Somatosensory evoked potential monitoring during carotid surgery

Controversy exists over the value of intraoperative monitoring and shunting in patients undergoing carotid endarterectomy. Although it is widely believed that contralateral carotid occlusion and previous stroke mandate intraoperative shunting, the susceptibility of these two groups of patients to cerebral ischemia during carotid artery endarterectomy is not well defined. Somatosensory evoked potentials (SSEPs) were monitored in 113 carotid artery endarterectomy patients. Of these, 32 (28.3%) had a previous stroke, 24 (21.2%) had a contralateral carotid occlusion and 33 (29.2%) were diabetic. There were no deaths and only one perioperative stroke (0.9%). Cerebral ischemia occurred in 14 patients (12.4%). Six of these patients had a contralateral carotid occlusion. Some 29 patients (25.7%) were shunted, including 10 with contralateral carotid occlusions that did not have major SSEP changes. In the latter half of the study, 14 patients with contralateral carotid occlusions were selectively shunted (six shunted, eight not shunted) with no neurological complications. Thirty-two patients with prior strokes were selectively shunted (nine shunted, 23 not shunted); of these, one shunted patient undergoing combined carotid artery endarterectomy and coronary artery bypass grafting had a perioperative stroke. Intraoperative monitoring with SSEPs accurately identifies cerebral ischemia secondary to carotid clamping as well as patients requiring shunts. With the use of intraoperative SSEP monitoring, selective shunting may be safely performed in patients with a contralateral carotid occlusion or a previous stroke.     

Somatosensory evoked potential monitoring of spinal cord ischemia during aortic operations

Somatosensory evoked potentials were monitored in 22 consecutive patients undergoing surgical correction of an aortic coarctation. Induction of spinal cord ischemia by cross clamping of the aorta elicited a change in the evoked potential in 9 patients (41%). These alterations occurred within 5 minutes of aortic clamping in 3 cases and after 18 to 21 minutes in the remaining 6 cases. Loss of the somatosensory evoked potential for more than 14 minutes was associated with postoperative neurological deficit. Alteration of the evoked potential within 5 minutes of aortic cross clamping was significantly related to poor collateral circulation shown on the preoperative aortogram. The pathophysiology of evoked potential changes in spinal ischemia is discussed in detail.     

Somatosensory evoked potential monitoring during closed humeral nailing: a preliminary report

OBJECTIVES: To assess the role of intraoperative somatosensory evoked potential (SSEP) monitoring of the radial and median nerves in preventing iatrogenic nerve injury during closed, locked intramedullary (IM) nailing of the humerus. DESIGN: Prospective clinical study. SETTING: Pacific Northwest Level One trauma center and Southern California military medical center. PATIENTS: Thirteen patients with indications for surgical stabilization of fractures of the humeral diaphysis and either unknown neurologic status of the affected limb or anticipated difficult reduction maneuvers due to fracture complexity or displacement. INTERVENTION: Closed, antegrade or retrograde locked IM nailing of the humerus was attempted while intraoperative monitoring of the radial and median nerves with SSEP was performed. MAIN OUTCOME MEASUREMENTS: Intraoperative radial and median nerve SSEP changes during closed fracture manipulation, guide rod insertion, reaming, and humeral nail placement. RESULTS: Baseline recordings were obtained in twelve of thirteen patients for both the radial and median nerves. An absence of radial nerve signal in one patient with a closed head injury prompted an open procedure, revealing entrapment of the radial nerve in the fracture. Intraoperative SSEP changes were observed in two of the twelve remaining patients during fracture manipulation and distal interlocking. The signal amplitude returned after discontinuation of manipulation and traction, and alteration of the interlocking maneuver. No neurologic deficits were noted in these two patients. CONCLUSIONS: Intraoperative radial nerve SSEP monitoring appears to reliably reflect the status of the radial nerve in those patients with a humerus fracture. In three of eleven patients, intraoperative signal changes prompted a change in surgical plan. In no patient did there appear to be evidence of iatrogenic nerve injury.     

