Failure of motor evoked potentials to predict neurologic outcome in experimental thoracic aortic occlusion

Motor evoked potential monitoring was tested as an alternative to somatosensory evoked potential monitoring in evaluating spinal cord function during thoracic aortic occlusion in dogs. Twenty-seven animals underwent 60 minutes of cross-clamping of the proximal descending thoracic aorta with (n = 18) or without (n = 9) cerebrospinal fluid drainage. Spinal cord blood flow was measured with microspheres, and neurologic outcome was evaluated at 24 hours with Tarlov's scoring system. Cerebrospinal fluid drainage improved neurologic outcome (p less than 0.05). Motor evoked potentials recorded over the lumbar spinal cord were lost in 9 of 20 dogs with ischemic cord injury and were not lost in any of the 7 dogs that were neurologically normal. Somatosensory evoked potential were lost in 19 of 20 paraplegic/paraparetic dogs and lost in 3 of 7 normal dogs (p less than 0.01). After reperfusion, motor evoked potentials returned in all nine neurologically injured dogs that lost the potentials and were still present at 24 hours. Changes in amplitude, latency, or time until loss or return of motor evoked potentials or somatosensory evoked potentials did not predict neurologic injury. Loss of somatosensory evoked potentials had a high sensitivity (95%) but had low specificity (67%) because of peripheral nerve ischemia. Loss of motor evoked potentials recorded from the spinal cord had high specificity (100%) but a low sensitivity (46%) and was therefore not a reliable predictor of neurologic injury. Return of motor evoked potentials during reperfusion did not correlate with functional recovery. Motor evoked potentials stimulated in the cortex and recorded from the spinal cord had low overall accuracy (59%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Intraoperative spinal somatosensory evoked potential monitoring

The relationship of intraoperative monitoring of spinal cord somatosensory evoked potentials and postoperative deficit in 220 cases (121 with scoliosis, 41 with neoplasms, and 58 others) is reported. Bilateral posterior tibial nerve stimulation was used in 181 cases and unilateral median nerve stimulation in 39. Spinal cord (interspinous ligament needles), subcortical (neck surface), and cortical (scalp surface) SEP's were monitored. Seven patients had worsening of neurological function after surgery, three of whom demonstrated significant changes in SEP's monitored. In an additional four cases, there was more than a 50% decrease in amplitude of subcortical/cortical SEP's during monitoring, but no change in neurological status postoperatively. Combined monitoring of spinal cord, subcortical, and cortical SEP's enhanced the certainty of detecting spinal cord dysfunction even though there was a significant number of false-negative and false-positive results. A marked change in the SEP's indicated a high chance of developing a neurological deficit (three or 43% of seven cases), and if there was no change the chance of any neurological postoperative deficit was extremely low (four or 1.87% of 213 cases). These data justify the use of intraoperative SEP monitoring.     

Intraoperative somatosensory evoked potential monitoring in achondroplasia

Surgical airway intervention in children with achondroplastic dwarfism poses potential neurological risk secondary to the neck manipulation required for tracheal intubation and operative head positioning. This is particularly true of achondroplastic dwarfs with radiographically documented foramen magnum and spinal canal stenosis. In these children, upper extremity somatosensory evoked potential monitoring establishes the integrity of sensory conduction from peripheral nerve to cortex, providing intraoperative notification of neurologically significant cervicomedullary compression during laryngoscopy and surgical positioning.     

Thoracic and thoracoabdominal aortic aneurysm repair: Use of evoked potential monitoring in 118 patients

