Transcranial Electrical Motor Evoked Potentials Research Articles

Transcranial electric motor evoked potential monitoring during scoliosis surgery in children with cerebral palsy and active seizure disorder: is it feasible and safe?

Use of spinal cord monitoring in children with cerebral palsy (CP) and neuromuscular scoliosis is challenging. The previous reports suggest low success rates in the setting of CP, and it is unclear if transcranial electric motor evoked potentials (TcMEP) monitoring is contraindicated in patients with an active seizure disorder. The purpose of this study was to determine (1) are patients with CP able to be appropriately monitored with TcMEP? and (2) does TcMEP cause an increase in seizure activity? This was an institutional review board-approved retrospective cohort study observing 304 patients from 2011 to 2020. Inclusion criteria included all patients with CP undergoing posterior spinal fusion during this time. Intraoperative data were examined for the ability to obtain monitoring and any intraoperative events. Patients were followed for 3months postoperatively to determine any increase in seizure activity that could have been attributed to the TcMEP monitoring. Of the 304 patients who were observed, 21% (20.8%) were unable to be monitored due to lacking baseline signals from the extremities. Seventy-seven percent (77.5%) were successfully monitored with TcMEP. For these patients, no increased seizure activity was documented either intra- or postoperatively. A high percentage of children (77.5%) with CP were able to be successfully monitored with TcMEP during posterior spinal fusion. Furthermore, the concerns about increased seizure activity after TcMEP were not supported by the data from this cohort. Technical details of successful neuromonitoring in these patients are important and included increased stimulation voltage requirements and latency times. III retrospective comparative study.

[Comparison of intraoperative neurophysiological monitoring between patients with arthrogryposis multiplex congenita and adolescent idiopathic scoliosis].

Objective: To compare the intraoperative neurophysiological monitoring (IONM) results between patients with arthrogryposis multiplex congenita (AMC) and adolescent idiopathic scoliosis (AIS) and to analyze the influence of congenital spinal deformity on IONM in AMC patients, thus to evaluate the efficiency of IONM in AMC patients. Methods: A cross-sectional study. The clinical data of 19 AMC patients underwent correction surgery from July 2013 to January 2022 in Nanjing Drum Tower Hospital were retrospectively reviewed. There were 13 males and 6 females with a mean age of (15.2±5.6) years, and the average Cobb angle of main curve was 60.8°±27.7°. And 57 female AIS patients of similar age and curve type with the AMC patients during the same period were selected as the control group, with an average age of (14.6±4.4) years and a mean Cobb angle of 55.2°±14.2°. The latency and amplitude of samatosensory evoked potentials (SSEPs) and transcranial electric motor evoked potentials (TCeMEPs) were compared between the two groups. The difference in IONM data between AMC patients with and without congenital spinal deformity was also evaluated. Results: The success rates of SSEPs and TCeMEPs were 100% and 14/19 for AMC patients, 100% and 100% for AIS patients. The SSEPs-P40 latency, SSEPs-N50 latency, SSEPs-amplitude, TCeMEPs-latency, TCeMEPs-amplitude showed no significant difference between AMC patients and AIS patients (P>0.05 for all). The side-difference of TCeMEPs-amplitude showed an increasing trend in AMC patients when compared with that in AIS patients, but there was no statistical difference between the two groups [(147.0±185.6) μV vs (68.1±311.4) μV, P=0.198]. The SSEPs-amplitude value was (1.4±1.1) μV on concave side in AMC patients with congenital spinal deformity, and it was (2.6±1.2) μV on concave side in AMC patients without congenital spinal deformity (P=0.041). The SSEPs-amplitude value was (1.4±0.8) μV on convex side in AMC patients with congenital spinal deformity, and it was (2.6±1.3) μV on convex side in AMC patients without congenital spinal deformity (P=0.028). Conclusions: The values of SSEPs-P40 latency, SSEPs-N50 latency, SSEPs-amplitude, TCeMEPs-latency and TCeMEPs-amplitude are similar in AMC and AIS patients. The SSEPs-amplitude of AMC patients with congenital spinal deformity is lower than that of AMC patients without congenital spinal deformity.

