Changes In Transcranial Motor Evoked Potentials Research Articles

Transcranial Motor Evoked Potentials as a Predictive Modality for Postoperative Deficit in Cervical Spine Decompression Surgery - A Systematic Review and Meta-Analysis.

Systematic Review and Meta-analysis. The purpose of this study was to evaluate whether transcranial motor evoked potential (TcMEP) alarms can predict postoperative neurologic complications in patients undergoing cervical spine decompression surgery. A meta-analysis of the literature was performed using PubMed, Web of Science, and Embase to retrieve published reports on intraoperative TcMEP monitoring for patients undergoing cervical spine decompression surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR), of overall, reversible, and irreversible TcMEP changes for predicting postoperative neurological deficit were calculated. A subgroup analysis was performed to compare anterior vs posterior approaches. Nineteen studies consisting of 4608 patients were analyzed. The overall incidence of postoperative neurological deficits was 2.58% (119/4608). Overall TcMEP changes had a sensitivity of 56%, specificity of 94%, and DOR of 19.26 for predicting deficit. Reversible and irreversible changes had sensitivities of 16% and 49%, specificities of 95% and 98%, and DORs of 3.54 and 71.74, respectively. In anterior procedures, TcMEP changes had a DOR of 17.57, sensitivity of 49%, and specificity of 94%. In posterior procedures, TcMEP changes had a DOR of 21.01, sensitivity of 55%, and specificity of 94%. TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in cervical spine decompression surgery. Patients with new postoperative neurological deficits were 19 times more likely to have experienced intraoperative TcMEP changes than those without new deficits, with irreversible TcMEP changes indicating a much higher risk of deficit than reversible TcMEP changes.

Utility of transcranial motor-evoked potential changes in predicting postoperative deficit in lumbar decompression and fusion surgery: a systematic review and meta-analysis.

The primary aim of this study was to evaluate whether TcMEP alarms can predict the occurrence of postoperative neurological deficit in patients undergoing lumbar spine surgery. The secondary aim was to determine whether the various types of TcMEP alarms including transient and persistent changes portend varying degrees of injury risk. This was a systematic review and meta-analysis of the literature from PubMed, Web of Science, and Embase regarding outcomes of transcranial motor-evoked potential (TcMEP) monitoring during lumbar decompression and fusion surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR) of TcMEP alarms for predicting postoperative deficit were calculated and presented with forest plots and a summary receiver operating characteristic curve. Eight studies were included, consisting of 4923 patients. The incidence of postoperative neurological deficit was 0.73% (36/4923). The incidence of deficits in patients with significant TcMEP changes was 11.79% (27/229), while the incidence in those without changes was 0.19% (9/4694). All TcMEP alarms had a pooled sensitivity and specificity of 63 and 95% with a DOR of 34.92 (95% CI 7.95-153.42). Transient and persistent changes had sensitivities of 29% and 47%, specificities of 96% and 98%, and DORs of 8.04 and 66.06, respectively. TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in lumbar decompression and fusion surgery. Patients who awoke with new postoperative deficits were 35 times more likely to have experienced TcMEP changes intraoperatively, with persistent changes indicating higher risk of deficit than transient changes. Diagnostic Systematic Review.

Transcranial Motor Evoked Potentials as a Predictive Modality for Postoperative Deficit in Cervical Spine Surgery – A Meta-analysis (P6-4.006)