PURPOSE: Paraplegia is the most dreaded and severe complication of surgery on the descending thoracic aorta (TAA) and thoracoabdominal aorta (TAAA). The functional integrity of the spinal cord can be monitored by means of intraoperative recording of myogenic-evoked responses after transcranial electrical stimulation (tcMEP) and somatosensory-evoked potential (SEP) monitoring. In this study, we evaluated the results of evoked potential monitoring and the adequacy of the strategy followed. METHOD: The spinal cord of 118 patients (78 men; age, 65 +/- 12 years; 79 TAAAs, 39 TAAs) undergoing surgery on the TAA or TAAA was monitored with tcMEP and SEP. Spinal cord protection was achieved by means of a multimodality approach: moderate hypothermia (32 degrees C rectal temperature), continuous cerebrospinal fluid drainage to keep the pressure less than 10 mm Hg, reimplantation of intercostal arteries, left ventricular bypass grafting, and staged clamping. In the case of evoked potential changes more than 50% of baseline, the strategy was adjusted: reattachment of more segmental arteries when technically feasible, higher distal and proximal perfusion pressures, and enhanced cerebrospinal fluid drainage. RESULTS: Forty-two of 118 patients (35.6%) had a more than 50% of baseline tcMEP reduction during cross-clamping. At this point, only 5 of those 42 cases were also associated with SEP reduction of more than 50% of baseline. On the basis of the tcMEP findings, the strategy was adjusted. Five patients had postoperative paraplegia (4.2%). CONCLUSION: tcMEP monitoring seems to be a useful adjunct of the protective techniques and may cause substantial adjustments in strategy, reducing the incidence of postoperative paraplegia.     

Intraoperative somatosensory evoked potential monitoring in scoliosis

During surgical correction of scoliosis, 63 patients had somatosensory evoked potential (SEP) monitoring of the spinal cord. Tibial nerves were unilaterally stimulated, and the potentials were recorded from the midcervical spine with surface and epidural needle electrodes. Over 85% had no significant change in their SEP and no postoperative neurologic deficits. Eleven percent had a significant change in their potential (amplitude decrease of greater than 60% and/or latency increase of greater than 2.5 msec) with no neurologic complications. One patient had a significant potential change and temporary postoperative sensory deficits did occur. One additional patient experienced postoperative neurologic complications but had no SEP change. This single false negative case, however, was clinically significant only for motor dysfunction, which is not monitored by the SEP. When changes in patient core temperature were compared to changes in SEP amplitude and latency, an intraoperative decrease in core temperature increased SEP latency and decreased amplitude, which may explain in part the false positive rate of the procedure.     

Intraoperative somatosensory evoked potential monitoring of the sciatic nerve: an animal model.

Sciatic, peroneal, and tibial nerves were isolated in 18 hind limbs in 10 adult mongrel cats. A pair of needle electrodes was used to stimulate both divisions of the sciatic nerve individually at the level of the popliteal fossa. The sciatic nerve was injured by complete or partial transection, crush, and controlled compression. Motor function was correlated with intraoperative cortical somatosensory evoked potential and spinal somatosensory evoked potential tracings. We observed that significant changes in the waveforms of cortical somatosensory evoked potential and spinal somatosensory evoked potential tracings immediately precede postoperative peripheral nerve deficits, and that loss of motor function may be avoided by immediate response to significant spinal somatosensory evoked potential and cortical somatosensory evoked potential waveform changes. A complete motor palsy can be created in one division of the sciatic nerve while normal tracings are being obtained in the other division of the nerve. Stimulating both divisions may result in a spinal somatosensory-evoked potential/cortical somatosensory evoked potential tracing that masks the deficit that is present in only one nerve division.     

脊柱侧凸术中皮层体感诱发电位(CSEP)监护的应用价值

近年来国内外在脊柱侧凸手术治疗方法及临床疗效方面取得了很大进展。但手术的安全性一直是影响手术疗效的最大隐患。一旦发生脊髓损伤,后果严重且不易恢复。自2000年4月~2005年6月我们对29例脊柱侧凸患者行术中皮层体感诱发电位监护,以提高手术的安全性,效果满意。1资料与方法1.1临床资料本组患者29例,男性10例,女性19例,平均年龄15.8岁(13~20岁)。其中特发性脊柱侧凸18例,先天性半椎体畸形8例,脊髓纵裂并脊柱侧凸1例,胸椎管内脂肪瘤并脊柱侧凸1例,Chiari畸形并脊柱侧凸1例。手术方式:后路楔形截骨、矫形内固定术15例;单纯后路矫形内固定…     

The impact of distal aortic perfusion and somatosensory evoked potential monitoring on prevention of paraplegia after aortic aneurysm operation

