Effect of Intra- and Extraoperative Factors on the Efficacy of Intraoperative Neuromonitoring During Cervical Spine Surgery

Transcranial Motor Evoked Potentials as a Predictive Modality for Postoperative Deficit in Cervical Spine Decompression Surgery - A Systematic Review and Meta-Analysis

STUDY DESIGN

Systematic Review and Meta-analysis.

OBJECTIVE

The purpose of this study was to evaluate whether transcranial motor evoked potential (TcMEP) alarms can predict postoperative neurologic complications in patients undergoing cervical spine decompression surgery.

METHODS

A meta-analysis of the literature was performed using PubMed, Web of Science, and Embase to retrieve published reports on intraoperative TcMEP monitoring for patients undergoing cervical spine decompression surgery. The sensitivity, specificity, and diagnostic odds ratio (DOR), of overall, reversible, and irreversible TcMEP changes for predicting postoperative neurological deficit were calculated. A subgroup analysis was performed to compare anterior vs posterior approaches.

RESULTS

Nineteen studies consisting of 4608 patients were analyzed. The overall incidence of postoperative neurological deficits was 2.58% (119/4608). Overall TcMEP changes had a sensitivity of 56%, specificity of 94%, and DOR of 19.26 for predicting deficit. Reversible and irreversible changes had sensitivities of 16% and 49%, specificities of 95% and 98%, and DORs of 3.54 and 71.74, respectively. In anterior procedures, TcMEP changes had a DOR of 17.57, sensitivity of 49%, and specificity of 94%. In posterior procedures, TcMEP changes had a DOR of 21.01, sensitivity of 55%, and specificity of 94%.

CONCLUSION

TcMEP monitoring has high specificity but low sensitivity for predicting postoperative neurological deficit in cervical spine decompression surgery. Patients with new postoperative neurological deficits were 19 times more likely to have experienced intraoperative TcMEP changes than those without new deficits, with irreversible TcMEP changes indicating a much higher risk of deficit than reversible TcMEP changes.

The Use of Intraoperative Neuromonitoring for Cervical Spine Surgery: Indications, Challenges, and Advances

Intraoperative neuromonitoring (IONM) has become an indispensable surgical adjunct in cervical spine procedures to minimize surgical complications. Understanding the historical development of IONM, indications for use, associated pitfalls, and recent developments will allow the surgeon to better utilize this important technology. While IONM has shown great promise in procedures for cervical deformity, intradural tumors, or myelopathy, routine use in all cervical spine cases with moderate pathology remains controversial. Pitfalls that need to be addressed include human error, a lack of efficient communication, variable alarm warning criteria, and a non-standardized checklist protocol. As the techniques associated with IONM technology become more robust moving forward, IONM emerges as a crucial solution to updating patient safety protocols.

Intraoperative Deterioration of Neurophysiological Potentials of the Spinal Tracts in Cervical Spine Surgery: Correlation With Patient-Related and Procedure-Related Variables

PURPOSE

To identify characteristics associated with higher incidence of intraoperative deterioration of neurophysiological potentials related to spinal tracts in cervical spine surgeries.

METHODS

Electrophysiological raw data and neurophysiological case reports of 1,611 patients from multiple medical centers, who underwent cervical spine surgery for decompression and/or fusion, were retrospectively reviewed. Patient-related and procedure-related variables were identified and analyzed for correlation with intraoperative neurophysiological event of the spinal tracts. The neurophysiological events were analyzed for identification of collective characteristics.

RESULTS

The study cohort presented consistent dominancy of male over female patients (67% vs. 33%). Intraoperative deterioration of spinal tract-derived potentials was noted in 10.5% of the total cases, which was not correlated with gender, age, or indication of the surgery. Higher incidence of neurophysiological events was noted in patients with impaired baseline of motor evoked potentials from the thenar muscle ( P = 0.01) or somatosensory evoked potentials of the posterior tibial nerve ( P = 0.0002). Procedures of circumferential approach or procedures that involved ≥3 spinal levels demonstrated higher incidence of neurophysiological events as well ( P = 0.0003 and 0.001, respectively).

