Spinal cord evoked potential monitoring after spinal cord stimulation during surgery of spinal cord tumors

Integration of multiple prognostic predictors in a porcine spinal cord injury model: A further step closer to reality

Introduction

Spinal cord injury (SCI) is a devastating neurological disorder with an enormous impact on individual's life and society. A reliable and reproducible animal model of SCI is crucial to have a deeper understanding of SCI. We have developed a large-animal model of spinal cord compression injury (SCI) with integration of multiple prognostic factors that would have applications in humans.

Methods

Fourteen human-like sized pigs underwent compression at T8 by implantation of an inflatable balloon catheter. In addition to basic neurophysiological recording of somatosensory and motor evoked potentials, we introduced spine-to-spine evoked spinal cord potentials (SP-EPs) by direct stimulation and measured them just above and below the affected segment. A novel intraspinal pressure monitoring technique was utilized to measure the actual pressure on the cord. The gait and spinal MRI findings were assessed in each animal postoperatively to quantify the severity of injury.

Results

We found a strong negative correlation between the intensity of pressure applied to the spinal cord and the functional outcome (P < 0.0001). SP-EPs showed high sensitivity for real time monitoring of intraoperative cord damage. On MRI, the ratio of the high-intensity area to the cross-sectional of the cord was a good predictor of recovery (P < 0.0001).

Conclusion

Our balloon compression SCI model is reliable, predictable, and easy to implement. By integrating SP-EPs, cord pressure, and findings on MRI, we can build a real-time warning and prediction system for early detection of impending or iatrogenic SCI and improve outcomes.

Prediction of Post-operative Long-Term Outcome of the Motor Function by Multimodal Intraoperative Neuromonitoring With Transcranial Motor-Evoked Potential and Spinal Cord-Evoked Potential After Microsurgical Resection for Spinal Cord Tumors

Objective

To examine the effect of multimodal intraoperative neuromonitoring on the long-term outcome of motor function after microsurgical resection for spinal cord tumors.

Materials and Methods

Consecutive fourteen patients with spinal tumors who were surgically treated at the University of Fukui Hospital between 2009 and 2020 [M:F = 10:4, ages ranging from 22 to 83 years (mean ± SD = 58 ± 21 years)] were included in this study. There were eight intra-axial tumors and six extra-axial tumors. There were four patients with hypertension, two patients with diabetes mellitus, and four patients with hyperlipidemia. Three patients were under antithrombotic medication, two were under steroid medication, four were current smokers, and four were current drinkers. Manual muscle test (MMT) of the upper and lower extremities of the patients was examined before surgery, 2 weeks after surgery, and at the final follow-up. The mean follow-up period was 38 ± 37 months. McCormick scores were examined before surgery and at the final follow-up. Microsurgical resection of the tumor was underwent through the posterior approach under transcranial motor-evoked potential (TcMEP) monitoring. The MEP of 46 extremities was recorded during the surgery. Gross total resection was achieved in 13 of 14 surgeries. Spinal cord-evoked potential (Sp-SCEP) monitoring was performed in eight of 14 patients.

Results

The length of peritumoral edema was significantly longer in patients with deterioration of McCormick scores than in patients with preservation of McCormick scores (p = 0.0274). Sp-SCEP could not predict the deterioration. The ratio of MEP at the beginning of the surgery to that at the end of the surgery was the only significant negative factor that predicts deterioration of motor function of the extremity at the final follow-up (p = 0.0374, odds ratio [OR] 1.02E-05, 95% CI 9.13E+01–7.15E+18). A receiver operating characteristic (ROC) analysis revealed that the cutoff value of the ratio of MEP to predict the deterioration at the final follow-up was 0.23 (specificity 100%, specificity 88%, positive predictive value 100%, and negative predictive value 88%) to predict deterioration at the final follow-up.

Conclusions

Ratio MEP was the most significant negative factor to predict the deterioration of motor weakness at spinal tumor surgery. The setting of the cutoff value should be more strict as compared to the brain surgery and might be different depending on the institutions.

