Multimodality monitoring of the central nervous system using motor-evoked potentials

Effect of dexmedetomidine on somatosensory- and motor-evoked potentials in patients receiving craniotomy under propofol-sevoflurane combined anesthesia

Introduction

Dexmedetomidine is often used as an adjunct to total intravenous anesthesia (TIVA) for procedures requiring intraoperative neurophysiologic monitoring (IONM). However, it has been reported that dexmedetomidine might mask the warning of a neurological deficit on intraoperative monitoring.

Methods

We reviewed the intraoperative neurophysiological monitoring data of 47 patients who underwent surgery and IONM from March 2019 to March 2021 at the Department of Neurosurgery, Renmin Hospital of Wuhan University. Pre- and postoperative motor function scores were recorded and analyzed. Dexmedetomidine was administered intravenously at 0.5 μg/kg/h 40 min after anesthesia and discontinued after 1 h in the dexmedetomidine group.

Results

We found that the amplitude of transcranial motor-evoked potentials (Tce-MEPs) was significantly lower in the dexmedetomidine group than in the negative control group (P < 0.0001). There was no statistically significant difference in the somatosensory-evoked potentials (SSEPs) amplitude or the Tce-MEPs or SSEPs latency. There was no significant decrease in postoperative motor function in the dexmedetomidine group compared with the preoperative group, suggesting that there is no evidence that dexmedetomidine affects patient prognosis. In addition, we noticed a synchronized bilateral decrease in the Tce-MEPs amplitude in the dexmedetomidine group and a mostly unilateral decrease on the side of the brain injury in the positive control group (P = 0.001).

Discussion

Although dexmedetomidine does not affect the prognosis of patients undergoing craniotomy, the potential risks and benefits of applying it as an adjunctive medication during craniotomy should be carefully evaluated. When dexmedetomidine is administered, Tce-MEPs should be monitored. When a decrease in the Tce-MEPs amplitude is detected, the cause of the decrease in the MEPs amplitude can be indirectly determined by whether the decrease is bilateral.

Imaging protocols for non-traumatic spinal cord injury: current state of the art and future directions

INTRODUCTION

Non-traumatic spinal cord injury (NTSCI) is a term used to describe damage to the spinal cord from sources other than trauma. Neuroimaging techniques such as computerized tomography (CT) and magnetic resonance imaging (MRI) have improved our ability to diagnose and manage NTSCIs. Several practice guidelines utilize MRI in the diagnostic evaluation of traumatic and non-traumatic SCI to direct surgical intervention.

AREAS COVERED

The authors review practices surrounding the imaging of various causes of NTSCI as well as recent advances and future directions for the use of novel imaging modalities in this realm. The authors also present discussions around the use of simple radiographs and advanced MRI modalities in clinical settings, and briefly highlight areas of active research that seek to advance our understanding and improve patient care.

EXPERT OPINION

Although several obstacles must be overcome, it appears highly likely that novel quantitative imaging features and advancements in artificial intelligence (AI) as well as machine learning (ML) will revolutionize degenerative cervical myelopathy (DCM) care by providing earlier diagnosis, accurate localization, monitoring for deterioration and neurological recovery, outcome prediction, and standardized practice. Some intriguing findings in these areas have been published, including the identification of possible serum and cerebrospinal fluid biomarkers, which are currently in the early phases of translation.

The adjunct use of descending neurogenic-evoked potentials when transcranial motor-evoked potentials degrade into warning criteria in pediatric spinal deformity surgery: minimizing false-positive events

PURPOSE

This studies objective was to evaluate the utility of descending neurogenic-evoked potentials (DNEPs) in the setting of transcranial motor-evoked potentials (TCeMEPs) degradation into warning criteria during pediatric spinal deformity surgery.

METHODS

An institutional spinal cord monitoring database was queried to identify all primary and revision pediatric spinal deformity cases, < / = 21 years of age performed from 1/2006 to 12/2021, in which TCeMEPs were the primary motor tract assessment modality which degraded into warning criteria, with subsequent initiation of adjunct DNEPs.

RESULTS

Fourteen surgical cases (0.42%; 3351 total cases) in fourteen patients met inclusion criteria. Mean age was 13.2 years (7.5-21.3).

DIAGNOSES

syndromic (n = 7), kyphosis (n = 3), congenital (n = 2), and idiopathic (n = 2). Three-column osteotomies (3CO)were done in eight patients. TCeMEPs degraded into warning criteria during screw placement (n = 7), 3CO performance/closure (n = 4), or deformity correction (n = 3). DNEPs were present in all cases of warning-criteria TCeMEPs and one case had degradation of DNEPs. Intraoperative Stagnara wake-up tests were performed in only 2/14 cases, with one transient new neurologic deficit (NND). In this specific scenario, DNEPs sensitivity was 50%, specificity 100%, positive predictive value 100%, and negative predictive value 92% to detect aNND.

CONCLUSION

DNEPs were useful in assessing spinal cord function in the setting of TCeMEP data degradation in complex pediatric deformity surgeries. DNEPs demonstrated a higher specificity and positive predictive value in this clinical setting than TCeMEPs when assessing long-term neurologic function after surgery. Based on this small cohort, DNEPs appear to be a useful adjunct modality to TCeMEPs, in this challenging clinical scenario.