CONCLUSIONS

Patients with deteriorated neurophysiological baseline and procedures of extensive intervention are at higher risk of intraoperative neurophysiological event in cervical spine surgery. Inclusion of intraoperative neurophysiological monitoring should be encouraged in complicated cases of cervical spine surgeries.

Need for head and neck repositioning to restore electrophysiological signal changes at positioning for cervical myelopathy surgery

OBJECTIVE

To evaluate the incidence of significant intraoperative electrophysiological signal changes during surgical positioning, and to assess the effectiveness of head and neck repositioning on the restoration of signals, among patients undergoing surgery for cervical myelopathy.

MATERIAL AND METHODS

We used multimodal intraoperative monitoring (somatosensory [SEP] and motor evoked potentials [MEP] and spontaneous electromyography) before and after patients' positioning in a consecutive cohort of 103 patients operated for symptomatic cervical myelopathy. Significant changes were defined as>50% attenuation in amplitude or>10% increase in latency of SEP, or abolishment or 50-80% attenuation of MEP.

RESULTS

Out of 103 patients (34.9% female, median age 54.5 years) 88 underwent laminectomy (85.4%) and 15 (14.6%) anterior approach. At the time of positioning, signal alterations occurred in 44 patients (42.7%), yet only 11 patients (10.7%) showed alarming changes. Immediate neck repositioning of these resulted in complete (n=6) or partial (n=4) restoration of potentials, yielding no postoperative deficits. The patient in which signals could not be restored after repositioning resulted in added postoperative deficit. The accuracy (true positives plus true negatives) of monitoring to detect new neurological deficits was 99.0% (102/103) for the entire cohort, and 100% (11/11) for those showing significant changes at the moment of positioning. Overall, only 1 patient, with non-significant SEP attenuation, experienced a new postoperative deficit, yielding a 0.97% rate of false negatives.

CONCLUSION

Among patients undergoing surgery for cervical myelopathy, 10.7% showed alarming electrophysiological signal changes at the time of positioning. Immediate repositioning of the neck resulted in near always restoration of potentials and avoidance of added neurological damage. Complete or partial restoration of potentials after repositioning yielded no postoperative deficits.

Study of the latency of transcranial motor evoked potentials in spinal cord monitoring during surgery for adolescent idiopathic scoliosis

OBJECTIVE

An increase in the latency of a motor evoked potential might be as significant as a decrease in amplitude to predict a significant and clinically symptomatic neurological injury in spinal surgery for adolescent idiopathic scoliosis. The aim of the study was to investigate the impact of monitoring of latency of motor evoked potentials during spinal surgery for adolescent idiopathic scoliosis by describing intraoperative data.

METHODS

Preoperative recordings of 50 patients undergoing posterior spinal fusion for idiopathic scoliosis were studied. Latencies of appearance of the motor evoked potential curves on the right and left side were recorded for each group of muscles at several key moments during the procedure (basal, before the first implant, before and after corrective maneuvers).

RESULTS

Mean latencies were approximately the same in each muscle group on the right and the left side, before and after correction. There was no significant increase in latency during surgery. Overall results showed that the measured latency did not differ significantly between the two age groups (p=0.07). Negative correlation between height and the means of latencies was recorded in the abductor pollicis brevis and abductor digiti minimi (r=0.4; p=0.009), rectus femoris (r=0.4; p=0.01), tibialis anterior (r=0.4; p=0.007), and abductor hallucis (r=0.5; p=0.0004). No significant correlation was found between age and intraoperative parameters.

CONCLUSION

Intraoperative latency could be a reliable intraoperative monitoring criteria with low variability, that might be used to predict postoperative motor deficits in surgery for adolescent idiopathic scoliosis.

Effect of reversal of residual neuromuscular blockade on the amplitude of motor evoked potentials: a randomized controlled crossover study comparing sugammadex and placebo

PURPOSE

To compare the amplitude changes in motor evoked potentials (MEP) with reversal of residual neuromuscular blockade using sugammadex or placebo in patients with cervical myelopathy.

