Evidence-based guideline update: Intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials: Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology and the American Clinical Neurophysiology Society

Intraoperative Monitoring: Recent Advances in Motor Evoked Potentials

Advances in electrophysiological monitoring have improved the ability of surgeons to make decisions and minimize the risks of complications during surgery and interventional procedures when the central nervous system (CNS) is at risk. Individual techniques have become important for identifying or mapping the location and pathway of critical neural structures. These techniques are also used to monitor the progress of procedures to augment surgical and physiologic management so as to reduce the risk of CNS injury. Advances in motor evoked potentials have facilitated mapping and monitoring of the motor tracts in newer, more complex procedures.

Contemporaneous Evaluation of Intraoperative Ulnar and Median Nerve Somatosensory Evoked Potentials for Patient Positioning: A Review of Four Cases

Somatosensory evoked potentials (SSEPs) are a valuable tool for assessing changes in peripheral nerve pathways caused by patient positioning during spinal surgeries. These changes, when left undiagnosed, may lead to postoperative neurological sequelae. Why an upper extremity SSEP attenuates due to positioning is not necessarily clear and can be multifactorial, affecting the peripheral nerves or elements of the brachial plexus. A conduction block can occur at any point along the course of the nerve secondary to entrapment, compression, and ischemia. These mechanisms of injury may be caused by extreme body habitus, the length of the procedure, or the patient's metabolic underpinnings. The goal of neuromonitoring for positional injury is to predict and prevent both peripheral nerve and brachial plexus injuries. Using ulnar and median nerve SSEPs contemporaneously may lead to better identification of compromised structures when an SSEP change to one or both of the nerves occurs. The investigators provide four case reports where intraoperative SSEP assessment of contemporaneous ulnar and median nerves prevented postoperative upper extremity neural deficits.

The Applicability of Intraoperative Neuromonitoring in Patients with Preoperative Motor Weakness during Spine Surgery

OBJECTIVE

The purpose of our study is to evaluate the success rate and feasibility of intraoperative neuromonitoring (IONM) focusing on transcranial motor evoked potential (TcMEP) monitoring for patients with preoperative motor weakness in spine surgery.

METHODS

Between November 2011 and December 2013, TcMEP and somatosensory evoked potential (SSEP) monitoring were attempted in 130 consecutive patients undergoing spine surgeries for cervical or thoracic cord lesions. Patients ranged in age from 14 to 81 years (mean±standard deviation, 56.7±14.8 years), and 84 patients were male. The success rates of both SSEP and MEPs monitoring were assessed according to the preoperative Medical Research Council (MRC) and Nurick grades.

RESULTS

TcMEP was recorded successfully in 0%, 28.6%, 72.3%, and 100% of patients with MRC grades 1, 2, 3, 4, and 5, respectively. SSEP was obtained from 0%, 37.5%, 21.5%, 61.4%, and 85.4% of patients with MRC grades 1, 2, 3, 4, and 5, respectively. TcMEP was recorded successfully in 84% of patients with Nurick grades 1-3 and 26% of patients with Nurick grades 4-5. SSEPs were recorded successfully in 76.3% of patients with Nurick grades 1-3 and 24% of patients with grades 4-5.

CONCLUSION

IONM during spine surgery may be useless in patients with MRC grades 1-2, applicable MRC grade 3, and useful MRC grades 4-5. MRC grade 3 is a critical point of indication for application of MEPs. In unmonitorable cases with MRC grade 3, increasing stimulus intensity or facilitation techniques may be considered to improve the usefulness of TcMEP.

Extended Motor Evoked Potentials Monitoring Helps Prevent Delayed Paraplegia After Aortic Surgery

OBJECTIVE

Motor evoked potentials (MEPs) monitoring can promptly detect spinal cord ischemia (SCI) from aortic clamping during open thoracoabdominal aneurysm repair (OTAAR) with distal aortic perfusion (DAP) and thus help decrease the risk of immediate postoperative SCI (IP-SCI). However, neither stable MEPs during aortic clamp interval (ACI) nor absence of IP-SCI eliminate the possibility of delayed postoperative SCI (DP-SCI). We hypothesized that extension of MEPs monitoring beyond ACI can also help decrease the risk of DP-SCI.