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

INTRODUCTION

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Safety and efficacy of posterior vertebral column resection in complex pediatric deformities

Background

Vertebral column resection (VCR) is a well-known technique used for correction of complex spinal deformities. VCR could be done through a posterior only approach (Pvcr), or a combined anteroposterior approach, with almost comparable results. Early studies of Pvcr have reported high rates of complications, while subsequent studies have reported a reasonable complication rate. In this study, the authors represent and evaluate the initial results of using the Pvcr technique to correct complex pediatric deformities.

Objective

To evaluate the safety and efficacy of performing Pvcr to correct complex pediatric deformities.

Methods

Retrospective cohort study of data was collected from the database of pediatric deformity patients who were operated for correction of their deformities using posterior instrumentation and Pvcr at a single institution from 2015 to 2019.

Results

Twenty-one pediatric patients with a mean age 15.2 ± 3.5 years were enrolled in this study. The mean follow-up period was 26.3 ± 3.1 months. The mean Cobb angle has been decreased significantly from 82.9 ± 23.9 degrees to 28.8 ± 14.2 immediately after correction (correction rate 66.9 ± 10.8%, p < 0.001) with slight increase to 30.2 ± 14.9 after 24 months of follow-up (correction loss 4.3 ± 3.1%). The mean kyphotic angle has decreased significantly from 74.1 ± 15.9 to 25.4 ± 4.5 immediately after correction (correction rate 65.4 ± 2.9%, p < 0.001) with slight increase to 26.7 ± 5.2 after 24 months of follow-up (correction loss 4.8 ± 3.5%). The mean estimated blood loss was 2816.7 ± 1441.5 ml. The mean operative time was 339 ± 84.3 min. Self-image domain (part of SRS-22 questionnaire) has significantly improved from a mean preoperative of 2.3 ± 0.5 to a mean postoperative of 3.9 ± 0.4 after 24 months of correction (p < 0.001). As regards complications, chest tubes were inserted in 17 cases (81%), one case (4.8%) had suffered from deep wound infection and temporary respiratory failure, while 3 cases (14.3%) had neurological deficits.

Conclusion

Posterior vertebral column resection is considered a highly effective release procedure that aids in the correction of almost any type of complex pediatric deformities with a correction rate reaching 66.9 ± 10.8%. However, Pvcr is a challenging procedure with high estimated blood loss and risk of neurological deficits, so it must be done only by experienced spine surgeons in the presence of good anesthesia and neuromonitoring teams.

Transcranial Electrical Motor Evoked Potential in Predicting Positive Functional Outcome of Patients after Decompressive Spine Surgery: Review on Challenges and Recommendations towards Objective Interpretation

Spine surgeries impose risk to the spine's surrounding anatomical and physiological structures especially the spinal cord and the nerve roots. Intraoperative neuromonitoring (IONM) is a technology developed to monitor the integrity of the spinal cord and the nerve roots via the surgery. Transcranial motor evoked potential (TcMEP) (one of the IONM modalities) is adopted to monitor the integrity of the motor pathway of the spinal cord and the motor nerve roots. Recent research suggested that the IONM is conducive as a prognostic tool towards the patient's functional outcome. This paper summarizes the researches of IONM being adopted as a prognostic tool. In addition, this paper highlights the problems associated with the signal parameters as the improvement criteria in the previous researches. Lastly, we review the challenges of TcMEP to achieve a prognostic tool focusing on the factors that could interfere with the generation of a stable TcMEP response. The final section will discuss recommendations for IONM technology to achieve an objective prognostic tool.

Effect of dexmedetomidine on evoked-potential monitoring in patients undergoing brain stem and supratentorial cranial surgery

BACKGROUND

Dexmedetomidine is used as adjuvant in total intravenous anaesthesia (TIVA), but there have been few studies concerning its effect on intraoperative neurophysiological monitoring (IONM) during cranial surgery. Our aim was to study the effect of dexmedetomidine on IONM in patients undergoing brain stem and supratentorial cranial surgery.

METHODS

Two prospective, randomized, double-blind substudies were conducted. In substudy 1, during TIVA with an infusion of propofol and remifentanil, 10 patients received saline solution (SS) (PR group) and another 10 (PRD group) received dexmedetomidine (0.5 mcg/kg/h). Total dosage of propofol and remifentanil, intensity, latency and amplitude of motor-evoked potentials following transcranial electrical stimulation (tcMEPs) as well as somatosensory-evoked potentials (SSEP) were recorded at baseline, 15, 30, 45 minutes, and at the end of surgery. In order to identify differences in the same patient after dexmedetomidine administration, we designed substudy 2 with 20 new patients randomized to two groups. After 30 minutes with TIVA, 10 patients received dexmedetomidine (0.5 mcg/kg/h) and 10 patients SS. The same variables were recorded.