METHODS

In this prospective randomized double-blind, placebo-controlled crossover trial, 38 patients with cervical myelopathy undergoing posterior cervical decompression and fusion were randomized to either sugammadex (2mg/kg) or placebo. The primary outcome measure was the increase in amplitude of the MEP in the first dorsal interossei (FDI) muscle at 3 min. Mann-Whitney U test was used to analyze the primary outcome measure.

RESULTS

There was a significant increase in the amplitude of MEP at 3 min with sugammadex when compared to placebo group. The median (IQR) increase in MEP amplitude (μV) at 3 min from the left FDI in sugammadex and placebo group was 652.9 (142:1650) and 20.6 (-183.5:297.5) (p <0.001), respectively. Corresponding values from right FDI were 2153.4 (1400:4536.8) and 55(-65.2:480.8) (p=<0.001).

CONCLUSION

Our study showed that there was a 200% increase in the MEP amplitude in the first dorsal interosseous muscle at 3 min following reversal of residual neuromuscular blockade with sugammadex. By ensuring that maximal MEP amplitude is recorded at baseline, early commencement of neuromonitoring can be achieved.

TRIAL REGISTRATION NUMBER AND DATE OF REGISTRATION

The study was registered at http://clinicaltrials.gov , ID NCT03087513, Feb 5^th 2018.

Need for head and neck repositioning to restore electrophysiological signal changes at positioning for cervical myelopathy surgery

OBJECTIVE

To evaluate the incidence of significant intraoperative electrophysiological signal changes during surgical positioning, and to assess the effectiveness of head and neck repositioning on the restoration of signals, among patients undergoing surgery for cervical myelopathy.

MATERIAL AND METHODS

We used multimodal intraoperative monitoring (somatosensory [SEP] and motor evoked potentials [MEP] and spontaneous electromyography) before and after patients' positioning in a consecutive cohort of 103 patients operated for symptomatic cervical myelopathy. Significant changes were defined as>50% attenuation in amplitude or>10% increase in latency of SEP, or abolishment or 50-80% attenuation of MEP.

RESULTS

Out of 103 patients (34.9% female, median age 54.5 years) 88 underwent laminectomy (85.4%) and 15 (14.6%) anterior approach. At the time of positioning, signal alterations occurred in 44 patients (42.7%), yet only 11 patients (10.7%) showed alarming changes. Immediate neck repositioning of these resulted in complete (n=6) or partial (n=4) restoration of potentials, yielding no postoperative deficits. The patient in which signals could not be restored after repositioning resulted in added postoperative deficit. The accuracy (true positives plus true negatives) of monitoring to detect new neurological deficits was 99.0% (102/103) for the entire cohort, and 100% (11/11) for those showing significant changes at the moment of positioning. Overall, only 1 patient, with non-significant SEP attenuation, experienced a new postoperative deficit, yielding a 0.97% rate of false negatives.

CONCLUSION

Among patients undergoing surgery for cervical myelopathy, 10.7% showed alarming electrophysiological signal changes at the time of positioning. Immediate repositioning of the neck resulted in near always restoration of potentials and avoidance of added neurological damage. Complete or partial restoration of potentials after repositioning yielded no postoperative deficits.

What is the predictive value of intraoperative somatosensory evoked potential monitoring for postoperative neurological deficit in cervical spine surgery?-a meta-analysis

BACKGROUND CONTEXT

Cervical decompression and fusion surgery remains a mainstay of treatment for a variety of cervical pathologies. Potential intraoperative injury to the spinal cord and nerve roots poses nontrivial risk for consequent postoperative neurologic deficits. Although neuromonitoring with intraoperative somatosensory evoked potentials (SSEPs) is often used in cervical spine surgery, its therapeutic value remains controversial.

PURPOSE

The purpose of the present study was to evaluate whether significant SSEP changes can predict postoperative neurologic complications in cervical spine surgery. A subgroup analysis was performed to compare the predictive power of SSEP changes in both anterior and posterior approaches.

