Somatosensory evoked potentials during spinal angiography and therapeutic transvascular embolization

Somatosensory evoked potentials (SEP's) were monitored during 42 angiographic examinations and 33 therapeutic embolization procedures in 41 patients. The SEP amplitude decreased in 36 of the 42 angiographic techniques, but recovered to baseline within 2 to 4 minutes in all but one case. Angiographic opacification of the anterior spinal artery reduced SEP amplitude in all but two patients, who had lost their proprioceptive sense and had no recognizable SEP prior to the procedure. No neurological complications resulted from any of the angiography procedures. Of the 33 embolizations, 15 were performed in 12 patients with arteriovenous malformations (AVM's) and 18 in 17 patients with spinal canal tumors. There was only one complication associated with embolization: that occurred in a patient with an intramedullary spinal cord AVM. Monitoring SEP amplitude in this series of patients provided a means of rapidly and reliably identifying the anterior spinal artery, served to assess the potential risk of contemplated steps in embolization, and aided in the execution of the angiographic procedures.     

Evoked potentials in the investigation of traumatic lesions of the peripheral nerve and the brachial plexus

Nerve conduction studies using nerve action potential (NAP), sensory nerve action potential (SNAP), evoked muscle action potential (M-response), retrograde conduction in the motor axon (F-response), and cortical and subcortical somatosensory evoked potential (SEP) are useful tools for evaluation of the peripheral nervous system. SEP recording has the advantages of being applicable to severely damaged nerves because of its amplification mechanism and of disclosing proximal root lesions that would not be disclosed by other methods. When SEP recording is used in an operating theater, the amplification mechanism is suppressed by the effect of the anesthetic. Nevertheless, it is valuable for evaluating proximal root lesions in conjunction with NAP recording and M-response. Strong M-response of the serratus anterior and paraspinal muscles is a most encouraging finding if nerve repair is performed more than seven days after brachial plexus injury. SEP recording can clarify the functional continuity of the spinal root to the spinal cord. Thus the presence of SEPs becomes an important positive finding and implies the potential of nerve repair even when an M-response is not provoked by a situation such as prolonged conduction block.     

300例截瘫的体感诱发电位检查

对唐山市１９７６年地震所致的截瘫伤员，随机抽样做体感诱发电位（ＳＥＰ）检查３００例，其中完全截瘫２０９例，不全截瘫９１例，共检查腓总神经和正中神经ＳＥＰ ６００侧，发现４１６侧完全性截瘫的ＳＥＰ全部消失，不全截瘫的１６６侧，５８％的ＳＥＰ存在。研究结果表明：不全截瘫病人ＳＥＰ消失与否与脊髓损伤平面以下的肌力状况无关，而深感觉则与ＳＥＰ的存在与消失显著相关。ＳＥＰ与足趾定位觉检查呈等级相关。ＳＥＰ不能直接反映急性脊髓损伤后运动功能是否良好，仅间接与脊髓的前索状况有关。本组根据９１幅异常ＳＥＰ图形，将其归纳为６种主要表现，并试图分析其发生基础及与临床的关系。急性脊髓损伤后ＳＥＰ消失多数预后不良，但在创伤初期确定其不恢复的最终时间仍有困难。     

Diagnostic and prognostic value of diaphragmatic electromyography and somatosensory evoked potentials in cervical spine and spinal cord injuries

SEP contribution to diagnosis is interesting but limited to hardly examined complete syndromes in an emergency care unit. The predictive value of SEP is high if electrophysiological data are correlated the 10th. day with the clinical status. A good prognostic value is shown when the clinical posterior column and pyramidal tract dysfunctions are equal in intensity and distribution, i.e. in complete syndromes or central spinal cord syndromes or Brown-Sequard's ones. However, not any correlation exists in cases of anterior spinal cord syndromes. Dg.EMG. is an easy, atraumatic useful tool for the clinician. It must be a systematic approach of the brain stem and cervical spinal cord phrenic centers vitality that may be involved by the trauma. When a respiratory deficiency occurs, it allows the diagnosis of a "peripheral" or "neurological" etiology. Its high prognostic value for m tor diaphragmatic function (increase or decrease) must be discussed before any therapeutic decision.     