Cathodal Genesis of Ipsilateral Hand (Crossover) Motor Evoked Potentials: Evidence from a Patient with Previous Stroke

ABSTRACT A case is described where baseline transcranial electrical motor evoked potentials (TcMEP) and somatosensory evoked potentials (SSEP) results were unilaterally absent in a patient with previous hemispheric stroke undergoing a right-sided carotid endarterectomy. SSEP data confirmed right cortical pathology and excluded a technical rationale for absent motor evoked responses. Attempts at generating left-hand (contralateral) TcMEP from right cortical anodal stimulation failed despite high stimulus intensities. However, TcMEP responses from anodal stimulation of the right cortex were recorded from the right-hand (ipsilateral) which were attributed to “crossover.” Ipsilateral TcMEP onset latencies derived from the stimulus-response data supports the idea that crossover is a product of cathodal stimulation initially acting on pericortical motor pathways.

Intraoperative Transcranial Electrical Motor Evoked Potential (TceMEP) as a Therapeutic Tool in Spine Surgery: A Case Series Report

ABSTRACT We report two cases of unilateral loss of TceMEP secondary to spinal instrumentation errors and the subsequent recovery of TceMEP responses following prompt intervention. During the period of TceMEP loss, there were no concomitant SSEP changes beyond the threshold criteria. Postoperative physical examination revealed normal strength and motion in the affected extremities in both patients. These cases illustrate that in addition to being a reliable intraoperative diagnostic tool, TceMEP monitoring displays therapeutic usefulness in appraising corrective actions to the existential risk of neurological injuries.

The utility of intraoperative neurophysiological monitoring in surgical treatment for spinal arteriovenous malformations: A historical control study

ObjectiveThis study sought to investigate the utility of intraoperative neurophysiological monitoring (IONM) in the surgical treatment for spinal arteriovenous malformations (SAVMs). MethodsWe retrospectively reviewed the data of 39 patients who underwent surgical treatment for SAVMs. Twenty-eight patients who received multimodal IONM (transcranial electrical motor-evoked potentials [MEPs], somatosensory-evoked potentials, continuous electromyography, and bulbocavernosus reflex [BCR]) between 2011 and 2020 were compared to 11 historical controls between 2003 and 2011. The rates of postoperative neurological deficits (PNDs), neurophysiological warnings, and their characteristics were analyzed. ResultsPNDs were developed in 10.7% and 54.5% of patients in the IONM and historical control (non-IONM) groups, respectively (p = 0.008). Moreover, not applying IONM was the only significant risk factor for the development of PNDs in the logistic regression analysis (odds ratio 10.0, p = 0.007). In the IONM group, a total of three electrophysiological warnings were observed, and two of these were true positives; one patient complained of leg motor weakness after surgery with loss of the abductor halluces MEPs. The other patient experienced disappearance of the BCR during surgery and newly developed urinary retention. Overall, the sensitivity, specificity, positive predictive value, and negative predictive value of IONM warnings for detecting PNDs were 66.7%, 96.0%, 66.7%, and 96.0%, respectively. ConclusionsThe neurological outcome of the IONM group was significantly better than that of the historical control group in the surgical treatments for SAVMs. SignificanceMultimodal IONM could be a useful tool to detect neurological damage with relatively high accuracy in this type of surgery.

Effect of Sugammadex During Transcranial Electrical Motor Evoked Potentials Monitoring in Spinal Surgery: A Randomized Controlled Trial.

Neuromuscular blockade suppresses transcranial electrical motor evoked potential (TceMEP) amplitude and is usually avoided during TceMEP monitoring. In this randomized controlled trial, we investigated whether rocuronium-induced suppression of TceMEP amplitude could be reversed by sugammadex in patients undergoing spine surgery. Seventy-six patients undergoing spinal surgery were randomly allocated into sugammadex and control groups. In the sugammadex group, a rocuronium infusion was titrated to maintain moderate neuromuscular blockade (2 twitches on train-of-four) until dural opening when the rocuronium infusion was discontinued and 2 mg/kg sugammadex administered. In the control group, no neuromuscular blockade was administered after induction of anesthesia. The primary outcome was a comparison between sugammadex and control groups of mean TceMEP amplitudes in the abductor pollicis brevis muscles of both upper extremities 5 minutes after dural. Secondary outcomes included TceMEP amplitudes at 10, 20, 30, and 60 minutes after dural opening. Sixty-six patients were included in the analysis. TceMEP amplitudes were significantly greater in the sugammadex group (629 μV, interquartile range: 987 μV) than in the control group (502 μV, interquartile range: 577 μV; P =0.033) at 5 minutes after dural opening. TceMEP amplitudes were also greater in the sugammadex group at 10 minutes ( P =0.0010), 20 minutes ( P =0.003), 30 minutes ( P =0.001), and 60 minutes ( P =0.003) after dural opening. Moderate neuromuscular blockade induced by continuous infusion of rocuronium was effectively reversed by sugammadex. This suggests that sugammadex could be used to enhance TceMEP waveform monitoring during spine surgery requiring muscle relaxation.