METHODS

We identified 150 consecutive patients at our institution between April 2005 and October 2014 who underwent OTAAR with DAP and MEPs monitoring and had no IP-SCI. Using logistic regression analysis, we studied the independent effect of extended MEPs monitoring on the risk of developing DP-SCI. We used a propensity score analysis to adjust for potential confounders, such as poorly controlled hypertension, previous aneurysm surgery, splenectomy, acute aortic dissection, aneurysm type, older age, and history of diabetes and smoking.

RESULTS

From the 150 patients, 129 (86%) remained neurologically intact whereas 21 (14%) developed DP-SCI. Nineteen of these twenty-one patients (90%) had no extended monitoring. Fifty-seven of fifty-nine (97%) patients who benefited from extended monitoring had no DP-SCI (p = 0.003). Extended MEPs monitoring was independently associated with decreased risk of DP-SCI (odds ratio = 0.14; 95% confidence interval: 0.03, 0.65; p = 0.01).

INTERPRETATION

MEPs detect the lowest systemic blood pressure that ensures appropriate spinal cord perfusion in the postoperative period. Thus, they inform the hemodynamic management of patients post-OTAAR, particularly in the absence of a reliable neurological exam.

Appraisal of the Quality of Neurosurgery Clinical Practice Guidelines

OBJECTIVE

The rate of neurosurgery guidelines publications was compared over time with all other specialties. Neurosurgical guidelines and quality of supporting evidence were then analyzed and compared by subspecialty.

METHODS

The authors first performed a PubMed search for "Neurosurgery" and "Guidelines." This was then compared against searches performed for each specialty of the American Board of Medical Specialties. The second analysis was an inventory of all neurosurgery guidelines published by the Agency for Healthcare Research and Quality Guidelines clearinghouse. All Class I evidence and Level 1 recommendations were compared for different subspecialty topics.

RESULTS

When examined from 1970-2010, the rate of increase in publication of neurosurgery guidelines was about one third of all specialties combined (P < 0.0001). However, when only looking at the past 5 years the publication rate of neurosurgery guidelines has converged upon that for all specialties. The second analysis identified 49 published guidelines for assessment. There were 2733 studies cited as supporting evidence, with only 243 of these papers considered the highest class of evidence (8.9%). These papers were used to generate 697 recommendations, of which 170 (24.4%) were considered "Level 1" recommendations.

CONCLUSION

Although initially lagging, the publication of neurosurgical guidelines has recently increased at a rate comparable with that of other specialties. However, the quality of the evidence cited consists of a relatively low number of high-quality studies from which guidelines are created. Wider implications of this must be considered when defining and measuring quality of clinical performance in neurosurgery.

Intraoperative Neurophysiological Monitoring (IONM) for Cordotomy Procedures

This case illustrates the benefits of utilizing intraoperative neurophysiological monitoring (IONM) for preventing injury to sensory/motor pathways of the spinal cord during a cordotomy procedure to relieve pain. Cordotomy has been used effectively in the treatment of visceral pain but comes with a high risk of damaging motor and sensory pathways due to close proximity of lesion. The subject is a 47-year-old female with a pancoast tumor of the left lung, left brachialplexopathy, and severe neuropathic pain syndrome, refractory to medical therapy. A palliative cordotomy procedure was elected for pain control. Baseline bilateral posterior tibial and median nerve somatosensory evoked potentials (SSEP) were present except in the left upper extremity. Transcranial electric motor evoked potential (TCeMEP) baselines were present in all extremities except the left upper. Total intravenous anesthesia was used. The spine was exposed at C2-C3 and a right single anterolateral cordotomy was performed with an immediate drop in TCeMEPs (70-80% amplitude reduction) in the right upper and right lower extremities. The surgeon decided to stop the cordotomy at that point. Postoperatively, the patient had no sensory or motor deficit. In this patient, TCeMEPs were used effectively to guide the surgeon in preventing damage to the spinal cord that could lead to motor deficits.

Does intraoperative neurophysiologic monitoring matter in noncomplex spine surgeries?