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.     

Posterior spinal fusion complicated by posterior column injury. A case report of a false-negative wake-up test

A case is reported of an isolated posterior column injury secondary to direct mechanical trauma complicating a posterior spinal fusion. This case documents a rare complication of posterior spinal surgery. Intraoperative somatosensory-evoked potential (SEP) monitoring documented the injury whereas two intraoperative wake-up tests did not. This case demonstrates the value of intraoperative spinal cord monitoring in general. It also demonstrates the value of combining means to assess both anterior and posterior cord separately, intraoperatively. It is recommended that the wake-up test be used in conjunction with SEPs intraoperatively.     

Reconstructive surgery in 59-year-old patient with coarctation of aorta under the monitoring of somatosensory evoked potential and spinal cord perfusion pressure]

Postoperative paraplegia is a relatively rare complication in reconstructive surgery for coarctation of the aorta and the operative treatment is usually performed without any adjuncts. A 59-year-old male patient underwent replacement of descending thoracic aorta with vascular prosthesis under the monitoring of SEP and spinal cord perfusion pressure (SCPP) [pressure difference between mean distal aortic pressure (MDAP) and the cerebrospinal fluid pressure (CSFP)]. During cross-clamping of the aorta, MDAP decreased from 61 to 40 mmHg and CSFP increased from 6 to 15 mmHg, SCPP was 25 mmHg, and the amplitude of the SEP waves rapidly decreased. As the ischemic changes of spinal cord were suspected, the aortic cross-clamping was released. The amplitude of SEP recovered to the preoperative level immediately after de-clamping. In order to prevent spinal cord ischemia, the partial cardio-pulmonary bypass was employed, and SCPP was maintained above 60 mmHg, so that SEP did not show any ischemic changes during cross-clamping of the aorta. The patient did not develop any neurological deficit postoperatively. The monitoring of SEP and SCPP appears to be useful for prevention of postoperative paraplegia in the surgical treatment for coarctation of the aorta.     

Change pattern of somatosensory-evoked potentials after occlusion of segmental vessels: possible indicator for spinal cord ischemia

Paraplegia was reported after occlusion of the segmental vessels during anterior spinal surgery. The aim of this study was to investigate the effect of occlusion of the segmental vessels on the somatosensory-evoked potential (SEP) monitoring and analyze its potential risk for cord ischemia. Thirty-one patients with thoracic scoliosis underwent anterior spinal surgery. T₅–T₁₁ segmental vessels on the convexity were occluded with microvascular clamps at the point 2 cm from the intravertebra foramen. The SEPs were recorded 5 min before occlusion and 2, 7, 12 and 17 min after occlusion. The SEPs were analyzed with two indices i.e. P40 latency and P40 amplitude. All SEP waveforms recorded during the test were regular and recognizable. Compared to 5 min before occlusion, the P40 latencies at 2 min and 7 min after occlusion significantly increased 3.39% and 2.76% on an average, the P40 amplitudes at 2 min after occlusion significantly declined 26% (peak to peak) or 22% (peak to baseline) on an average (P<0.05). But the changes of SEPs were temporary. The SEPs began to restore at 12 min after occlusion and returned to the pre-occlusion level at 17 min after occlusion. No neurologic complications occurred in all patients after surgery. These results suggest that SEP is a possible indicator for ischemia of the spinal cord which is a dynamic course and cannot be considered an all-or–none phenomenon. Without the factors such as developmental deformities of the spinal cord, vascular variation and potential cord ischemia, occlusion of the segmental vessels would be safe during the anterior spinal surgery.     

Intra-operative spinal cord monitoring during surgery for scoliosis using somatosensory evoked potentials

The method of intra-operative monitoring of spinal cord function by spinal somatosensory evoked potentials (SEP), as used at the Royal Alexandra Hospital for Children during surgery for scoliosis is described. Using a non-polarisable platinum spinal epidural electrode, SEP elicited by tibial and peroneal nerve stimulation in the popliteal fossa are recorded proximal to the level of spinal correction. The large amplitude and discrete waveform of the SEP enable rapid signal acquisition and easy interpretation. The spinal SEP is stable under both therapeutic hypotension and general anaesthesia. Electrophysiological monitoring has now superceded the 'wake-up' test as an index of spinal cord function during corrective surgery for scoliosis.     