Intraoperative Spinal Cord Monitoring: Focusing on the Basic Knowledge of Orthopedic Spine Surgeon and Neurosurgeon as Members of a Team Performing Spine Surgery under Neuromonitoring

An intraoperative functional spinal cord monitoring system is a technology used by spine and spinal cord surgeons to perform a safe surgery and to gain further surgical proficiency. However, no existing clinical neurophysiological method used in the operating room can monitor all complex spinal cord functions. Therefore, by observing the activities of certain neural action potentials transferred via limited neural tissues, surgeons need to deductively estimate the function of the whole spinal cord. Thus, as the number of spinal cord functions that need to be observed increases, spinal cord monitoring can be more reliable. However, in some situations, critical decision-making is affected by the limited capability of these methods. Nevertheless, good teamwork enables sharing of seamless information within the team composed of a surgeon, anesthesiologist, monitoring technician and nurses greatly contributes to making quick and accurate decisions. The surgeon, who is the person in charge of the team, should communicate with multidisciplinary team members using common technical terms. For this reason, spine and spinal cord surgeons must have appropriate knowledge of the methods currently used, especially of their utility and limitations. To date, at least six electrophysiological methods are available for clinical utilization: three are used to monitor sensory-related tracts, and three are used to monitor motor-related spinal cord functions. If surgeons perform electrode setting, utilizing their expertise, then the range of available methods is broadened, and more meticulous intraoperative functional spinal cord monitoring can be carried out. Furthermore, if the team members share information effectively by utilizing a clinically feasible judicious checklist or tools, then spinal cord monitoring will be more reliable.

A new criterion for the alarm point for compound muscle action potentials

Object

The purpose of this study was to review the present criteria for the compound muscle action potential (CMAP) alert and for safe spinal surgery.

Methods

The authors conducted a retrospective study of 295 patients in whom spinal cord monitoring had been performed during spinal surgery. The waveforms observed during spinal surgery were divided into the following 4 grades: Grade 0, normal; Grade 1, amplitude decrease of 50% or more and latency delay of 10% or more; Grade 2, multiphase pattern; and Grade 3, loss of amplitude. Waveform grading, its relationship with postoperative motor deficit, and CMAP sensitivity and specificity were analyzed. Whenever any wave abnormality occurred, the surgeon was notified and the surgical procedures were temporarily suspended. If no improvements were seen, the surgery was terminated.

Results

Compound muscle action potential wave changes occurred in 38.6% of cases. With Grade 1 or 2 changes, no paresis was detected. Postoperative motor deficits were seen in 8 patients, all with Grade 3 waveform changes. Among the 287 patients without postoperative motor deficits, CMAP changes were not seen in 181, with a specificity of 63%. The false-positive rate was 37% (106 of 287). However, when a Grade 2 change was set as the alarm point, sensitivity was 100% and specificity was 79.4%. The false-positive rate was 20% (59 of 295).

Conclusions

Neither the Grade 1 nor the Grade 2 groups included patients who demonstrated a motor deficit. All pareses occurred in cases showing a Grade 3 change. Therefore, the authors propose a Grade 2 change (multiphasic waveform) as a new alarm point. With the application of this criterion, the false-positive rate can be reduced to 20%.

The value of intraoperative motor evoked potential monitoring during surgical intervention for thoracic idiopathic spinal cord herniation

OBJECT

Thoracic idiopathic spinal cord herniation (TISCH) is a rare neurological disorder characterized by an incarceration of the spinal cord at the site of a ventral dural defect. The disorder is associated with clinical signs of progressive thoracic myelopathy. Surgery can withhold the natural clinical course, but surgical repair of the dural defect bears a significant risk of additional postoperative motor deficits, including permanent paraplegia. Intraoperative online information about the functional integrity of the spinal cord and warning signs about acute functional impairment of motor pathways could contribute to a lower risk of permanent postoperative motor deficit. Motor evoked potential (MEP) monitoring can instantly and reliably detect dysfunction of motor pathways in the spinal cord. The authors have applied MEPs during intraoperative neurophysiological monitoring (IOM) for surgical repair of TISCH and have correlated the results of IOM with its influence on the surgical procedure and with the functional postoperative outcome.