Low-dose Droperidol Reduces the Amplitude of Transcranial Electrical Motor-evoked Potential: A Randomized, Double-blind, Placebo-controlled Trial.

Low-dose droperidol has been reported to suppress the amplitude of transcranial electrical motor-evoked potentials (TCE-MEPs), but no randomized controlled trials have been conducted to assess this. This randomized, double-blinded, placebo-controlled trial aimed to test the hypothesis that low-dose droperidol reduced TCE-MEP amplitudes. Twenty female patients with adolescent idiopathic scoliosis, aged between 12 and 20 years, and scheduled to undergo corrective surgery were randomly allocated to receive droperidol (20 µg/kg) or 0.9% saline. After recording baseline TCE-MEPs, the test drug was administered, following which TCE-MEP recordings were carried out every 2 minutes for up to 10 minutes. The primary outcome was the minimum relative TCE-MEP amplitude (peak-to-peak amplitude, percentage of baseline value) recorded in the left tibialis anterior muscle. Secondary outcomes included minimum relative MEP amplitudes recorded from all other muscle groups monitored in the study. Data are expressed as medians (interquartile range). The TCE-MEP amplitude of the left tibialis anterior muscle was significantly reduced following droperidol administration compared with saline (37% [30% to 55%] vs. 76% [58% to 93%], respectively, P <0.01). In the other muscles, the amplitudes were reduced in the droperidol group, except for the bilateral abductor pollicis brevis and the left quadriceps femoris muscles. The relative amplitude of the bilateral F waves recorded from the gastrocnemius was decreased in the droperidol group. Low-dose droperidol (20 µg/kg) reduced TCE-MEP amplitudes. Anesthesiologists should pay attention to the timing of droperidol administration during intraoperative TCE-MEP recordings, even if used in a low dose.

P-IM003. The utility of intraoperative Neurophysiological monitoring in surgical correction for spinal arteriovenous shunts: A historical control study

Introduction . This study aimed to investigate the utility of intraoperative neurophysiological monitoring (IONM) in surgical correction for spinal arteriovenous shunts (SAVSs). Methods . We retrospectively reviewed 42 patients underwent surgical correction for SAVSs. 29 patients who underwent multimodal IONM (transcranial electrical motor-evoked potentials [tcMEP], somatosensory-evoked potentials [SSEP], continuous electromyography, and bulbocavernosus reflex [BCR]) from 2011 to 2020 were compared to 13 historical controls (non-IONM groups) from 2003 to 2009. The rates of postoperative neurological deficits, neurophysiological warnings, and their characteristics were analyzed. Postoperative neurological deficits were evaluated at one month, six months, and one year after surgery, respectively. Results . Among 42 patients, postoperative neurological deficit rates were 13.8% and 46.2% in the IONM and non-IONM groups, respectively (p = 0.046). In total, 5 warnings were observed during IONM (3 tcMEP; 1 tcMEP and SSEP; 1 BCR). Three cases were true-positive. The amplitude of right abductor halluces MEP decreased during surgery in patient 1 who had no weakness of the right leg previously. After surgery, weakness of right leg was newly observed in patient 1. Patient 2 who had both leg weakness previously got worse both leg weakness than before surgery. Her left abductor halluces MEP disappeared and never recovered during surgery. Patient 3 had normal bladder function before surgery. His baseline BCR was successfully recorded but the end of the surgery, the bilateral BCR was completely disappeared. He had severe urinary retention after surgery. Sensitivity, specificity, positive predictive value, and negative predictive value of IONM warnings for detecting postoperative neurological complications were 75.0%, 92.0%, 60.0%, and 95.8% respectively. Conclusion . The utility of IONM in surgical correction for SAVSs has not been evaluated due to its rarity. This is the first study to provide results revealing that IONM helps to improve postoperative neurological outcome through comparison with non-IONM group in surgical correction for SAVSs.