Intra-operative recording of cortical somatosensory evoked potentials as a method of spinal cord monitoring during spinal surgery

The experience with cortical somatosensory evoked potential (SEP) recording during 13 cases of spinal neurological surgery is described. Good quality cortical SEPs were obtained in eight patients with a variety of intradural and extradural spinal disorders. The short latency components of these waveforms were stable during anaesthesia with nitrous oxide, 0.5% halothane and fentanyl. Fluctuations in signal amplitude were, however, common. In the one patient in whom the cortical SEP waveform was distorted intra-operatively, there was an increased neurological deficit. In one normal and four patients with impairment of dorsal column function, no intra-operative cortical SEP was recorded. In these five patients spinal SEPs were recorded rostral to the level of spinal disease. Monitoring spinal cord function using cortical SEPs can provide useful neurophysiological information, however, there are limitations to its utility. These relate to difficulties in signal acquisition, the low signal amplitude, attenuation of the signal during intramedullary surgery and uncertainties in signal interpretation. All these problems are exacerbated if the patient has a pre-operative clinical somatosensory deficit. Although most of these problems can be overcome using spinal SEP monitoring, intra-operative SEP recordings are not an infallible guide to spinal cord integrity since they reflect the functional status of only the dorsal column-medial lemniscus pathway.     

Motor evoked potential in cats with acute spinal cord injury

We have previously reported that a motor evoked potential (MEP) can be produced by transcranial stimulation of the motor cortex in cats and humans. This signal travels in both dorsolateral and ventral spinal cord. We report here the evaluation of this evoked potential in comparison to the somatosensory evoked potential (SEP) in an acute spinal cord weight drop model. In all animals, the peripheral nerve signal was the component of the MEP most sensitive to injury. Often, it was significantly reduced in amplitude by incidental manipulation of the spinal cord during a careful laminectomy and then returned. It was lost first in animals with weight drop spinal cord injury and was abolished with as little as 50 to 75 g/cm of force. The spinal cord signal of the MEP was consistently more sensitive to injury than the SEP and was abolished at about 100 to 150 g/cm of impact. The cortical SEP was abolished at about 200 to 250 g/cm, and the spinal cord SEP was abolished at similar levels. The SEP returned earlier after injury than the MEP. Anesthetic agents had an effect on the MEP in the spinal cord and substantially changed the peripheral nerve signal, in both wave form shape and optimal stimulation frequency. Marginal cord injury and abnormal metabolic conditions caused the peripheral nerve signal to decrement in amplitude with increasing trial numbers during a run and become unstable. These latter effects need further characterization and are critical guides to investigative and clinical use of this test. This study indicates that the MEP is more sensitive than the SEP in detecting spinal cord injury.     

脊髓急性牵拉损伤动物模型机理研究

目的对犬脊髓(神经根)急性牵拉损伤的病理机制进行初步探讨。方法12只健康成年杂种犬，随机分为对照组和不同程度牵拉损伤组。前后路联合手术离断脊柱后施加纵向牵拉损伤，对牵拉应变率、体感诱发电位(SEP)、神经源性脊髓运动诱发电位(NMEP)、硬膜下压力(SP)、硬膜血流量(EBF)等进行持续观察。伤后取脊髓及神经根标本进行HE、髓鞘神经中丝(NF)及胶原纤维酸性蛋白(GFAP)抗体免疫组织化学染色及电镜超微结构观察。结果牵拉损伤涉及牵拉节段和其上下脊髓及神经根的损伤。牵拉后出现硬膜下压力的显著增高和硬膜血流的显著降低。SEP异常的出现较NMEP更早。结论牵拉后脊髓内压力的增加导致脊髓血流减少。以及直接的机械性牵拉损伤可能是脊髓牵拉损伤的重要机制。     