METHODS

The authors retrospectively reviewed the intraoperative neurophysiological data and clinical records of 4 patients who underwent surgical treatment for TISCH in 3 institutions where IOM, including somatosensory evoked potentials and MEPs, is routinely used for spinal cord surgery. In all 4 patients the spinal cord was reduced from a posterior approach and the dural defect was repaired using a dural graft.

RESULTS

Motor evoked potential monitoring was feasible in all patients. Significant intraoperative changes of MEPs were observed in 2 patients. The changes were detected within seconds after manipulation of the spinal cord. Monitoring of MEPs led to immediate revision of the placement of the dural graft in one case and to temporary cessation of the release of the incarcerated spinal cord in the other. Changes occurred selectively in MEPs and were reversible. In both patients, transient changes in intraoperative MEPs correlated with a reversible postoperative motor deficit. Patients without significant changes in somatosensory evoked potentials and MEPs demonstrated no additional neurological deficit postoperatively and showed improvement of motor function during follow-up.

CONCLUSIONS

Surgical repair of the dural defect is effected by release and reduction of the spinal cord and insertion of dural substitute over the dural defect. Careful monitoring of the functional integrity of spinal cord long tracts during surgical manipulation of the cord can detect surgically induced impairment. The authors' documentation of acute loss of MEPs that correlated with reversible postoperative motor deficit substantiates the necessity of IOM including continuous monitoring of MEPs for the surgical treatment of TISCH.

Intraoperative neurophysiological monitoring of the spinal cord during spinal cord and spine surgery: a review focus on the corticospinal tracts

Recent advances in technology and the refinement of neurophysiological methodologies are significantly changing intraoperative neurophysiological monitoring (IOM) of the spinal cord. This review will summarize the latest achievements in the monitoring of the spinal cord during spine and spinal cord surgeries. This overview is based on an extensive review of the literature and the authors' personal experience. Landmark articles and neurophysiological techniques have been briefly reported to contextualize the development of new techniques. This background is extended to describe the methodological approach to intraoperatively elicit and record spinal D wave and muscle motor evoked potentials (muscle MEPs). The clinical application of spinal D wave and muscle MEP recordings is critically reviewed (especially in the field of Neurosurgery) and new developments such as mapping of the dorsal columns and the corticospinal tracts are presented. In the past decade, motor evoked potential recording following transcranial electrical stimulation has emerged as a reliable technique to intraoperatively assess the functional integrity of the motor pathways. Criteria based on the absence/presence of potentials, their morphology and threshold-related parameters have been proposed for muscle MEPs. While the debate remains open, it appears that different criteria may be applied for different procedures according to the expected surgery-related morbidity and the ultimate goal of the surgeon (e.g. total tumor removal versus complete absence of transitory or permanent neurological deficits). On the other hand, D wave changes--when recordable--have proven to be the strongest predictors of maintained corticospinal tract integrity (and therefore, of motor function/recovery). Combining the use of muscle MEPs with D wave recordings provides the most comprehensive approach for assessing the functional integrity of the spinal cord motor tracts during surgery for intramedullary spinal cord tumors. However, muscle MEPs may suffice to assess motor pathways during other spinal procedures and in cases where the pathophysiology of spinal cord injury is purely ischemic. Finally, while MEPs are now considered the gold standard for monitoring the motor pathways, SEPs continue to retain value as they provide specificity for assessing the integrity of the dorsal column. However, we believe SEPs should not be used exclusively--or as an alternative to motor evoked potentials--during spine surgery, but rather as a complementary method in combination with MEPs. For intramedullary spinal tumor resection, SEPs should not be used exclusively without MEPs.

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.

