ORIGINAL RESEARCH

Overview of Intraoperative Neurophysiological Monitoring During Spine Surgery Parastou Shilian, Gabriel Zada, Aaron C. Kim, and Andres A. Gonzalez University of Southern California, Los Angeles, CA, U.S.A.

Summary: Intraoperative neurophysiologic monitoring has had major advances in the past few decades. During spine surgery, the use of multimodality monitoring enables us to assess the integrity of the spinal cord, nerve roots, and peripheral nerves. The authors present a practical approach to the current modalities in use during spine surgery, including somatosensory evoked potentials, motor evoked potentials, spinal D-waves, and free-run and triggered electromyography. Understanding the complementary

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ver the past several decades, various modalities of electrophysiological tests have been increasingly used in the operating room to monitor different parts of the nervous system specifically at risk, to prevent or minimize the probability of neurological injury. In addition, the information gleaned from intraoperative neurophysiological monitoring provides guidance to the neurosurgical team throughout the course of the operation. Intraoperative neurophysiological monitoring has become a useful adjunct to a variety of spinal operations, including spinal tumor resection, spinal decompression and fusion, deformity surgery, and vascular surgery of the spinal cord. Intraoperative monitoring has been in use since the 1970s. One of the first methods used to detect neurological injury during surgery was the wake-up test, pioneered by Vauzele (1973). As part of this cursory, yet pioneering monitoring test, general anesthesia was transiently discontinued after insertion of spinal hardware to perform a neurological examination. Benefits of the Stagnara wake-up test were that it was relatively simple to perform, without the need for special equipment. Although the wake-up test was functional, it had several inherent limitations, such as a potential delay in identification of neurological deficits (because it was only performed at one time point), risk of accidental extubation, or other anesthesia complications, air embolization, and possible movement of surgical instrumentation (Hall et al., 1978; Nuwer and Dawson, 1984; Vauzelle et al., 1973). In recent decades, the evolution of safer and more sophisticated real-time modalities for neurophysiological monitoring have essentially replaced the need to perform such wake-up tests and have transformed the subspecialty of neurophysiological monitoring and modern spinal surgery into the discipline it is today.

SOMATOSENSORY EVOKED POTENTIALS Somatosensory evoked potentials (SSEPs) are an extremely useful and sensitive modality for the intraoperative assessment of Address correspondence and reprint requests to Parastou Shilian D.O., Department of Neurology, University of Southern California, 1520 San Pablo, Suite 3000, Los Angeles, CA 90033; email: [email protected] Copyright Ó 2014 by the American Clinical Neurophysiology Society

ISSN: 0736-0258/14/3304-0333

DOI 10.1097/WNP.0000000000000132

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nature of these modalities will help tailor monitoring to a particular procedure to minimize postoperative neurologic deficit during spine surgery. Key words: Intraoperative Neurophysiological Monitoring, Spine surgery, Somatosensory evoked potentials, Motor evoked potentials, Electromyography. (J Clin Neurophysiol 2016;33: 333–339)

spinal cord function. A typical protocol includes delivery of a peripheral stimulus and subsequent recording proximally in the region of the somatosensory cortex, thereby monitoring the integrity of major afferent pathways of the dorsal spinal cord. Somatosensory evoked potentials were first recorded by Dr. Dawson in 1947, by stimulating the peripheral nerve and recording responses over the somatosensory cortex (Dawson, 1947). Two decades later, this technology was applied for the first time in the operating room in an institution affiliated with the University of Southern California. In 1974, Nash et al introduced the use of SSEP for intraoperative monitoring of the nervous system during spine surgery. Early SSEP monitoring used middle and long-latency cortical potentials but had limited use due to a high degree of variability, excess noise, and sensitivity to anesthesia. Nuwer and Dawson established parameters for SSEP monitoring to improve its reproducibility and efficacy in the operating room. These modifications involved optimizing the stimulation rate, filter settings, anesthesia protocol, and scalp montages to achieve a more favorable signal-to-noise ratio (Nuwer and Dawson, 1984).