<h3>Objective:</h3> To evaluate whether intraoperative transcranial motor evoked potential (TcMEP) changes can predict postoperative neurologic complications in patients undergoing cervical spine surgery. <h3>Background:</h3> Cervical decompression and fusion surgeries are commonly performed to relieve spinal cord and nerve root impingement. Potential intraoperative injury to the spinal cord and nerve roots poses a nontrivial risk for consequent postoperative deficits. Although neuromonitoring with intraoperative TcMEPs is often used in cervical spine surgery, its therapeutic value remains controversial. <h3>Design/Methods:</h3> A meta-analysis of the literature using PubMed to retrieve literature on intraoperative TcMEP monitoring during cervical spine surgery, excluding aneurysms, tumors, and trauma, was performed. Data collection included study design, patient demographics, procedure type/approach/indication, modalities used, TcMEP alarm criteria, TcMEP changes (including reversible and irreversible changes), and postoperative neurological deficit. The sensitivity, specificity, and diagnostic odds ratio (DOR) of overall, reversible, and irreversible TcMEP changes for predicting postoperative neurological deficit were calculated. <h3>Results:</h3> Nineteen studies were included in the final analysis. The total cohort consisted of 45,367 patients, and the incidence of postoperative neurological deficits was 0.37% (168/45367). Of the total cohort, 1.36% (619/45367) had a significant intraoperative TcMEP change. The incidence of postoperative neurological deficits in patients with intraoperative TcMEP changes was 15.67% (97/619), while the incidence in those without was 0.16% (71/44677). TcMEP changes had a sensitivity of 59%, specificity of 95%, and DOR of 26.92 for predicting neurologic deficit. Reversible and irreversible changes had sensitivities of 17% and 47%, specificities of 95% and 98%, and DORs of 3.02 and 56.29, respectively. <h3>Conclusions:</h3> TcMEP monitoring has high specificity but low sensitivity for predicting deficits in cervical spine surgery. Patients with postoperative deficits were 27 times more likely to have experienced intraoperative TcMEP changes than those without deficits, with irreversible changes indicating a higher risk of injury than reversible changes. <b>Disclosure:</b> Mr. Reddy has nothing to disclose. Dr. Gorijala has nothing to disclose. Mr. Chang has nothing to disclose. Dr. Anetakis has nothing to disclose. Jeffery Balzer has nothing to disclose. Donald Crammond has nothing to disclose. Dr. Shandal has nothing to disclose. Dr. Lee has nothing to disclose. The institution of Dr. Shaw has received research support from LSRS. The institution of Dr. Shaw has received research support from CSRS. The institution of Dr. Shaw has received research support from AO Spine. Dr. Shaw has received intellectual property interests from a discovery or technology relating to health care. The institution of Dr. Thirumala has received research support from University of Pittsburgh.

Changes in transcranial motor evoked potentials during hemorrhage are associated with increased serum propofol concentrations.

Transcranial motor evoked potentials (TcMEPs) monitor the integrity of the spinal cord during spine surgery. Propofol-based anesthesia is favored in order to enhance TcMEP quality. During intraoperative hemorrhage, TcMEP amplitudes may be reduced. The serum concentration of propofol may increase during hemorrhage. No study has determined whether changes in TcMEPs due to hemorrhage are related to changes in propofol blood levels. We monitored TcMEPs, mean arterial pressure (MAP), and cardiac output (CO) and hemoglobin in pigs (n = 6) undergoing controlled progressive hemorrhage during a standardized anesthetic with infusions of propofol, ketamine, and fentanyl. We recorded TcMEPs from the rectus femoris (RF) and tibialis anterior (TA) muscles bilaterally. A pulmonary artery catheter was placed to measure CO. Progressive hemorrhage of 10% blood volume increments was done until TcMEP amplitude decreased by >60% from baseline. Serum propofol levels were also measured following removal of each 10% blood volume increment. TcMEP responses were elicited every 3min using constant stimulation parameters. We removed between 20 and 50% of total blood volume in order to achieve the >60% reduction in TcMEP amplitude. MAP and CO decreased significantly from baseline. At maximum hemorrhage, TcMEP amplitude decreased in the RF and TA by an average of 73 and 62% respectively from baseline (P < 0.01). Serum propofol levels varied greatly among animals at baseline (range 410-1720ng/mL) and increased in each animal during hemorrhage. The mean propofol concentration rose from 1190 ± 530 to 2483 ± 968ng/mL (P < 0.01). The increased propofol concentration correlated with decreased CO. Multivariate analysis using hierarchical linear models indicated that the decline of TcMEP amplitude was primarily associated with rising propofol concentrations, but was also independently affected by reduced CO. We believe that the decrease in blood volume and CO during hemorrhage increased the serum concentration of propofol by reducing the volume of distribution and/or rate of hepatic metabolism of the drug. Despite wide acceptance of propofol as the preferred anesthetic when using TcMEPs, intravenous anesthetics are vulnerable to altered pharmacokinetics during conditions of hemorrhage and could contribute to false-positive TcMEP changes.

Alarm criteria for motor evoked potentials.