Chronically implanted electrodes for repeated stimulation and recording of spinal cord potentials

We have recorded and characterized the spinal cord evoked potentials (SCEPs) from the epidural space in the halothane-anesthetized rats. A group of 11 adult Wistar male rats was chronically implanted with two pairs of epidural electrodes. SCEPs were repeatedly elicited by applying electrical stimuli via bipolar U-shaped electrodes to the dorsal aspect of the spinal cord at C3-4 or Th11-12 levels, respectively. Responses were registered with the other pair of implanted electrodes, thus allowing us to monitor the descending (stimulation cervical/recording thoracic) and ascending SCEPs (stimulation thoracic/recording cervical). We studied the time-dependent changes of several SCEP parameters, among them the latency and amplitude of two major negative waves N1 and N2. During 4-weeks' survival, all major components of recordings remained stable and only minor changes in some parameters of the SCEPs were detected. We concluded that this technique enables repeated quantitative analysis of the conductivity of the spinal cord white matter in the rat. Our results indicate that SCEPs could be used in long-term experiments for monitoring progressive changes (degeneration/regeneration) in long projection tracts, primarily those occupying the dorsolateral quadrants of the spinal cord. These include projections that are of interest in spinal cord injury studies, i.e. ascending primary afferents, and important descending pathways including corticospinal, rubrospinal, reticulospinal, raphespinal and vestibulospinal tracts.

Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord

In scoliosis surgery, intraoperative somatosensory evoked potential (SSEP) monitoring has reduced the incidence of postoperative neurologic deficits. Many factors affect the amplitude and latency of SSEP waveforms during surgery. Somatosensory evoked potential amplitude decreases with ischemia and anoxia because of temporal dispersion of the afferent volley and conduction block in damaged axons. In conjunction with surgical manipulations, minor drops in blood pressure may result in substantial SSEP changes that reverse when perfusion pressure is increased. Irreversible anoxic injury to central nervous system white matter with loss of SSEP waveforms is dependent on calcium influx into the intracellular space. Somatosensory evoked potential monitoring may be less sensitive for detecting acute insults in the presence of preexisting white matter lesions. Increased extracellular potassium from acute baro-trauma can block axonal conduction transiently even when there is no axonal disruption. Marked temperature-related drops in SSEP amplitude may occur after exposure of the spine but before instrumentation and deformity correction. Hypothermia may increase false-negative outcomes. Short-interval double-pulse stimulation may improve the sensitivity of the SSEP in detecting early ischemic changes. For neurosurgical procedures on the spinal cord the use of SSEP monitoring in improving postoperative outcome is less well established.

Discrepancy between decreases in the amplitude of compound muscle action potential and loss of motor function caused by ischemic and compressive insults to the spinal cord

We examined the relationship between decreases in the amplitude of the compound muscle action potential (CMAP), caused by ischemic and compressive insults to the spinal cord, and postoperative motor deficits. Results were compared with those for other evoked potentials commonly used for multimodal monitoring of the spinal cord. CMAP was more sensitive than the other evoked potentials employed to ischemic and compressive insults to the spinal cord, although the disappearance of CMAP did not always result in a residual motor deficit. A decrease of more than 50% in the amplitude of the motor-evoked potential (MEP) from the spinal cord correlated well with the postoperative motor deficit. CMAP is a sensitive tool for the early detection of spinal cord impairment caused by ischemic or compressive insults to the spinal cord. The time after the disappearance of the CMAP amplitude was important for predicting postoperative motor deficit, but it is also necessary to employ CMAP concomitantly with other conductive potentials in spinal cord monitoring.

Prevention of spinal cord injury with time-frequency analysis of evoked potentials: an experimental study

OBJECTIVES

To verify the applicability and validity of time-frequency analysis (TFA) of evoked potential (EP) signals in detecting the integrity of spinal cord function and preventing spinal cord injury.

