Effect of stimulation parameters on intraoperative spinal cord evoked potential monitoring

The purpose of this study was to investigate the effects of the stimulus parameters on spinal cord evoked potential (SCEP) and to recommend a practical epidural stimulation protocol for intraoperative spinal cord monitoring. This prospective study compared the latencies and amplitudes of SCEP obtained on epidural stimulation of 30 patients with scoliosis under anesthesia using different stimulus pulse duration and stimulation rates. SCEP was found to be undetectable with shorter stimulus duration (<0.05 ms). The SCEP latencies did not show any significant difference among different stimulation parameters. However, the SCEP amplitude showed significant changes with differing stimulus durations. The SCEP amplitudes were found to significantly decrease when the pulse durations become shorter than 0.2 ms. Stimulus parameters showed significant effects on SCEP amplitude but not latency. Stimulus rates in the range of 21 to 61 Hz are equivalent for quick and reliable detection of SCEP. Considering the short latency of SCEP, a pulse duration of 0.2 ms is recommended for SCEP using epidural stimulation.     

Facial nerve motor evoked potentials elicited by transcranial electrical stimulation for intraoperative monitoring

OBJECTIVE: To determine whether monitoring facial nerve motor evoked potentials (FNMEPs) elicited by transcranial electrical stimulation during skull base tumor surgery is useful for predicting facial nerve outcome. METHODS: We analyzed FNMEP findings in 31 patients with skull base tumor. Surgery was performed twice in 2 of the 31 patients because of tumor regrowth. FNMEP monitoring was conducted 33 times in the present study. Corkscrew electrodes positioned at C3 or C4 and Cz were used to deliver supramaximal stimuli (140-550V). FNMEPs were recorded from the orbicularis oculi and oris muscles. Correlation between the final-to-baseline FNMEP ratio and postoperative facial nerve function (House & Brackmann grade) was examined. RESULTS: Valid FNMEPs were obtained in 26 of the 33 (78.8%) recordings from the orbicularis oculi muscle and in 31 of the 33 (93.9%) recordings from the orbicularis oris muscle. Facial nerve function correlated significantly with the FNMEP ratios in the orbicularis oculi (r = -0.52 N=26, p < 0.01) and orbicularis oris (r = -0.60, N=31, p < 0.001) muscles. An FNMEP ratio of -50% consistently predicted immediate postoperative facial palsy, although the degree of palsy differed among the patients. CONCLUSIONS: Intraoperative FNMEP monitoring is useful for predicting facial nerve function after skull base surgery.     

Recording of spinal somatosensory evoked potentials for intraoperative spinal cord monitoring

The authors' experience with intradural and epidural recording of spinal somatosensory evoked potentials (SSEP's) during 26 cases of spinal surgery is described. The techniques of monitoring spinal cord function provided good quality SSEP waveforms in patients both with and without neurological deficits. The SSEP configuration and peak latencies remained stable for up to 5 hours during anesthesia with nitrous oxide, halothane, and fentanyl. Patterns of baseline SSEP's were characteristic of different spinal segments. Distortion and asymmetry of these baseline patterns were seen in several patients with spinal neoplasms. Loss of waveform components during surgery occurred with profound hypotension, overdistraction of the vertebral axis, dorsal midline myelotomy, and removal of intramedullary tumors. Persistent loss of waveform components was associated with an acquired neurological deficit. Fluctuations in the amplitude of the SSEP's were common but were not associated with postoperative neurological deficits. Spinal cord monitoring by means of SSEP recording would appear to be useful during extradural spinal surgery, but there are limitations associated with this technique during some types of intradural surgery.     

脊柱手术中经颅电刺激运动诱发电位监护的应用探讨

目的探讨脊柱手术中经颅电刺激运动诱发电位（transcranial electrical stimulation motor evoked potential,TES-MEP）监护的可行性和应用价值。方法2006年7月至2008年10月,在241例胸椎手术中对双侧胫前肌、足踇短屈肌、大鱼际肌或小鱼际肌（颈椎病变时）实施TES-MEP监护。术中全静脉麻醉58例,静脉麻醉＋七氟烷吸入麻醉（浓度〈1％）67例,静脉麻醉＋小剂量肌松剂116例。结果TES-MEP的检出率为89．2％,虽然3种麻醉方式的检出率无显著性差异,但各年龄组、不同靶肌肌力的检出率有显著性差异。术中TES-MEP阳性26例,其中不明原因的假阳性6例,真阳性20例,且均与手术操作有直接相关性。TES-MEP对脊髓运动功能监护的灵敏度为100％,特异度为97．9％,约登指数为0．979;对脊髓感觉功能监护的灵敏度为74．1％,特异度为97．9％,约登指数为0．72。结论异丙芬静脉麻醉＋七氟烷吸入麻醉（浓度〈1％）为首选方案,异丙芬静脉麻醉＋小剂量肌松剂为次选方案。TES-MEP不但能瞬间、直接、准确地监护脊髓的运动传导功能,而且能间接反映脊髓的感觉传导功能,是安全监护脊柱手术的新方法。     