To evaluate three commonly used alarm criteria for interpreting the significance and diagnostic value of transcranial motor evoked potential (TcMEP) changes during spinal surgery. A systematic literature search was performed using PubMed/MEDLINE, Web of Science, and EMBASE from 1945 to January 2014. We included all those studies that were (1) randomized controlled trials, prospective studies, or retrospective cohort studies, (2) conducted among patients undergoing surgery on the spine or spinal cord with TcMEP monitoring, (3) conducted in a group of ≥50 patients, (4) that were inclusive of immediate postoperative neurological assessment (within 24 h), and (5) which were published in English. Twenty-five studies involving 9409 patients were included. The incidence of neurological deficits was 1.82%. The overall sensitivity and specificity of all reported TcMEP changes was 82.1% (95% confidence interval [CI]: 73-88.6%) and 95.7% (95% CI: 93.7-97.1%), respectively. The sensitivity and specificity of each alarm criteria were evaluated: 50% reduction in amplitude, sensitivity 63.2% (95% CI: 47-76.8%), and specificity 96.7% (95% CI: 96.4-99.2%); 80% reduction in amplitude, sensitivity 71.7% (95% CI; 42-89.9%), and specificity 98.3% (95% CI: 96.4-99.2%); total signal loss, sensitivity 30% (95% CI: 17.6-46.4%), and specificity 99.3% (95% CI: 98.6-99.7%). No statistically significant differences between using reductions in amplitude of 50% and 80% as alarm criteria were found in terms of sensitivity and specificity. Total loss was found to have a statistically significant increase in specificity. TcMEP monitoring is a highly specific and sensitive diagnostic tool for the detection of neurological defects during spinal surgery.

Diagnostic accuracy of motor evoked potentials to detect neurological deficit during idiopathic scoliosis correction: a systematic review.

OBJECTIVE The goal of this study was to evaluate the efficacy of intraoperative transcranial motor evoked potential (TcMEP) monitoring in predicting an impending neurological deficit during corrective spinal surgery for patients with idiopathic scoliosis (IS). METHODS The authors searched the PubMed and Web of Science database for relevant lists of retrieved reports and/or experiments published from January 1950 through October 2014 for studies on TcMEP monitoring use during IS surgery. The primary analysis of this review fit the operating characteristic into a hierarchical summary receiver operating characteristic curve model to determine the efficacy of intraoperative TcMEP-predicted change. RESULTS Twelve studies, with a total of 2102 patients with IS were included. Analysis found an observed incidence of neurological deficits of 1.38% (29/2102) in the sample population. Of the patients who sustained a neurological deficit, 82.8% (24/29) also had irreversible TcMEP change, whereas 17.2% (5/29) did not. The pooled analysis using the bivariate model showed TcMEP change with sensitivity (mean 91% [95% CI 34%-100%]) and specificity (mean 96% [95% CI 92-98%]). The diagnostic odds ratio indicated that it is 250 times more likely to observe significant TcMEP changes in patients who experience a new-onset motor deficit immediately after IS correction surgery (95% CI 11-5767). TcMEP monitoring showed high discriminant ability with an area under the curve of 0.98. CONCLUSIONS A patient with a new neurological deficit resulting from IS surgery was 250 times more likely to have changes in TcMEPs than a patient without new deficit. The authors' findings from 2102 operations in patients with IS show that TcMEP monitoring is a highly sensitive and specific test for detecting new spinal cord injuries in patients undergoing corrective spinal surgery for IS. They could not assess the value of TcMEP monitoring as a therapeutic adjunct owing to the limited data available and their study design.

Is intraoperative neurophysiological monitoring valuable predicting postoperative neurological recovery?

We investigated the ability of intraoperative neurophysiological monitoring to predict postoperative neurological recovery in intradural-extramedullary spinal cord tumors. From 2010 to 2014, we operated on 173 intradural-extramedullary spinal cord tumor patients with intraoperative neurophysiological monitoring. We retrospectively compared preoperative and postoperative clinical status using a modified McCormick grading scale and correlated with intraoperative neurophysiological monitoring. We followed patients for at least 1 year and correlated neurological outcomes with intraoperative changes in intraoperative neurophysiological monitoring. We then compared the degree of intraoperative neurophysiological monitoring change with the duration of the neurological deficit. Monitorability was 92% and 57% with transcranial motor-evoked potential and somatosensory-evoked potential modalities, respectively. Waveform attenuation on transcranial motor-evoked potentials was detected in 8.17% of cases. For somatosensory-evoked potentials, waveform attenuation was detected in 7% of the patients. A multimodality approach incorporating any transcranial motor-evoked potential changes had a sensitivity of 0.91 and a specificity of 0.98. The McCormick grade scale increased until 1 month in patients with alarm criteria on transcranial motor-evoked potentials (P<0.05). Patients suffered neurological deterioration in case of abolishment or >50% irreversible attenuation of the waveform in transcranial motor-evoked potentials. All patients gradually recovered after 1 postoperative month with alarm criteria from 50% to 80% irreversible amplitude drop on transcranial motor-evoked potentials.

