重度脊柱畸形翻修截骨术中神经监测变化的危险因素

[目的]评估联合体感诱发电位(somatosensory evoked potential,SSEP)和经颅运动诱发电位(transcranial motor evoked potential,TcMEP)监测在重度脊柱畸形翻修截骨矫形手术中的应用价值,探讨术中出现神经监测变化的危险因素。[方法]回顾性分析2015年1月~2017年1月于本科全麻下进行重度脊柱畸形翻修截骨矫形手术54例患者,男19例,女35例。术中均应用SSEP和TcMEP联合监测。统计比较单模式SSEP、单模式TcMEP及双模式联合监测的阳性预测值和阴性预测值、敏感性及特异性。分析术中出现真阳性电生理监测变化的原因和危险因素,并提出相应的管理措施。[结果]联合SSEP及TcMEP监测成功率、阳性预测值、阴性预测值、敏感性及特异性均为最高。54例患者中共有14例(25.93%)出现阳性电生理监测变化。经术中干预后,随访时最终2例(3.70%)未恢复至术前神经功能状态。术前合并胸椎管狭窄、主弯Cobb角130°为出现真阳性电生理变化的危险因素。[结论]在重度脊柱畸形翻修截骨矫形手术中,联合SSEP及TcMEP监测能有效地检测早期脊髓损伤,有更好地进行预警的价值。积极进行干预能扭转电生理变化并可以避免严重脊髓损伤并发症发生。翻修术中截骨矫形过程出现电生理变化概率较高。术前合并胸椎管狭窄以及主弯Cobb角130°的患者更易导致真阳性监测变化发生。     

经颅刺激运动诱发电位联合体感诱发电位监测在脊柱畸形手术中的应用

 目的分析联合应用经颅刺激运动诱发电位(transcranial electric stimulation motor evoked potential, TcMEP)+体感诱发电位(somatosensory-evoked potential, SEP)的多模式术中神经功能监测对预 测脊柱畸形矫形手术中医原性神经功能损害的意义。方法 在脊柱畸形矫形手术中, 同时应用 TcMEP 和(或)SEP进行神经功能监测。 MEP监测采用经颅刺激 ₃、C₄, 记录外周肌源性 MEP, SEP监测采用刺 激双侧胫后神经, 记录置于 C_z-FP_z。阳性诊断标准为, 与基线相比, MEP波幅下降 75%, SEP波幅下降 50%。结果 153例脊柱畸形患者中, 150例成功进行了术中 MEP监测, 83例进行了术中 SEP监测。联 合 MEP、SEP监测的检出率为 100%。MEP监测阳性共 12例, 所有患者中有 1例出现永久性神经功能障 碍, 4例出现一过性神经功能障碍。 MEP监测的敏感性为 90.9%, 特异性为 98.6%; SEP监测敏感性为 54.5%, 特异性为 94.3%;联合 MEP、SEP监测的敏感性达 92.3%, 特异性为 99.3%。结论 联合 MEP+ SEP的多模式术中神经功能监测可提高监测的敏感性及特异性, 可预测术中神经功能损伤事件的发生。 MEP是多模式监测的基础, 而 SEP是重要补充。     