Somatosensory evoked potential

Somatosensory evoked potential (SEP) has been widely used for monitoring the abnormal nerve conduction in various diseases. In non-anesthetized patients, Abeta fibers are electrically stimulated during SEP measurements. In anesthesiological field, it is used as a short latency somatosensory potential (SSEP), because its latency and amplitude are relatively constant. To detect the conduction abnormality from the upper extremities to the brain, median nerve stimulation is used. For the detection of spinal cord abnormality during operation, posterior tibial nerve stimulation is often used. It is important to know the origin of the wave appearing in SSEP to find the lesion in the nervous system. SSEP has been used in scoliosis surgery, carotid endarterectomy, thoracoabodominal aortic surgery and cervical operations to detect brain and spinal ischemia. In an intensive care unit, it is used for the diagnosis of brain death or ischemia and other neuronal diseases such as Guillain-Barre syndrome and polyneuritis etc. In pain clinic, laser evoked potential (LEP) has been recently introduced for the analysis of the mechanisms of nerve and spinal cord diseases. Using the LEP, pain mechanism would be clarified. During SSEP measurements, it is necessary for the anesthesiologists, intensivists and pain clinicians to understand the effect of anesthetic drugs and hypothermia on SSEP.     

Somatosensory evoked potential

Summary Somatosensory evoked potentials (SSEPs) have been used to help minimize neurologic morbidity during spinal surgery. While this is a sensory test it has been used as an inference of motor function. The failure to always achieve the latter goal has resulted in some pessimism regarding the value of this test. In this series of 161 operations in 150 patients, it was demonstrated that SSEPs were recordable under anesthesia in 87% of patients. Of these patients, 12% had their spinal surgery interrupted due to significant neurophysiologic changes; of these patients, 18% had new neurologic deficits postoperatively. There were no cases with new neurologic deficits who had no changes in their SSEPs. It was concluded that SSEP monitoring may be helpful in identifying potentially neurologically threatening surgical maneuvers in a significant number of patients.     

Somatosensory evoked potential monitoring of temporary middle cerebral artery occlusion during aneurysm operation

Somatosensory evoked potentials (SEPs) in response to median nerve stimulation were used as a guide to cortical function during temporary occlusion of the distal M1 segment of the middle cerebral artery (MCA) in the surgical treatment of five large aneurysms of the MCA bifurcation. MCA occlusion times ranged from 8 to 19 minutes under moderate hypothermia at 28.8 degrees to 30.3 degrees C. SEPs were preserved for variable times during MCA occlusion, ranging from no increase in latency after 13 minutes of occlusion to severe deterioration after 6 minutes. In no case was MCA occlusion maintained for longer than 3 minutes in the presence of a severely disturbed SEP. Recovery of the SEP to its preoperative relationship with that of the nonoperated hemisphere was seen in all cases before the end of operation. All patients were awake after rewarming at the end of operation without any neurological deficit. Monitoring the SEP pertaining to the territory of a cerebral artery during its temporary occlusion can help avoid ischemic damage and will allow the surgeon to take advantage of the several benefits of this technique in aneurysm surgery.     

Somatosensory evoked potential monitoring during carotid endarterectomy in patients with a stroke.

The aim of our study was to assess the characteristics and feasibility of somatosensory evoked potential (SSEP) monitoring in patients who have had a stroke undergoing carotid endarterectomy. We retrospectively reviewed the medical and SSEP records of 204 patients. The patients were divided into two groups: Stroke (n = 65) and No-Stroke (n = 139). The amplitude and latency of the N20-P25 cortical complex on the ipsilateral side (surgical) were compared with the contralateral side in each group and between groups. Stroke patients showed asymmetry of their cortical waveforms; the ipsilateral N20-P25 baseline amplitude was 1.5 +/- 1.0 microv versus 1.9 +/- 1.2 microv for the contralateral (P = 0.001), for No-Stroke patients 2.0 +/- 1.1 microv versus 2.1 +/- 1.1 microv (P = 0.2). Forty-eight percent of Stroke patients had a ratio (ipsilateral/contralateral amplitude) of <1.0 +/- 0.2 compared with 26% for No-Stroke patients (P = 0.01). There were no differences in latency measurements, in the incidences of significant SSEP changes (four Stroke, six No-Stroke) and immediate postoperative neurological deficits (two Stroke, six No-Stroke) between the two groups. Nine patients (three Stroke, six No-Stroke) had a decrease in ipsilateral N20-P25 amplitude >50% after cross-clamping, and had a shunt inserted. In conclusion, patients with a history of a stroke before surgery had a decrease in the amplitude of the ipsilateral cortical peak. There were no differences in the incidences of SSEP changes or neurological deficits. Implications: Patients who have had a preoperative stroke may show asymmetry of their cortical baseline somatosensory evoked potential waveforms; however, this does not interfere with the ability to use somatosensory evoked potential as a monitor during surgery.     

