Intraoperative direct cortical stimulation motor evoked potentials: Stimulus parameter recommendations based on rheobase and chronaxie (original) (raw)
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Stimulus Threshold for Providing Intraoperative Motor Evoked Potential
Medical Bulletin of Haseki, 2020
Intraoperative neurophysiological monitoring (IOM) has been increasingly used in surgeries associated with a risk of neurological impairment. Motor evoked potential (MEP), which is a part of intraoperative neurophysiological tests, evaluates motor function intraoperatively. Most anesthetic agents have negative effect on neurophysiologic recordings because of neuronal excitability changes. Our aim was to compare the effect of anesthetic methods consisting of volatile anesthetics and intravenous anesthetics (propofol + remifentanil) on eliciting of MEP during baseline recordings for spinal surgery which is a part of neurosurgical operations. Methods: Fifty patients (29 males and 21 females; 21 to 85 years) who underwent spinal surgery with IOM in our department between 2016 and 2018 were randomly chosen for retrospective evaluation. A multipulse stimulation technique (6-9 stimuli) was used for electrical stimulation. Results: There was a statistically significant difference in stimulus threshold in voltage stimulation between the two groups. In order to elicit muscle MEP, a higher voltage threshold had to be implemented for patients who had been given volatile anaesthesia compared to those who had been given total intravenous anesthesia (TIVA) (Mann-Whitney U test, p<0.005). Conclusion: TIVA is considered better than volatile for eliciting muscle MEPs in lower stimulus threshold. In addition, TIVA provides easy recording in all proximal and distal muscles.
Clinical Neurophysiology, 2007
Objective: To evaluate the efficacy of constant current transcranial electric stimulation (TES) parameters for eliciting muscle motor evoked potentials (MEPs) in the abductor pollicis brevis muscles (APB) and the tibialis anterior muscles (TA). The following parameters were tested intraoperatively: interstimulus interval (ISI), individual stimulation pulse duration within a train of five stimuli. Different montages of stimulating electrodes were assessed for effectiveness and focality. Further, reference values for APB and TA motor thresholds in neurosurgical patients with normal motor status under total intravenous anesthesia were determined. Methods: Motor thresholds of contralateral muscle MEPs were determined at 0.1, 0.2, 0.4, and 0.5 ms pulse duration and ISIs of 2, 3, 4, and 5 ms using a train of five monophasic constant current pulses with C3/C4 (27 patients). The stimulating electrodes were positioned at C1, C2, C3, C4, Cz, and Cz+6 cm. Different montages were used to determine the most effective and the most focal stimulation montages for the APB and TA muscles (30 patients). Eighty-six patients with clinically normal motor function were studied for motor threshold reference values. Results: The prolongation of the pulse duration has the strongest effect to decrease the motor threshold, which proportionally increases the delivered charge. The lowest stimulation threshold to elicit muscle MEPs in the APB and TA muscles is achieved with a train of stimuli consisting of an individual stimulus pulse duration of 0.5 ms. An ISI of 4 ms gave the lowest motor thresholds, but did not reach statistical significance compared to 3 ms. The stimulating electrode montage C3/C4 (C4/C3) allows for the lowest stimulation thresholds, but the vigorous muscle contractions it has is a disadvantage. The most focal stimulating electrode montages for the contralateral APB muscles are C3/Cz and C4/Cz, respectively, and for the TA muscles Cz/Cz+6 cm. Conclusions: In adult neurosurgical patients with a normal motor status under total intravenous anesthesia, an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor thresholds. Pragmatically, C1/C2, resp., C2/C1 montage provides monitorable responses in both APB and TA muscles at reasonable stimulation thresholds without inducing movements disturbing surgery and especially microdissection. If the most focal hemispheric stimulation for the distal upper extremity muscles is required, the use of C3 or C4 referenced to Cz is recommended. Significance: The stimulation parameters within a train of five pulses with an individual pulse duration of 0.5 ms and an ISI of 4 ms provide the lowest motor threshold. These data confirm not only studies for D wave recovery but also provide optimal stimulation parameters for intraoperative near threshold stimulation.