无前柱支撑PVCR治疗脊髓功能Ⅰ型重度僵硬性脊柱侧后凸的神经并发症分析

背景:无前柱支撑后路全椎体切除术(posterior vertebral column resection,PVCR)治疗脊髓功能Ⅰ型重度僵硬性脊柱侧后凸畸形的神经并发症发生原因尚未明确,对神经并发症的充分认识有助于对该手术方式的深入理解。目的:分析无前柱支撑PVCR治疗脊髓功能I型重度僵硬性脊柱侧后凸畸形的神经并发症发生原因。方法:回顾性收集2013年3月至2019年2月无前柱支撑PVCR治疗的36例脊髓功能Ⅰ型重度僵硬性脊柱侧后凸患者的术中电生理监测资料。男15例,女21例;年龄12~51岁,平均(17.6±6.1)岁。手术前,所有患者均无脊髓神经功能障碍,MRI均未显示脊髓发育异常。术中采用体感诱发电位、运动诱发电位、下行神经源性诱发电位的联合监测模式。评估术中诱发电位变化数据资料,分析神经并发症发生的原因。结果:所有36例患者均成功接受无前柱支撑PVCR手术并获得满意的手术矫形效果,术后随访3~60个月,平均(32.5±8.2)个月。术中电生理监测无假阴性发生,共出现电生理阳性事件10例(27.8%,10/36):7例发生于截骨阶段,置钉、矫形、矫形后各出现1例。通过系统排查并采取相关处理措施后按照评价标准确定真阳性6例(60%,6/10)、假阳性4例(40%,4/10)。2例(5.6%,2/36)患者表现为术后神经功能障碍,均发生于截骨阶段。1例在随访期间表现为持久性神经功能障碍;1例出现术后短暂性神经功能障碍,在术后9个月随访期间内神经功能障碍完全恢复(ASIA E级)。结论:无前柱支撑PVCR是治疗脊髓功能Ⅰ型重度僵硬性脊柱侧后凸畸形的有效方式。本组患者神经并发症发生率为5.6%。70%神经电生理阳性事件发生于截骨阶段,主要为截骨阶段的平均动脉压过低、血红蛋白过低及机械性刺激所致。多模式诱发电位监测在无前柱支撑PVCR矫形手术中可有效地发现并辅助降低术后神经系统并发症的发生。     

脊柱畸形截骨矫形的问题与思考

正目前,脊柱截骨矫形术作为一种有效的手术方式,在脊柱畸形,尤其是重度脊柱畸形的治疗中广泛应用。相比单纯的后路内固定术,截骨矫形术对矫正脊柱的畸形,重建脊柱的整体平衡具有更好的疗效。根据截骨的方式和范围,其主要包括Smith-Peterson截骨术(SmithPeterson osteotomy,SPO),经椎弓根截骨术(pedicle     

术中电生理监测在脊柱侧凸翻修截骨手术中的应用

目的探讨经颅电刺激运动诱发电位(transcranial electric motor evoked potentials,TCeMEP)和体感诱发电位(somatosensory evoked potentials,SSEP)监测在脊柱侧凸翻修截骨手术中的应用价值。方法回顾性分析2011年3月至2016年3月于我科全麻下行脊柱侧凸翻修截骨术的患者176例,均行SSEP监测,其中134例同时应用TCeMEP监测。分别统计单独SSEP、单独TCeMEP及TCeMEP联合SSEP监测的真阳性率、假阳性率、真阴性率、假阴性率、阳性预测值、阴性预测值、敏感性及特异性。结果单独SSEP成功监测162例(92.0%),TCeMEP成功监测109例(81.3%)。134例应用TCeMEP联合SSEP监测患者,有124例(92.5%)采用任意一种监测方式成功监测。162例成功监测的患者中共有14例报警,报警率为8.6%(14/162)。最终残留神经损伤患者3例,占1.9%(3/162)。统计单独SSEP监测组的敏感性和特异性分别为72.7%和98.7%,单独TcMEP组为90.9%和98.0%,而联合TcMEP及SSEP监测组的敏感性为最高100%,特异性为98.2%。联合TcMEP及SSEP监测组阳性及阴性预测值为85.7%和100%,高于单独SSEP组(80.0%和98.0%)及单独TcMEP组(83.3%和99.0%)。结论脊柱侧凸翻修截骨术手术操作复杂,联合TcMEP及SSEP监测较单一监测能更早地发现神经损害,降低手术风险。我们建议对于脊柱侧凸翻修截骨患者应常规应用TcMEP及SSEP进行联合监测。     