Anatomy Somatosensory evoked potentials assess the integrity of the dorsal column-medial lemniscus pathway, as initially described by D’Angelo et al. (1973). The dorsal column–medial lemniscus pathway conducts the sensory modalities of vibration, proprioception, and fine touch. From the peripheral mechanoreceptors and stretch receptors, signal travels through dorsal horn neurons. First-order neuron axons ascend through the cuneatus and gracilis fasciculi and synapse on second-order neurons in the cuneate and gracile nuclei, respectively. These fibers cross midline as internal arcuate fibers and ascend as the medial lemniscus en route to the pathway’s second synapse in the ventral posterolateral nucleus of the thalamus. Axons of the third-order neurons ascend through the posterior limb of the internal capsule to the primary somatosensory cortex.

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METHODOLOGY Stimulation sites are selected based on the spinal cord level of interest. The median nerve is typically monitored for high cervical procedures, and the ulnar nerve is generally used for lower cervical procedures. Even if the pathway of the upper extremity nerve used is outside the area at risk (i.e., thoracolumbar procedures), monitoring can provide general information about systemic (blood pressure, temperature), anesthetic, or changes due to positioning. For thoracolumbar and cervical operations, the posterior tibial nerve at the ankle is the preferred monitoring site. If the posterior tibial nerve is compromised (i.e., below the knee amputation or severe peripheral neuropathy), the peroneal nerve at the knee can be used as an alternate. A stimulation rate of approximately 5 Hz (that are not multiple of 60, i.e., 4.47 Hz) is optimal (Nuwer and Dawson, 1984) for SSEP monitoring. A slower stimulation frequency will yield higher amplitude responses but will slow the time to obtain averaged sets of responses. The cortical N20 potential can be recorded at CPc-CPi or CPc-FPz (International 10-10 system), and P37 can be recorded at CPi-CPc, CPi-FPz, and Cz-FPz channels (Fig. 1). Subcortical far field potentials, including N13, P14, N18, P31, and N34 can be recorded from C5s-FPz channel. It is advisable to use multiple channels to record cortical potentials. This allows monitoring to continue without interruption should one channel become compromised. Because subcortical channels are less susceptible to anesthesia, the reliability of SSEP and subsequent interpretation of SSEPs may be higher than other monitoring modalities (Sloan and Heyer, 2002). The typical filter settings used to record SSEPs can be found in the Appendix 1.

EFFICACY OF SSEP MONITORING The use of SSEP monitoring has virtually eliminated the necessity to wake patients up during surgery and has greatly improved the safety and ability to provide near continuous

FIG. 1. Multiple channels are recommended for recording cortical and subcortical potentials in the upper and lower extremities. Subcortical channels can be recorded from brainstem and thalamic sources and are less affected by anesthetics. 334