Variability of somatosensory evoked potential monitoring during scoliosis surgery

OBJECTIVE: Somatosensory evoked potentials (SEPs) of 65 patients undergoing scoliosis surgery were monitored by stimulation of posterior tibial nerve to observe variations in latencies and amplitudes. METHODS: Monitoring was divided into five stages: pre incision, spine exposure, instrumentation loading, deformity correction, and wound closure (stages 1-5, respectively). RESULTS: We found the latency showed significant increase and the amplitude significant reduction from stages 1 to 2. There was no significant variability from stages 2, 3, and 4, but both latency and amplitude recovered significantly from stage 4 to 5. This variability correlated with the changes in mean arterial pressure and end-tidal concentrations of isoflurane and was not dependent on the type of surgical procedure. If either 50% amplitude reduction or 10% latency prolongation of SEP compared with baseline recordings at stage 1 (pre incision) was used as warning criterion, the overall false-positive rate was 23.1%. It was significantly reduced to 7.7% if stage 2 (spine exposure) recordings were used as the baseline (P < 0.05). The false-positive rate decreased to 0% if a combined 50% amplitude reduction and 10% latency prolongation of SEP compared with the stage 2 baseline were used (P < 0.001). CONCLUSION: Based on these findings, we concluded that the time to obtain SEP baseline data should be adjusted to be post incision instead of pre incision.     

Motor evoked potential monitoring during upper cervical spine surgery

Motor evoked potential (MEP) produced by transcranial electrical stimulation was recorded from an epidural electrode in 20 consecutive patients during upper cervical spine surgery. In 5 patients, transient attenuation to approximately 50% followed by complete recovery was observed, and no neurologic deficit was noted. One patient had complete loss of MEP and was left a respiratory quadriplegic. In 2 cases, MEP amplitudes increased after tumor extirpation and remarkable remissions were observed. The MEP correlated with clinical outcomes and was a useful monitoring technique for upper cervical spine surgery, free of complication. In cat experiments designed to analyze conducting pathways, the maximal amplitude of the initial spike of MEP existed in the ventromedial spinal cord, which contains the extrapyramidal tracts. Motor evoked potential was proven to reflect motor function based on the spinal cord compression study.     

Variability of somatosensory cortical evoked potential monitoring during spinal surgery

The intraoperative variability of somatosensory cortical evoked potentials (SCEPs) has been measured for 320 consecutive spinal surgeries and found to be a function of patient diagnosis, neuromuscular status, age, and procedural factors. In many cases, it is likely that this variability severely limits the reliability and usefulness of spinal cord monitoring in detecting early cord compromise. Patients with idiopathic scoliosis, spondylolisthesis, and pseudarthrosis have the smallest spontaneous variability and strongest amplitudes, while those with congenital, paralytic scoliosis, stenosis, or tumor have very variable, weak SCEPs. Patients with neurologic disorders, particularly cerebral palsy, myelomeningocele, Friedreich's ataxia, and peripheral deficits, also have high variability and weak amplitudes. A monitoring quality scoring system is proposed that may be useful during surgery in judging how well the SCEPs can discern surgically related changes in cord function from background variations.     