体感诱发电位联合运动诱发电位监测在颈动脉内膜剥脱术中的应用

目的评估在颈动脉内膜剥脱术中(carotid endarterectomy,CEA)中采用体感诱发电位(somatosensory evoked potential,SSEP)与运动诱发电位(motor evoked potential,MEP)联合监测的方案对于预防术中脑缺血发生的准确性。方法选择因颈动脉狭窄择期拟行CEA患者90例,男71例,女19例,年龄18~80岁,ASAⅡ或Ⅲ级。术中监测SSEP和MEP,记录颈内动脉阻断前、颈动脉阻断时、阻断期间及开放后直至术毕SSEP和MEP波幅和潜伏期。评估术后5d内神经功能缺失情况,以发生神经功能缺失作为评判术中脑缺血发生的金标准。结果本研究中14例(15.6%)患者发生术后神经功能缺失。SSEP预测脑缺血发生的灵敏度79%、特异度92%;MEP预测脑缺血发生的灵敏度86%、特异度89%、SSEP+MEP联合监测的灵敏度为79%、特异度99%。结论在颈动脉内膜剥脱术中,体感诱发电位预测脑缺血发生的特异度高,运动诱发电位灵敏度高;二者联合监测可提高监测的特异性,弥补单一监测的不足。     

体感诱发电位监测在脊柱畸形Ponte截骨矫形手术中的应用

[目的]探讨体感诱发电位(SEP)监测在脊柱畸形Ponte截骨矫形手术中的应用价值.[方法]对36例因脊柱畸形行Ponte截骨矫形手术的患者进行术中SEP监测,其中男10例,女26例;年龄6.5～45.2岁,平均18.8岁.成人脊柱侧凸8例,青少年特发性脊柱侧凸14例,先天性脊柱侧凸4例.手术均采用后路Ponte截骨矫形.SEPP40波幅下降＞50％和(或)潜伏期延长超过10％或波形消失为异常标准.[结果]截骨、减压和矫形过程中8例患者出现SEPP40波异常,立即停止手术操作,寻找原因,并作相应处理.其中2例因术中出血导致血压下降,1例为胸腰段截骨,1例为中胸段截骨:另4例考虑与手术操作因素有关.2例为中胸段,2例为胸腰段.2例同时有波幅下降＞50％和潜伏期延长超过10％患者.1例成人脊柱侧凸患者术后出现短期的神经功能障碍,1例成人脊柱侧凸患者术后神经功能正常.[结论]术中体感诱发电位监测可作为指示Ponte截骨矫形术中脊髓功能的重要手段,敏感性较高,对其变化应积极应对并正确处理,以避免脊髓损伤.     

后路脊柱截骨矫形术的临床应用进展

在脊柱截骨矫形术中,后路截骨应用最为普遍,可应用于多种常见的脊柱侧后凸畸形,如强直性脊柱炎、先天性脊柱侧凸、青少年特发性脊柱侧凸以及严重的后凸畸形等。本文就近年来后路截骨矫形治疗重度脊柱畸形的临床应用进展进行综述。     

体感诱发电位监测在重度脊柱畸形后路全脊椎截骨术中的应用

目的探讨体感诱发电位(somatosensory evoked potential,SEP)在重度脊柱畸形后路全脊椎截骨术中的应用价值及影响因素。方法对2007年6月至2013年5月我院收治的97例行Ⅰ期后路全脊椎截骨治疗的重度脊柱畸形患者进行术中SEP监测,男性47例,女性50例,平均年龄(17.8±8.2)岁(6~46岁)。先天性脊柱畸形91例,强直性脊柱炎后凸畸形5例,结核后凸1例。SEP监测异常的标准为波幅下降大于50%和/或潜伏期延长大于10%。分析体感诱发电位波幅变化率与手术因素的相关性。结果本组患者中,12例患者出现术中SEP监测异常,其中10例患者术后出现神经并发症,2例为假阳性病例;1例患者术中SEP未见异常,术后出现神经并发症,为假阴性病例。本组资料中SEP监测敏感性达90.9%,特异性97.7%,假阳性率2.3%,假阴性率9.1%。手术时间、出血百分比、固定节段与术中SEP监测波幅的下降率存在直线相关(P=0.000,P=0.000,P=0.000),出血百分比影响最大。结论SEP监测敏感性较高,但影响因素多、单独使用SEP存在缺陷,因此需要合理的联合使用多种监测手段,并注意对各种干扰因素的分析、处理。     