Temporary distal aortic perfusion and somatosensory evoked potential monitoring were attempted prospectively in 198 patients to prevent neurologic complications from occurring after operation for descending thoracic and thoracoabdominal aortic aneurysm. These 198 patients were divided into two groups. Group 1 consisted of 99 (50%) patients in whom adequate (60 mm Hg) distal bypass was achieved and combined with somatosensory evoked potential monitoring. Group 2 consisted of 99 (50%) in whom this could not be achieved. Of the latter, four patients were excluded because of operative death in one and preexisting neurologic deficits in three. The rates of early and delayed neurologic complications were 8% and 12%, respectively, in the former and 7% and 8%, respectively, in the latter. Using the logistic regression method of statistical analysis, adjusting for the difference in patient mix, we found no statistical difference in the incidence of neurologic complications in the two groups. The incidence of false negative somatosensory evoked potential response was 13% and false positive response 67%. Localization of critical spinal arteries for reattachment was not possible. Thus, the method had no significant impact upon the prevention of neurologic deficits, which varied from mild or transient to severe and which either occurred during the operation or were delayed from 12 hours to 21 days.     

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.     

Transcranial Doppler sonography and somatosensory evoked potential monitoring in carotid surgery

Ninety-seven patients undergoing 103 carotid operations were studied intraoperatively using somatosensory evoked potentials after median nerve stimulation (SEP) and transcranial Doppler sonography (TCD). SEP were recorded from the scalp (C3'-Fz or C4'-Fz) and from the second cervical vertebra. The amplitude of the primary cortical response (N20P25) was measured peak-to-peak. Central conduction time (CCT) resulted from the difference between the first negative cortical (N20) and cervical (N14) response. TCD was performed using a pulsed 2-MHz-Doppler device to record the mean blood flow velocity of the middle cerebral artery (Vm-MCA) transtemporally. TCD and SEP variables were registered prior to and after carotid clamping, at short intervals during the clamping period, and after declamping. Critical SEP alterations (N20P25 less than 50% and/or CCT greater than 20% compared to the preceding values) were regarded as significant indicators of cerebral ischaemia, and selective intraluminal shunting was generally based on SEP criteria. The incidence of critical SEP changes was compared to Vm-MCA reductions greater than 60% using the Chi2-test. With SEP always recordable, additional TCD monitoring was possible in only 78 patients in our series for technical or anatomical reasons. Vm-MCA reductions greater than 60% were associated with critical SEP alterations in six cases. In five patients, Vm-MCA was reduced greater than 60% without relevant SEP changes, whereas one patient with critical SEP findings had only a minor Vm-MCA reduction (33%). In the remaining 66 cases, carotid clamping was tolerated without critical SEP changes associated with Vm-MCA reductions not exceeding 60%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Continuous monitoring of short-latency somatosensory evoked potentials during cardiac and aortic surgery

The effectiveness of monitoring somatosensory evoked potentials (SEPs) intraoperatively to detect brain damage early remains controversial. To assess the diagnostic accuracy of this modality, a study was conducted between 1991 and 1994, recording SEPs in 287 consecutive patients undergoing cardiac and aortic surgery using cardiopulmonary bypass (CPB) with moderate hypothermia or deep hypothermic circulatory arrest. From P1 to N2 of the SEPs occurring within 50 ms latency in response to electrical stimulation of the median nerve were recorded over the contralateral postcentral cortex at 5-min intervals using a Neuropack-2 (Nihon Koden, Tokyo, Japan). Normal SEPs were recovered in 247 patients postoperatively; however, 2 of these patients had suffered a cerebral infarction and 1, a transient stroke intraoperatively, demonstrating a false-negative incidence of 1.2%. On the other hand, three different types of abnormal SEPs were recorded postoperatively. P1 and N1 absence, probably caused by a subcortical lesion, was observed in 4 patients; P2 and N2 absence, probably caused by a cortical lesion, was observed in 8 patients; and a flat SEP, representing diffuse damage, was observed in 2 patients. Among these 14 patients with abnormal SEPs, 7 showed no neurologic disturbance at all, demonstrating a false-positive incidence of 50%. Thus, we concluded that when normal SEPs are recovered during weaning from CPB, the incidence of brain damage could be predicted at below 5%. Conversely, when abnormal SEPs are demonstrated, the incidence of brain dysfunction impeding a return to active life is estimated to be about 70%.     