Overview of IOM During Spine Surgery

assessment of spinal cord function during spinal surgery. However, SSEP monitoring has its own set of limitations and is very sensitive to various anesthetics (particularly halogenated agents and nitrous oxide), as well as temperature and blood pressure (Eager et al., 2011; Jou, 2000; Porkkala et al., 1997; Sloan and Heyer, 2002). Optimization of many intraoperative parameters and a close working relationship with the anesthesia team is therefore generally required during these operations. Because of a low signal-to-noise ratio in the operating room, averaging of many stimuli is usually required to provide a reproducible signal. Many monitoring practitioners use an amplitude and latency criteria to raise alarm during SSEP monitoring. Most accepted criteria include either a 50% decrease in SSEP waveform amplitude or a 10% increase in latency from baseline (Nuwer, 2008; Nuwer et al., 1995). However, although not systematically studied, a 30% drop in amplitude observed during a critical portion of the surgery with an otherwise stable waveform may be significant. Changes due to anesthesia need to be taken into account when evaluating cortical potential amplitudes. Subcortical responses are more resistant and can be helpful in distinguishing changes caused by anesthetics. Changes in SSEP monitoring can sometimes be offset by optimization of blood pressure, patient temperature, and/or anesthesia medications or dosing. The clinical efficacy of SSEP monitoring was evaluated in a multicenter outcome survey of 51,263 spinal cases performed by 53 US surgeons as part of the Scoliosis Research Society. The study reported a sensitivity of 92% and specificity of 98.9% in the ability of SSEP monitoring to detect postoperative deficits and a 60% ability to reduce major neurologic deficits (Nuwer et al., 1995). The same study also demonstrated that using SSEP monitoring as a sole modality is associated with a false-negative rate of 0.127%. Many studies have since calculated a sensitivity range of 80% to 100% in detecting postoperative deficits when using SSEP monitoring alone. In one operative series of spinal tumor resections, the sensitivity of SSEP was found to be 88% for detecting any neurological deficits and 100% for detecting severe deficits (Wiedemayer et al., 2004). The literature regarding SSEP monitoring demonstrates a disparity regarding false-negative and false-positive results, which is an inherent limitation of many of these studies. An example of a false positive might be a case in which there are significant changes in the monitoring, with notification of surgeon, yet no detectable neurological deficits postoperatively. Although these cases are usually considered to be false positives according to the majority of the literature, this may underestimate the test’s sensitivity because the detection and notification in some cases may have altered the course of the surgery, thereby preventing a deficit if the surgeon had not been notified. Perhaps, more concerning is the specter of false-negative monitoring, where the patient wakes up with motor deficits with no detectable changes in SSEP monitoring. Given that SSEP are not representative of corticospinal tract function, the relative inability of SSEP monitoring to detect isolated motor deficits may be considered a limitation of SSEP monitoring, rather than a failure of this test. Motor changes with unchanged SSEP signals should therefore not be considered to be a false-negative result.

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INTRODUCTION TO MULTIMODALITY Because of their sensitivity for detecting motor deficits and the lack of a more specific modality, for two decades, SSEP monitoring was the only way to monitor global spinal cord function. We now know that this SSEP monitoring reflects only the integrity of the dorsal column–medial lemniscus pathway. In recent decades, however, the advent of multimodality neuromonitoring techniques has provided the ability to monitor both motor and sensory pathways, in addition to nerve root function. In addition to SSEP monitoring, multimodality testing often includes some permutation of transcranial motor evoked potential (TcMEP), continuous free running electromyography, evoked or triggered electromyography, dermatomal SSEP (DSSEP), and spinal D-wave monitoring. Selection of the appropriate combination of monitoring modalities depends on the structure(s) at risk, as determined by an experienced neurophysiologist in conjunction with the neurosurgeon. The widespread availability and experience gained with multimodality neurophysiologic monitoring have greatly improved the efficacy of this strategy in the operating room.

DERMATOMAL SOMATOSENSORY EVOKED POTENTIALS Dermatomal somatosensory evoked potentials provide the ability to monitor nerve root function, by way of dermatomal stimulation in the cervical and lumbosacral regions. Needle or surface electrodes can be used for surface stimulation of dermatomes of interest, and recording is typically done at the scalp. In general, C39 and C49 (2 cm posterior to C3 and C4 of International 10-20 system) electrodes can be used for the upper extremities and Cz9 and Fpz9 for the lower extremities. There are limited studies regarding the effectiveness of DSSEP in monitoring nerve root function. If DSSEPs are obtained, they may provide valuable information to the surgeon regarding nerve root function. However, many authors allude to the variability of its usefulness depending on the level being monitored (Owen et al., 1993; Owen et al., 1991). Dermatomal somatosensory evoked potentials are very small potentials with amplitudes averaging less than half of median or tibial SSEPs. Furthermore, dermatomes are inherently variable regarding anatomical distribution, potentially compromising the specificity of this technique. Dermatomal patterns across individuals are inconsistent, and adjacent dermatomes often overlap, making the recording an interpretation of DSSEP signals frequently challenging (Tsai et al., 1997). In addition, high sensitivity of DSSEPs to anesthesia further limits their use in the operating room (Herdmann et al., 1996; Sloan and Heyer, 2002). On account of this variability and poor reproducibility, DSSEPs have limited use in the operating room.