Basic Principles and Recent Trends of Transcranial Motor Evoked Potentials in Intraoperative Neurophysiologic Monitoring.

Transcranial motor evoked potentials (TcMEPs), which are muscle action potentials elicited by transcranial brain stimulation, have been the most popular method for the last decade to monitor the functional integrity of the motor system during surgery. It was originally difficult to record reliable and reproducible potentials under general anesthesia, especially when inhalation-based anesthetic agents that suppressed the firing of anterior horn neurons were used. Advances in anesthesia, including the introduction of intravenous anesthetic agents, and progress in stimulation techniques, including the use of pulse trains, improved the reliability and reproducibility of TcMEP responses. However, TcMEPs are much smaller in amplitude compared with compound muscle action potentials evoked by maximal peripheral nerve stimulation, and vary from one trial to another in clinical practice, suggesting that only a limited number of spinal motor neurons innervating the target muscle are excited in anesthetized patients. Therefore, reliable interpretation of the critical changes in TcMEPs remains difficult and controversial. Additionally, false negative cases have been occasionally encountered. Recently, several facilitative techniques using central or peripheral stimuli, preceding transcranial electrical stimulation, have been employed to achieve sufficient depolarization of motor neurons and augment TcMEP responses. These techniques might have potentials to improve the reliability of intraoperative motor pathway monitoring using TcMEPs.

Multimodality Intraoperative Neurophysiological Monitoring during Onyx Embolization of Cerebrovascular Malformations

ABSTRACTGeneral anesthesia prohibits neurological examination during embolization of cerebrovascular malformations when provocative testing prior to pedicle occlusion is needed. Intraoperative neurophysiological monitoring (IONM) has the potential to fill this gap but remains relatively unexplored. We conduct a retrospective review of consecutive patients with cerebrovascular malformations treated with Onyx® (ethylene vinyl alcohol copolymer, dissolved in dimethyl sulfoxide) embolization under general anesthesia with IONM from 2009 to 2012. Somatosensory evoked potentials (SSEPs), transcranial motor evoked potentials (TcMEPs), visual evoked potential (VEPs), auditory brainstem response (ABR), and electroencephalography (EEG) were used selectively in all patients depending on the location of the malformation. Provocative testing combined with IONM was performed in 28 patients over 75 sessions. Three patients demonstrated changes in TcMEPs or ABR during provocative testing, which halted the planned embolization. Two patients demonstrated changes in baseline SSEPs after embolization, despite normal IONM during provocative testing, correlating with postprocedural contralateral weakness. Six patients developed visual deficits after arterial occlusion despite unchanged VEPs and occipital EEG during provocative testing and embolization. We therefore conclude that the sensitivity of TcMEPs and SSEPs is preferable to EEG, and we strongly caution against relying on occipital recorded VEPs to predict visual deficits.

Efficacy of transcranial motor evoked potentials, mechanically elicited electromyography, and evoked electromyography to assess nerve root function during sustained compression in a porcine model.