RESULTS

In substudy 1, propofol requirements were significantly lower (P = .004) and tcMEP intensity at the end of surgery was significantly higher in PRD group, but no statistically significant differences were observed for remifentanil requirements, SSEP and tcMEP latency or amplitude. In substudy 2, no differences in any of the variables were identified.

CONCLUSIONS

The administration of dexmedetomidine at a dosage of 0.5 mg/kg/h may reduce propofol requirements and adversely affect some neuromonitoring variables. However, it can be an alternative on IONM during cranial surgeries. REDEX EudraCT: 2014-000962-23.

Tetanic stimulation of the pudendal nerve prior to transcranial electrical stimulation augments the amplitude of motor evoked potentials during pediatric neurosurgery

OBJECTIVE

Reportedly, tetanic stimulation prior to transcranial electrical stimulation (TES) facilitates elicitation of motor evoked potentials (MEPs) by a mechanism involving increased corticomotoneuronal excitability in response to somatosensory input. However, the posttetanic MEP following stimulation of a pure sensory nerve has never been reported. Furthermore, no previous reports have described posttetanic MEPs in pediatric patients. The aim of this study was to investigate the efficacy of posttetanic MEPs in pediatric neurosurgery patients and to compare the effects on posttetanic MEP after tetanic stimulation of the sensory branch of the pudendal nerve versus the standard median and tibial nerves, which contain a mixture of sensory and motor fibers.

METHODS

In 31 consecutive pediatric patients with a mean age of 6.0 ± 5.1 years who underwent lumbosacral surgery, MEPs were elicited by TES without tetanic stimulation (conventional MEPs [c-MEPs]) and following tetanic stimulation of the unilateral median and tibial nerves (mt-MEPs) and the sensory branch of the pudendal nerve (p-MEP). Compound muscle action potentials were elicited from abductor pollicis brevis (APB), gastrocnemius (Gc), tibialis anterior (TA), and adductor hallucis (AH) muscles. The success rate of monitoring each MEP and the increases in the ratios of mt-MEP and p-MEP to c-MEP were investigated.

RESULTS

The success rate of monitoring p-MEPs was higher than those of mt-MEPs and c-MEPs (87.5%, 72.6%, and 63.3%, respectively; p < 0.01, adjusted by Bonferroni correction). The mean increase in the ratio of p-MEP to c-MEP for all muscles was significantly higher than that of mt-MEP to c-MEP (3.64 ± 4.03 vs 1.98 ± 2.23, p < 0.01). Subanalysis of individual muscles demonstrated significant differences in the increases in the ratios between p-MEP and mt-MEP in the APB bilaterally, as well as ipsilateral Gc, contralateral TA, and bilateral AH muscles.

CONCLUSIONS

Tetanic stimulation prior to TES can augment the amplitude of MEPs during pediatric neurosurgery, the effect being larger with pudendal nerve stimulation than tetanic stimulation of the unilateral median and tibial nerves. TES elicitation of p-MEPs might be useful in pediatric patients in whom it is difficult to elicit c-MEPs.

The Use of Intraoperative Neurophysiological Monitoring in Spine Surgery

STUDY DESIGN

Narrative review.

OBJECTIVE

To summarize relevant studies regarding the utilization of intraoperative neurophysiological monitoring (IONM) techniques in spine surgery implemented in recent years.

METHODS

A literature search of the Medline database was performed. Relevant studies from all evidence levels have been included. Titles, abstracts, and reference lists of key articles were included.

RESULTS

Multimodal intraoperative neurophysiological monitoring (MIONM) has the advantage of compensating for the limitations of each individual technique and seems to be effective and accurate for detecting perioperative neurological injury during spine surgery.

CONCLUSION

Although there are no prospective studies validating the efficacy of IONM, there is a growing body of evidence supporting its use during spinal surgery. However, the lack of validated protocols to manage intraoperative alerts highlights a critical knowledge gap. Future investigation should focus on developing treatment methodology, validating practice protocols, and synthesizing clinical guidelines.

Characterization of Intraoperative Motor Evoked Potential Monitoring for Surgery of the Pediatric Population with Brain Tumors

OBJECTIVE

We investigated the relationship between the reliability of the transcranial or transcortical motor evoked potential (MEP) response and age in pediatric patients aged ≤15 years with brain tumor.

METHODS

We retrospectively analyzed the data from 60 consecutive patients aged ≤15 years who had undergone brain tumor surgery that involved intraoperative MEP monitoring from October 2009 to May 2016.

RESULTS

A total of 41 patients with reliable signals (MEP response group) and 19 patients without reliable signals (MEP nonresponse group) were included in the present study. The mean age at surgery, body height, and body weight were significantly greater in the MEP response group than in the MEP nonresponse group. When the MEP success rates during surgery of the pediatric population with brain tumors were analyzed in relation to patient age, the transcortical MEP success rate in the 0-5-year age group (10.0%) was significantly lower than that in the 6-10-year age group (71.4%; P = 0.009) and that in the 11-15-year age group (75.0%; P = 0.015).

CONCLUSIONS

The transcortical MEP response was monitored less successfully during brain tumor surgery in patients aged ≤5 years than in patients aged 6-15 years. Although MEP monitoring techniques can be applied during surgery of pediatric populations with brain tumors similar to that used for adult patients, the limitations of the low transcortical MEP response rate in young patients should be considered.

