- Chief of Neurosurgical Spine and Education, Winthrop University Hospital, Mineola, NY 11051, USA
Correspondence Address:
Nancy E. Epstein
Chief of Neurosurgical Spine and Education, Winthrop University Hospital, Mineola, NY 11051, USA
DOI:10.4103/2152-7806.120782
Copyright: © 2013 Epstein NE. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.How to cite this article: Epstein NE. The need to add motor evoked potential monitoring to somatosensory and electromyographic monitoring in cervical spine surgery. Surg Neurol Int 29-Oct-2013;4:
How to cite this URL: Epstein NE. The need to add motor evoked potential monitoring to somatosensory and electromyographic monitoring in cervical spine surgery. Surg Neurol Int 29-Oct-2013;4:. Available from: http://sni.wpengine.com/surgicalint_articles/the-need-to-add-motor-evoked-potential-monitoring-to-somatosensory-and-electromyographic-monitoring-in-cervical-spine-surgery/
Abstract
Intraoperative neural monitoring (IONM), utilizing somatosensory evoked potentials (SEP) and electromyography (EMG), was introduced to cervical spine surgery in the late 1980's. However, as SEP only provided physiological data regarding the posterior cord, new motor deficits were observed utilizing SEP alone. This prompted the development of motor evoked potential monitoring (MEP) which facilitated real-time assessment of the anterior/anterolateral spinal cord. Although all three modalities, SEP, EMG, and MEP, are routinely available for IONM of cervical spine procedures, MEP are not yet routinely employed. The purpose of this review is to emphasize that MEP should now routinely accompany SEP and EMG when performing IONM of cervical spine surgery. Interestingly, one of the most common reasons for malpractice suits involving the cervical spine, is quadriparesis/quadriplegia following a single level anterior cervical diskectomy and fusion (ACDF). Previously, typical allegations in these suits included; negligent surgery, lack of informed consent, failure to diagnose/treat, and failure to brace. Added to this list, perhaps, as the 5th most reason for a suit will be failure to monitor with MEP. This review documents the value of MEP monitoring in addition to SEP and EMG monitoring in cervical spine surgery. The addition of MEP0 should minimize major motor injuries, and more accurately and reliably detect impending anterior cord deterioration that may be missed with SEP monitoring alone.
Keywords: Cervical surgery, electromyography, intraoperative monitoring, motor evoked potentials, neurological, somatosensory evoked potentials, spine surgery
Editorial Comments
At times, editorials provide guidance as to how to perform a procedure, or select patients for a specific operation. However, in this case, this editorial is focused on why it is essential that more and more spine surgeons utilize intraoperative motor evoked potential monitoring (MEP) to supplement the more commonly employed somatosensory evoked potentials (SEP) and electromyography (EMG). Even if one cannot recall an instance in which MEP helped avoid a neurological deficit, one can read the medicolegal literature to find a plethora of cases in which MEP were not performed and patients incurred major deficits (e.g. quadriplegia, paraplegia). With the availability of TIVA (total intravenous anesthesia), real-time MEP monitoring is feasible, and there is no “waiting”. While some spine surgeons may think they have to perform cervical operations with the patient paralyzed in order to avoid motion during critical phases, those of us who perform these procedures with TIVA and MEP without paralysis think otherwise. Whether operating on the anterior or posterior cervical spinal cord, MEP provide critical and essential information regarding the status of the anterior or anterolateral cervical cord that may be missed by SEP. Those presuming that MEP are only important when dealing with anterior cervical disease are sadly mistaken; MEP can pick up changes and frequently do when both anterior or posterior cervical surgical procedures go awry.
Certainly, the evidence points to the value of SEP and MEP monitoring when operating on the spinal cord or spine. This is the principle I follow in my practice from the evidence in the literature and my own experience. Under optimal circumstances, patients should be transferred to a place where this technology is available or the patient and or family should be informed that the circumstances do not permit this technological addition to the surgery, and therefore, the risks will be higher of spinal cord damage.
However, I am fully aware that in different places one or both of these options may not be available.
Then what do they do? Are they guilty of malpractice? Say in a small community far from a neurological monitoring source? Or in another country? There is no set answer for all circumstances. Nevertheless, when given the option to include MEP, the answer should typically be in the affirmative.
Nancy Epstein, MD
Editor, SNI: Spine
INTRODUCTION
When performing cervical spine surgery, “real time” intraoperative neural monitoring (IONM) should now include not only somatosensory evoked potentials (SEP) and electromyography (EMG s), but also motor evoked potentials (MEP). While SEP classically monitor the posterior cord, MEP provide better information regarding the status of the anterior/anterolateral cord. When combined, SEP and MEP provide physiological coverage of essentially the entire cord, and thereby reduce the risk of incurring new neurological deficits without sufficient warning. This review progressively documents the “value added” of supplementing SEP/EMG IONM with MEP for cervical spine surgery.
