刺激电流造成医源性面神经损伤，将刺激电流上限定为1 mA。根据预实验结果，0.30.5 mA和0.81.0 mA的刺激电流分别能引起暴露组和非暴露组面神经稳定的EEMG反应，且术后均未引起面神经的损伤，因此将0.5 mA和1.0 mA分别作为组A和组B的固定刺激电流，观察该刺激电流下的EEMG反应振幅。结果 NMB50%，所有病人均能诱发EEMG，NMB75%，部分病人（4/40）无法诱发EEMG（刺激电流上限为1 mA）；刺激阈值与NMB呈正相关（P0.01），反应振幅与NMB呈负相关（P0.001）；两组间比较：在各个NMB水平，组A刺激阈值均显著低于组B（P0.01）；每组内比较：对不同NMB水平的刺激阈值和反应振幅分别进行两两比较，发现均存在显著性差异（P0.05）。结论 部分神经肌肉阻滞技术，能同时满足麻醉制动和面神经监测的条件，是适合需行面神经监测的耳显微外科手术麻醉的较佳选择；面神经EEMG的反应性与NMB程度间存在直线相关关系，刺激阈值与NMB呈正相关，反应振幅与NMB呈负相关；中耳手术行面神经EEMG监测时最佳的外周神经肌阻滞水平为50NMB左右。The Relationship between Facial Nerve Evoked-Electromyography Responses and neuromuscular blockade levelsEye Ear Nose & Throat Hospital of Fudan University，Shanghai 200031，ChinaXU Jing, CAI Yi-rong, CHEN Lian-huaAbstract Purpose: To observe the relationship between facial nerve evoked-electromyography responses and neuromuscular blockade levels; to determine the adequate level of neuromuscular blockade for facial nerve monitoring in middle ear surgery. Methods: Intraoperative facial nerve evoked electromyography (EEMG) and peripheral neuromuscular blockade (NMB) monitoring were performed simultaneously in 40 patients undergoing tympanoplasty. The level of peripheral NMB was evaluated by the percentage of the first myopalmus response (T1%) compared to the baseline value, i.e. NMB1T1%. All patients were divided in two groups, facial nerve exposure group (group A) and unexposure group (group B). General anesthesia was maintained with regular intravenous-inhalation combination. Rocuronium intravenous infusion was used to control the NMB at the targeted levels. The stimulating threshold and amplitude of EEMG response were recorded at a series of NMB levels with 100%、75%、50%、25%、10% and 0% respectively. Results：All of the patients displayed detectable EMGG responses at the levels of NMB50%; Parts of the patients (4/40) had no EEMG response at the levels of NMB75%. There was a linear positive correlation between threshold and NMB, while a linear negative correlation between amplitude and NMB, P0.01. The stimulating threshold in group A was significantly lower than that in group B at each NMB level, P0.01. Significant differences were found in both thresholds and amplitudes at each NMB levels in either group, P0.05. Conclusions: Partial neuromuscular blockade could provide reliable conditions for intraoperative facial nerve monitoring as well as adequate immobilization; There was a significant linear correlation between facial nerve response and NMB, with a positive correlation between thresholds and NMB, while a negative correlation between amplitude and NMB; The 50%NMB should be considered as the choice of anesthetic management for facial nerve monitoring in otologic microsurgery. Key words partial neuromuscular blockade, facial nerve, evoked electromyographyIntroductionPostoperative facial nerve paralysis is a devastating complication for both the patient and the surgeon. Iatrogenic facial nerve injury occurs in 0.6-3.6% of primary and 4-10% of revision otologic surgeries 1. Intraoperative facial electromyographic(EMG) monitoring is a helpful adjunct for surgeon to identify and map the course of facial nerve and this technique has been shown to reduce the rate of iatrogenic facial nerve injury during ear operations 234. The facial EMG monitoring needs a functional intact facial nerve muscle junction to enable an EMG to be recorded. So neuromuscular blocking agents have been avoided for these types of procedures to exclude any compromise of facial EMG monitoring capability. To keep the patient immobile, large doses of narcotics and high levels of volatile anesthetic agents are used. However, these high levels of anesthetic agents are not well tolerated by some patients 5. Several reports have suggested that partial neuromuscular blockade (NMB) can be used to prevent patient movement while still retaining the ability to elicit EMG responses with facial nerve stimulation 67. Our study was designed to examine the possibility of introducing controlled levels of peripheral neuromuscular blockade while preserving the ability to adequately monitor facial nerve EMG; to determine the adequate level of neuromuscular blockade for facial nerve monitoring in middle ear surgery; to evaluate the relationship between facial EMG responses and peripheral NMB levels.Material and methodsForty patients ( 19 male, 21 female, ASA-, 20-59 years old) undergoing open cavity tympanoplasty were studied. Preoperatively, all patients demonstrated clinically normal facial nerve function (House-Brackmann Class). Markedly obese patients and patients with neuromuscular disease were excluded. Approval of this study was obtained from the hospital Human Research Committee and written informed consent was obtained from all patients. Intraoperative facial and ulnar nerve monitoring was accomplished simultaneously. Evoked facial EMG monitoring was obtained using NIMResponse system (MEDTRONIC XOMED Corp). After the patient was anesthetized, the needle electrodes were inserted into the upper and lower orbicularis oris and orbicularis oculi muscles on the operative side. The facial nerve was directly stimulated with a Prass 4-Hz monopolar stimulator and the response was measured in millivolts. The maximal stimulation current was limited within 1mA to avoid the iatrogenic facial nerve injury. The same surgeon