Neuromonitoring in Spinal Deformity Surgery: A Multimodality Approach

STUDY DESIGN

Literature review.

OBJECTIVE

The aim of this study was to provide an overview of the available intraoperative monitoring techniques and the evidence around their efficacy in vertebral column resection.

METHODS

The history of neuromonitoring and evolution of the modalities are reviewed and discussed. The authors' specific surgical techniques and preferred methods are outlined in detail. In addition, the authors' experience and the literature regarding vertebral column resection and surgical mitigation of neurologic alarms are discussed at length.

RESULTS

Risk factors for signal changes have been identified, including preoperative neurologic deficit, severe kyphosis, increased curve magnitude, and significant cord shortening. Even though no evidence-based treatment algorithm exist for signal changes, strategies are discussed that can help prevent alarms and address them appropriately.

CONCLUSION

Through implementation of multimodal intraoperative monitoring techniques, potential neurologic injuries are localized and managed in real time. Intraoperative monitoring is a valuable tool for improving the safety and outcome of spinal deformity 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.

Recent technological advances in pediatric brain tumor surgery

X-rays and ventriculograms were the first imaging modalities used to localize intracranial lesions including brain tumors as far back as the 1880s. Subsequent advances in preoperative radiological localization included computed tomography (CT; 1971) and MRI (1977). Since then, other imaging modalities have been developed for clinical application although none as pivotal as CT and MRI. Intraoperative technological advances include the microscope, which has allowed precise surgery under magnification and improved lighting, and the endoscope, which has improved the treatment of hydrocephalus and allowed biopsy and complete resection of intraventricular, pituitary and pineal region tumors through a minimally invasive approach. Neuronavigation, intraoperative MRI, CT and ultrasound have increased the ability of the neurosurgeon to perform safe and maximal tumor resection. This may be facilitated by the use of fluorescing agents, which help define the tumor margin, and intraoperative neurophysiological monitoring, which helps identify and protect eloquent brain.

Intraoperative spinal cord monitoring using low intensity transcranial stimulation to remove post-activation depression of the H-reflex

OBJECTIVE

To investigate whether low intensity transcranial electrical stimulation (TES) can be used to condition post-activation depression of the H-reflex and simultaneously monitor the integrity of spinal motor pathways during spinal deformity correction surgery.

METHODS

In 20 pediatric patients undergoing corrective surgery for spinal deformity, post-activation depression of the medial gastrocnemius H-reflex was initiated by delivering two pulses 50-125ms apart, and the second H-reflex was conditioned by TES.

RESULTS

Low intensity TES caused no visible shoulder or trunk movements during 19/20 procedures and the stimulation reduced post-activation depression of the H-reflex. The interaction was present in 20/20 patients and did not diminish throughout the surgical period. In one case, the conditioning effect was lost within minutes of the disappearance of the lower extremity motor evoked potentials.

CONCLUSION

Post-activation depression was used to detect the arrival of a subthreshold motor evoked potential at the lower motor neuron. The interaction produced minimal movement within the surgical field and remained stable throughout the surgical period.

SIGNIFICANCE

This is the first use of post-activation depression during intraoperative neurophysiological monitoring to directly assess the integrity of descending spinal motor pathways.

Rare true-positive outcome of spinal cord monitoring in patients under age 4 years

BACKGROUND CONTEXT

Intraoperative monitoring (IOM) is becoming an essential component in spinal surgery, but there are many different viewpoints about it in patients under age 4 years.

PURPOSE

This study aims to report some IOM features in children under age 4 years.

DESIGN/SETTING

This is a retrospective cases study.

PATIENT SAMPLE

A total of 37 children (35.76 months±1.47) and 120 patients with adolescent idiopathic scoliosis (AIS, 14.2 years) were recruited between September 2012 and December 2014.

OUTCOME MEASURES

Relevant monitoring changes were identified as transcranial motor evoked potentials (MEP) or somatosensory evoked potentials (SEP) loss associated with high-risk surgical maneuvers.

METHODS

Motor evoked potential, SEP, and free-run electromyography (free-run EMG) were used for IOM. The IOM parameters (amplitude, latency, and waveform) and monitoring outcomes (signal changes, true positive, and false positive) were mainly analyzed in the patients under age 4 years.

RESULTS

All young patients presented stable MEP (90.6 µV±20.3) and SEP (1.01 µV±0.3) baseline. The baseline success rate (100%) was the same as that in patients with AIS; however, the MEP amplitude of young patients was significantly lower than that of patients with AIS (90.6 µV±20.3 vs. 312.1 µV±25.2, n=120; **p<.01) under the same stimulus parameters. Moreover, children under age 4 years have more monitoring changes (18.9%, 7 of 37), but true-positive findings are rare (0%) in our population.

CONCLUSIONS

Intraoperative monitoring baseline can be obtained satisfactorily in children under age 4 years, but true-positive findings are rare; meanwhile, low MEP amplitude and poor waveforms are common.