STUDY DESIGN

The present study was a meta-analysis of the literature from PubMed, Web of Science, and Embase to identify prospective/retrospective studies with outcomes of patients who underwent cervical spine surgeries with intraoperative SSEP monitoring.

PATIENT SAMPLE

The total cohort consisted of 7,747 patients who underwent cervical spine surgery with intraoperative SSEP monitoring.

METHODS

Inclusion criteria for study selection were as follows: (1) prospective or retrospective cohort studies, (2) studies conducted in patients undergoing elective cervical spine surgery not due to aneurysm, tumor, or trauma with intraoperative SSEP monitoring, (3) studies that reported postoperative neurologic outcomes, (4) studies conducted with a sample size ≥20 patients, (5) studies with only adult patients ≥18 years of age, (6) studies published in English, (7) studies inclusive of an abstract.

OUTCOME MEASURES

The sensitivity, specificity, diagnostic odds ratio (DOR), and likelihood ratios of overall SSEP changes, reversible SSEP changes, irreversible SSEP changes, and SSEP loss for predicting postoperative neurological deficit were calculated.

RESULTS

The total rate of postoperative neurological deficits was 2.50% (194/7,747) and the total rate of SSEP changes was 7.36% (570/7,747). The incidence of postoperative neurological deficit in patients with intraoperative SSEP changes was 16.49% (94/570) while only 1.39% (100/7,177) in patients without. All significant intraoperative SSEP changes had a sensitivity of 46.0% and specificity of 96.7% with a DOR of 27.32. Reversible and irreversible SSEP changes had sensitivities of 17.7% and 37.1% and specificities of 97.5% and 99.5%, respectively. The DORs for reversible and irreversible SSEP changes were 9.01 and 167.90, respectively. SSEP loss had a DOR of 51.39, sensitivity of 17.3% and specificity 99.6%. In anterior procedures, SSEP changes had a DOR of 9.60, sensitivity of 34.2%, and specificity of 94.7%. In posterior procedures, SSEP changes had a DOR of 13.27, sensitivity of 42.6%, and specificity of 94.0%.

CONCLUSIONS

SSEP monitoring is highly specific but weakly sensitive for postoperative neurological deficit following cervical spine surgery. The analysis found that patients with new postoperative neurological deficits were nearly 27 times more likely to have had significant intraoperative SSEP change. Loss of SSEP signals and irreversible SSEP changes seem to indicate a much higher risk of injury than reversible SSEP changes.

Successful Motor Evoked Potential Monitoring in Cervical Myelopathy : Related Factors and the Effect of Increased Stimulation Intensity

Objective

Intraoperative neurophysiological monitoring (IONM) has been widely used during spine surgery to reduce or prevent neurologic deficits, however, its application to the surgical management for cervical myelopathy remains controversial. This study aimed to assess the success rate of IONM in patients with cervical myelopathy and to investigate the factors associated with successful baseline monitoring and the effect of increasing the stimulation intensity by focusing on motor evoked potentials (MEPs).

Methods

The data of 88 patients who underwent surgery for cervical myelopathy with IONM between January 2016 and June 2018 were retrospectively reviewed. The success rate of baseline MEP monitoring at the initial stimulation of 400 V was investigated. In unmonitorable cases, the stimulation intensity was increased to 999 V, and the success rate final MEP monitoring was reinvestigated. In addition, factors related to the success rate of baseline MEP monitoring were investigated using independent t-test, Wilcoxon rank-sum test, chi-squared test, and Fisher’s exact probability test for statistical analysis. The factors included age, sex, body mass index, diabetes mellitus, smoking history, symptom duration, Torg-Pavlov ratio, space available for the cord (SAC), cord compression ratio (CCR), intramedullary increased signal intensity (SI) on magnetic resonance imaging, SI length, SI ratio, the Medical Research Council (MRC) grade, the preoperative modified Nurick grade and Japanese Orthopedic Association (JOA) score.

