Stimulation Of Motor Evoked Potentials Research Articles

Does persistent crossover (ipsilateral) motor evoked potential (MEP) responses represent a technical failure for intracranial motor tract monitoring? A case example and practical solution.

Attention to motor evoked potential (MEP) stimulation intensity is necessary to avoid false negative MEP results during intracranial procedures. Observing ipsilateral (crossover) MEP responses has been hypothesized to indicate inappropriately strong stimulation intensity. We describe a case where persistent crossover MEP responses falsely suggested that stimulus intensity was too high and describe an alternative method to guide the selection of MEP stimulation intensity. A patient undergoing a suboccipital craniotomy for tumor resection had bilateral transcranial electrical MEP monitoring under total intravenous anesthesia. MEP results were obtained from left and right hand using C4-Cz and C3-Cz stimulation montages respectively. Selection of an appropriately superficial stimulus intensity was guided using MEP onset latencies. MEP acquisition proceeded normally for contralateral left hand (C4-Cz montage). However, using the C3-Cz montage, persistent crossover responses were noted at stimulation intensities as low as threshold for contralateral right hand MEP (94V/166mA). Appropriate MEP stimulus intensity for subsequent monitoring (approximately 96V/172mA) was determined utilizing onset latency measurements from contralateral hand MEP responses. The stimulus intensity chosen was predicated on onset latency being ≥ 2 ms longer than latency at maximal stimulus level (shortest latency). A stimulus intensity-latency plot was generated offline to illustrate this important relationship for intracranial MEP use. MEP acquisition proceeded without incident and gross total resection was achieved without postoperative motor deficits. Despite crossover appearance contralateral hand MEP were quantitatively validated for intraoperative application using onset latency guidance.

Location-specific cutaneous electrical stimulation of the footsole modulates corticospinal excitability to the plantarflexors and dorsiflexors during standing.

Non‐noxious electrical stimulation to distinct locations of the foot sole evokes location‐specific cutaneous reflex responses in lower limb muscles. These reflexes occur at latencies that may enable them to be mediated via a transcortical pathway. Corticospinal excitability to the plantarflexors and dorsiflexors was measured in 16 participants using motor evoked potentials (MEPs). Spinal excitability was measured in eight of the original participants using cervicomedullary motor evoked potentials (CMEPs). Measurements were collected with and without preceding cutaneous stimulus to either the heel (HEEL) or metatarsal (MET) locations of the foot sole, and evoked potentials were elicited to coincide with the arrival of the cutaneous volley at either the motor cortex or spinal cord. Plantarflexor MEPs and CMEPs were facilitated with cutaneous stimulation to the HEEL for MEPs (soleus p = 0.04, medial gastrocnemius (MG) p = 0.017) and CMEPs (soleus p = 0.047 and MG p = 0.015), but they were unchanged following MET stimulation for MEPs or CMEPs. Dorsiflexor MEPs were unchanged with cutaneous stimulation at either location, but dorsiflexor CMEPs increased with cutaneous stimulation (p = 0.05). In general, the increase in CMEP amplitudes was larger than the increase in MEP amplitudes, indicating that an increase in spinal excitability likely explains most of the increase in corticospinal excitability. The larger change observed in the CMEP also indicates that excitability from supraspinal sources likely decreased, which could be due to a net change in the excitability of intracortical circuits. This study provides evidence that cutaneous reflexes from foot sole skin are likely influenced by a transcortical pathway.

Predictive factors of unacceptable movement and motor-evoked potentials during intraoperative neurophysiological monitoring in adult patients undergoing brain surgery: A retrospective study.

Motor-evoked potential (MEP) monitoring is an essential monitoring for clinicians to improve outcomes. Although unacceptable movement during MEP is a rare complication but it can lead to terrible results. The aim of this study was to evaluate the risk factors associated with unacceptable movements in patients undergoing brain surgery with MEP monitoring.We performed a retrospective observational study of patients who underwent brain surgery with MEP monitoring under general anesthesia while using a partial neuromuscular blocker in a tertiary care hospital from January 2014 to August 2017. Unacceptable movement was defined as a condition in which MEP stimulation induced vigorous movement of patient hindered the smooth progress of the operation. We compared the baseline patient characteristics and laboratory results according to unacceptable movements during surgery to identify factors associated with unacceptable movement during MEP monitoring.768 patients were included in this analysis, and unacceptable movements were observed in 278 patients (36.2%). A multivariate logistic regression analysis revealed that an increase in ionized calcium was associated with the most strongly unpredictable movement during surgery [odds ratio (OR): 1.79, 95% confidence interval (CI): 1.37–2.36, P < .001]. In addition, age (OR, 0.98; 95% CI, 0.96–0.99; P = .001), male sex (OR, 1.59; 95% CI, 1.09-2.33; P = .017), and body mass index (OR, 0.90; 95% CI, 0.86-0.95; P <0.0010) were also associated with unacceptable movement. Serum ionized calcium concentration was the best predictor associated with unacceptable movement with MEP monitoring under general anesthesia.Serum ionized calcium concentration was the best predictor associated with unacceptable movement with MEP monitoring under general anesthesia.