Objectives:

To determine associations between intraoperative neurophysiologic monitoring (IOM) for spinal decompressions and simple fusions with neurologic complications, length of stay, and hospitalization charges.

Methods:

Adult discharges in the Nationwide/National Inpatient Sample (NIS) (2007–2012) with spinal decompressions and simple spinal fusions were included. Revision surgeries, instrumentations, complicated approaches, and tumor- and trauma-related surgeries were excluded. Extracted data included patient demographics, medical comorbidities, primary spinal surgery type, and hospital characteristics. Bivariate and multiple regression analyses using NIS survey design variables correlated IOM use with neurologic complications, hospital charges, and length of stay.

Results:

IOM was reported in 4.9% of an estimated 1.1 million discharges in the weighted sample. Discharges reporting IOM were more often privately insured (61% vs 57%, p < 0.001) and had slightly more comorbidities (25% vs 24% with 3+ comorbidities, p = 0.01). Spinal fusions more often reported IOM than decompressions. The IOM group had fewer neurologic complications (0.8% vs 1.4% of controls) with no difference in length of stay (3.0 days for each group), but increased hospital charges (39% greater). Multiple regression adjustment showed significant associations of IOM with fewer neurologic complications (odds ratio 0.60, 95% confidence interval [CI] 0.47, 0.76, p < 0.001), while the estimated percentage of hospital charges was sizably diminished from the unadjusted analysis (IOM effect +9%, 95% CI +4%, +13%, p < 0.001), and length of stay was reduced (IOM effect −0.26 days, 95% CI −0.42, −0.11, p < 0.001).

Conclusions:

IOM was associated with better clinical outcomes and some increased hospital charges among discharges of simple spinal fusions and laminectomies in a large, multiyear, nationally representative dataset.

Electrical stimulation threshold in chronically compressed lumbar nerve roots: Observational study

OBJECTIVES

Intraoperative neuromonitoring (IONM) is a common practice in spinal surgery, mostly during pedicle screw placement. However, there is not enough information about the factors that can interfere with IONM data. One of these factors may be existing damage of the nerve root whose function must be preserved. The main purpose of the present study is to evaluate the effect of chronic compression in lumbar nerve roots in terms of stimulation thresholds during direct nerve stimulation.

PATIENTS AND METHODS

Direct electrical stimulation was performed in 201 lumbar nerve roots during lumbar spinal procedures under general anaesthesia in 80 patients with different lumbar spinal pathologies. Clinical and radiological data were reviewed in order to establish the presence of chronic compression.

RESULTS

Chronically compressed nerve roots showed a higher stimulation threshold than non compressed nerve roots (11.93 mA vs. 4.33 mA). This difference was confirmed with intra-subject comparison (paired sample t test, p=0.012). No other clinical factors were associated with this higher stimulation threshold in lumbar nerve roots.

CONCLUSION

A higher stimulation threshold is present in compressed lumbar nerve roots than non compressed roots. This needs to be taken into consideration during pedicle screw placement, where intraoperative neurophysiological monitoring is being used.

Interpretation of surgical neuromonitoring data in Canada: a survey of practising surgeons

Intraoperative neuromonitoring is a specialized skill set performed in the operating room to reduce the risk of neurologic injury. There appears to be a shortage of qualified personnel and a lack of Canadian guidelines on the performance of the task. We distributed a web-based survey on the attitude of the surgeons to the interpretation of intraoperative neuromonitoring data among surgeons who use the technique. At present, most of the interpretation is performed by either technologists or by the surgeons themselves. Most surgeons would prefer professional oversight from a neurologist or neurophysiologist at the doctoral level. There is a lack of personnel in Canada with the appropriate training and expertise to interpret intraoperative neuromonitoring data.

Role of multimodal intraoperative neurophysiological monitoring during positioning of patient prior to cervical spine surgery

OBJECTIVE

To determine the use of multimodal intraoperative neurophysiological monitoring (IONM) during positioning procedures in cervical spine surgery.

METHODS

IONM data was collected from 75 patients from the onset of positioning to the end of the surgical procedure. These included: transcranial motor evoked potentials (TcMEP), somatosensory evoked potentials (SEP) and free running electromyography (EMG) recordings. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (PNV) were calculated.