Comparison of false-negative/positive results of intraoperative evoked potential monitoring between no and partial neuromuscular blockade in patients receiving propofol/remifentanil-based anesthesia during cerebral aneurysm clipping surgery: A retrospective analysis of 685 patients

Although the elicited responses of motor evoked potential (MEP) monitoring are very sensitive to suppression by anesthetic agents and muscle relaxants, the use of neuromuscular blockade (NMB) during MEP monitoring is still controversial because of serious safety concerns and diagnostic accuracy. Here, we evaluated the incidence of unacceptable movement and compared false-negative MEP results between no and partial NMB during cerebral aneurysm clipping surgery. We reviewed patient medical records for demographic data, anesthesia regimen, neurophysiology event logs, MEP results, and clinical outcomes. Patients were divided into 2 groups according to the intraoperative use of NMB: no NMB group (n = 276) and partial NMB group (n = 409). We compared the diagnostic accuracy of MEP results to predict postoperative outcomes between both groups. Additionally, we evaluated unwanted patient movement during MEP monitoring in both groups. Of the 685 patients, 622 (90.8%) manifested no intraoperative changes in MEP and no postoperative motor deficits. Twenty patients showed postoperative neurologic deficits despite preserved intraoperative MEP. False-positive MEP results were 3.6% in the no NMB group and 3.9% in the partial NMB group (P = 1.00). False-negative MEP results were 1.1% in the no NMB group and 4.2% in the partial NMB group (P = 0.02). No spontaneous movement or spontaneous respiration was observed in either group. Propofol/remifentanil-based anesthesia without NMB decreases the stimulation intensity of MEPs, which may reduce the false-negative ratio of MEP monitoring during cerebral aneurysm surgery. Our anesthetic protocol enabled reliable intraoperative MEP recording and patient immobilization during cerebral aneurysm clipping surgery.

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.

Spinal Cord Monitoring Data in Pediatric Spinal Deformity Patients With Spinal Cord Pathology

STUDY DESIGN

Retrospective.

OBJECTIVES

The purpose of this study is to review the efficacy of monitoring data and outcomes in pediatric patients with spinal cord pathology.

SUMMARY OF BACKGROUND DATA

The incidence of spinal cord pathology in pediatric patients with scoliosis has been reported between 3% and 20%. Previous studies demonstrated that intraoperative spinal cord monitoring (IOM) during scoliosis surgery can be reliable despite underlying pathology.

METHODS

A single-center retrospective review of 119 spinal surgery procedures in 82 patients with spinal cord pathology was performed. Diagnoses included Arnold-Chiari malformation, syringomyelia, myelomeningocele, spinal cord tumor, tethered cord, and diastematomyelia. Baseline neurologic function and history of prior neurosurgical intervention were identified. Outcome measures included ability to obtain reliable monitoring data during surgery and presence of postoperative neurologic deficits. Results were compared for 82 patients with adolescent idiopathic scoliosis (AIS).

RESULTS

Usable IOM data were obtained in 82% of cases (97/119). Twenty-two cases (18%) had no lower extremity data. Patients with Arnold-Chiari malformation or syringomyelia pathologies, in isolation or together, had a significantly higher rate of reliable data compared to other pathologies (p < .0001). Among study group cases with usable data, there were 1 false negative (1%) and 4 true positive (4%) outcomes. There were no permanent neurologic deficits. The spinal cord pathology group demonstrated 80% sensitivity and 92% specificity.

CONCLUSIONS

Spinal cord monitoring is a valuable tool in pediatric patients with spinal cord pathology undergoing spinal deformity surgeries. When obtained, data allow to detect changes in spinal cord function. Patients with a diagnosis of Arnold-Chiari or syringomyelia have monitoring data similar to those patients with AIS. Patients with other spinal cord pathologies have less reliable data, and surgeons should have a lower threshold for performing wake-up tests to assess spinal cord function intraoperatively.

A comparison of the effects of desflurane versus propofol on transcranial motor-evoked potentials in pediatric patients

PURPOSE

The aim was to compare the effects of propofol and desflurane anesthesia on transcranial motor evoked potentials (MEPs) from pediatric patients undergoing surgery for spinal deformities.

METHODS

Desflurane and propofol cohorts (25 patients each) were obtained retrospectively and matched for patient characteristics and surgical approach. MEPs from the thenar eminence and abductor hallucis were compared during maintenance anesthesia on desflurane (0.6-0.8 MAC) or propofol infusion (150-300 μg/kg/min). MEP amplitudes and durations were obtained for successive 30-min intervals for 150 min, beginning 60 min after maintenance anesthesia.

RESULTS

Mean peak to peak amplitudes of MEPs under desflurane anesthesia from the thenar eminence (419 μV) and abductor hallucis (386 μv) were not significantly different from those under propofol (608 μV, 343 μV, thenar, and abductor hallucis, respectively). Stimulation was greater by 42 V and 136 mA, and trains were slightly longer in the desflurane compared to the propofol group (p < 0.05). Most MEP amplitudes for the desflurane and propofol cohorts remained the same or increased (71 % of cases) when those after 150 min were compared to those in the first 30-min interval.