Transcranial electrical stimulation through screw electrodes for intraoperative monitoring of motor evoked potentials. Technical note

The feasibility of high-frequency transcranial electrical stimulation (TES) through screw electrodes placed in the skull was investigated for use in intraoperative monitoring of the motor pathways in patients who are in a state of general anesthesia during cerebral and spinal operations. Motor evoked potentials (MEPs) were elicited by TES with a train of five square-wave pulses (duration 400 microsec, intensity < or = 200 mA, frequency 500 Hz) delivered through metal screw electrodes placed in the outer table of the skull over the primary motor cortex in 42 patients. Myogenic MEPs to anodal stimulation were recorded from the abductor pollicis brevis (APB) and tibialis anterior (TA) muscles. The mean threshold stimulation intensity was 48 +/- 17 mA for the APB muscles, and 112 +/- 35 mA for the TA muscles. The electrodes were firmly fixed at the site and were not dislodged by surgical manipulation throughout the operation. No adverse reactions attributable to the TES were observed. Passing current through the screw electrodes stimulates the motor cortex more effectively than conventional methods of TES. The method is safe and inexpensive, and it is convenient for intraoperative monitoring of motor pathways.     

History of the development of intraoperative spinal cord monitoring

In the early 1970s, spinal instrumentation and aggressive surgical technology came into wide use for the treatment of severe spinal deformities. This background led to the development of intraoperative spinal cord monitoring by orthopaedic spine surgeons themselves. The author's group (T.T.) and Kurokawa's group invented a technology in 1972 to utilize the spinal cord evoked potential (SCEP) after direct stimulation of the spinal cord. In the United States, Nash and his group started to use SEPs. Following these developments, the Royal National Orthopaedic Hospital group of Stanmore, UK employed spinal somatosensory evoked potential in 1983. However, all of these methods were used to monitor sensory mediated tracts in the spinal cord. The only way to monitor motor function was the Wake up test developed by Vauzelle and Stagnara. In 1980, Merton and Morton reported a technology to stimulate the brain transcranially and opened the doors for motor tract monitoring. Presently, in the operating theatre, monitoring of motor-related functions is routinely performed. We have to remember that multidisciplinary support owing to the development of hardware and, software and the evolution of anesthesiology has made this possible. Furthermore, no single method can sufficiently cover the complex functions of the spinal cord. Multimodality combinations of the available technologies are considered necessary for practical and effective intra-operative monitoring (IOM). In this article, the most notable historic events and articles that are regarded as milestones in the development of IOM are reviewed.

     

Sensitivity of spinal cord monitoring to intraoperative events

Intraoperative somatosensory evoked potentials in 50 patients were reviewed; each waveform was correlated with intraoperative surgical events and conditions. Twenty-two patients maintained reproducible waveforms and awoke without neurological deficit. Two patients had random waveform changes not correlated with a surgical event and awoke without deficit. Twelve patients showed waveform changes temporally related to circumstances that might endanger cord function; two of these awoke with transient neurological abnormality. Satisfactory waveforms were not obtained from 14 patients. Somatosensory evoked potential monitoring in scoliosis surgery appears to be sensitive, but may not be sufficiently specific; waveform changes do not necessarily indicate objective neurological damage.     

急性脊髓损伤时经颅磁刺激运动诱发电位监测的实验研究

目的 通过观察经颅磁刺激运动诱发电位(TMS-MEP)在急性脊髓损伤时的表现及其与功能预后的关系,探讨TMS—MEP于临床手术时在脊髓运动功能监测中的应用。方法 32只家兔被随机分成4组,对照组了解麻醉及手术对实验的影响,另3组动物为脊髓损伤组,观察脊髓损伤后动物TMS—MEP和运动功能的变化情况以及脊髓的病理学改变。结果 TMS—MEP在脊髓损伤后有不同程度的恶化但并未完全消失的动物,大部分动物的运动功能能基本恢复正常;脊髓损伤后TMS-MEP完全消失但其后1h内能有不同程度恢复的动物,其运动功能可以大部保存;对于TMS-MEP在脊髓损伤后完全消失而且后来一直未见有恢复迹象的动物,其运动功能的恢复大多较差。结论 TMS—MEP监测对脊髓的损伤非常敏感,伤时TMS-MEP的表现与其后运动功能的恢复有着很好的相关性,可以有效地应用于临床术中监测。     

Efficacy of intraoperative direct electrical stimulation of the spinal root and measurement of distal motor latency in lumbar spinal stenosis

Purpose

The measurement of distal motor latency (DML) is an established method for diagnosing entrapment peripheral neuropathy. DML can also serve as an index for disease severity and prognosis. We considered that measuring DML could be useful in estimating the severity of spinal root impairment and predicting prognosis in patients with lumbar spinal stenosis (LSS). The purpose of this study was to investigate the efficacy of intraoperative direct electrical stimulation of the spinal root and the measurement of DML in LSS.