应用头颅-骨盆环牵引辅助后路截骨治疗重度脊柱侧后凸畸形的临床效果

目的探讨应用头颅-骨盆环牵引辅助后路截骨矫形治疗重度脊柱侧后凸畸形的临床效果。方法回顾分析2014年3月至2018年3月贵州省骨科医院脊柱外科收治的重度脊柱侧后凸畸形患者32例的临床资料。其中男14例,女18例,年龄(17.5±4.8)(14~23)岁。均行Halo骨盆牵引后后路截骨矫形手术治疗。牵引力取患者可承受的极限,牵引时间为(3.2±0.6)(3~4)周,后行后路截骨内固定融合术。对患者治疗前左右侧屈位、牵引后和术后的侧后凸矫正率进行比较。采用SPSS 24.0软件对数据进行统计学处理。结果32例患者均顺利完成手术。行经椎弓根椎体截骨(pedicle subtraction osteotomy,PSO)或邻椎截骨12例、Smith-Petersen截骨(Smith-Petersen osteotomy,SPO)或Ponte截骨20例。未见脊髓与神经损伤并发症发生。治疗前脊柱冠状面Cobb角为(136.8±38.0)°(96°~172°),矢状面Cobb角为(90.4±24.0)°(45°~125°)。患者平卧左右侧屈位侧凸矫正率为(8.9±3.2)%,Halo骨盆牵引后侧凸矫正率为(37.6±4.3)%,后路截骨矫形术后侧凸矫正率为(68.7±4.8)%;牵引后矢状面侧凸矫正率为(30.7±5.6)%,后路矫形术后矢状面侧凸矫正率(60.6±4.3)%;各时间点差异均有统计学意义(均P<0.05)。结论应用Halo头颅-骨盆牵引辅助后路截骨矫形治疗重度脊柱侧后凸畸形患者,可预测矫形效果,简化手术,降低操作难度,提高畸形矫正率,安全有效。     

Evaluation of various evoked potential techniques for spinal cord monitoring during scoliosis surgery

STUDY DESIGN: This prospective study compared the outcomes of different evoked potential (EP) techniques for intraoperative spinal cord monitoring. OBJECTIVES: To evaluate the reliability of different EP techniques administered during scoliosis surgery. SUMMARY OF BACKGROUND DATA: A number of different methods of intraoperative spinal cord monitoring are available. Because each has its own advantages and limitations, multimodal spinal cord monitoring has been proposed to improve monitoring reliability. MATERIALS AND METHODS: Cortical somatosensory-evoked potential (CSEP), cortical motor-evoked potential (CMEP), spinal somatosensory-evoked potential (SSEP), and spinal cord-evoked potential (SCEP) were applied simultaneously to 30 patients undergoing surgical correction for spinal deformity. The presence of the EP waveforms and their reproducibilities over separate tests were compared. In addition, the monitoring outcomes were evaluated with the clinical results. RESULTS: Of the 30 patients, CSEP waveforms were successfully recorded in 28 cases (93%), SCEP in 25 cases (83%), CMEP in 24 cases (80%), and SSEP in 21 cases (70%). Latencies of each EP technique showed no significant variability. However, amplitudes showed significant differences between different techniques. SCEP and CMEP showed clearer waveforms of greater amplitude that could be detected faster than CSEP and SSEP waveforms. SCEP and SSEP waveforms were more easily influenced by the surgical procedure. CONCLUSION: CSEP and CMEP are recommended for routine monitoring, so that both ascending and descending tracts are monitored. If adequate signals for either of these proposed monitoring methods cannot be easily obtained, SSEP can substitute for CSEP, whereas SCEP can substitute for CMEP.     