Motor evoked potential monitoring with supratentorial surgery

OBJECTIVE: To assess feasibility and clinical value of motor evoked potential (MEP) monitoring with surgery close to supratentorial motor areas and pathways. METHODS: Functional mapping by somatosensory evoked potential phase reversal and continuous MEP recording after high-frequency repetitive electrical cortex stimulation was performed during 182 operations in 177 patients. Significant MEP changes were reported to trigger surgical reaction. Intraoperative surgical and electrophysiological findings were documented prospectively. Patient files were reviewed for clinical data. MEP monitoring results were correlated with motor outcome. RESULTS: MEP recording was successful in 167 cases (91.8%). Inadequate electrode placement was an important reason for failed recording in the remaining patients, whereas preoperative paresis and anesthesia had no significant effect. Permanently disabling new motor deficit occurred in 8 cases (4.9%), whereas transient and nondisabling weakness was frequent (27.4%). Significant MEP changes occurred during 64 operations (39%). Irreversible MEP loss always predicted new, usually permanent, paresis. Unaltered MEP recordings indicated unimpaired motor function in the monitored muscle groups, except for rare transient deficit because of late edema and rebleeding. Irreversible MEP deterioration without loss and reversible changes could be associated with new paresis, which was transient in most patients. No major complications were observed, except for intraoperative generalized seizure in one epilepsy patient under insufficient anticonvulsant therapy. CONCLUSION: MEP monitoring with supratentorial surgery is feasible and safe. It may help to maximize resection within the limits of preserved motor function. Further evidence is needed to confirm these results.     

Somatosensory evoked potential monitoring in the surgical management of acute acetabular fractures

Fifty patients undergoing acute acetabular fracture surgery had intraoperative somatosensory evoked potential (SSEP) monitoring. Group II, the final 38 patients, in addition had independent neurological evaluation preoperatively and postoperatively. Thirteen of 50 patients (26%) had preoperative sciatic nerve involvement. Fourteen of 50 patients (28%) developed significant intraoperative SSEP changes (decreased amplitude, increased latency). When the nerve was involved preoperatively (high-risk group), changes in SSEP occurred in 60% of patients. Iatrogenic sciatic/peroneal neuropraxia occurred in only one patient in the series (2%), and this resolved within 4 months. These results compare favorably to the incidence of 5-18% reported in the literature. We conclude SSEP is feasible and should be used in the operative treatment of acetabular fractures, especially the posterior fracture patterns and for those in the high-risk group.     

颈椎后纵韧带骨化症术中诱发电位消失2例报告

正颈椎后纵韧带骨化症(OPLL)是颈椎后纵韧带异位骨化引起的颈脊髓压迫症状。研究证实约有25%的脊髓型颈椎病患者伴有后纵韧带骨化。其症状是进行性痉挛性四肢瘫痪,有较高的致残率。无论是前路手术还是后路手术,都有较高的手术并发症发生率。其中术后瘫痪和神经症状加重是较严重的并发症。我院收治2例颈椎OPLL患者,在术中麻醉成功、体位摆放后即出现诱电位消失,行后路椎管扩大成形术,麻醉复苏后患者出现不同程度的瘫痪,经     

Somatosensory evoked potentials in carotid surgery

During carotid surgery a monitoring device that will identify patients with inadequate cerebral perfusion and impending cerebral damage after carotid clamping is desirable. Such patients may benefit from cerebral protective measures, which should be applied selectively as their use can also lead to complications. METHODS. In order to evaluate the reliability of somatosensory evoked responses as a means of detecting patients with insufficient collateral perfusion after carotid cross clamping, a prospective study involving 482 operations for reconstruction of supraaortic vessels was performed. Somatosensory evoked potentials (SEPs) were recorded from a cervical (C2-Fz) and a parietal (C3'/C4'-Fz) electrode above the ipsilateral hemisphere following stimulation of the contralateral median nerve. RESULTS. In 22 procedures (4.6%) complete flattening of the cortical SEP occurred after carotid cross clamping. In 7 of 9 cases in which no indwelling shunt was used despite electrical silence neurological deficits were found postoperatively. The SEP amplitude was restored in 12 of the remaining 13 patients with complete loss of the SEP after shunt insertion. Only 3 of these patients demonstrated neurological impairment. During 460 operations evoked potentials were always present. Nevertheless, 5 neurological sequelae were noticed despite unchanged SEP after carotid artery clamping. All deficits, however, were caused by embolization and were unrelated to reduced blood flow after carotid cross clamping. CONCLUSIONS. Our results confirm the reliability of SEP monitoring for the detection of significant cerebral ischemia after carotid clamping. In absence of the cortical SEP immediate shunt placement is necessary to avoid neurological deficits. On the other hand, the risks attendant on indiscriminate cerebral support (embolism after shunt placement, cardiac ischemia due to induced hypertension) can be avoided in the presence of cortical potentials. This allows protection of the heart and the brain by anesthetic management and enables the surgeon to perform endarterectomy with no hurry, to avoid technical failure. SEP data may also be helpful in decision making on reoperation to look for sources of embolization. In conclusion, advanced monitoring by somatosensory evoked responses may help to improve the outcome of carotid surgery.     