This is an animal experiment using transcranial motor evoked potentials (TcMEPs), mechanically elicited electromyographic (EMG) responses, and evoked EMG responses during nerve root compression in a pig model. To compare these 3 electrophysiological measures for compression applied to a lumbar nerve root. Lumbar nerve root injury may result in motor weakness in up to 30% of spinal deformity cases. Compressive injury may occur during the surgical approach, decompression, and manipulation of the spine. Using an established porcine model, we examined the changes to TcMEPs, mechanically elicited EMG responses, and evoked EMG responses during varied compressive forces. TcMEPs, mechanically elicited EMG responses, and evoked EMG responses were recorded for the tibialis anterior muscle in 16 experiments. Precompression TcMEP and nerve root stimulation threshold (NRT) were obtained. The dominant root was compressed at 1 N (n = 8) or 2 N (n = 8) for 10 minutes. TcMEP was recorded every minute during compression, and TcMEP and NRT were recorded after both compression and 10 minutes of recovery. After 10 minutes of 1-N compression, TcMEP amplitude of the tibialis anterior muscle decreased to 69% ± 13% of baseline (P < 0.02 vs. baseline). The mean NRT increased to 645% ± 433% (P < 0.02 vs. baseline NRT). After the recovery period, TcMEP in the 1-N group returned to 98% ± 11% of baseline (P = 0.36 vs. baseline). After 10 minutes of 2-N compression, TcMEPs from the tibialis anterior muscle decreased to 27% ± 15% of baseline (P < 0.02 vs. baseline). After the recovery period, TcMEP in the 2-N group returned to 30% ± 10% of baseline (P < 0.02 vs. baseline). Tonic EMG activity was observed in 3 nerve roots compressed at 2 N. Compression at 1 and 2 N produced consistent changes in TcMEPs and EMG responses. TcMEP monitoring is sensitive to an increase in compressive force. TcMEP amplitude change was correlated to the force applied and the ability of the nerve root to recover. Mechanically elicited EMG responses were not sensitive to nerve root compression. N/A.

Intraoperative changes in transcranial motor evoked potentials and somatosensory evoked potentials predicting outcome in children with intramedullary spinal cord tumors

Intraoperative dorsal column mapping, transcranial motor evoked potentials (TcMEPs), and somatosensory evoked potentials (SSEPs) have been used in adults to assist with the resection of intramedullary spinal cord tumors (IMSCTs) and to predict postoperative motor deficits. The authors sought to determine whether changes in MEP and SSEP waveforms would similarly predict postoperative motor deficits in children. The authors reviewed charts and intraoperative records for children who had undergone resection for IMSCTs as well as dorsal column mapping and TcMEP and SSEP monitoring. Motor evoked potential data were supplemented with electromyography data obtained using a Kartush microstimulator (Medtronic Inc.). Motor strength was graded using the Medical Research Council (MRC) scale during the preoperative, immediate postoperative, and follow-up periods. Reductions in SSEPs were documented after mechanical traction, in response to maneuvers with the cavitational ultrasonic surgical aspirator (CUSA), or both. Data from 12 patients were analyzed. Three lesions were encountered in the cervical and 7 in the thoracic spinal cord. Two patients had lesions of the cervicomedullary junction and upper spinal cord. Intraoperative MEP changes were noted in half of the patients. In these cases, normal polyphasic signals converted to biphasic signals, and these changes correlated with a loss of 1-2 grades in motor strength. One patient lost MEP signals completely and recovered strength to MRC Grade 4/5. The 2 patients with high cervical lesions showed neither intraoperative MEP changes nor motor deficits postoperatively. Dorsal columns were mapped in 7 patients, and the midline was determined accurately in all 7. Somatosensory evoked potentials were decreased in 7 patients. Two patients each had 2 SSEP decreases in response to traction intraoperatively but had no new sensory findings postoperatively. Another 2 patients had 3 traction-related SSEP decreases intraoperatively, and both had new postoperative sensory deficits that resolved. One additional patient had a CUSA-related SSEP decrease intraoperatively, which resolved postoperatively, and the last patient had 3 traction-related sensory deficits and a CUSA-related sensory deficit postoperatively, none of which resolved. Intraoperative TcMEPs and SSEPs can predict the degree of postoperative motor deficit in pediatric patients undergoing IMSCT resection. This technique, combined with dorsal column mapping, is particularly useful in resecting lesions of the upper cervical cord, which are generally considered to be high risk in this population. Furthermore, the spinal cord appears to be less tolerant of repeated intraoperative SSEP decreases, with 3 successive insults most likely to yield postoperative sensory deficits. Changes in TcMEPs and SSEP waveforms can signal the need to guard against excessive manipulation thereby increasing the safety of tumor resection.