Propofol reduces the amplitude of transcranial electrical motor-evoked potential without affecting spinal motor neurons: a prospective, single-arm, interventional study.

Propofol inhibits the amplitudes of transcranial electrical motor-evoked potentials (TCE-MEP) in a dose-dependent manner. However, the mechanisms of this effect remain unknown. Hence, we investigated the spinal mechanisms of the inhibitory effect of propofol on TCE-MEP amplitudes by evaluating evoked electromyograms (H-reflex and F-wave) under general anesthesia. We conducted a prospective, single-arm, interventional study including 15 patients scheduled for spine surgery under general anesthesia. Evoked electromyograms of the soleus muscle and TCE-MEPs were measured at three propofol concentrations using target-controlled infusion (TCI: 2.0, 3.0, and 4.0µg/mL). The primary outcome measure was the left H-reflex amplitude during TCI of 4.0- compared to 2.0-µg/mL propofol administration. The median [interquartile range] amplitudes of the left H-reflex were 4.71 [3.42-6.60] and 5.6 [4.17-7.46] in the 4.0- and 2.0-μg/mL TCI groups (p = 0.4, Friedman test), respectively. There were no significant differences in the amplitudes of the right H-reflex and the bilateral F-wave among these groups. However, the TCE-MEP amplitudes significantly decreased with increased propofol concentrations (p < 0.001, Friedman test). Propofol did not affect the amplitudes of the H-reflex and the F-wave, whereas TCE-MEP amplitudes were reduced at higher propofol concentrations. These results suggested that propofol can suppress the TCE-MEP amplitude by inhibiting the supraspinal motor pathways more strongly than the excitability of the motor neurons in the spinal cord.

Distal Stimulation Site at the Medial Tibia for Saphenous Nerve Somatosensory Evoked Potentials (DSn-SSEPs) in Lateral Lumbar Spine Procedures

ABSTRACT Lateral lumbar interbody fusion procedures are performed with multimodality neuromonitoring of the femoral nerve to prevent lumbosacral plexus and peripheral nerve injury from positioning, dilation, retraction, and hardware implantation. The integrity of the femoral nerve can be continuously assessed during these procedures by Somatosensory Evoked Potentials of the Saphenous nerve (Sn-SSEPs). Sn-SSEPs are technically challenging to acquire and necessitate advanced troubleshooting skills with a more rigid anesthetic regimen and physiological parameters. We performed a retrospective analysis of Sn-SSEP data for 100 consecutive lateral lumbar surgeries where the stimulation electrodes were placed distally below the knee and medial to the tibia bone (i.e., DSn-SSEPs). Monitorable baseline responses were present in 87% of patients after the exclusion of fourteen cases where the tibial nerve SSEP was absent, quadriceps transcranial electrical motor evoked potentials (TCeMEPs) were absent or not utilized. Sex, age, body mass index (BMI), diagnosis, mean arterial pressure (MAP), inhalational anesthetic levels, reliability of ulnar and posterior tibial nerve SSEPs, and the reliability of femoral nerve innervated quadriceps TCeMEPs were evaluated but were not of statistically significant consequence between cases where the DSn-SSEP was present or absent in this study. We found the utilization of DSn-SSEPs to be a valuable adjunct to femoral nerve monitoring. Stimulation electrode placement is easy to palpate with clear anatomical borders. Significant muscle artifact and patient movement from stimulation do not affect waveform morphology, allowing for continuous and reliable monitoring. We recommend including DSn-SSEPs to optimize recordings during lateral lumbar procedures.

Neurophysiological monitoring during anterior cervical discectomy and fusion for ossification of the posterior longitudinal ligament