METHODS

The spinal cord was simulated during surgery in 20 mature rats by mechanically damaging the spinal cord. Cortical somatosensory evoked potential (CSEP), spinal somatosensory evoked potential (SSEP), cortical motor evoked potential (CMEP), and spinal cord evoked potential (SCEP) were used to monitor spinal cord function. Short time Fourier transform (STFT) was applied to the CSEP signal, and cone shaped distribution (CSD) was used as the TFA algorithm for SSEP, CMEP, and SCEP signals. The changes in the latency and amplitude of EP signals were measured in the time domain, and peak time, peak frequency, and peak power were measured in the time-frequency distribution (TFD).

RESULTS

The TFDs of EPs were found to concentrate in a certain location under normal conditions. When injury occurred, the energy decreased in peak power, and there was a greater dispersion of energy across the time-frequency range. Strong relations were found between latency and peak time, and amplitude and peak power. However, the change in peak power after injury was significantly larger than the corresponding change in amplitude (p<0.001 by ANOVA).

CONCLUSIONS

It was found that TFA of EPs provided an earlier and more sensitive indication of injury than time domain monitoring alone. It is suggested that TFA of EP signals should therefore be useful in preventing spinal cord injury during surgery.

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.

Monitoring of evoked potentials during spinal cord ischaemia: experimental evaluation in a rabbit model

OBJECTIVES

Somatosensory evoked potentials (SEPs), spinal evoked potentials (Spinal-EPs), and motor-evoked potentials (MEPs) were monitored in a rabbit model of spinal cord ischaemia to evaluate their accuracy and relationship to clinical status.

METHODS

A modified rabbit spinal cord ischaemia model of infrarenal aortic occlusion for 21 min was employed (30 rabbits). After baseline SEPs, Spinal-EPs, and MEPs were obtained, evoked potentials were recorded continuously during and after clamping of the aorta (30 min). Neurological outcome at 24 h was correlated with evoked potentials, and histopathological findings.

RESULTS

Fifteen animals became paraplegic. MEPs were always abolished after clamping of the aorta while Spinal-EPs and SEPs remained. The sensory evoked potentials (SEPs and Spinal-EPs) were the least sensitive to spinal cord ischaemia, and their presence had no correlation with the final clinical status (50% of false negatives). This was consistent with histopathological examination that showed damage almost entirely confined to the anterior horn, while the dorsal columns were generally well preserved. High spine MEPs evoked by twitch stimulation was the best predictor of clinical outcome (0% of false negatives, 0% of false positives).

CONCLUSIONS

SEPs and Spinal-EPs cannot be used as safe monitors of ischaemia of the spinal cord. High spine MEPs evoked by twitch stimulation was the most useful for real-time evaluation of spinal cord ischaemia, and the best predictor of neurologic outcome during reperfusion.

Surgical monitoring of motor pathways

Intraoperative monitoring of corticospinal function is no longer an experimental technique, having been introduced into routine practice in a number of centers, each of which has now accumulated large series of some hundreds of cases. Different techniques have been developed by these centers; each has advantages and disadvantages, and it is clear that no one technique in particular is optimal for all surgical procedures. The corticospinal system can be activated by transcranial stimulation of the motor cortex or by direct stimulation of the spinal cord with electrical or magnetic stimuli delivered singly or as double or multiple pulses. The evoked activity may be recorded directly from the spinal cord using epidural electrode, or as a postsynaptic volley in motor axons ("neurogenic motor evoked potentials," MEP), or as a compound muscle action potential (CMAP) from innervated muscles. For scoliosis surgery, we use transcranial electrical stimulation, recording the evoked volley from the spinal cord using epidural electrodes at two spinal levels. By simultaneously stimulating the tibial nerves in the popliteal fossae, descending corticospinal volleys and ascending somatosensory volleys can be recorded in the same sweep. Accordingly, this technique allows monitoring of two different modalities of function at two separate levels of the nervous system, a goal that is most desirable because it helps identify the earliest evidence of dysfunction and at the same time minimizes false-positive reports to the surgeon. Our technique has the advantage of being relatively immune to the depressant effects of anesthesia, and full muscle relaxation is possible--even desirable. More peripheral recordings of neurogenic MEP or CMAP, are sensitive to the choice of anesthetic, and the latter requires incomplete curarization. However, these techniques may be appropriate when the pathology is in the low spinal cord or nerve roots.