Editorial: Use of intraoperative monitoring in children

The holy grail of intraoperative monitoring is accurate correlation of electrophysiological changes and postoperative neurological changes. Ideally, feedback provided to the surgeon in real time would allow for an alteration in technique and thus the opportunity to prevent or reverse neurological deficits. While intraoperative neuromonitoring modalities continue to evolve, the perfect predictive value of this tool remains elusive. Intraoperative spinal cord monitoring is essentially the standard of care for adults harboring intramedullary tumors.5–7 Less information is available in the pediatric population, perhaps given the rarity of these lesions.2–4 Cheng et al.1 report on their experience using both transcranial motor evoked potentials (TcMEPs) and somatosensory evoked potentials (SSEPs) in a retrospective series of 12 patients. Overall, they found that intraoperative electrical changes predicted postoperative neurological outcomes. They correlated changes in TcMEP and SSEP monitoring with specific intraoperative maneuvers, including traction on the spinal cord and tumor resection via the cavitational ultrasonic surgical aspirator. They also used dorsal column mapping to accurately predict where to perform a midline myelotomy, novel information in the pediatric population. Several patients in the series had intraoperative changes in their monitoring, which correlated with new postoperative deficits. Not all of these deficits resolved, and the correlation between intraoperative changes and postoperative dysfunction was not perfect. While the use of intraoperative monitoring in children undergoing intramedullary spinal cord tumor resection appears to be useful, the results of this study must be interpreted with some caution. The study is retrospective in nature with only 12 patients, 5 of whom did not undergo dorsal column mapping. Data were collected over a period of 8 years, and the last patient in the series underwent surgery a decade ago. Moreover, D-wave monitoring,8–10 a more recent advance in the intraoperative assessment of motor function, was not utilized. Nevertheless, the data contribute to our understanding of spinal cord tumor resection in the pediatric population. The authors noted that raising the blood pressure above normal was not helpful in reversing SSEP changes and that releasing traction proved the most reliable maneuver for correcting the first SSEP change. Finally, the provided data offer some guidance in the intraoperative balancing act faced by every surgeon regarding how aggressive the tumor resection should be to avoid tumor recurrence, while doing no harm in preserving neurological function. (http://thejns.org/doi/abs/10.3171/2013.9.PEDS13439)

Effect of Hemorrhage and Hypotension on Transcranial Motor-evoked Potentials in Swine

Transcranial motor-evoked potentials (TcMEPs) monitor spinal cord motor tract integrity. Using a swine model, the authors studied the effects of vasodilatory hypotension, hemorrhage, and various resuscitation efforts on TcMEP responses. Twelve pigs were anesthetized with constant infusions of propofol, ketamine, and fentanyl. Animals were incrementally hemorrhaged, until bilateral tibialis anterior TcMEP amplitude decreased to less than 40% of baseline or until 50% of the blood volume was removed. Mean arterial pressure (MAP), cardiac output (CO), and oxygen delivery (DO2) were examined. Resuscitation with phenylephrine, epinephrine, and colloid were evaluated. In seven animals, vasodilatory hypotension was examined. Paired comparisons and multivariate analysis were performed. Hemorrhage significantly reduced (as a percentage of baseline, mean±SD) TcMEPs (left, 33±29%; right, 26±21%), MAP (60±17%), CO (49±12%), and DO2 (43±13%), P value less than 0.001 for all. Vasodilation reduced MAP comparably, but TcMEPs, CO, and DO2, were not significantly lowered. After hemorrhage, restoration of MAP with phenylephrine did not improve TcMEPs, CO, or DO2, but similar restoration of MAP with epinephrine restored (to percentage of baseline) TcMEPs (59±40%), and significantly increased CO (81±17%) and DO2 (72±19%) compared with both hemorrhage and phenylephrine, P value less than 0.05 for all. Resuscitation with colloid did not improve TcMEPs. Multivariate analysis revealed that changes in TcMEPs were more closely associated with changes in CO and DO2 as compared with MAP. Hypotension from hemorrhage, but not vasodilation, is associated with a decrease in TcMEP amplitude. After hemorrhage, restoration of TcMEPs with epinephrine but not phenylephrine indicates that CO and DO2 affect TcMEPs more than MAP. Monitoring CO may be beneficial in major spine surgery when using TcMEP monitoring.