Spinal cord monitoring during surgery by direct recording of somatosensory evoked potentials. Technical note

A simple method of spinal cord monitoring that can be readily used during surgery for spinal disorders in children or adults is described. A spinal subdural recording electrode is placed rostral to the site of surgery and the peroneal nerve is stimulated in the popliteal fossa; in this way, large-amplitude polyphasic spinal somatosensory evoked potentials (SEP's) can be directly recorded. The large amplitude of the spinal SEP's recorded intrathecally facilitates spinal cord monitoring by allowing: 1) rapid acquisition of the evoked response, which provides continuous monitoring during surgery; 2) relatively easy interpretation of the signal, there being no significant ultrashort- or long-latency components to the waveform; and 3) signal acquisition in an electrical environment that would be unacceptable using standard methods of spinal and cortical SEP recording.     

Clinical evaluation of spinal cord monitoring in scoliosis surgery

The somatosensory evoked potential (SEP) is a technique that can be used to monitor sensory conduction within the spinal cord throughout the course of spinal surgery. The authors describe the technique, stimulation, and recording parameters, which most critically affect the success and reliability of monitoring trials. In addition, we show that in all 40 patients tested fully, the SEP results were in complete agreement with the clinical findings at the time of the wake-up test. In this series, there was no instance of a "false-positive" SEP result, or of the SEP failing to detect neural damage. Temporary, neurologic deficit occurred on two occasions, which are described in detail. These show that the SEP is rapid, enables neurologic complications to be detected at an early stage of surgery, and can identify lateralized problems. It is concluded that the technique may provide a clinically valuable method for continuous and prolonged monitoring of spinal cord function.     

应用皮层体感诱发电位监测全麻下颈椎脱位颅骨牵引复位

目的 应用皮层体感诱发电位技术,观察颈椎脱位颅骨牵引复位过程中患者脊髓功能的改变,避免因过度牵引造成脊髓损伤. 方法 2004年6月至2006年10月12例颈椎脱位患者在全身麻醉下行颅骨牵引复位前路植骨融合内固定术,术中进行皮层体感诱发电位监测.观察皮层电位潜伏期及波幅变化.牵引重量从5kg开始,每间隔5～10 min增加重量2.5 kg直至复位成功.牵引重量5～20 kg,平均13.5 kg.在牵引前(麻醉后)、牵引过程中,复位后进行皮层体感诱发电位监测.将电位信号分为改善[波幅增加50%和(或)潜伏期缩短10%]、异常[波幅下降50%和(或)潜伏期延长10%]无变化. 结果 牵引复位过程中10例患者皮层电位潜伏期、波幅改善,且临床复位效果满意;2例曾出现皮层电位波幅下降50,波形改变,立即减轻重量,改变体位,5 min后波形、波幅恢复.12例患者术后神经损害均未加重.8例患者获得3～6个月随访,按照ASIA法分类,转变情况为:术前B级4例,术后转成C级2例,2例无变化;术前C级2例,术后1例无变化,1例失访;术前D级4例,3例转成E级,1例失访.8例中有3例于术后6个月复查体感诱发电位,皮层电位潜伏期缩短,其中2例恢复至正常标准,波幅、波形改善. 结论 应用皮层体感诱发电位监测颈椎脱位颅骨牵引复位前路植骨融合内固定治疗,避免了过度牵引可能带来的脊髓损伤问题,具有重要的临床意义.     

Prevention of Ischemic Spinal Cord Injury Following Aortic Cross-Clamping: Use of Corticosteroids