MEDICOLEGAL HISTORY FOR CERVICAL SPINE SURGERY
In the past, the most common reasons for malpractice suits involving the cervical spine included new postoperative neurological deficits (e.g., including quadriplegia) typically incurred during single level anterior cervical diskectomy and fusion (ACDF).[
It is easier to confuse a jury than convince a judge: the crisis in medical malpractice
Insurance rates for medical malpractice are exorbitant, physicians practice defensive medicine, and both the patient and society pay a huge price. In 2002, Epstein explored different tort reform models to resolve the crisis in medical malpractice.[
Tort reform and other malpractice models
In Epstein's 2002 study, although 6 different tort reform models were also identified, only two would likely work better than the present malpractice system.[
Cases involving quadriplegia following cervical spine surgery
In 2010, Epstein again utilized Verdict Search to identify patients across the US who developed quadriplegia following cervical spine surgery between 1988-2008.[
Review of medicolegal malpractice suits involving the cervical spine
In 2011, Epstein asked 4 major questions about medicolegal suits involving the cervical spine occurring predominantly before MEP accompanied routine SEP/EMG IONM; (1) What operations/neurologic deficits led to suits?, (2) Who was sued?, (3) What “malpractice” events prompted the suits?, and (4) What were the outcomes?[
ANESTHETIC CONSIDERATIONS: AWAKE INTUBATION PROTOCOLS UTILIZING NASOTRACHEAL OR ENDOTRACHEAL FIBEROPTIC INTUBATION
For patients undergoing anterior, posterior or circumferential cervical surgery, particularly for those with OPLL with marked cord compression, there are multiple intubation techniques that should now be performed under SEP, EMG, and MEP monitoring (patients are transiently sedated to obtain baseline MEP prior to intubation).[
Keeping patients intubated after multilevel OPLL surgery (2002)
In patients under 65 years of age, multilevel OPLL is often treated with circumferential procedures including IONM (SEP and EMG as MEP were not yet routinely available/approved), multilevel anterior corpectomy/fusion, with immediate posterior fusion and often halo immobilization.[
Whether on the first or subsequent postoperative days, anesthesiologists would test whether extubation was feasible.[
Maximizing preoperative and IONM utilizing awake fiberoptic intubation and positioning in patients with cervical instability (2012)
Continuous preoperative neurological monitoring for cervical spine surgery is best achieved utilizing topical anesthesia (oropharyngeal and/or transtracheal lidocaine) in order to perform awake fiberoptic intubation and self-positioning. In Malcharek et al., study, the safety and efficacy of awake fiberoptic intubation and awake prone positioning were evaluated in 14 patients with cervical instability.[
TIVA TOTAL INTRAVENOUS ANESTHESIA
Patients undergoing NT or ET intubation for cervical pathology usually receive sedation (e.g., Versed) and local anesthetics to numb the airway (e.g., Lidocaine). Anesthetic considerations are typically dictated by the necessity for real time IONM including SEP, MEP, and EMG. This typically requires utilizing the “balance technique” or TIVA (total intravenous anesthesia), consisting of propofol and alfentanil, without inhalation anesthetics (e.g., nitrous oxide, flurane) to avoid interfering with intraoperative monitoring parameters. Advantages of TIVA include facilitation of a smooth induction, reliable/titratable maintenance, and the advantage of rapid emergence for immediate patient evaluation. For MEP monitoring it is also essential that paralytic agents are avoided, although they may transiently be utilized during the initial operative approach once MEP baselines have been recorded and adequately reproduced [
Value of SEP and MEP monitoring to avoid hypotension utilizing TIVA anesthesia for cervical spine trauma (2009)
Intraoperative MEP monitoring utilized in conjunction with TIVA anesthesia may signal intraoperative hypotension occurring during anterior cervical procedures for cervical spine trauma.[
Interaction of total intravenous anesthetic techniques (TIVA) with intraoperative monitoring and patient variables (hypertension, diabetes, age, weight) (2010)
Deiner evaluated the interactions of IONM (SEP, EMG, MEP) with anesthetic techniques utilized in spinal surgery.[
INTRAOPERATIVE MONITORING IN CERVICAL SURGERY
Evaluation of intraoperative SEP monitoring in 100 cervical operations (1993)
Epstein et al., prospectively evaluated the efficacy of real time intraoperative SEP (note: MEP monitoring was not yet approved) monitoring for cervical spine surgery in 100 patients (1989-91) and contrasted these with 218 previously unmonitored patients (1985-9).[
IONM consisting of SEP during 508 cervical corpectomies (2006)