Spinal Cord Monitoring With Transcranial Motor Evoked Potentials in Patients With Neural Axis Abnormalities Undergoing Spinal Deformity Surgery

Study DesignRetrospective, case-control study. ObjectivesTo report the effectiveness of transcranial motor evoked potentials (TcMEPs) in patients undergoing scoliosis surgery with neural axis abnormalities (NAAs). Summary of Background DataTranscranial motor evoked potentials are a safe and sensitive modality to identify impending spinal cord injury in adolescent idiopathic scoliosis (AIS). Previous studies have analyzed somatosensory evoked potentials (SSEPs) and neurogenic motor evoked potentials in NAA patients, but to our knowledge, no study has addressed the use of TcMEPs in these patients. MethodsWe performed an institutional review board–approved retrospective review of a consecutive series of patients with NAA at a single institution and compared them with a consecutive series of AIS patients undergoing scoliosis surgery with spinal cord monitoring using TcMEP and SSEP. We compared the ability to obtain baseline data and the incidence of critical changes in TcMEPs and SSEPs between groups and examined a correlation with postoperative neurologic deficits. ResultsWe compared 38 patients with NAA (15 Chiari malformations, 12 syrinx, 7 tethered cords, and 4 spinal cord tumors) with 184 patients with AIS. The age was similar and preoperative curve magnitude was greater in the NAA group. Good baseline data were obtained less frequently in the NAA group for TcMEPs (94.7% vs. 100%; p < .001) and SSEPs (89.5% vs. 100%; p < .001). There was no statistical difference in critical deviation from baseline in the NAA group for TcMEPs (3 of 38 [7.9%] vs. 5 of 184 [2.7%]; p = .120) or SSEPs (0 of 38 vs. 3 of 184 [1.6%] (p = .430). There were no postoperative neurologic deficits in the NAA or AIS group. ConclusionsThe ability to obtain baseline spinal cord monitoring in patients with NAA approaches that of an AIS group and accurately identifies impending neurologic deficits with high sensitivity. Surgeons should be confident that TcMEP baseline data can be obtained in patients with spinal cord pathology and should trust critical changes in TcMEPs intraoperatively to prevent spinal cord injury.

Evaluation of Combined Use of Transcranial and Direct Cortical Motor Evoked Potential Monitoring During Unruptured Aneurysm Surgery

The feasibility and reliability of combined use of transcranial and direct cortical motor evoked potential (MEP) monitoring during unruptured aneurysm surgery were evaluated. Forty-eight patients with unruptured cerebral aneurysms underwent craniotomy and neck clipping accompanied by muscle MEP monitoring. MEPs were elicited successfully by transcranial electrical stimulation in all patients. Direct cortical stimulation elicited MEPs in 44 patients. Reduction in MEP amplitude to less than 50% of baseline was considered significant. No postoperative motor paresis occurred in 39 patients in whom transcranial and direct MEPs remained unchanged. Four patients in whom direct MEPs could not be recorded had no intraoperative abnormality in transcranial MEPs and no postoperative motor dysfunction. Four of the other 5 patients manifested significant transient direct MEP changes without transcranial MEP changes. The transient MEP changes were observed in 3 patients during temporary clipping of the parent artery and in one patient with inadequate clipping of an middle cerebral artery aneurysm, and were considered due to insufficiency of blood flow. Decrease or disappearance of direct MEP waves recovered immediately after re-application of the clip and release of the temporary clip. Direct MEP waves disappeared and did not recover until the end of microsurgical procedures in one patient, although transcranial MEP amplitude remained at less than 50% of baseline. She developed hemiparesis postoperatively, which recovered within 6 hours. The duration of temporary occlusion in patients with direct MEP changes was significantly longer than that in patients without (p < 0.05). Direct MEP was sensitive in detecting ischemic stress to descending motor pathways during aneurysm surgery. Transcranial MEPs could be elicited in patients in whom direct MEPs could not be obtained, and during periods such as craniotomy or after dural closure, in which direct MEPs could not be recorded. These findings suggest that combined transcranial and direct cortical MEP recording may improve the feasibility and reliability of MEP monitoring during unruptured aneurysm surgery.

Relative Efficacy of Transcranial Motor Evoked Potentials, Mechanically-Elicited Electromyography, and Evoked EMG to Assess Nerve Root Function During Sustained Retraction in a Porcine Model