Intraoperative motor evoked potential monitoring: overview and update
2006
Amidst controversy about methodology and safety, intraoperative neurophysiology has entered a new era of increasingly routine transcranial and direct electrical brain stimulation for motor evoked potential (MEP) monitoring. Based on literature review and illustrative clinical experience, this tutorial aims to present a balanced overview for experienced practitioners, surgeons and anesthesiologists as well as those new to the field. It details the physiologic basis, indications and methodology of current MEP monitoring techniques, evaluates their safety, explores interpretive controversies and outlines some applications and results, including aortic aneurysm, intramedullary spinal cord tumor, spinal deformity, posterior fossa tumor, intracranial aneurysm and peri-rolandic brain surgeries. The many advances in motor system assessment achieved in the last two decades undoubtedly improve monitoring efficacy without unduly compromising safety. Future studies and experience will likely clarify existing controversies and bring further advances.
Clinical neurophysiology, 2001
Objective and methods: Direct (D) and transynaptic, (i.e. indirect) (I) corticospinal tract (CT) discharges were simultaneously recorded epidurally with muscle motor evoked potentials (MEPs) in patients under different levels of anesthesia. The effects of the one, two or more equal electrical stimuli, applied transcranially or directly to the motor cortex, were studied at different interstimulus intervals (ISIs) to determine the optimal conditions for eliciting I and MEP responses. Results and conclusion: At anesthetic levels permiting large D and I responses to single stimuli, optimal D and I wave facilitation and MEPs occurred with two stimuli at ISIs greater than 4 ms (e.g. at 5.9 and 8 ms). When single electrical stimuli elicit only a D response, optimal MEP responses are determined by the number of stimuli and the recovery of CT ®bers excitability (e.g. at an ISI of 4 ms).
Neurophysiological mechanisms underlying motor evoked potentials in anesthetized humans
Clinical Neurophysiology, 2001
Direct (D) corticospinal tract discharges were recorded epidurally in patients at anesthetic depths suppressing indirect (I) activity and were elicited by two equal transcranial electrical stimuli. The recovery of amplitude of the second D wave (D2) was a function of the interstimulus interval (ISI) and the stimulus duration. For example, with a 100 micros pulse, there was no response at an ISI of 1.1 ms, but partial recovery occurred with a 500 micros pulse. This indicates a relative refractory component at this ISI. Both D2 amplitude and conduction time recovered completely using a 4 ms ISI, with evidence of increased amplitude and reduced conduction time (supernormality) at longer ISIs. These findings are relevant in explaining high frequency D and I discharges and facilitation of motor responses by two transcranial magnetic pulses. Furthermore, these data help to understand why an ISI of 4 ms would be optimal in eliciting limb muscle responses when a short train of transcranial stimuli elicits only D waves in anesthetized patients (Deletis et al., Clin Neurophysiol 112 (2001) 445).
World Neurosurgery, 2019
Corkscrew (CS) electrodes are usually used for transcranial electrical stimulation (TES) in the intraoperative monitoring of motor evoked potentials (MEP). Direct cranial stimulation with peg-screw (PS) electrodes can elicit MEP. The present study investigated the difference in the initial threshold between PS and CS electrodes for intraoperative MEP monitoring.-METHODS: We retrospectively analyzed TES-MEP monitoring for supratentorial surgery in 72 patients. Of these 72 patients, 44 were monitored with PS and CS electrodes (PS/CS group) and 28 were monitored with CS and CS electrodes (CS/CS group). TES was used to deliver electrical stimulation by a train of 4-pulse anodal constant current stimulation. The initial threshold in each electrode was checked and analyzed.-RESULTS: In the PS/CS group, the initial threshold with the PS electrode was 38.3 AE 15.1 mA (mean AE standard deviation) on the affected side, and the initial threshold with the CS electrode was 51.4 AE 13.9 mA on the unaffected side. The initial threshold with the PS electrode was significantly lower than that with the CS electrode (P [ 0.0001). In the CS/CS group, the initial threshold was 56.2 AE 16.5 mA on the affected side and 62.1 AE 18.6 mA on the unaffected side, with no statistically significant difference (P [ 0.23).-CONCLUSION: The initial threshold to elicit MEP was significantly lower with the PS electrode than with the CS electrode. A PS electrode can be used as a feasible stimulation electrode for TES-MEP.