"Threshold-level" multipulse transcranial electrical stimulation of motor cortex for intraoperative monitoring of spinal motor tracts: description of method and comparison to somatosensory evoked potential monitoring

Numerous methods have been pursued to evaluate function in central motor pathways during surgery in the anesthetized patient. At this time, no standard has emerged, possibly because each of the methods described to date requires some degree of compromise and/or lacks sensitivity.

OBJECT

The goal of this study was to develop and evaluate a protocol for intraoperative monitoring of spinal motor conduction that: 1) is safe; 2) is sensitive and specific to motor pathways; 3) provides immediate feedback; 4) is compatible with anesthesia requirements; 5) allows monitoring of spontaneous and/or nerve root stimulus-evoked electromyography; 6) requires little or no involvement of the surgical team; and 7) requires limited equipment beyond that routinely used for somatosensory evoked potential (SSEP) monitoring. Using a multipulse electrical stimulator designed for transcranial applications, the authors have developed a protocol that they term "threshold-level" multipulse transcranial electrical stimulation (TES).

METHODS

Patients considered at high risk for postoperative deficit were studied. After anesthesia had been induced and the patient positioned, but prior to incision, "baseline" measures of SSEPs were obtained as well as the minimum (that is, threshold-level) TES voltage needed to evoke a motor response from each of the muscles being monitored. A brief, high-frequency pulse train (three pulses; 2-msec interpulse interval) was used for TES in all cases. Data (latency and amplitude for SSEP; threshold voltage for TES) were collected at different times throughout the surgical procedure. Postoperative neurological status, as judged by evaluation of sensory and motor status, was compared with intraoperative SSEP and TES findings for determination of the sensitivity and specificity of each electrophysiological monitoring technique. Of the 34 patients enrolled, 32 demonstrated TES-evoked responses in muscles innervated at levels caudal to the lesion when examined after anesthesia induction and positioning but prior to incision (that is, baseline). In contrast, baseline SSEPs could be resolved in only 25 of the 34 patients. During surgery, significant changes in SSEP waveforms were noted in 12 of these 25 patients, and 10 patients demonstrated changes in TES thresholds. Fifteen patients experienced varying degrees and durations of postoperative neurological deficit. Intraoperative changes in TES thresholds accurately predicted each instance of postoperative motor weakness without error, but failed to predict four instances of postoperative sensory deficit. Intraoperative SSEP monitoring was not 100% accurate in predicting postoperative sensory status and failed to predict five instances of postoperative motor deficit. As a result of intraoperative TES findings, the surgical plan was altered or otherwise influenced in six patients (roughly 15% of the sample population), possibly limiting the extent of postoperative motor deficit experienced by these patients.

CONCLUSIONS

This novel method for intraoperative monitoring of spinal motor conduction appears to meet all of the goals outlined above. Although the risk of postoperative motor deficit is relatively low for the majority of spine surgeries (for example, a simple disc), high-risk procedures, such as tumor resection, correction of vascular abnormalities, and correction of major deformities, should benefit from the virtually immediate and accurate knowledge of spinal motor conduction provided by this new monitoring approach.

Spinal cord and nerve root monitoring in spine surgery and related procedures

Intensive research in the field of intraoperative neurophysiologic monitoring has been performed directed at finding reliable stimulating and recording techniques and adequate anesthetic regimes applicable to spinal procedures. The aim is a comprehensive monitoring not only of afferent and efferent spinal cord pathways but also of sensory and motor nerve roots and cauda equina fibers. Conventional somatosensory evoked potentials (SEPs) are complemented by motor evoked potentials, dermatomal sensory evoked potentials, spinal cord evoked potentials, evoked electromyography, sensory and motor fiber mapping of the cauda equina, bulbocavernosus reflex testing, and neurogenic evoked potentials. Apart from describing the essentials of these techniques and their indications and limitations, this article deals with the influence of anesthetic management on the production and interpretation of evoked potentials.