ObjectiveThis study aimed to investigate the value of intraoperative neurophysiological monitoring (IONM) in anterior cervical spine discectomy with fusion (ACDF) for ossification of the posterior longitudinal ligament (OPLL). MethodsPatients who underwent multimodal IONM (transcranial electrical motor-evoked potentials [tcMEP], somatosensory-evoked potentials, and continuous electromyography) for ACDF from 2009 to 2019 were compared to historical controls from 2003 to 2009. The rates of postoperative neurological deficits, neurophysiological warnings, and their characteristics were analyzed. ResultsAmong 196 patients, postoperative neurological deficit rates were 3.79% and 14.06% in the IONM and historical control (non-IONM) groups, respectively (p < 0.05). The use of IONM (OR: 0.139, p = 0.003) and presence of myelopathy (OR: 8.240, p = 0.013) were associated with postoperative neurological complications on multivariate regression. In total, 23 warnings were observed during IONM (17 tcMEP and/or electromyography; six electromyography). Sensitivity and specificity of IONM warnings for detecting neurological complications were 84.2% and 93.7%, respectively. ConclusionsIONM, especially multimodal IONM, may be a useful tool to detect neurological damage in ACDF for high-risk conditions such as OPLL with pre-existing myelopathy. SignificanceThe utility of IONM in ACDF for OPLL has not been evaluated due to its rarity. This study supports the use of IONM in cervical OPLL with myelopathy.

Utility of Motor and Somatosensory Evoked Potentials for Neural Thermoprotection in Ablations of Musculoskeletal Tumors

PurposeTo characterize the utility of monitoring transcranial electrical motor evoked potentials (TCeMEPs) and somatosensory evoked potentials (SSEPs) for neural thermoprotection during musculoskeletal tumor ablations. Materials and MethodsRetrospective review of 29 patients (16 male; median age, 46 y; range, 7–77 y) who underwent musculoskeletal tumor radiofrequency ablation (n = 8) or cryoablation (n = 22) with intraprocedural TCeMEP and SSEP monitoring was performed. The most common tumor histologies were osteoid osteoma (n = 6), venous malformation (n = 5), sarcoma (n = 5), renal cell carcinoma (n = 4), and non–small-cell lung cancer (n = 3). The most common tumor sites were spine (n = 22) and lower extremities (n = 4). Abnormal TCeMEP change was defined by 100-V increase above baseline threshold activation for a given myotome; abnormal SSEP change was defined by 60% reduction in baseline amplitude and/or 10% increase in latency. ResultsAbnormal changes in TCeMEP (n = 9; 30%) and/or SSEP (n = 5; 17%) occurred in 12 procedures (40%) and did not recover in 5 patients. Patients with unchanged TCeMEP/SSEP activities throughout the procedure (n = 18) did not have motor or sensory symptoms after the procedure; 3 (60%) with unrecovered activity changes and 2 (29%) with transient activity changes had new motor (n = 1) or sensory (n = 4) symptoms. Relative risk for neurologic sequelae for patients with unrecovered TCeMEP/SSEP changes vs those with transient or no changes was 7.50 (95% confidence interval, 1.66–33.9; P = .009). ConclusionsAbnormal activity changes of TCeMEP or SSEP during percutaneous ablative procedures correlate with postprocedural neurologic sequelae.

Bulbocavernosus Reflex Monitoring During Intramedullary Conus Tumor Surgery

A T10 to L2 spinal cord tumor exploration and biopsy was performed with intraoperative neurophysiological monitoring (IONM) on a 75-year-old male diagnosed with an intradural intramedullary appearing spinal cord lesion with no other lesions in the central nervous system, chest, abdomen or pelvis.Intraoperative neurophysiology consisted of transcranial electrical motor evoked potentials (TCeMEPs), somatosensory evoked potentials (SSEPs), triggered and spontaneous electromyography (S-EMG, T-EMG), bulbocavernosus reflex (BCR) and train of four (TOF) monitoring. Loss of BCR responses during conus exposure and identification were resolved with multiple small pauses in manipulation throughout the procedure. T-EMG mapping aided in identification and avoiding the removal of nervous tissue.Postoperatively the patient experienced some mild weakness in his left foot and leg that correlated with a significant amplitude drop in the left abductor hallucis TCeMEP. By the following day, the patient was almost back to preoperative baseline. The patient’s bowel and bladder function were preserved, consistent with final BCR recordings. The patient was discharged to rehabilitation postoperatively. Pathology results indicated glioblastoma.This case study demonstrates the utility of a multimodality approach with bulbocavernosus reflex and urethral sphincter monitoring to optimize intraoperative data to the surgeon during conus tumor surgeries.

Anterolateral S1 screw malposition detected with intraoperative neurophysiological monitoring during posterior lumbosacral fusion.