Acute deformity correction of lower extremities under SSEP-monitoring control

Intraoperative somatosensory evoked potential (SSEP) monitoring was performed in eight children who had undergone an acute deformity correction in the lower extremities using external fixation. Five patients showed stable evoked potentials during surgery and had no neurologic complications postoperatively. Three patients experienced evoked potential abnormalities. In one patient, 60 degrees external rotation of the foot produced significant SSEP changes. The reduction of rotation to 40 degrees resulted in tibial but not peroneal SSEP recovery. Peroneal nerve deficit was noted postoperatively. The second patient showed substantial SSEP attenuation after 45 degrees correction of distal tibial valgus. However, spontaneous recovery of the response occurred, which allowed maintenance of the achieved correction. In a third patient, significant SSEP changes occurred after 90 degrees external rotation and 10 mm medial translation of the distal femur. Total release of translation allowed 75 degrees external rotation without SSEP abnormalities. Neither of the latter two patients had peripheral nerve deficits postoperatively. Intraoperative SSEP monitoring thus helps to define a neurologically safe limit of acute deformity correction.     

Neurophysiological monitoring of lumbar spinal nerve roots: A case report of postoperative deficit and literature review

IntroductionIntraoperative neurophysiological monitoring (IONM) has proven to help reduce the probability of postoperative neurological deficit for spinal deformity correctional surgeries. However, in rare cases new deficits may still happen. We report a surgical case in which the patient had postoperative paralysis. We would like to call for more case reports with postoperative neurological deficits as they present difficult clinical cases.Presentation of caseA 61-year-old male patient with severe thoracolumbar kyphoscoliosis underwent posterior spinal correction and fusion with segmental T10-L5 pedicle screws and rods instrumentation with IONM. The only intraoperative event was a pedicle breach at left L3 which was detected by triggered electromyography (EMG) testing, and the pedicle screw was repositioned. Left lower extremity paralysis was observed upon patient awakening. He received rehabilitation treatment and had limited recovery of muscle strength. Partial lumbar nerve root injury was likely the cause of the paralysis.DiscussionThis is a case with new lumbar nerve root deficit, with positive EMG signal change, but negative somatosensory evoked potential (SSEP) and motor evoked potential (MEP) findings. We discuss the different neurophysiological modalities for monitoring lumbar spinal nerve root function. We review journal articles from the past two decades which reported lumbar root deficits, and list neuromonitoring events during the surgeries.ConclusionMultimodality monitoring with spontaneous and electrically triggered EMG combined with SSEP and MEP may provide the best chance to detect lumbar nerve root injuries.     

Multimodal intraoperative neuromonitoring in corrective surgery for adolescent idiopathic scoliosis: Evaluation of 354 consecutive cases

Background:

Multimodal intraoperative neuromonitoring is recommended during corrective spinal surgery, and has been widely used in surgery for spinal deformity with successful outcomes. Despite successful outcomes of corrective surgery due to increased safety of the patients with the usage of spinal cord monitoring in many large spine centers, this modality has not yet achieved widespread popularity. We report the analysis of prospectively collected intraoperative neurophysiological monitoring data of 354 consecutive patients undergoing corrective surgery for adolescent idiopathic scoliosis (AIS) to establish the efficacy of multimodal neuromonitoring and to evaluate comparative sensitivity and specificity.

Materials and Methods:

The study group consisted of 354 (female = 309; male = 45) patients undergoing spinal deformity corrective surgery between 2004 and 2008. Patients were monitored using electrophysiological methods including somatosensory-evoked potentials and motor-evoked potentials simultaneously.