Clinical Neurophysiology: Introperative Monitoring

Abstract 1 Erik J. Kobylarz, 2 Mark H. Bilsky, 1 Sonia K. Sandhu, 1 Edward A. Avila, and 1 Jonathan D. Victor ( 1 Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, NY ; and 2 Department of Neurosurgery, Memorial Sloan Kettering Cancer Center, New York, NY ) Rationale: Transcranial electrical motor evoked potential (MEP) intraoperative monitoring can help reduce morbidity from spine surgery. However, it poses some risks, including intraoperative seizures. Transcranial electrical and magnetic stimulation at sufficiently high intensities have both been shown to produce epileptiform afterdischarges, as well as seizures. The purpose of this study is to determine the effects of transcranial electrical stimulation on the electroencephalogram (EEG), and the possible utility of the EEG during MEP monitoring for spine surgery. Methods: Twenty-seven patients with no history of seizures or anticonvulsant treatment and no known intracranial lesions underwent intraoperative MEP monitoring during spine tumor resection and instrumentation surgery. An electrode montage surrounding the MEP scalp stimulation site (C1, C2) was used for EEG monitoring (Cz-Fpz, C3-Fpz, C4-Fpz, Fz-Fpz, F3-Fpz, F4-Fpz, Pz-Fpz). Baseline, post-stimulus and inter-stimulus EEGs were recorded with the stimulation amplifiers temporarily disconnected to decrease electrical noise. MEP stimulation settings varied between patients: 250–600V, 4–6 pulse trains at 1.5 to 2 ms intervals. Electrical stimulation consistently caused a polyspike burst in all EEG channels lasting several seconds. The pure midline EEG derivations returned to baseline more rapidly after transcranial stimulation than those involving C3, C4, F3 and F4. For this study an afterdischarge was defined as a spike-and-aftercoming slow wave, not looking like artifact, that is separated in time from the polyspike burst that immediately follows the electrical stimulation. Results: Baseline EEGs revealed no epileptiform activity or electrographic seizures. In four of 27 patients, there were single or brief bursts of afterdischarges lasting up to several seconds, following transcranial MEP stimulation. In all cases, there was spontaneous return of the EEG to normal baseline activity. No patients demonstrated clinical or electrographic seizures prior to or after transcranial MEP stimulation during the intraoperative monitoring period. Conclusions: Concurrent electroencephalography during motor evoked potential stimulation is practical and occasionally reveals afterdischarges. This suggests that concurrent EEG monitoring may improve the safety of MEP monitoring.

Transcranial electrical motor evoked potential monitoring for brain tumor resection.

This study was designed to examine whether transcranial electrical motor evoked potential (MEP) monitoring is safe, feasible, and valuable for brain tumor surgery. Fifty consecutive patients undergoing brain tumor resection were studied, using nitrous oxide/propofol anesthesia. MEPs were continuously recorded throughout surgery, using a Sentinel 4 evoked potential system (Axon Systems, Inc., Hauppauge, NY). The MEPs were elicited by transcranial electrical stimulation (train of 5; stimulation rate, 0.5-2 Hz; square wave pulse with a time constant of 0.5 ms; stimulation intensity, 40-160 mA) through spiral electrodes placed over the primary motor cortex and were recorded by needle electrodes inserted into the contralateral orbicularis oris, biceps, abductor pollicis brevis, and anterior tibialis muscles. When MEP amplitudes decreased by more than 50%, MEP stimulation was repeated, with increased stimulation intensity, and MEP changes were reported to the surgeon. The motor function of each patient was examined before and after surgery, using a reproducible scale. The relationship between MEP amplitude decreases and worsening motor status was analyzed using linear regression. Preoperative neurological examinations revealed mild to moderate motor deficits (2/5 to 4/5) for 38% of patients (19 of 50 patients). Most of the patients (96%) exhibited recordable baseline MEPs. Persistent MEP decreases of more than 50% were noted for eight patients (16%) (11 muscles). The MEPs were completely abolished in two patients (three muscles). The degree of postoperative worsening of motor status was correlated with the degree of intraoperative MEP amplitude reduction (r = -0.864; P < 0.001). Persistent intraoperative MEP reductions of more than 50% were associated with postoperative motor deficits. The degree of MEP amplitude reduction was correlated with postoperative worsening of motor status. Transcranial electrical MEP monitoring is feasible, safe, and valuable for brain tumor surgery.