Background:The standard of care is to utilize intraoperative neurophysiological monitoring (IOM) of triggered electromyography (tEMG) during posterior lumbosacral instrumented-fusion surgery. IOM should theoretically signal misplacement of S1 screws into the neural L5–S1 foramen or spinal canal, utilizing screw stimulation, and recording of the lower limb muscles and the anal sphincter. Here, we evaluated when and whether anterolateral S1 screw malposition could be detected by IOM/tEMG during open posterior lumbosacral instrumented fusion surgery.Methods:tEMG, somatosensory-evoked potential (SSEP), and transcranial electrical motor-evoked potential (TcMEP) data were retrospectively reviewed from 2015 to 2017 during open posterior lumbosacral instrumented fusions. We utilized screw stimulation alert thresholds of <14 mA (tEMG) and recorded from the lower extremity muscles and anal sphincter. Furthermore, all patients underwent routine postoperative computed tomography (CT) scans to confirm the screw location.Results:There were 106 S1 screws placed in 54 patients: 52 bilateral and 2 unilateral. In 6 patients (11.1%), 7 screws (6.6%) registered at low tEMG thresholds. In 1 patient, the postoperative CT scan documented external malposition of the screw despite no intraoperative IOM/tEMG alert. When S1 misplaced screws were stimulated, the most sensitive muscle was the tibialis anterior; the sensitivity of the IOM/tEMG was 87.5%, the specificity was 97.9%, the positive predictive value was 77.8%, and the negative predictive value was 98.9%. TcMEP and SSEP did not change during any of the operations. Notably, no patient developed a new neurological deficit.Conclusion:Anterolateral S1 screw malposition can be detected accurately utilizing IOM/tEMG stimulation of screws. When alerts occur, they can largely be corrected by partially backing out the screw (e.g., a few turns) and/ or changing the screw trajectory.

Scoliosis in chronic neuronopathic Gaucher disease: Characterization in the treatment era

Intraoperative monitoring (IOM) using somatosensory-evoked potentials (SSEPs) plays an important role in reducing iatrogenic neurologic deficits during corrective pediatric idiopathic procedures for scoliosis. However, for unknown reasons, recent reports have cited that the sensitivity of SSEPs to detect neurologic deficits has decreased, in some to be less than 50%. This current trend, which is coincident with the addition of transcranial motor-evoked potentials, is surprising given that SSEPs are robust, reproducible responses that were previously shown to have sensitivity and specificity of >90%.Our primary aim was to assess whether SSEPs alone can detect impending neurologic deficits with similar sensitivity and specificity as originally reported. Our secondary aim was to estimate the potential predictive value of adding transcranial motor-evoked potentials to SSEP monitoring in idiopathic scoliosis procedures.This was a retrospective review to analyze the efficacy of SSEP monitoring in the group of pediatric instrumented scoliosis fusion cases.We retrospectively reviewed all consecutive cases of patients who underwent idiopathic scoliosis surgery between 1999 and 2009 at Children’s Hospital of Pittsburgh. We identified 477 patients who had the surgery with SSEP monitoring alone. Exclusion criteria included any patients with neuromuscular disorders or unreliable SSEP monitoring. Patients who had incomplete neurophysiology data or incomplete postoperative records were also excluded.Major outcomes measured were clinically significant postoperative sensory or motor deficits, as well as significant intraoperative SSEP changes.Continuous interleaved upper- and lower-extremity SSEPs were obtained throughout the duration of all procedures. We considered a persistent 50% reduction in primary somatosensory cortical amplitude or a prolongation of response latency by >10% from baseline to be significant. Persistent changes represent significant deviation in SSEP amplitude or latency in more than two consecutive averaged trials. Patients were classified into one of four categories with respect to SSEP monitoring: true positive, false positive, true negative, and false negative. The sensitivity, specificity, positive predictive value, and negative predictive value were then calculated accordingly.Our review of 477 idiopathic scoliosis surgeries monitored using SSEPs alone revealed a new deficit rate of 0.63% with no cases of permanent injury. Sensitivity = 95.0%, specificity = 99.8%, positive predictive value = 95%, negative predictive value = 99.8%. Using evidence-based epidemiologic measures, we calculated that the number needed to treat was 1,587 patients for one intervention to be performed that would have been missed by SSEP monitoring alone. In addition, the number needed to harm, which represents the increase in false positives with the addition of transcranial electrical motor-evoked potentials, was 200.SSEP monitoring alone during idiopathic scoliosis continues to be a highly reliable method for the detection and prevention of iatrogenic injury. Our results confirm the high sensitivity and specificity of SSEP monitoring alone published in earlier literature. As such, we suggest the continued use of SSEP alone in idiopathic scoliosis surgeries. At this time we do not believe there are sufficient data to support the addition of MEP monitoring, although more studies and revised criteria for the use of MEP may provide added value for its use in the future.