Khan et al., retrospectively analyzed the utility of intraoperative SEP monitoring during 508 cervical single/multilevel corpectomies (average age 55.7).[
Significant SEP changes were observed in 5.3% (27 of 508 patients) cases, while new postoperative deficits were observed in 2.4% of patients; deficits included 11 root injuries, and 1 instance of quadriplegia (SEP loss irreversible). SEP loss mostly signaled hypotension or deltoid (C5) paresis. SEP s detected impending or permanent neurological deficits with a 77.1% sensitivity and 100% specificity; if root deficits were excluded, both values were 100%. The authors concluded that the majority of SEP changes can be reversed, and result in no permanent deficit [
Neurophysiological alerts (SEP, MEP, EMG) during anterior cervical surgery (2006)
Lee et al., retrospectively evaluated 1445 patients undergoing anterior cervical diskectomy/corpectomy with fusion utilizing SEP, MEP and EMG monitoring.[
Value of IONM (SEP, MEP, EMG) in 246 cervical spine operations (2007)
In a prospective study of 246 patients under cervical surgery (most with spinal stenosis), the sensitivity and specificity of multimodal intraoperative monitoring (MIOM) (SEP, MEP, EMG) was assessed.[
Predictive value of IONM (SEP, MEP, EMG) in 1055 cervical spinal operations (2008)
In Kelleher et al., prospective series of 1055 (average age 55) cervical operations, they documented the frequency of significant IONM (sensitivity, specificity, positive predictive values (PPVs), negative predictive values (NPVs)) changes and correlated these with the incidence of new postoperative neurological deficits.[
The IONM included; SEP (1055 patients), MEP (26 patients) patients, and EMG (427 patients). New postoperative deficits were observed in 34 patients (3.2%): 21 fully resolved, 9 showed partial improvements, while 4 were permanent. SEP sensitivity was 52%, and specificity was 100% (PPV 100%/NPV 97%), MEP sensitivity was 100%, and specificity 96% (PPV 96%/NPV 100%), while EMG sensitivity was 46%, with a specificity of 73% (PPV 3%/NPV 97%). They concluded that IONM helped prevent neurological damage during cervical spine surgery [
Combined 100% sensitivity of SEP/MEP in adult spinal deformity cases (2009)
Quraishi et al., retrospectively assessed IONM (SEP, EMG, MEP) in 102 spinal deformity/extensive thoracolumbar fusion cases.[
Value of SEP and MEP in avoiding brachial plexus injury attributed to positioning before anterior cervical spine surgery (2011)
Janahangiri documented that intraoperative SEP and MEP monitoring during anterior cervical spine surgery helped avoid brachial plexus injuries.[
Value of somatosensory evoked potentials (SEP) and transcranial motor evoked potentials (MEP) combined: 100% in cervical surgery (2012)
Li et al., discussed the value of intraoperative somatosensory-evoked potential (SEP) and transcranial electrical motor-evoked potential (Tc MEP s) IONM during 200 spinal operations performed utilizing TIVA (total intravenous anesthesia).[
MEP warning thresholds (amplitude) for cervical cord compression (2012)
In 350 cases, Sakaki et al., correlated the levels of cervical spine surgery with outcomes and MEP loss (differentiating tracts, segments).[
Compartment syndrome avoided by loss of SEP and MEP during cervical surgery (2012)
Bronson et al., described a case in which SEP and MEP were lost indicating a compartment syndrome evolving during a 2 level ACDF.[
Significant changes/loss of IONM (SEP, MEP, EMG) over 25 years in 12,375 patients (2013)
Raynor et al., evaluated the efficacy of IONM (SEP, MEP, EMG) in 12,375 patients involving the cervical (29.7% (3671)), thoracic/thoracolumbar (45.4% (5624)), and lumbosacral (24.9% (3080)) spine.[
Value of MEP and EMG monitoring in cervical diskectomy (2013)
Fotakopoulos et al., assessed the prospective value and efficacy of “free running” MEP and EMG monitoring during cervical microdiskectomy/fusion for 38 patients with cervical radiculopathy attributed to disc herniations.[
MEP role in surgery for cervical spondylotic myelopathy (CSM) (2013)
As MEP monitor the corticospinal tracts for patients with CSM, Capone et al., correlated the preoperative and postoperative MEP with the clinical results of cervical spine surgery in 38 patients with CSM.[
CONCLUSION
MEP should become a routine addition to SEP/EMG intraoperative monitoring in cervical spine surgery
This review emphasizes that, in the future, MEP should be routinely incorporated into the IONM protocol for cervical spine surgery. Overwhelmingly, the recent literature supports the safety/efficacy as well as sensitivity and specificity of MEP monitoring and emphasizes how adding MEP to SEP/EMG IONM should provide maximal warnings of impending intraoperative injury and thereby minimize postoperative neurological deficits. Furthermore, anesthetic TIVA protocols allow for effective MEP monitoring while markedly reducing anesthesia-related loss of potentials [
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