Results:

Mean age of patients was 13.6 years (±2.3 years). The operative procedures involved were instrumented fusion of the thoracic/lumbar/both curves, Baseline somatosensory-evoked potentials (SSEP) and neurogenic motor-evoked potentials (NMEP) were recorded successfully in all cases. Thirteen cases expressed significant alert to prompt reversal of intervention. All these 13 cases with significant alert had detectable NMEP alerts, whereas significant SSEP alert was detected in 8 cases. Two patients awoke with new neurological deficit (0.56%) and had significant intraoperative SSEP + NMEP alerts. There were no false positives with SSEP (high specificity) but 5 patients with false negatives with SSEP (38%) reduced its sensitivity. There was no false negative with NMEP but 2 of 13 cases were false positive with NMEP (15%). The specificity of SSEP (100%) is higher than NMEP (96%); however, the sensitivity of NMEP (100%) is far better than SSEP (51%). Due to these results, the overall sensitivity, specificity and positive predictive value of combined multimodality neuromonitoring in this adult deformity series was 100, 98.5 and 85%, respectively.

Conclusion:

Neurogenic motor-evoked potential (NMEP) monitoring appears to be superior to conventional SSEP monitoring for identifying evolving spinal cord injury. Used in conjunction, the sensitivity and specificity of combined neuromonitoring may reach up to 100%. Multimodality monitoring with SSEP + NMEP should be the standard of care.     

Monitoring evoked potentials during spinal surgery in one institution

Purpose

To review the experience of one tertiary care institution with somatosensory evoked potential (SSEP) monitoring during spinal surgery in order to assess the ability to monitor and predict neurological outcome effectively.

Methods

Records of all patients undergoing spinal surgery during 18 mo were retrospectively reviewed. Information from the patient chart included preoperative neurological status, surgical procedure, anaesthetic management, and postoperative neurological outcome. Information regarding the techniques used and interpretation of all SSEP tracings were obtained from evoked potential data sheets completed for each patient. The incidences of clinically important SSEP changes and new postoperative neurological deficits were analysed.

Results

Somatosensory evoked potential monitoringof the lower and upper extremities with non invasive techniques was used in 309 patients undergoing surgery on the cervical (88), thoracic (52), and lumbar spine (169). Thirty seven patients (11%) did not have suitable tracings for interpretation and 17 (5.5%) had baseline tracings described as poor. An intraoperative SSEP change occurred in 16 patients (6%) with SSEP and seven (2.6%) had a new neurological deficit postoperatively. Three persistent deficits were predicted by permanent SSEP change, and one transient deficit by a transient SSEP change. False positive results occurred in 12 patients (4.4%) and false negative results occurred in three (1.1%), with a sensitivity of 57% and a specificity of 95%. The incidence of SSEP changes was greater in the thoracic (18%) than in the cervical (1.2%) or lumbar (5.4%) groups (P < 0.05).

Conclusion

Effective SSEP monitoring was possible despite the many factors which may have interfered with monitoring. More improvements in the techniques and conditions of monitoring are needed to decrease the incidence of false positive and negative results.     

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.     

Studies on motor action potentials following transcranial stimulation and somatosensory evoked potentials including absolute refractory time in experimental spinal cord injury

The motor action potential (MAP) following transcranial stimulation and absolute refractory time (ART) in somatosensory evoked potential (SSEP) were investigated after experimental spinal cord injuries in rabbits. The thoracic cords were injured at the level of the 11th vertebrae by Allen's method. The paralysis after the trauma was classified into 4 groups depend on its severity; severe, mild, transient and non palsy group. A single transcranial stimulation evoked the double MAPs (MAP1 and MAP2) which were characteristic for the palsy groups. The amplitude of the MAP1 was greater than MAP2 in the transient palsy group, while that of the MAP1 was lower than MAP2 in both severe and mild palsy groups. The amplitude of the MAP was significantly reduced in all injured animals. There was no correlation between the amplitude or latency of the SSEP and the severity of the palsy. However, the ART of the SSEP was considerably prolonged in all injured animals regardless of the severity of the palsy.     