经颅磁刺激运动诱发电位在脊柱脊髓术中监测的应用研究

目的 探索应用经颅磁刺激运动诱发电位(TMS-MEP)在脊柱脊髓手术中进行神经监测的可行性和有效性.方法 2001年2月至2004年6月间在我科接受脊柱脊髓手术共37例患者,术中分别使用常规方法和依托咪酯+芬太尼技术进行麻醉,应用双频指数(BIS)和四个成串刺激(TOF)监测麻醉深度与肌松状态,使用TMS-MEP进行术中监测.比较不同麻醉方法和麻醉深度对TMS-MEP的影响,并分析TMS-MEP监测操作的可行性及其对手术操作的影响.结果 以安氟醚或异氟醚维持麻醉的11例患者无法记录到TMS-MEP;使用依托咪酯+芬太尼技术麻醉的26例患者,MEP均记录良好.与麻醉前相比,术中的MEP波形一般都能够保持,但其波幅显著下降、潜伏期亦明显延长(P<0.05).随着麻醉和肌松的加深,MEP的波幅会进一步降低,而潜伏期的变化相对较小.在麻醉相对平稳的情况下,MEP波幅能保持相当的平稳.MEP操作对手术没有明显的不良影响.成功记录MEP的患者中有6例(23%)因为术中MEP波幅下降超过50%而向术者发出报警,其中仅1例患者术后肌力较术前下降.结论 应用TMS-MEP进行脊柱脊髓手术的术中监测是一项有效而切实可行的技术,依托咪酯+芬太尼麻醉技术适用于使用TMS-MEP进行术中监测的手术,BIS、TOF等麻醉、肌松监测指标的应用有助于维持术中麻醉的平稳和对TMS-MEP监测结果的判断.     

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。     

听觉诱发电位监测用于脊柱侧凸术中唤醒

目的研究听觉诱发电位(AEP)监测用于脊柱侧凸术中唤醒试验时预测患者苏醒时间的可行性。方法40例ASAⅠ或Ⅱ级,在低流量(新鲜气流量0.8L/min)吸入麻醉下行后路矫正内固定手术的青少年脊柱侧凸患者,随机分为两组,术中均吸入异氟醚及氧化亚氮(O2∶N2O=1∶1)维持听觉诱发电位指数(AAI)在15~20。Ⅰ组于患者安装完双侧内固定棒开始唤醒试验时停止吸入异氟醚及氧化亚氮并升高新鲜气流量(6L/min)至患者对指令产生正确反应;Ⅱ组于患者安装完一侧内固定棒后停止吸入异氟醚,维持新鲜气体流量及氧化亚氮吸入浓度不变,在安装完另一侧后升高新鲜气流量至患者对指令产生正确反应。所有患者唤醒成功后立即恢复低流量吸入麻醉。结果两组患者在唤醒时的AAI值差异无显著意义,但唤醒时间差异有极显著意义(P<0.01)。除1例(Ⅱ组)首次唤醒试验失败的患者,其他患者对术中事件及唤醒过程均无回忆。AAI值与MAP、HR及呼气末异氟醚浓度(ETiso)无相关性。结论利用AEP监测能比较准确地预测脊柱侧凸术中唤醒试验时患者的苏醒时间。