Design and Evaluation of a Novel Laminectomy Auxiliary Device Based on Rats.

Most types of spinal cord injury (SCI) observed in humans can be replicated in adult rat models, which are widely used for laboratory studies of SCI rehabilitation. To ensure the effectiveness and efficiency of an SCI rat model, the minimal time spent performing the laminectomy procedure and the damage caused to the body are of great importance. We describe and evaluate the effectiveness and advantages of a laminectomy auxiliary device (LAD) for removing the rat vertebral lamina without injuring the spinal cord. The incision size, success rate, operation duration, body weight, BBB score, step detection, latency and amplitude of transcranial electrical motor-evoked potentials (tceMEPs), and serum MDA and SOD levels were recorded in 8 normal rats, 8 rats treated with traditional laminectomy and 8 rats treated with LAD laminectomy. Compared with traditional laminectomy, in our LAD, the surgical incision was smaller (approximately 2.2 and 1.3 cm, respectively), the success rate was higher (88.89% and 100%, respectively) and the duration shorter (14.644±1.617 and 4.821±0.668 minutes, respectively). Compared with normal rats, those treated with either laminectomy using LAD or the traditional method showed slower body weight gain and temporarily increased oxidative stress levels. However, there were no significant differences between these two groups. Our results show that laminectomy using this LAD provides three main advantages in rats: a high success rate, time savings, small incisions and reduced trauma. We believe this LAD can be used as an effective assistant tool for rodent laminectomy.

Intraoperative neuromonitoring in spine deformity surgery: modalities, advantages, limitations, medicolegal issues - surgeons' views.

In spine deformity surgery, iatrogenic neurologic injuries might occur due to the mechanical force applied to the spinal cord from implants, instruments, and bony structures, or due to ischemic changes from vessel ligation during exposure and cord distraction/compression during corrective manoeuvres.Prompt reaction within the reversible phase (reducing of compressive/distractive forces) usually restores functionality of the spinal cord, but if those forces continue to persist, a permanent neurological deficit might be expected.With monitoring of sensory pathways (dorsal column–medial lemniscus) by somatosensory-evoked potentials (SSEPs), such events are detected with a sensitivity of up to 92%, and a specificity of up to 100%.The monitoring of motor pathways by transcranial electric motor-evoked potentials (TceMEPs) has a sensitivity and a specificity of up to 100%, but it requires avoidance of halogenated anaesthetics and neuromuscular blockades.Different modalities of intraoperative neuromonitoring (IONM: SSEP, TceMEP, or combined) can be performed by the neurophysiologist, the technician or the surgeon. Combined SSEP/TceMEP performed by the neurophysiologist in the operating room is the preferable method of IONM, but it might be impractical or unaffordable in many institutions. Still, many spine deformity surgeries worldwide are performed without any type of IONM. Medicolegal aspects of IONM are different worldwide and in many cases some vagueness remains.The type of IONM that a spinal surgeon employs should be reliable, affordable, practical, and recognized by the medicolegal guidelines.Cite this article: EFORT Open Rev 2020;5:9-16. DOI: 10.1302/2058-5241.5.180032

Transcranial electrical stimulation motor-evoked potentials in a spinal cord ischaemia rabbit model

BackgroundSpinal cord ischaemia animal models were established by selective ligation of the lumbar artery in a craniocaudal direction between the renal artery and the aortic bifurcation. Transcranial electrical stimulation motor-evoked potentials were measured to enable their use in future studies on spinal cord ischaemia protection.MethodsThirty-three New Zealand rabbits were randomly divided into 6 groups. Transcranial electrical stimulation motor-evoked potentials were recorded before vascular ligation, 30 min after vascular ligation, and 2 days after vascular ligation. Motor functions were assessed after surgery and 2 days after vascular ligation. The specimens were taken 2 days after ligation for histopathologic observation.ResultsWith increased numbers of ligations, a transient extension of the latency became clear, but there were no significant differences in the statistical analysis. Analysis of variance after ligation at the same time in each group and t tests before and after ligation (P > 0.05) were not significant. One or 2 ligations did not cause spinal cord ischaemic damage. There were no significant differences before and after ligation for the amplitude (P > 0.05). With increased numbers of ligations, the amplitude before and after ligation was gradually reduced in the 3–5 ligation groups (P < 0.05).ConclusionsLigation of segmental spinal cord vessels on 1 or 2 levels did not cause ischaemic damage. Spinal cord ischaemia was observed after 3, 4, or 5 ligations. The amplitude was more sensitive to spinal cord ischaemia than latency. Spinal cord function can be predicted by early changes in the amplitude.