Journal of Neurosurgery, 2006
Object The goal of this study was to compare motor evoked potentials recorded from muscles (muscle MEPs or corticomuscular MEPs) with corticospinal MEPs recorded from the cervical epidural space (spinal MEPs or corticospinal MEPs) to assess their efficacy in the intraoperative monitoring of motor function. Methods Muscle and spinal MEPs were simultaneously recorded during surgery in 80 patients harboring brain tumors. Each case was assigned to one of four groups according to final changes in the MEPs: 1) Group A, in which there was an increased amplitude in the muscle MEP with an increased I3 wave amplitude (12 cases); 2) Group B, in which there was no significant change in the MEP (43 cases); 3) Group C, in which there was a decreased muscle MEP amplitude (< 35% of the control) with a decreased I wave amplitude but an unchanged D wave (15 cases); or 4) Group D, in which there was an absent muscle MEP with a decreased D wave amplitude (10 cases). In patients in Group A, the incre...
Significance of cathodal stimulation for motor evoked potential monitoring
The Kitasato medical journal, 2017
Objective: Intraoperative motor evoked potential (MEP) monitoring is essential to reduce the risk of neurosurgical procedures damaging the motor system. The standard technique of recording MEP uses high-frequency anodal monopolar stimulation of the primary motor cortex. The present study investigated the possibility that cathodal stimulation allows MEP recording at lower intensities than does anodal stimulation in certain patients. Methods: Motor threshold (MT) was measured and compared for anodal and cathodal stimulation in 65 patients in Kitasato University Hospital. The patients were divided into 3 groups based on the polarity of the lower MT: anodal less than cathodal stimulation (Group A), cathodal less than anodal stimulation (Group B), and anodal similar to cathodal stimulation (Group C). Magnetic resonance (MR) imaging findings of hyperintensity extending to the precentral knob accompanied by brain tumor were evaluated to correlate with the polarity of lower MT. Results: The...
Clinical Neurophysiology, 2007
Objective: To explore the significance of intra-operative motor evoked potentials (MEPs) obtained by monopolar and bipolar stimulation in determining the location of the electrode(s) giving most pain relief in chronic motor cortex stimulation (MCS). Methods: Eight patients with chronic refractory neuropathic pain were implanted epidurally with two parallel leads of four electrodes each and placed normal to the central sulcus (CS). We measured the peak-peak amplitude (V p-p) of the MEPs recorded intra-operatively at the contralateral hand with the same stimulus delivered by each single electrode used as an anode or a cathode. Those electrodes giving the largest MEPs in monopolar stimulation were also tested in bipolar stimulation with an adjacent electrode located on the same or the other lead. It was analyzed whether a relation was present between the electrode providing the largest V p-p in the monopolar condition and the bipolar combination selected for chronic stimulation. Results: In monopolar stimulation the median amplitude of MEPs evoked with an anode was 59% larger than with a cathode. The mean amplitude of the bipolarly evoked MEPs was only 21% and 37%, respectively, of the corresponding monopoles when the anode and cathode were separated by 6 mm and by more than 8 mm. A significant pain relief was obtained in 5 out of 8 patients post-operatively. In all these patients, one of the cathodes used in chronic stimulation was one of the anodes producing the largest MEP intra-operatively. Conversely, in the 3 patients who did not benefit from MCS, one of the cathodes used in chronic stimulation was one of the cathodes producing the largest MEPs intra-operatively. Conclusions: Monopolar stimulation should be applied in intra-operative neurophysiological testing because, contrary to bipolar stimulation, the corresponding MEPs are unambiguously related to a single stimulating electrode and their amplitude is not affected by the anode-cathode distance. The anode providing the largest MEPs intra-operatively should be selected as the cathode in chronic stimulation. However, implantable pulse generators allowing monopolar (cathodal and anodal) stimulation for MCS should become available to compare the respective analgesic efficacy of monopolar and bipolar chronic cortical stimulation. Significance: Intra-operative MEP recordings can predict which electrode should be used as the cathode to obtain the best analgesic effect with chronic MCS.