RESULTS

IONM warnings were given in 5 cases during neck positioning. These consisted of the disappearance of TcMEP in all the cases, while two cases showed a loss of SEPs as well. Four of these patients presented a complete recovery of TcMEP and SEPs after neck repositioning. The patient in which this recovery was not present, woke up with new postoperative neurological deficits. Sensitivity, specificity, PPV and NPV of TcMEP during cervical positioning were all 100%. Sensitivity of SEPs was 40%; specificity and PPV were 100%; and the NPV of SEPs was 95.9%.

CONCLUSION

Multimodal IONM is a useful method to prevent spinal cord injury during neck positioning in cervical spine surgical procedures. TcMEPs showed the highest sensitivity in detecting injuries to cervical spine related to neck positioning.

SIGNIFICANCE

Multimodal IONM should not only be considered for detecting intra-operative warnings, but also during positioning.

Combined muscle motor and somatosensory evoked potentials for intramedullary spinal cord tumour surgery

PURPOSE

To evaluate whether intraoperative neurophysiologic monitoring (IONM) with combined muscle motor evoked potentials (mMEPs) and somatosensory evoked potentials is useful for more aggressive and safe resection in intramedullary spinal cord tumour (IMSCT) surgery.

MATERIALS AND METHODS

We reviewed data from consecutive patients who underwent surgery for IMSCT between 1998 and April 2012. The patients were divided into two groups based on whether or not IONM was applied. In the monitored group, the procedures were performed under IONM using 75% muscle amplitude decline weaning criteria. The control group was comprised of patients who underwent IMSCT surgery without IONM. The primary outcome was the rate of gross total excision of the tumour on magnetic resonance imaging at one week after surgery. The secondary outcome was the neurologic outcome based on the McCormick Grade scale.

RESULTS

The two groups had similar demographics. The total gross removal tended to increase when intraoperative neurophysiologic monitoring was used, but this tendency did not reach statistical significance (76% versus 58%; univariate analysis, p=0.049; multivariate regression model, p=0.119). The serial McCormick scale score was similar between the two groups (based on repeated measure ANOVA).

CONCLUSION

Our study evaluated combined IONM of trans-cranial electrical (Tce)-mMEPs and SEPs for IMSCT. During IMSCT surgery, combined Tce-mMEPs and SEPs using 75% muscle amplitude weaning criteria did not result in significant improvement in the rate of gross total excision of the tumour or neurologic outcome.

Transcranial magnetic stimulation--may be useful as a preoperative screen of motor tract function

Transcranial motor stimulation with noninvasive cortical surface stimulation, using a high-intensity magnetic field referred to as transcranial magnetic stimulation generally, is considered a nonpainful technique. In contrast, transcranial electric stimulation of the motor tracts typically cannot be done in unanesthesized patients. Intraoperative monitoring of motor tract function with transcranial electric stimulation is considered a standard practice in many institutions for patients during surgical procedures in which there is potential risk of motor tract impairment so that the risk of paraplegia or paraparesis can be reduced. Because transcranial electric stimulation cannot be typically done in the outpatient setting, transcranial magnetic stimulation may be able to provide a well-tolerated method for evaluation of the corticospinal motor tracts before surgery.

METHODS

One hundred fifty-five patients aged 5 to 20 years were evaluated preoperatively with single-stimulation nonrepetitive transcranial magnetic stimulation for preoperative assessment.

RESULTS AND CONCLUSIONS

The presence of responses to transcranial magnetic stimulation reliably predicted the presence of responses to transcranial electric stimulation intraoperatively. No complications occurred during the testing, and findings were correlated to the clinical history and used in the setup of the surgical monitoring.

Intraoperative neurophysiologic monitoring: basic principles and recent update

The recent developments of new devices and advances in anesthesiology have greatly improved the utility and accuracy of intraoperative neurophysiological monitoring (IOM). Herein, we review the basic principles of the electrophysiological methods employed under IOM in the operating room. These include motor evoked potentials, somatosensory evoked potentials, electroencephalography, electromyography, brainstem auditory evoked potentials, and visual evoked potentials. Most of these techniques have certain limitations and their utility is still being debated. In this review, we also discuss the optimal stimulation/recording method for each of these modalities during individual surgeries as well as the diverse criteria for alarm signs.