CONCLUSIONS

MEPs with good amplitudes were obtained under desflurane only anesthesia that were comparable to propofol only anesthesia in pediatric patients during surgery for spinal deformities. There was no evidence for anesthetic fade over the time period examined. When used by itself, desflurane can be considered a viable alternative to propofol anesthesia.

Transcranial motor evoked potential monitoring outcome in the high-risk brain and spine surgeries: Correlation of clinical and neurophysiological data - An Indian perspective

Objective:

The objective of this study is to assess the safety, feasibility and clinical value of transcranial motor evoked potential (MEP) monitoring by electrical stimulation.

Setting:

Clinical neurophysiology department of tertiary reach hospital.

Materials and Methods:

MEP monitoring was attempted in 44 “high risk” patients. Intraoperative surgical, anesthesia and neurophysiological findings were documented prospectively. MEP monitoring results were correlated with motor outcome.

Results:

The success for reliable MEP recording from the lower limbs was 75%. Incidence of new permanent post-operative motor deficit was zero. Nearly, 76.5% of the cases (13 out of 17 cases) who showed unobtainable and unstable MEP outcome had lesion location in the spine as compared with 23.5% (4 out of 17 cases) that had lesion location in the brain. Chi-square test demonstrated a statistically significant difference between these two groups (P = 0.0020). Out of these 13 spine surgery cases, 8 (62%) were operated for deformity. Seven out of 12 (60%) patients less than 12 years of age had a poor MEP monitoring outcome suggesting that extremes of age and presence of a spine deformity may be associated with a lesser incidence of successful MEP monitoring. No complications related to the repetitive transcranial electrical stimulation for eliciting MEP were observed.

Conclusion:

MEP monitoring is safe. The protocol used in this study is simple, feasible for use and has a fairly high success rate form the lower limbs. Pediatric age group and spine lesions, particularly deformities have an adverse effect on stable MEP recording.

Clinical features and surgical management of spinal osteoblastoma: a retrospective study in 18 cases

OBJECTIVES

To investigate the clinical manifestation and surgical outcome of spinal osteoblastoma.

METHODS

From June 2006 to July 2011, 18 patients with spinal osteoblastoma treated surgically were analyzed retrospectively. There were 11 males and 7 females with an average age of 27.5 years（range, 16-38 years). The tumors were located at C5 in 7, C6 in 6, C7 in 3, C6-T1 1 in 1 and T11 in 1. Based on WBB classification, 16 were 1-3 or 10-12 and 2 were 4-9 and 1-3. 18 operations had been performed with en bloc resection. A posterior approach was used for 16 patients, and a combined posterior and anterior approach was used for 2 patients. Reconstruction using instrumentation and fusion was performed using spinal instrumentation in 13 patients. We used visual analogue scales (VAS) to evaluate the change of pain before and after the operation, and the McCormick System to assess functional status of the spine. Imaging test was used to review the stability and recurrence rate of spine cord, and the confluence of graft bones.

RESULTS

All cases were followed up for 24-80 months (average, 38.4 months). The average surgical time was 120.8 minutes (range, 80-220 minutes), with the average intraoperative blood loss of 520 ml (range, 300-1200 ml). During the follow-up period, the VAS grade reduced from 6.46±1.32 to 2.26±1.05 (P <0.05). 15 patients had neurological function improved and 3 remained no change which was evaluated by McCormick scale for spinal function status at final follow-up.

CONCLUSIONS

Spinal osteoblastoma has its own specific radiographic features. There is some recurrence in simple curettage of tumor lesion. The thoroughly en bloc resection of tumor or spondylectomy, bone fusion and strong in Ter fixation are the key points for successful surgical treatment.

Quantification of the proportion of motor neurons recruited by transcranial electrical stimulation during intraoperative motor evoked potential monitoring

Transcranial motor evoked potentials (TcMEPs) are widely used to monitor motor function during spinal surgery. However, they are much smaller and more variable in amplitude than responses evoked by maximal peripheral nerve stimulation, suggesting that a limited number of spinal motor neurons to the target muscle are excited by transcranial stimulation. The aim of this study was to quantify the proportion of motor neurons recruited during TcMEP monitoring under general anesthesia. In twenty patients who underwent thoracic and/or lumbar spinal surgery with TcMEP monitoring, the triple stimulation technique (TST) was applied to the unilateral upper arm intraoperatively. Total intravenous anesthesia was employed. Trains of four stimuli were delivered with maximal intensity and an inter-pulse interval of 1.5 ms. TST responses were recorded from the abductor digiti minimi muscle, and the negative peak amplitude and area were measured and compared between the TST test (two collisions between transcranial and proximal and distal peripheral stimulation) and control response (two collisions between two proximal and one distal peripheral stimulation). The highest degree of superimposition of the TST test and control responses was chosen from several trials per patient. The average ratios (test:control) were 17.1 % (range 1.8-38 %) for the amplitudes and 21.6 % (range 2.9-40 %) for the areas. The activity of approximately 80 % of the motor units to the target muscle cannot be detected by TcMEP monitoring. Therefore, changes in evoked potentials must be interpreted cautiously when assessing segmental motor function with TcMEP monitoring.