Results

The overall success rate for reliable MEP response was 52.3% after increasing the stimulation intensity. No complications were observed to be associated with increased intensity. The factors related to the success rate of final MEP monitoring were found to be SAC (p<0.001), CCR (p<0.001), MRC grade (p<0.001), preoperative modified Nurick grade (p<0.001), and JOA score (p<0.001). The cut-off score for successful MEP monitoring was 5.67 mm for SAC, 47.33% for the CCR, 3 points for MRC grade, 2 points for the modified Nurick grade, and 12 points for the JOA score.

Conclusion

Increasing the stimulation intensity could significantly improve the success rate of baseline MEP monitoring for unmonitorable cases at the initial stimulation in cervical myelopathy. In particular, the SAC, CCR, MRC grade, preoperative Nurick grade and JOA score may be considered as the more important related factors associated with the success rate of MEP monitoring. Therefore, the degree of preoperative neurological functional deficits and the presence of spinal cord compression on imaging could be used as new detailed criteria for the application of IONM in patients with cervical myelopathy.

Intraoperative monitoring of corticospinal tracts in anterior cervical decompression and fusion surgery: Excitability differentials of lower extremity muscles

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Lower extremity (LE) muscles demonstrate intraoperative excitability differences.

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Abductor hallucis is a suitable LE muscle for monitoring the corticospinal tract (CST).

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CST monitoring with two LE muscles includes advantages but also practical limitations.

Objective

This study examines and compares excitability characteristics of tibialis anterior (TA) and abductor hallucis (AH) transcranial motor evoked potentials (tcMEP) during anterior cervical decompression and fusion (ACDF) surgery.

Methods

Electrophysiological and clinical data of 89 patients who underwent ACDF procedure were retrospectively reviewed. TcMEP data of TA and AH muscles from 178 limbs were analyzed for availability, robustness and stability during the procedure.

Results

TA tcMEP was available at 83% whereas AH tcMEP was available at 99% of the monitored lower limbs at preposition baseline. Availability of both TA and AH tcMEP was demonstrated in 147/178 limbs. The baseline amplitude of AH tcMEP was significantly greater than that of TA tcMEP recorded from the same limb (744.6 ± 54.0 and 326.9 ± 33.3 µV, respectively). Simultaneous deterioration of TA and AH tcMEP data was demonstrated in 10/147 limbs. Deterioration of either TA or AH tcMEP data accompanied by unchanged tcMEP data from the other lower limb muscle was noted in 32/147 compared to 1/147 limbs, respectively. The deteriorated TA and AH tcMEP data returned to baseline before closing at incidence of 17% compared to 46%, respectively. No new lower extremity (LE) neurological deficit was presented postoperatively in any patient.

Conclusions

AH tcMEP is a more reliable candidate than TA tcMEP for intraoperative LE monitoring in ACDF procedure.

Significance

The excitability differentials in LE tcMEP in ACDF is a variable that need to be considered while interpreting intraoperative neurophysiological data.

Neurophysiological monitoring during neurosurgery: anesthetic considerations based on outcome evidence

PURPOSE OF REVIEW

This article reviews the recent outcome studies that investigated intraoperative neurophysiological monitoring (IONM) during spine, neurovascular and brain tumor surgery.

RECENT FINDINGS

Several recent studies have focused on identifying which types of neurosurgical procedures might benefit most from IONM use. Despite conflicting literature regarding its efficacy in improving neurological outcomes, many experts have advocated for the use of IONM in neurosurgery. Several themes have emerged from the recent literature: the entire perioperative team must always work together to ensure adequate communication and intervention; systems and checklists, in which each member of the perioperative team has a clearly defined role, can be useful in the event of a sudden intraoperative changes in electrophysiological signals; regardless of the IONM modality used, any sudden change in electrophysiological signal should prompt an immediate and appropriate intervention; a multimodal IONM approach is often, but not always, advantageous over a single IONM approach.

SUMMARY

For neurosurgical procedures that can be complicated by neural injury, the use of IONM should be considered according to specific patient and surgical factors. Future studies should focus on improving IONM technology and optimizing sensitivity and specificity for detecting any impending neural damage.