The contribution of the dorsal and ventral roots of the tibial nerve in the propagation of the spinal somatosensory evoked potential in cats

This study employed selective unilateral dorsal and ventral rhizotomy to examine the contribution of both the dorsal and ventral roots of the tibial nerve in the induction of the spinal somatosensory evoked potential (SSEP) in the cat. The spinal roots of origin of the tibial nerve in the cat were determined by retrograde transport of horseradish peroxidase (HRP). Spinal roots L6, L7, and S1 were found to give rise to the cat tibial nerve. Physiologic monitoring showed that the dorsal roots at these levels primarily contribute to the induction of the SSEP, but the ventral roots also make a small contribution. Because bilateral tibial nerve stimulation was found to mask a root injury on one side, we recommend sequential unilateral peripheral nerve stimulation when using SSEP during operations on the spine.     

Use of somatosensory evoked potentials to detect peripheral ischemia and potential injury resulting from positioning of the surgical patient: case reports and discussion.

BACKGROUND: Somatosensory evoked potentials (SSEPs) have long been recognized as an excellent tool for detecting neural and vascular compromise during vascular, neurosurgical and orthopedic procedures. SSEPs have the ability to localize, central versus peripheral, the area of compromise. Many surgeons use only lower-limb SSEP monitoring when performing lumbar spinal surgery. The upper extremities are usually not monitored during such procedures, and monitoring oxygen saturation does not detect neural compromise. PURPOSE: To report that the expanded use of SSEP monitoring during surgery can be beneficial in detecting peripheral ischemia or neural compromise resulting from positioning. STUDY DESIGN: Three case reviews of orthopedic spine surgeries where SSEP monitoring provided early warnings of vascular and neural compression. METHODS: The cases review three different lumbar procedures in which evidence of peripheral ischemia and nerve compression were detected by SSEP monitoring. RESULTS: By the use of upper- and lower-extremity monitoring during lumbar procedures, early detection of ischemia and nerve compression were noted intraoperatively. These changes prompted examination of the patient and repositioning to correct the ischemia or compression. The repositioning in these cases corrected the problem, and no lasting effects were found. CONCLUSIONS: Including SSEP monitoring of the bilateral upper extremities should be considered during lumbar spinal procedures. Such monitoring can be offered for a slightly increased expense and only minimal time delay to place the additional required electrodes by the technician. As a direct result of the early warning of the SSEP monitoring, we were able to avoid potential ischemic injuries and improve patient outcomes.     

Effect of graded hypoxia on cortical and spinal somatosensory evoked potentials.

Cortical somatosensory evoked potential (CSEP), spinal somatosensory evoked potential (SSEP), and electroencephalogram were recorded in rats under pentobarbital anesthesia. After baseline recordings in room air (21% O2), animals were subjected to a graded hypoxia at 15.75%, 10.5%, and 5.25% oxygen levels for 10 minutes. Each level of hypoxia was followed by a 15-minute reoxygenation period. With a moderate hypoxia (15.75% O2), measured latencies for the CSEP and the SSEP were not significantly different compared with baseline (p greater than 0.05). The CSEP amplitude showed a significant increase (p = 0.02) during reoxygenation after the moderate hypoxia. Change in the latency or amplitude of SSEP at 15.75% hypoxia or during the reoxygenation period was not significant compared with the room air (p greater than 0.05). No change in the electroencephalogram was noticed with the moderate hypoxia. At severe hypoxia (10.5% O2), 80% of the animals lost CSEP within 2 minutes. The loss of CSEP was concomitant with significant attenuation of the electroencephalogram waves. The SSEP was resistant to the severe hypoxia and was present in all animals. We concluded that hypoxia affects CSEP with the tendency to increase the amplitude at moderate hypoxia (15.75%) and loss of the latency and amplitude with severe (10.5%) and extreme (5.25%) hypoxia.