TRANSCRANIAL MOTOR EVOKED POTENTIALS Selective activation of the human cortex by direct electrical stimulation was first demonstrated by Penfield and Boldrey clinicalneurophys.com

(1939). Forty years later, in the early in the 1980’s, cortical stimulation through an intact skull was first developed by Merton and Morton (1980). This technique was later adapted to provide intraoperative monitoring of the major components of the motor pathway, the corticospinal tracts. During TcMEP monitoring, motor fibers are nonspecifically stimulated transcranially, and responses are recorded from appropriate muscles as dictated by the surgical procedure. Transcranial stimulation may recruit motor fibers from the motor cortex or deeper structures, such as corona radiata and the internal capsule. Most centers use a multipulse train, ranging from 3 to 7 pulses, which can help overcome anesthetic inhibition of the anterior horn cell synapse (Husain, 2008). Stimulation is performed through an interpulse interval ranging from 2 to 4 milliseconds (Legatt, 2002), typically using corkscrew or needle electrodes. Electrodes are placed over C1 and C2 (International 10-10 system) or more laterally at C3 and C4 to optimize desired potentials. Recording is performed by placing intramuscular needles 2 to 3 cm apart in the desired target muscles. At least two muscles distal to the surgical level(s) are monitored, and one muscle proximal to the surgical level(s) is typically used as a control. The monitoring of distal rather than proximal muscles is typically favored, on account of their richer corticospinal representation. Increasing the number of muscles monitored improves the specificity and the predictive value of motor evoked potentials (Sala et al., 2006). Alarm criteria for TcMEP monitoring are not as well established as with SSEP monitoring. When a robust baseline signal is present, a complete loss or abrupt decrease in amplitude of $ 80% has been described as a preferred method used to report critical changes. The “all or none” method for TcMEP monitoring may lack sensitivity and may delay the time to notifying the surgeon of a potential injury. Other criteria, like changes in the morphology of responses, such as a complex multiphasic response evolving to a biphasic or a monophasic response, can also be cause for alarm (Quinones-Hinojosa et al). It is important to consider that a gradual loss of signal may indicate a potentially reversible anesthetic effect (Husain, 2008). Overall, routine use of TcMEP neurophysiological assessment has improved spinal cord monitoring by effectively evaluating the integrity and functionality of the corticospinal tract during surgery and improving predictability of postoperative motor deficits. A study by Sala et al. (2006) showed significant improvement in motor outcomes in patients undergoing TcMEP monitoring during intramedullary spinal cord tumor removal, as compared with nonmonitored historical controls. Some of the limitations inherent to using TcMEP monitoring during spinal surgery include susceptibility to anesthetic medications (particularly inhalational and neuromuscular blockade agents) and intrinsic variability. The use of total intravenous anesthesia is sometimes preferred when responses are difficult to obtain or demonstrate high variability. Chen et al. (2007) reported a success rate of 94.8% for the upper extremity and 66.6% for the lower extremity in the ability to obtain reliable MEPs. These rates drop to 81% and 39.1%, respectively, in the presence of preexisting weakness (Chen et al., 2007). Furthermore, TcMEPs are more sensitive than SSEPs in detecting spinal cord ischemia and can be helpful in preventing paraplegia if

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appropriate measures are undertaken by the surgical team during thoracic and thoracoabdominal aneurysm surgery (Dong et al., 2002). Although TcMEPs are conventionally used to monitor spinal cord function, there is evidence to suggest that they may also be used to assess nerve root function (Fig. 2). A study by Fan et al showed that addition of TcMEP monitoring of the deltoids and biceps, in addition to spontaneous EMG of the same muscles, provided sufficient warning for the surgeon during posterior cervical spine surgery. In patients with MEP changes in addition to EMG firing, a foraminotomy was performed at C4-C5 level to decompress the C5 nerve root. Patients undergoing this monitoring technique generally recovered within 1 to 7 days, compared with up to 2 years in patients operated on with the use of conventional multimodality techniques (Fan et al., 2002). A follow-up study done by Bose et al. (2007) evaluated similar techniques during anterior cervical spine surgeries. They also demonstrated that the addition of TcMEP to spontaneous EMG offered complementary information and improved prognostication of postoperative deficits (Bose et al., 2007). Lieberman et al studied MEP monitoring in 35 patients undergoing complex lumbar surgery. They showed that a drop in the MEP amplitude