Time-frequency analysis of somatosensory evoked potentials for intraoperative spinal cord monitoring

PURPOSE

To evaluate the potential use of time-frequency analysis and its reliability in intraoperative somatosensory evoked potential (SEP) monitoring.

METHODS

One hundred ninety-one patients undergoing thoracic and/or lumbar spinal surgery were studied retrospectively. The SEP signals were recorded during different stages of surgery. Averaged SEP was analyzed by short-time Fourier transform. The main peak in the time-frequency interpretation of SEP was measured in peak power, peak time, and peak frequency. The variability of these parameters was compared with that of amplitude and latency during different stages of surgery. The reliability of these parameters was also compared in true-positive and false-positive cases.

RESULTS

During different surgical stages for the posterior tibial nerve SEP, the intrasubject variability of peak power was found to be more stable than that of amplitude, while the intrasubject variability of peak time did not show any difference compared with that of latency. The peak frequency presented stable during surgery. Moreover, the true-positive SEP case showed that peak power may detect the potential injury earlier than amplitude does. The false-positive outcomes could be reduced by the proposed method.

CONCLUSIONS

The SEP peak component was found stable and reliable during the different stages of surgery. For clinical application purpose, time-frequency analysis was suggested to be an additional monitoring method besides the conventional amplitude/latency measurement since it provided a more reproducible and prompt response to the potential injury in intraoperative SEP monitoring.

A comparison of a commercially made pedicle stimulating probe with a custom-made device: does the commercial device detect pedicle wall breaches more reliably?

STUDY DESIGN

Clinical trial.

OBJECTIVE

To compare the efficacy of a commercially available stimulating pedicle probe with a custom-made probe for the detection of pedicle wall breaches during screw insertion for the surgical correction of scoliosis.

SUMMARY OF BACKGROUND DATA

Stimulus triggered electromyography has been used to detect small breaches in the walls of the spinal pedicles during pedicle screw insertion. We routinely use a reusable, custom-made clip that can be attached to the screw, pedicle probe, or other instruments. Commercial systems are available in which the instrument is electrically instrumented to deliver current.

METHODS

In five patients (173 pairs of tests), we compared the threshold current required to trigger an electromyographic response during testing of the pedicle. Each track or screw was tested with both the custom-made and the commercial probe and the threshold current recorded.

RESULTS

Both systems were able to detect pedicle wall breaches using triggered electromyography. The threshold current recorded was not significantly different between the two systems (P > 0.1, paired t test) nor was the difference (0.16 mA) clinically significant.

CONCLUSION

No difference was found between the thresholds detected with either system. There is however, a significant difference in the costs of the two probe systems.

Improving successful rate of transcranial electrical motor-evoked potentials monitoring during spinal surgery in young children

INTRODUCTION

This prospective study was to investigate the successful rate of intraoperative motor evoked potentials (MEP) monitoring for children (<12 years old) with congenital scoliosis.

MATERIALS AND METHODS

A consecutive series of 27 young children (7 girls and 20 boys; from 1 to 11 years old) between September 2007 and November 2009, were enrolled to this study. 12 patients received general anesthesia based on TIVA, induced with propofol 2-4 mg/kg and fentanyl 3-5 µg/kg followed by a continuous infusion of propofol (20-150 µg/kg/min, at mean of 71.7 µg/kg/min). The other 15 patients received combined inhalation and intravenous anesthesia, induced with sevoflurane and fentanyl 3-5 µg/kg and maintained by sevoflurane (0.5-1%). The maintenance of anaesthesia management was performed with stable physiological parameters during surgery.

RESULTS

Intraoperative MEP monitoring was successfully performed in all patients, while SEP was successfully performed in 26 of 27 patients. There was no significant difference of successful rates between SEP and MEP monitoring (P > 0.05). As well, no difference in MEP successful rates was observed in two groups with different anesthetic techniques. No wake-up test and no post-operative neurological deficits occurred in this series of patients.

CONCLUSION

Low dose anesthesia by either TIVA with propofol or sevoflurane-based mixture anesthesia protocol can help the intraoperative spinal cord monitoring to successfully elicit MEP and perform reliable monitoring for patients below 12 years of age.

Intraoperative electrophysiological monitoring in spine surgery

STUDY DESIGN

Review of the literature with analysis of pooled data.

OBJECTIVE

To assess common intraoperative neuromonitoring (IOM) changes that occur during the course of spinal surgery, potential causes of change, and determine appropriate responses. Further, there will be discussion of appropriate application of IOM, and medical legal aspects. The structured literature review will answer the following questions: What are the various IOM methods currently available for spinal surgery? What are the sensitivities and specificities of each modality for neural element injury? How are the changes in each modality best interpreted? What is the appropriate response to indicated changes? Recommendations will be made as to the interpretation and appropriate response to IOM changes.

SUMMARY OF BACKGROUND DATA

Total number of abstracts identified and reviewed was 187. Full review was performed on 18 articles.