completed all surgery manipulations and facial nerve stimulations. The level of peripheral neuromuscular blockade was determined using the TOFWatch SX instrument (Organon Corp). Stimulation of the ulnar nerve was performed using surface electrodes placed over the ulnar nerve 2 and 9cm proximal to the distal end of the ulna. The ulnar nerve received a supramaximal 2-Hz constant current stimulation of four twitches at 2-Hz every 0.5 second over 2 seconds (train-of-four, TOF). The hypothenar muscle movements were assessed by an accelerometer. The percentage of the first twitch response compared to baseline (T1%) was used to determine the level of peripheral neuromuscular blockade. NMB =1T1%. None of the patients were premedicated. Anesthesia was induced with midazolam 2-3mg, fentanyl 2g/ kg, propofol 2 mg/ kg. After the patient was anesthetized, the TOFWatch should be calibrated. The tracheal intubation was facilitated with succinylcholine 2 mg/ kg. Anesthesia was maintained with a continuous infusion of remifentanil 0.2g/ (kg.min) and isoflurane (0.6 MAC) inhalation. All patients were monitored by electrocardiography, sphygmomanometry, pulse oximetry. Ventilation was mechanically controlled and was adjusted to keep an end tidal PCO2 at 35 to 40 mmHg throughout the surgical procedure. Controlled hypotention (MAP 55-65mmHg) was applied to achieve a clear operation field in all patients. All patients were divided into two groups, facial nerve exposure group (group A) and unexposure group (group B). The stimulations were applied through the defective areas in patients who had Fallopians channel dehiscence or otherwise over the non-dehiscent area of the tympanic segment. Rocuronium intravenous infusion rate was adjusted to control the NMB at the targeted levels. The stimulation thresholds and amplitudes of EMG responses were recorded at progressive NMB levels with 0%, 25%, 50%, 75%, 90% and 100% respectively. Stimulation thresholds were determined by stimulating in increments of 0.05 mA from 0.1mA until recordable EMG responses were obtained. Response amplitudes were determined by stimulating facial nerve with 0.5 mA in group A , while 1.0 mA in group B. Analyses were performed using SPSS 11.5 software. Average values and standard deviations were calculated, and statistical analyses were performed by ANOVA with Student Newman Keuls Test for multiple comparison. Spearmans Rank Correlation analysis was employed to assess the correlation of facial EMG monitoring results and different NMB levels. A P value of 0.05 was considered significant.ResultsOf all cases, 31 patients suffered from chronic otitis media and 9 patients suffered from cholesteatoma; 36 cases were primary surgeries and the other 4 cases were revisions. In the operative field, the facial nerve was found to be exposed in 16 of the cases, then Group A contained 16 cases and Group B contained 24 cases.（Tab1） All of the patients had recordable EMG responses when the levels of peripheral NMB were 50%. However, when the levels of peripheral NMB were 75%, no response to facial nerve stimulation was measured in 4 patients, all of whom were in unexposure group. An increase in the stimulation thresholds and a decrease in the facial EMG amplitudes generally occurred as NMB levels increased in both dehiscent and intact facial nerves. There was a linear positive correlation between stimulation thresholds and NMB levels, while a linear negative correlation between EMG amplitudes and NMB levels, P0.01. (Fig1,2) The recordings of facial nerve stimulation thresholds and EMG amplitudes for different NMB levels are shown in Fig3-4. The stimulation threshold in Group A was significantly lower than that in Group B at each NMB level, P0.01. Significant differences were found between each NMB levels for stimulation thresholds and EMG amplitudes in two groups, P0.05. All patients were kept stable hemodynamics and immobility during the operation. Postoperatively, all 40 patients demonstrated clinically normal facial nerve function.DiscussionPostoperative facial nerve dysfunction is a common complication following otologic surgical procedures. Intraoperative EMG monitoring of the facial nerve has been commonly used and resulted in improved preservation of facial nerve function in patients undergoing acoustic neuroma resection8. Recently, the role of facial nerve monitoring in middle ear and mastoid surgery has been promoted 9. The use of such a monitoring unit may place additional constraints on the anesthetic management of these patients. Since the use of neuromuscular blockade can prevent an effective facial muscle response and lead to the erroneous conclusion, anesthetists are asked to avoid the use of neuromuscular blocking agents when maintaining anesthesia during otologic surgery. However, delicate microsurgical interventions demand absolute immobility of the patient. So large doses of narcotics and volatile anesthetic agents are used to keep the patient immobilized without neuromuscular blocking agents. Some patients with severe hemodynamic instability, necessitating the use of vasopressors to support circulation, poorly tolerate these high levels of anesthetic agents. The anesthetic management of these patients should provide hemodynamic stability and absolute immobility while preserving an optimal environment