Methods

In 39 patients with LSS, a total of 93 spinal roots were stimulated, and evoked electromyography was recorded at the leg muscles after decompression. DML was measured and its correlation with clinical severity, as evaluated by Zurich claudication questionnaire (ZCQ) and Short Form 36 (SF-36), was investigated.

Results

For the stimulation of the L3, L4, and L5 spinal root, the mean DML (ms) were 6.8 (±1.4), 7.4 (±1.3), and 6.0 (±1.3) in gluteus medius, 9.3 (±1.5), 9.2 (±1.5), and 9.0 (±1.6) in biceps femoris, 9.7 (±1.0), 9.8 (±1.8), and 9.4 (±1.2) in vastus medialis, 16.1 (±1.0), 14.7 (±1.3), and 14.1 (±1.5) in tibialis anterior, and 16.4 (±1.4), 14.3 (±1.8), and 13.9 (±1.9) in gastrocnemius muscles. Statistically significant positive correlations were observed between DML and height. Preoperative symptom and function scores of ZCQ and postoperative bodily pain scores of SF-36 were significantly worse in the patients with prolonged DML.

Conclusions

DML is thought to be useful for estimating the severity of spinal root impairment and for predicting the prognosis.

     

脊柱侧凸矫形术中脊髓监护基准的选择

目的 对脊柱侧凸矫形手术中体感诱发电位（ SEP)的监护基准进行选择,以降低监护过程中脊髓损伤预报之假阳性率,从而提高脊柱外科手术中对脊髓监护的可靠性。方法 回顾分析 160例特发性脊柱侧凸患者在不同手术阶段中的 SEP潜伏期和波幅值及其百分比变化率,比较脊柱暴露前后 SEP波变化对术中脊髓损伤预报的准确性与可靠性,由此而选择脊髓监护基准。结果 各监护阶段 SEP潜伏期的变化差异无显著性意义 (P >0.05);第二阶段的 SEP波幅值与第一阶段相比明显降低,差异有显著性意义 (P0.05)。观察结果显示,在术中,当以脊柱暴露前 (第一阶段 )的 SEP值作为监护基准时, 160例中有 5例假阳性 (3.2％ )预报,而改以脊柱暴露后 (第二阶段 )的 SEP值作为监护基准时则无一例假阳性结果。结论 SEP波幅值在不同手术阶段具有正常变异性,以脊柱暴露后的 SEP值作为监护基准稳定性较好,可以提高对脊髓监护的可靠性。     

Relevance of intraoperative motor evoked potentials and D-wave monitoring for the resection of intramedullary spinal cord tumors in children

Neurosurgical Review - The purpose of this study was to evaluate the reliability of motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), and D-wave monitoring as predictors of...     

Spinal cord monitoring using intraoperative somatosensory evoked potentials for spinal trauma

BACKGROUND: Intraoperative spinal cord monitoring is commonplace in scoliosis surgery as an adjunct to evaluate functional integrity of the cord; however, limited information is available on its applicability in spinal trauma. METHODS: We investigated the efficacy of somatosensory evoked potential (SEP) recording during reconstructive procedures in 82 patients who sustained 20 cervical, 8 thoracic, 6 thoracolumbar, and 48 lumbar vertebral fractures or fractures-dislo-cations. Seventy-one patients underwent single anterior or posterior operations and 11 combined anterior-posterior procedures. Forty patients had incomplete injuries, and 42 had no preoperative neurologic deficit. SEP trace amplitude at insertion of electrode was considered as the baseline value and was compared with the lowest intraoperative signal amplitude and the amplitude at completion of operation. RESULTS: Fifty-nine patients had a depression in wave amplitude of >25% during surgery; in 25 patients, the trace fell by >50%, and in 7 cases, a >75% diminution was recorded. A loss of 50% in SEP signal amplitude showed 67% sensitivity and 71% specificity in predicting neurologic outcome. Increasing trace deterioration threshold from 50% to 60% improved specificity to 81% without compromising sensitivity. A loss of >50% in SEP amplitude occurred with significantly increased incidence during the anterior compared with the posterior spinal procedures. More than 20% recovery in signal amplitude at the conclusion of the procedure in patients with incomplete injuries was correlated with favorable neurologic function. CONCLUSION: Persistent intraoperative decrement in SEP amplitude and poor restitution at completion of surgery increase the risk for postoperative neurologic compromise.     