METHODS

The MEDLINE database was queried using the search terms IOM, spinal surgery, SSEP, wake-up test, MEP, spontaneous and triggered electromyography alone and in various combinations. Abstracts were identified and reviewed. Individual case reports were excluded. Detailed information and data from appropriate articles were assessed and compiled.

RESULTS

Ability to achieve IOM baseline data varied from 70% to 98% for somatosensory-evoked potentials (SSEP) and 66% to 100% for motor-evoked potentials (MEP) in absence of neural axis abnormality. Multimodality intraoperative neuromonitoring (MIOM) provided false negatives in 0% to 0.79% of cases, whereas isolated SSEP monitoring alone provided false negative in 0.063% to 2.7% of cases. MIOM provided false positive warning in 0.6% to 1.38% of cases.

CONCLUSION

As spine surgery, and patient comorbidity, becomes increasingly complex, IOM permits more aggressive deformity correction and tumor resection. Combination of SSEP and MEP monitoring provides assessment of entire spinal cord functionality in real time. Spontaneous and triggered electromyography add assessment of nerve roots. The wake-up test can continue to serve as a supplement when needed. MIOM may prove useful in preservation of neurologic function where an alteration of approach is possible. IOM is a valuable tool for optimization of outcome in complex spinal surgery.

Brachial plexus injury following spinal surgery

OBJECT

In the present study, the authors identified the etiology, precipitating factors, and outcomes of perioperative brachial plexus injuries following spine surgery.

METHODS

We reviewed all the available literature regarding postoperative/perioperative brachial plexus injuries, with special concern for the patient's position during surgery, duration of surgery, the procedure performed, neurological outcome, and prognosis. We also reviewed the utility of intraoperative electrophysiological monitoring for prevention of these complications.

RESULTS

Patient malpositioning during surgery is the main determining factor for the development of postoperative brachial plexus injury. Recovery occurs in the majority of cases but may require weeks to months of therapy after initial presentation.

CONCLUSION

Brachial plexus injuries are an increasingly recognized complication following spinal surgery. Proper attention to patient positioning with the use of intraoperative electrophysiological monitoring techniques could minimize injury.

Validity and reliability of intraoperative monitoring in pediatric spinal deformity surgery: a 23-year experience of 3436 surgical cases

STUDY DESIGN

This was a 23-year retrospective study of 3436 consecutive pediatric orthopedic spinal surgery patients between 1995 and 2008.

OBJECTIVE

To demonstrate the effectiveness of multimodality electrophysiologic monitoring in reducing the incidence of iatrogenic neurologic deficit in a pediatric spinal surgery population.

SUMMARY OF BACKGROUND DATA

The elective nature of many pediatric spinal surgery procedures continues to drive the need for minimizing risk to each individual patient. Electrophysiologic monitoring has been proposed as an effective means of decreasing permanent neurologic injury in this population.

METHODS

A total of 3436 consecutive monitored pediatric spinal procedures at a single institution between January 1985 and September 2008 were reviewed. Monitoring included somatosensory-evoked potentials, descending neurogenic-evoked potentials, transcranial electric motor-evoked potentials, and various nerve root monitoring techniques. Patients were divided into 10 diagnostic categories. True-positive and false-negative monitoring outcomes were analyzed for each category. Neurologic deficits were classified as transient or permanent.

RESULTS

Seven of 10 diagnostic groups demonstrated true positive findings resulting in surgical intervention. Seventy-four (2.2%) potential neurologic deficits were identified in 3436 pediatric surgical cases. Seven patients (0.2%) had false-negative monitoring outcomes. These patients awoke with neurologic deficits undetected by neuromonitoring. Intervention reduced permanent neurologic deficits to 6 (0.17%) patients. Monitoring data were able to detect permanent neurologic status in 99.6% of this population. The ratio of intraoperative events to total monitored cases was 1 event every 42 surgical cases and 1 permanent neurologic deficit every 573 cases.

CONCLUSION

The combined use of somatosensory-evoked potentials, transcranial electric motor-evoked potentials, descending neurogenic-evoked potentials, and electromyography monitoring allowed accurate detection of permanent neurologic status in 99.6% of 3436 patients and reduced the total number of permanent neurologic injuries to 6.

Human motor evoked potential responses following spinal cord transection: an in vivo study

Motor evoked potential (MEP) monitoring has been used increasingly in conjunction with somatosensory evoked potential monitoring to monitor neurological changes during complex spinal operations. No published report has demonstrated the effects of segmental spinal cord transection on MEP monitoring.

The authors describe the case of an 11-year-old girl with lumbar myelomeningocele and worsening thoracolumbar scoliosis who underwent a T11–L5 fusion and spinal transection to prevent tethering. Intraoperative MEP and somatosensory evoked potential monitoring were performed, and the spinal cord was transected in 4 quadrants. The MEPs were lost unilaterally as each anterior quadrant was sectioned.

This is the first reported case that demonstrates the link between spinal cord transection and MEP signaling characteristics. Furthermore, it demonstrates the relatively minor input of the ipsilateral ventral corticospinal tract in MEP physiology at the thoracolumbar junction. Finally, this study further supports the use of MEPs as a specific intraoperative neuromonitoring tool.