for facial EMG monitoring. Partial peripheral neuromuscular blockade may be a way to decrease the morbidity of movement without loss of the ability to monitor facial nerve EMG activity67. With the introduction of the peripheral nerve stimulator using train-of-four (TOF) stimulation, the anesthesiologist can measure and titrate the level of neuromuscular blockade. Our study showed all of the patients had recordable EMG responses when the levels of peripheral NMB were 50%. The intraoperative facial EMG monitoring is used to identify and map the facial nerve, so we consider the results of patients who had non-dehiscent Fallopians channel to be more important. In these patients, when the levels of peripheral NMB were 75%, 4 patients (4/24) had no recordable EMG response. The stimulation threshold of the facial nerve and the EMG amplitude at 75% NMB were statistically distinguishable from that at 50% NMB. Blair EA et al reported that T1 and T4/T1 had a wider variability at levels of paralysis greater than 75 percent and reliability may decrease. Based on these findings, we conclude that the NMB levels greater than 75% are not fit for facial EMG monitoring during tympanoplasty. On the other hand, although the NMB levels lower than 25% can provide an optimal environment for facial EMG monitoring, they are not sufficient to prevent all movements of patients. Adequate surgical relaxation may occur with 55-60% EMG twitch height reduction10. Thus, the 50% NMB should be considered as the most suitable level for facial nerve monitoring in middle ear microsurgery. Reports from the literature suggest that there is a distinct difference in sensitivity between the facial and ulnar nerve responses to non-depolarizing muscle relaxants. The facial musculature seems to be less sensitive than the hypothenar muscle to neuromuscular blocking agents 1112. That is, at a given level of blockade, the facial response is always stronger. The explanation for this relative insensitivity remains unclear. The facial muscles have a greater number of neuromuscular junctions than have other muscles in the body 13. It is unknown, whether a different affinity of the facial acetylcholine-receptor for acetylcholine or non-depolarizing muscle relaxants plays an additional role. This knowledge allows us to speculate that intraoperative monitoring of the facial nerve can be regarded as a reliable method in conditions of partial NMB. Our study also explored the relationship between facial EMG responses and peripheral NMB levels. The results suggested that there was a linear positive correlation between stimulation thresholds and NMB levels, while a linear negative correlation between EMG amplitudes and NMB levels. Several studies previously evaluated facial EMG monitoring with partial NMB. Blair EA et al reported that in patients undergoing cerebellopontine angle tumor resection, there was a strong linear correlation between both T1 and T4/T1 to the percent of baseline amplitude of facial EMG5. But in another study conducted in patients undergoing acoustic neuroma resection, a correlation was not found between the degree of peripheral NMB and the magnitude of the facial action potential 14. The author attributed the results to some methodological problems. There have been no reports regarding the relationship between facial EMG responses and peripheral NMB levels in middle ear surgery. Despite several differences between the otologic and neurootologic approaches, the results of the present study demonstrate the correlation. In conclusion, this study suggests that partial neuromuscular blockade can provide reliable conditions for intraoperative facial EMG monitoring as well as adequate immobilization. The 50% NMB is the most suitable level for facial nerve monitoring in middle ear microsurgery. There is a linear correlation between facial EMG responses and peripheral NMB levels, with a positive correlation between stimulation thresholds and NMB levels, while a negative correlation between EMG amplitudes and NMB levels.Table 1. Characteristics of patientsGroup A（16）Group B（24）Age (y)41 15 35 12 Weight (kg)64 1261 13Sex (M/F)8 / 811 / 13Pathology (Chronic otitis media / Cholesteatoma)12 / 419 / 5Times of surgery (First / Second )14 / 222 / 2r=0.38 （P0.01）exposure group-unexposure groupr=0.26 （P0.01）Fig. 1. Relationship between facial nerve stimulation thresholds and peripheral NMB levels.exposure group-unexposure groupr =0.66(P0.01）r =0.55 (P0.01）Fig. 2. Relationship between facial EMG amplitudes and peripheral NMB levels.*Fig. 3. Facial nerve stimulation thresholds at different NMB levers. ( * P0.05)*Fig. 4. Facial EMG amplitudes at different NMB levels. (* P0.05)References1. Wiet RJ. Iatrogenic facial paralysisJ. Otolaryngol Clin North Am, 1982, 15: 773- 778.2. Prass RL. Iatrogenic facial nerve injury: the role of facial nerve monitoringJ. Otolaryngol Clin North Am, 1996，29: 265-275.3. Noss RS, Lalwani AK, Yingling CD. Facial nerve monitoring in middle ear and mastoid surgeryJ. Laryngoscope, 2001,111: 831-836.4. Morikawa M, Tamaki N, Nagashima T, et al. Long-term results of facial nerve function after acoustic neuroma surgery-clinical benefit of intraoperative facial nerve monitoring J. Kobe J Med Sci, 2000, 46: 113-124.5. Blair EA, Teeple E, Sutherland RM, et al. Effect of neuromuscu