Overview of IOM During Spine Surgery

of greater than 80% from baseline was 100% sensitive for detecting nerve root injury. Conversely, no patients had a new motor deficit if the final MEP was at least 67% of baseline. In addition, the severity and duration of injury was reduced in MEP monitored patients compared with patients from previous studies (Lieberman et al., 2008). Review of the literature by MacDonald et al suggests that the use of MEP monitoring for assessing nerve root function may be limited due to radicular overlap (each nerve root supplies many different muscles and each muscle is innervated by many different nerve roots), limited sampling (only a small portion of motor axons are sampled with MEPs), and variability (intrinsic quality of MEP, variability in amplitude, threshold, and morphology) (Macdonald et al., 2012).

SPINAL D-WAVE Another method used to assess corticospinal tract function is recording of spinal D-waves. Stimulation is given at the cortical level, and responses are recorded from the spinal cord through an epidural electrode. Some of the benefits of this method include less sensitivity to anesthesia and an ability to monitor after

FIG. 2. This is a 58-year-old man who underwent an anterior cervical discectomy and fusion for a herniated nucleus pulposus. Intraoperatively, changes developed in the right intrinsic hand muscle motor evoked potential. The patient developed postoperative right hand weakness suggesting a C8 or T1 root compromise. 336

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neuromuscular blockade. D-waves can be used in conjunction with TcMEPs to provide improved prediction of postoperative outcomes (Fig. 3). Kothbauer et al. (1998) studied 100 cases of intramedullary spinal cord tumor resections. The authors found that although unaffected MEPs prognosticate no motor deficit, significant changes in the TcMEP, along with a change in the D-wave, suggest a permanent deficit. A change in TcMEP recording, however, with no changes in D-wave, was more likely to predict a transient neurological deficit (Kothbauer et al., 1998).

SPONTANEOUS ELECTROMYOGRAPHY To record spontaneous EMG activity, active and reference electrodes are placed in the muscles of interest, depending on the nerve roots at risk. Nerve roots of cervical, lumbar, and sacral segments can all be monitored. Spontaneous free-run EMG shows no activity at baseline in the presence of healthy nerve root function (Fig. 4). However, discharges can be seen with nerve stretch, blunt trauma, compression, or ischemia (Nichols and Manafov, 2012). High-frequency and/or high-amplitude trains are clinically significant and suggest irritation to the nerve roots (Fig. 5). Myokymic discharges may suggest more severe damage to the nerve root. Spontaneous EMG allows monitoring of multiple nerve roots at the same time, with immediate and continuous feedback as there is no need for signal averaging. Furthermore, this modality is not as affected by parameters such as blood pressure and temperature as are other neurophysiological monitoring methods. Muscle relaxants, however, should be avoided whenever possible because they can significantly attenuate EMG activity. One of the pitfalls of this modality occurs with sharp nerve transection, as the EMG may not show any abnormal activity (Nelson and Vasconez, 1995). Gunnarsson et al. (2004) demonstrated that spontaneous electromyography has a high sensitivity (100%), yet a low specificity (23.7%) to detect postoperative neurologic deficits and is therefore more reliable as a screening tool for nerve root function.

FIG. 4. Baseline spontaneous electromyogram is quiet with no discharges seen.

Accurate placement of pedicle screws is often challenging, mainly on account of anatomical and pathological variations, and the proximity of the spinal cord and nerve roots. Pedicle screw breaches may cause compression of the spinal cord or nerve roots and have been reported in as high as 10% of spinal fixation sites (Parker et al., 2011). Radiologic imaging has a sensitivity of only 63% in detecting a breach of the medial or inferior aspect of the pedicle wall (Maguire et al., 1995). Triggered EMG may be a useful adjunct in detecting compression of the neural elements during spinal surgery and involves electrical stimulation of the screw while recording timelocked EMG activity from the corresponding myotome. Because Calancie et al. (1994) demonstrated the sensitivity and reliability of this technique, it has been commonly used to detect pedicle wall breaches. Trigger EMG increases the sensitivity of identifying

TRIGGERED ELECTROMYOGRAPHY Pedicle screws are commonly used for mechanical stabilization of the thoracic, lumbosacral, and more recently cervical spinal levels.