Prior to proximal aortic cross-clamping, baseline measurements of spinal cord blood flow and function were done. Blood flow was evaluated with radioactive microspheres and function determined by assessment of somatosensory evoked potential (SEP). Group 1 (N = 6) animals had aortic cross-clamping for 5 minutes after ischemic spinal cord dysfunction (SEP loss) was documented. Group 2 (N = 9) underwent aortic cross-clamping for 10 minutes after loss of SEP. Group 3 (N = 6) also underwent 10 minutes of cross-clamping after initial SEP loss, but were treated intravenously with methylprednisolone (30 mg per kilogram of body weight) 10 minutes prior to cross-clamping and again 4 hours postoperatively. After release of the cross-clamp, the animals were allowed to recover and serial evaluations of spinal cord blood flow and neurological status were carried out for seven days. Group 1 animals recovered uneventfully without evidence of neurological injury. Group 2 animals sustained a 67% incidence of permanent spastic paraplegia (p = 0.02 versus Group 1). In contrast, methylprednisolone-treated animals sustained no clinically detectable neurological injury (p = 0.02 versus Group 2). Measurements of spinal cord blood flow at the time of SEP loss revealed similar degrees of spinal cord ischemia in all groups. No significant differences were observed in the duration of aortic cross-clamping prior to SEP loss among the three groups. The data indicate that short periods of cross-clamping (5 minutes) following SEP loss are well tolerated, whereas longer periods (10 minutes) are associated with a high incidence of paraplegia. This injury can be prevented if an adequate dose of methylprednisolone is given before and after cross-clamping. Beneficial effects of steroid administration do not appear to be related to changes in spinal cord blood flow, but may be related to protective effects on cellular and subcellular components. Clinical investigations employing this regimen of corticosteroid protection during surgical procedures on the thoracoabdominal aorta appear to be indicated.     

Comparison of the Interference Effects on Somatosensory Evoked Potential from Tonic,Burst, and High-dose Spinal Cord Stimulations

Spinal cord stimulations have been used widely to treat intractable neuropathic pain. The conventional spinal cord stimulation paradigm, the “tonic” type, suppresses excessive activation of wide dynamic range neurons in the dorsal horn via the collateral branch from the dorsal column. Therefore, preserved dorsal column function is an important prerequisite for tonic spinal cord stimulations. A tonic spinal cord stimulation requires eliciting paresthesia in the painful area due to stimulation of the dorsal column and dorsal root. Recent spinal cord stimulation paradigms, including burst and high-dose, are set below the paresthesia threshold and are proposed to have different pain reduction mechanisms. We conducted an interference study of these different stimulation paradigms on the somatosensory evoked potential (SEP) to investigate differences in the sites of action between tonic and new spinal cord stimulations. We recorded posterior tibial nerve-stimulated SEP in seven patients with neuropathic pain during tonic, burst, and high-dose stimulations. The total electrical energy delivered was calculated during SEP-spinal cord stimulation interference studies. High-dose stimulations could not reduce the SEP amplitude despite higher energy delivery than tonic stimulation. Burst stimulation with an energy similar to the tonic stimulation could not reduce SEP amplitude as tonic stimulation. The study results suggested different sites of action and effects on the spinal cord between the conventional tonic and burst or high-dose spinal cord stimulations.     

躯体感觉诱发电位在脊柱手术监护中的应用

目的 探讨躯体感觉诱发电位（SEP）在脊柱手术监护中的应用价值。方法 分析４５８例脊柱手术中SEP监护的结果,特征,适用范围,其中颈部手术275例,胸椎,腰椎部手术183例,刺激电极为手指、足趾的环状电极或腕、踝的表面电极,记录电极为头皮针电极。结果 大部分患者的肌电图改变在器质性改变的范围内。409例（89．3％）,术中SEP有波幅轻度下降,潜伏期轻度延长,术后又恢复后近手术开始时水平;32例（7．1％）,SEP波幅有一定程度的提高,潜伏期部分缩短;12例（2．6％）有术中SEP明显恢复;2例（0．4％）术中未见SEP明显改变,术后有功能障碍;3例（0．7％）,术中出现SEP的波幅明显下降,潜伏期轻度延长,术持恢复欠佳。结论 SEP在脊柱手术监护中的作用是肯定的,但有一定的局限性。     

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.     

体感诱发电位在椎体后凸成形术中的脊髓监测

目的探讨体感诱发电位（SEP）在椎体后凸成形术（PKP）中的脊髓监测作用。方法33例46个椎体行PKP,术中均予SEP监护。结果46个椎体疼痛均好转,椎体复位良好,2例出现波幅降低,1例出现潜伏期延长,无重大并发症。结论SEP在PKP中对脊髓有良好的监测作用。