Changes to CMS reimbursement rules for intraoperative neurophysiological monitoring: implications for telemedicine

Intraoperative neurophysiological monitoring (IONM) is used as an adjunct for surgeries that pose risk to nervous system structures. IONM is performed by a technologist in the operating room and is overseen by a highly trained fellowship-trained physician clinical neurophysiologist. Telemedicine has allowed the professional oversight component to be done remotely, with reimbursement for multiple simultaneous cases. Recent changes to Current Procedure Terminology coding and Medicare reimbursement policies provide options only for exclusive 1:1 technologist:oversight physician billing. This policy change may create profound repercussions in the practice of telemedicine by actively discouraging the leveraging of highly specialized and scarce expertise through on-site physician extenders.

Advances in pediatric neurocritical care

Because pediatric intensive care units (PICUs) improve survival for a range of acute diseases, attention has turned toward ensuring the best possible functional outcomes after critical illness. The neurocritical care of children is of increasing interest. However, the pediatric population encompasses a heterogeneous set of neurologic conditions, with several possible models of how best to address them. This article reviews the special challenges faced by PICUs with regards to diseases, technologies, and skills and the progress that has been made in treatment, monitoring, and prognostication. Recent advances in translational research expected to modify the field in the near-term are described.

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

STUDY DESIGN

Retrospective, case-control study.

OBJECTIVES

To report the effectiveness of transcranial motor evoked potentials (TcMEPs) in patients undergoing scoliosis surgery with neural axis abnormalities (NAAs).

SUMMARY OF BACKGROUND DATA

Transcranial motor evoked potentials are a safe and sensitive modality to identify impending spinal cord injury in adolescent idiopathic scoliosis (AIS). Previous studies have analyzed somatosensory evoked potentials (SSEPs) and neurogenic motor evoked potentials in NAA patients, but to our knowledge, no study has addressed the use of TcMEPs in these patients.

METHODS

We performed an institutional review board-approved retrospective review of a consecutive series of patients with NAA at a single institution and compared them with a consecutive series of AIS patients undergoing scoliosis surgery with spinal cord monitoring using TcMEP and SSEP. We compared the ability to obtain baseline data and the incidence of critical changes in TcMEPs and SSEPs between groups and examined a correlation with postoperative neurologic deficits.

RESULTS

We compared 38 patients with NAA (15 Chiari malformations, 12 syrinx, 7 tethered cords, and 4 spinal cord tumors) with 184 patients with AIS. The age was similar and preoperative curve magnitude was greater in the NAA group. Good baseline data were obtained less frequently in the NAA group for TcMEPs (94.7% vs. 100%; p < .001) and SSEPs (89.5% vs. 100%; p < .001). There was no statistical difference in critical deviation from baseline in the NAA group for TcMEPs (3 of 38 [7.9%] vs. 5 of 184 [2.7%]; p = .120) or SSEPs (0 of 38 vs. 3 of 184 [1.6%] (p = .430). There were no postoperative neurologic deficits in the NAA or AIS group.

CONCLUSIONS

The ability to obtain baseline spinal cord monitoring in patients with NAA approaches that of an AIS group and accurately identifies impending neurologic deficits with high sensitivity. Surgeons should be confident that TcMEP baseline data can be obtained in patients with spinal cord pathology and should trust critical changes in TcMEPs intraoperatively to prevent spinal cord injury.

Is intraoperative neuromonitoring a good idea in my practice?

Intraoperative neuromonitoring (IONM) is a growing field within neurology. IONM uses a variety of neurophysiologic modalities to detect signs of potential injury to neural structures while a patient is undergoing surgery. An early warning to the surgeon about signal changes may prevent permanent neurologic disability. Since all monitoring is done in real time, the work pace is fast. The operating room environment poses additional challenges for signal acquisition and interpretation. Specific training in the field is becoming increasingly available. Several practice models exist and IONM can be performed in an academic or a private practice setting. A career in intraoperative neuromonitoring can offer lots of opportunities, a high degree of job satisfaction, and flexibility to those choosing to enter the field.