FIG. 3. Obtaining D-wave in addition to TcMEP during spinal cord surgery can help with prognosis. With loss of MEP, stability of Dwaves can be used by surgeons to decide on a more aggressive resection without causing a permanent deficit. clinicalneurophys.com

FIG. 5. Trains of firing are observed in the left tibialis anterior and left foot.

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The true efficacy of IOM has not been directly studied in humans because of inability to perform double-blinded randomized controlled trials. Evidence-based guidelines established by Nuwer et al, however, concluded that intraoperative monitoring is effective in predicting postoperative paraparesis, paraplegia, and quadriplegia during spinal surgery (Nuwer et al., 2012). This was based on four class I and seven class II studies (based on the AAN four-tiered evidence classification scheme). These combined data resulted in a level A recommendation to alert the surgical team about increased risk of severe adverse neurologic outcomes in patients with reported IOM changes. FIG. 6. Anterior lumbar interbody fusion: increased latency and decreased amplitude in the left lower SSEP, followed by complete loss of left N20 response. The cortical SSEP response recovered after replacement of the retractor (descending timeline).

a misplaced pedicle screw in up to 93% of lumbosacral instrumentation cases (Maguire et al., 1995). Calancie et al reported that EMG thresholds $ 10 mA in the lumbosacral spine suggest absence of a pedicle wall breach. Another study by Raynor et al. (2007) showed that using a threshold of 8 mA, triggered electromyography has a specificity of 94% and a sensitivity of 86% in identifying a pedicle screw breach. With thoracic pedicle screws, Shi et al show that stimulation thresholds .11 mA have a 97.5% negative-predictive value. Practitioners should remain mindful that the use of muscle relaxants, preexisting radiculopathy, or current shunting may increase the threshold of stimulation of lumbosacral nerve roots, potentially resulting in false-negative results.

ANTERIOR LUMBAR INTERBODY FUSION Special consideration needs to be given to anterior lumbar surgery due to the risk of vascular compromise. It is reported that up to 57% of patients undergoing anterior lumbar interbody fusion at the L4-L5 level are subject to left iliac artery compression (Brau et al., 2003). Vascular compromise and oxygen desaturation correlates with changes in the left lower extremity SSEP (Fig. 6). These changes are usually transient and typically resolve with adjustment or removal of the retractor. If SSEP recovery is not seen, thrombosis to the corresponding iliac artery should be considered.

MULTIMODALITY PREDICTIVE VALUE A prospective study by Kelleher et al. (2008) of 1055 patients undergoing cervical spine surgery using multimodality monitoring showed a 52% sensitivity and 100% specificity for SSEP monitoring, 100% sensitivity and 96% specificity for MEP monitoring, and 46% sensitivity and 73% specificity for EMG in predicting postoperative motor deficits. Multimodality monitoring provides independent and complementary information in monitoring spinal cord function. Sutter et al studied multimodality testing in 1017 patients undergoing spine surgery. They showed that multimodality intraoperative monitoring had a sensitivity of 89% and a specificity of 99%, with a false-negative rate of 0.8%. Using multimodality monitoring can help prevent and/or minimize the degree of neurologic deficits in patients undergoing spinal surgery. 338

CONCLUSIONS The ability to monitor the functional integrity of the nervous system in real-time fashion is crucial to the very essence of surgery of the spinal cord and central nervous system as a whole. The discipline of intraoperative neurophysiological monitoring has evolved rapidly over the past several decades, from rudimentary wake-up tests to advanced and sophisticated methods for multimodality monitoring. Selective use of various intraoperative modalities, including SSEP, TcMEP, spinal D-wave, and EMG monitoring now provide a methodology for complimentary and highly sensitive screening of specific anatomical subsets of the nervous system. Multimodality neurophysiological monitoring has been shown to augment the course of many spinal operations and is known to prevent and minimize the degree of major postoperative neurological deficits.