Functional electrical stimulation after spinal cord injury.

This article reviews work mainly from my own laboratory on the effects of electrical stimulation for therapy and function following spinal cord injury. One to two hours per day of intermittent stimulation can increase muscle strength and endurance and also reverse some of the osteoporosis in bones that are stressed by the stimulation. Stimulation during walking can also be used to improve speed and other parameters of the gait. Surface stimulation systems with 1-4 channels of stimulation were used in a multicenter study. Initial increases of almost 20% in walking speed were seen and overall increases of nearly 50% in subjects who continued to receive stimulation for a year on average. Some changes were due to improved strength and coordination with stimulation and additional walking, but a specific effect of stimulation persisted throughout the trial. Improved devices will soon be available commercially that were developed on the basis of feedback from users.     

Cortical evoked potential monitoring. A system for intraoperative monitoring of spinal cord function

This report describes the intraoperative use of a somatosensory cortical evoked potential system to monitor spinal cord function during 300 orthopedic surgical procedures. This system requires sophisticated equipment and the establishment of normative data but has performed well with no false negatives noted. The most frequent technical problem encountered was the effect of medications and anesthetic agents, some of which impair the evoked response significantly. In this series of 300 cases, three neurologic deficits were documented intraoperatively and confirmed postoperatively. There were four cases in which changes in evoked potentials led to change in operative procedure, with no subsequent neurologic deficit. In the remaining cases, the monitoring indicated no neurologic problems during surgery, and none were noted postoperatively.     

"Backfiring" in spinal cord monitoring. High thoracic spinal cord stimulation evokes sciatic response by antidromic sensory pathway conduction, not motor tract conduction.

Spinal cord stimulation has been advocated as an alternative to motor cortex stimulation for motor tract activation. To test this theory, evoked responses were recorded from lumbar spinal cord (L2; n = 14), spinal roots (L4-L7; n = 112), peripheral nerves (sciatics; n = 28), and hind limb muscles (n = 28) after epidural stimulation of the T1-T2 segment of the spinal cord in dogs (n = 12), cats (n = 2), and monkeys (n = 2). The spinal response evoked by spinal cord stimulation was resistant to a dorsal hemisectioning (depth, 7-8 mm) of the midthoracic spinal cord. A minimal attenuation of latency and amplitude occurred with dorsal hemisectioning, suggesting signal transmission through descending or ascending pathways in the ventrolateral and ventral quadrants of the spinal cord. The sciatic nerve response was abolished by a dorsal column transection (depth, 3-4 mm) or ipsilateral lumbar dorsal rhizotomy (four dorsal roots). This shows that the evoked response recorded from the sciatic nerve in our animals was not travelling, as we expected, through the ventral roots, but rather was conducted antidromically through sensory fibers in dorsal roots.     

术中经颅电刺激运动诱发电位监测在术前脊髓损伤患者中的应用

背景:经颅电刺激运动诱发电位(TceMEP)监测已经广泛应用于脊柱外科手术中,但是到目前为止,针对术前脊髓损伤(POSD)患者的神经监测有效性还存有争议。目的:探讨POSD患者术中TceMEP监测的可行性,并且分析Tce MEP信号快速消失的临床意义。方法:共收集2014年1月至2018年1月349例POSD患者的术中神经监测数据,其中332例患者获得了有效的术中TceMEP基线,17例神经功能障碍较为严重者(11例瘫痪和6例不完全截瘫)未获得。332例中,27例术中TceMEP信号显著消失,收集其临床特征,并严格随访术后3个月的神经功能变化。结果:在POSD患者中,TceMEP基线获得成功率为95.1%(332/349);27例患者出现了明显的TceMEP信号消失,其中23例为真阳性,4例为假阳性。其中21例患者术后出现新发脊髓损伤(13例为暂时性脊髓损伤,8例为永久性脊髓损伤)。预测脊髓损伤的术中TceMEP监测敏感度为100%,特异度为98.7%,阳性预测值为85.2%,阴性预测值为100%。与颈椎管狭窄症相比,先天性脊柱后凸、结核性脊柱后凸和胸椎管狭窄是TceMEP信号消失的高危诊断。结论:术中TceMEP监测对大多数POSD来说是可行的。在高危诊断和复杂的外科手术过程中,快速的TceMEP信号消失可能预示着新的脊髓损伤。