Transcranial Electrical Motor Evoked Potential Monitoring for Brain Tumor Resection

OBJECTIVE This study was designed to examine whether transcranial electrical motor evoked potential (MEP) monitoring is safe, feasible, and valuable for brain tumor surgery. METHODS Fifty consecutive patients undergoing brain tumor resection were studied, using nitrous oxide/propofol anesthesia. MEPs were continuously recorded throughout surgery, using a Sentinel 4 evoked potential system (Axon Systems, Inc., Hauppauge, NY). The MEPs were elicited by transcranial electrical stimulation (train of 5; stimulation rate, 0.5–2 Hz; square wave pulse with a time constant of 0.5 ms; stimulation intensity, 40–160 mA) through spiral electrodes placed over the primary motor cortex and were recorded by needle electrodes inserted into the contralateral orbicularis oris, biceps, abductor pollicis brevis, and anterior tibialis muscles. When MEP amplitudes decreased by more than 50%, MEP stimulation was repeated, with increased stimulation intensity, and MEP changes were reported to the surgeon. The motor function of each patient was examined before and after surgery, using a reproducible scale. The relationship between MEP amplitude decreases and worsening motor status was analyzed using linear regression. RESULTS Preoperative neurological examinations revealed mild to moderate motor deficits (2/5 to 4/5) for 38% of patients (19 of 50 patients). Most of the patients (96%) exhibited recordable baseline MEPs. Persistent MEP decreases of more than 50% were noted for eight patients (16%) (11 muscles). The MEPs were completely abolished in two patients (three muscles). The degree of postoperative worsening of motor status was correlated with the degree of intraoperative MEP amplitude reduction (r = −0.864;P < 0.001). CONCLUSION Persistent intraoperative MEP reductions of more than 50% were associated with postoperative motor deficits. The degree of MEP amplitude reduction was correlated with postoperative worsening of motor status. Transcranial electrical MEP monitoring is feasible, safe, and valuable for brain tumor surgery.

Transcranial Electrical Motor Evoked Potential Monitoring for Brain Tumor Resection

OBJECTIVE This study was designed to examine whether transcranial electrical motor evoked potential (MEP) monitoring is safe, feasible, and valuable for brain tumor surgery. METHODS Fifty consecutive patients undergoing brain tumor resection were studied, using nitrous oxide/propofol anesthesia. MEPs were continuously recorded throughout surgery, using a Sentinel 4 evoked potential system (Axon Systems, Inc., Hauppauge, NY). The MEPs were elicited by transcranial electrical stimulation (train of 5; stimulation rate, 0.5–2 Hz; square wave pulse with a time constant of 0.5 ms; stimulation intensity, 40–160 mA) through spiral electrodes placed over the primary motor cortex and were recorded by needle electrodes inserted into the contralateral orbicularis oris, biceps, abductor pollicis brevis, and anterior tibialis muscles. When MEP amplitudes decreased by more than 50%, MEP stimulation was repeated, with increased stimulation intensity, and MEP changes were reported to the surgeon. The motor function of each patient was examined before and after surgery, using a reproducible scale. The relationship between MEP amplitude decreases and worsening motor status was analyzed using linear regression. RESULTS Preoperative neurological examinations revealed mild to moderate motor deficits (2/5 to 4/5) for 38% of patients (19 of 50 patients). Most of the patients (96%) exhibited recordable baseline MEPs. Persistent MEP decreases of more than 50% were noted for eight patients (16%) (11 muscles). The MEPs were completely abolished in two patients (three muscles). The degree of postoperative worsening of motor status was correlated with the degree of intraoperative MEP amplitude reduction (r = −0.864;P < 0.001). CONCLUSION Persistent intraoperative MEP reductions of more than 50% were associated with postoperative motor deficits. The degree of MEP amplitude reduction was correlated with postoperative worsening of motor status. Transcranial electrical MEP monitoring is feasible, safe, and valuable for brain tumor surgery.