皮层下体感诱发电位监测脊柱侧凸手术的临床研究

目的：研究皮层下体感诱发电位对脊柱侧凸矫正手术监测的准确性,提高术中预防神经损伤的有效性。方法：对４１例脊柱侧凸患者于矫正术中采用皮层下体感诱发电位和皮层体感诱发电位监测脊髓功能。结果：皮层下体感诱发电位波形稳定可靠,很少受麻醉的影响;皮层体感诱发电位受麻醉影响较大,波幅几乎可消失。全组５例皮层下体感诱发电位出现异常,其中２例与临床相符,３例为假阳性;无假阴性发生。准确率为９２７％。结论：应用体感诱发电位术中监测脊髓功能,皮层下体感诱发电位是目前较理想的方法。     

Intraoperative somatosensory evoked potential monitoring of pelvic and acetabular fractures.

The efficacy of intraoperative somatosensory evoked potential (SSEP) monitoring was evaluated in the surgical management of 82 patients with pelvic and acetabular fractures. The injuries consisted of 45 acetabular fractures, 30 pelvic ring disruptions, and seven combined injuries. Preoperative neurological deficits were recorded in 34% of the study group (29% of those with an acetabular fracture and 47% of those with a pelvic ring injury). Three patients sustained an iatrogenic sciatic nerve injury during the study period (all of which were documented in the first 40 cases). Two patients sustained an exacerbation of an existing sciatic nerve injury. In the group of pelvic fractures, hazardous parts of the exposure, reduction, and fixation were identified by the SSEP monitoring. Removal of the provocative stimulus by the surgeon led to reversal of the SSEP abnormalities, and none of this group of patients sustained an iatrogenic injury. When the intraoperative SSEP changes were noted during an acetabular fracture fixation, immediate attempts were made to relieve the excessive tension on the sciatic nerve by replacing or removing a retractor, flexing the knee, extending the hip, or dividing the femoral insertion of the gluteus maximus. None of the SSEP changes were associated with the lacerative injury to the sciatic nerve. For the method to be clinically effective in reducing the incidence of neurological deficit, even subtle changes in the SSEP tracing must be recognized immediately by the neurophysiologist so that a corresponding corrective measure can be rapidly undertaken by the surgeon to remove the offending stimulus.     

Spinal somatosensory evoked potential monitoring during microsurgery for syringomyelia: case reports

Spinal cord function was monitored during surgery in 2 cases of syringomyelia. The intraoperative recording of spinal segmental and conduction potentials evoked at cervical levels by the stimulation of median and tibial nerves were essential in the definition of the extent of the lesion and was consistent with postoperative neurological outcome.     

皮层体感诱发电位监护在胸椎管狭窄症手术中的应用

目的：探讨皮层体感诱发电位（CSEP）监护在胸椎管狭窄症手术中的应用价值。方法：自2000年4月～2003年11月共有32例胸椎管狭窄症患者接受术中体感诱发电位监护，男21例，女11例，年龄38～75岁；其中单纯胸椎黄韧带骨化症13例，胸椎间盘突出症合并胸椎黄韧带骨化症10例，胸椎间盘突出症合并胸椎孤立后纵韧带骨化9例。单纯胸椎后路全椎板切除术4例，单纯后路全椎板截骨原位再植、椎管扩大减压术9例，全椎板截骨原位再植、环脊髓减压、椎管扩大减压成形术19例。术中均应用丹迪Key—Poim脊髓监护系统进行皮层体感诱发电位监护。结果：23例术中监护无异常，术后未出现神经系统并发症。其中12例患者术中即可见波形改善。4例术中出现波形异常，其中2例术后发生神经功能障碍。4例术中监护未见异常。术后症状加重，假阴性率12．5％。1例术中波形异常，但术后无脊髓损伤表现，假阳性率3.1％。结论：皮层体感诱发电位（CSEP）监护可及时发现术中危及脊髓的因素，但存在一定的假阳性或假阴性率。与其它监测方法合用可提高手术安全性。     

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.