A Bolus Dose of Ketamine Reduces the Amplitude of the Transcranial Electrical Motor-evoked Potential: A Randomized, Double-blinded, Placebo-controlled Study.

A low-dose bolus or infusion of ketamine does not affect transcranial electrical motor-evoked potential (MEP) amplitude, but a dose ≥1 mg/kg may reduce MEP amplitude. We conducted a randomized, double-blinded, placebo-controlled study to evaluate the effect of ketamine (1 mg/kg) on transcranial electrical MEP. Twenty female patients (aged 12 to 18 y) with adolescent idiopathic scoliosis scheduled to undergo posterior spinal fusion were randomly allocated to receive ketamine or saline. General anesthesia was induced and maintained with continuous infusions of propofol and remifentanil. MEP was elicited by supramaximal transcranial electrical stimulation. MEP recordings were obtained at baseline and then at 2, 4, 6, 8, and 10 minutes after administration of ketamine (1 mg/kg) or saline (0.1 ml/kg). The primary endpoint was the minimum relative MEP amplitude (peak-to-peak amplitude, % of baseline value) recorded from the left tibialis anterior muscle. The baseline amplitude recorded before test drug administration was defined as 100%. Medians (interquartile range) minimum MEP amplitudes in the left tibialis anterior muscle in the ketamine and saline groups were 26% (9% to 34%) and 87% (55% to 103%) of the baseline value, respectively (P<0.001). MEP amplitudes in other muscles were significantly reduced by ketamine. The suppressive effect of ketamine lasted for at least 10 minutes in each muscle. A 1-mg/kg bolus dose of ketamine can reduce MEP amplitude. Anesthesiologists should consider the dosage and timing of intravenous ketamine administration during MEP monitoring.

Intraoperative Triggered Electromyography Recordings from the External Urethral Sphincter Muscles During Spine Surgeries.

Introduction: Bowel and bladder function are at risk during tumor resection and other surgeries of the conus, cauda equina, and nerve roots. This study demonstrates the ability to acquire triggered electromyography (t-EMG) from the external urethral sphincter (EUS) muscles by utilizing a urethral catheter with an electrode attached.Methods: A retrospective analysis of neurophysiological monitoring data from two medical centers was performed. Seven intradural tumors and three tethered cord release surgeries that used urethral sphincter electrodes to record t-EMG were included in the analysis. The patients consisted of five females and five males with ages ranging from eight months to 67 years (median: 49 years). Our neuromonitoring paradigm included upper and lower extremity somatosensory evoked potentials (SSEPs) and transcranial electrical motor evoked potentials (TCeMEPs), as well as spontaneous and triggered electromyography (EMG) from the external anal sphincter (EAS), EUS muscles and lower extremity muscles bilaterally. A catheter with urethral electrodes attached was used for recording spontaneous electromyography (s-EMG), t-EMG, and TCeMEPs from the skeletal muscle of the EUS. Train of four (TOF) was also recorded from the abductor hallucis muscle as well for monitoring the level of muscle relaxant.Results: We were able to successfully record t-EMG responses from the EUS muscles in all patients (100%). It is worthy to note that only one patient presented preoperatively with bladder incontinence, urgency, and frequency. Almost immediately in the postoperative phase, the patient’s frequency and urgency improved, and the bladder function normalized within two weeks of having the tumor removed.Conclusions: In this small series, we were able to acquire t-EMG in 100% of patients when recorded from the EUS using a urethral catheter with electrodes built into it. T-EMGs can be attempted in surgeries that put the function of the pelvic floor at risk. More study is needed to establish better statistical methods, better modality efficacy, and a better understanding of intraoperative countermeasures that may be employed when an alert is encountered to prevent impending neurological sequelae.