This is an animal experiment using transcranial motor evoked potentials (TcMEP), mechanically elicited electromyography (EMG), and evoked EMG during spinal nerve root retraction in a pig model. To compare the sensitivity of these 3 electrophysiological measures for a constant retraction force applied to an isolated lumbar nerve root for a specific duration of time. The incidence of nerve root injury during lumbar spine surgery ranges from 0.2% to 31%. Direct retraction of spinal nerve roots may cause these injuries, but the amount and duration of force that may safely be applied is not clear. Using an established porcine model, we examined the changes occurring to multimyotomal TcMEPs, mechanically elicited EMGs, and evoked EMGs during continuous retraction of a nerve root at a constant force applied over 10 minutes. TcMEP, mechanically elicited EMG, and evoked EMG responses were recorded from the tibialis anterior (TA) muscle in 10 experiments. The dominant root innervating the TA was determined with evoked EMG; preretraction TcMEP and nerve root stimulation threshold (NRT) was obtained. The dominant root was retracted at 2 Newton (N) for 10 minutes. TcMEP trials were elicited every minute during retraction. NRT was measured immediately after retraction. TcMEP and NRT were measured after 10 minutes of recovery. RESULTS.: During the 10 minutes of retraction at 2 N, the amplitude of the TA muscle progressively decreased in all trials in a highly significant curvilinear fashion. The mean TcMEP amplitude decreased 59% +/- 14% from baseline values. The mean NRT after 10 minutes of retraction at 2 N rose to 1.8 +/- 0.7 mA (P < 0.01 vs. baseline). The NRT increase after retraction strongly correlated with the decrease in motor evoked potentials amplitude in the TA (R = 0.90, P < 0.001). EMG activity was variable; tonic EMG was observed in only 2 nerve roots (20%). Three electrophysiologic methods were used intraoperatively to assess neural function during retraction of a single nerve root. Retraction produced consistent changes in TcMEPs and evoked EMG. These 2 methods show promise for assessing the limits on the force and duration of nerve root retraction during spine surgery. Mechanically elicited EMG was not sensitive to the amount and duration of nerve root retraction.

The Efficacy of Motor Evoked Potentials in Fixed Sagittal Imbalance Deformity Correction Surgery

Retrospective analysis of transcranial motor evoked potential (TcMEP) responses and clinical outcome. To determine the sensitivity and specificity of TcMEPs to detect and predict isolated nerve root injury in selected patients having complex lumbar spine surgery. The surgical correction of fixed sagittal plane deformity involves posterior-based osteotomies and significant changes in the length of and space for the neural elements. The role of transcranial motor-evoked potential (TcMEP) monitoring in osteotomies below the conus has not been established. The purpose of this paper is to describe the relationship between neural complications from surgery and intraoperative TcMEP changes. We retrospectively studied 35 consecutive patients in a single center treated with posterior-based osteotomies for the correction of fixed sagittal plane deformity. Transcranial motor-evoked potentials, free-running and evoked electromyography data were assessed for each case. Analysis includes description of the intraoperative changes observed, and a correlation of changes with postoperative clinical findings. Thirty-five consecutive patients underwent surgery for fixed sagittal plane deformity with complete neuromonitoring data. Twenty-five patients (71%) had an episode of greater than 80% reduction in MEP amplitude to at least 1 muscle. Fifteen of 25 had improvement of TcMEPs after repositioning of the legs (1), additional surgical decompression (4), or volume and pharmacologic resuscitation (10). All 15 of these awoke with no detectable neurologic injury. Ten patients (29%) had reduced TcMEP signals that did not improve despite further decompression and manipulation of the osteotomy site. All 10 had a greater than 67% drop in TcMEPs for at least 1 muscle persisting at the end of the case, and all had a postoperative neurologic deficit. The TcMEP changes in patients who demonstrated nerve injury postoperatively were observed most often during osteotomy closure or sustained dural retraction. 9 patients had weakness involving the iliopsoas or quadriceps; 1 patient had isolated unilateral dorsiflexion weakness. Monitoring TcMEPs in multiple muscle groups was both highly sensitive and specific for predicting injury. Nine patients had recovered motor function completely by discharge, and all but 1 patient (grade 4/5) had a normal motor examination at 6-week follow-up. The use of TcMEPs is sensitive and specific to change in neural function. No patients had a false negative test. The rate of neural deficits is consistent with previous literature, suggesting that TcMEP monitoring may not prevent neural injury. However, there were several cases in which intraoperative intervention resulted in recovery of TcMEPs, and none of these patients sustained any postoperative neural deficit. The severity of neural deficits in this series was minor and the duration was limited. TcMEPs may contribute to calling attention to the need for intraoperative corrections including widening decompressions, improving perfusion, and limiting deformity correction so that more severe neural compromise may be prevented.