REFERENCES Bose B, Sestokas AK, Schwartz DM. Neurophysiological detection of iatrogenic C-5 nerve deficit during anterior cervical spinal surgery. J Neurosurg Spine 2007;6:381–385. Brau SA, Spoonamore MJ, Snyder L, et al. Nerve monitoring changes related to iliac artery compression during anterior lumbar spine surgery. Spine J 2003;3:351–355. Calancie B, Madsen P, Lebwohl N. Stimulus-evoked EMG monitoring during transpedicular lumbosacral spine instrumentation. Initial clinical results. Spine (Phila Pa 1976) 1994;19:2780–2786. Chen X, Sterio D, Ming X, et al. Success rate of motor evoked potentials for intraoperative neurophysiologic monitoring: effects of age, lesion location, and preoperative neurologic deficits. J Clin Neurophysiol 2007;24:281–285. D’Angelo CM, Van Gilder JC, Taub A. Evoked cortical potentials in experimental spinal cord trauma. J Neurosurg 1973;38:332–336. Dawson GD. Cerebral responses to electrical stimulation of peripheral nerve in man. J Neurol Neurosurg Psychiatry 1947;10:134–140. Dong CCJ, Macdonald DB, Janusz MT. Intraoperative spinal cord monitoring during descending thoracic and thoracoabdominal aneurysm surgery. Ann Thorac Surg 2002;74:S1873–S1876; discussion S1892–S1898. Eager M, Shimer A, Jahangiri FR, et al. Intraoperative neurophysiological monitoring (IONM): lessons learned from 32 case events in 2069 spine cases. Am J Electroneurodiagnostic Technol 2011;51:247–263. Fan D, Schwartz DM, Vaccaro AR, et al. Intraoperative neurophysiologic detection of iatrogenic C5 nerve root injury during laminectomy for cervical compression myelopathy. Spine (Phila Pa 1976) 2002;27:2499–2502. Gunnarsson T, Krassioukov AV, Sarjeant R, Fehlings MG. Real-Time Continuous Intraoperative Electromyographic and Somatosensory Evoked Potential Recordings in Spinal Surgery: Correlation of Clinical and Electrophysiologic Findings in a Prospective, Consecutive Series of 213 Cases. Spine (Phila Pa 1976) 2004;29:677. Hall JE, Levine CR, Sudhir KG. Intraoperative awakening to monitor spinal cord function during Harrington instrumentation and spine fusion.

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Description of procedure and report of three cases. J Bone Joint Surg Am 1978;60:533–536. Herdmann J, Deletis V, Edmonds HL, Morota N. Spinal cord and nerve root monitoring in spine surgery and related procedures. Spine (Phila Pa 1976) 1996;21:879–885. Husain AM. A practical approach to neurophysiologic intraoperative monitoring. New York, Demos, 2008. Jou IM. Effects of core body temperature on changes in spinal somatosensoryevoked potential in acute spinal cord compression injury: an experimental study in the rat. Spine (Phila Pa 1976) 2000;25:1878–1885. Kelleher MO, Tan G, Sarjeant R, Fehlings MG. Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: a prospective analysis of 1055 consecutive patients. J Neurosurg Spine 2008;8:215–221. Kothbauer KF, Deletis V, Epstein FJ. Intraoperative monitoring. Pediatr Neurosurg 1998;29:54–55. Legatt AD. Current practice of motor evoked potential monitoring: results of a survey. J Clin Neurophysiol 2002;19:454–460. Lieberman JA, Lyon R, Feiner J, et al. The efficacy of motor evoked potentials in fixed sagittal imbalance deformity correction surgery. Spine (Phila Pa 1976) 2008;33:E414–E424. Macdonald DB, Stigsby B, Homoud Al I, et al. Utility of motor evoked potentials for intraoperative nerve root monitoring. J Clin Neurophysiol 2012;29:118–125. Maguire J, Wallace S, Madiga R, et al. Evaluation of intrapedicular screw position using intraoperative evoked electromyography. Spine (Phila Pa 1976) 1995;20:1068–1074. Merton PA, Morton HB. Stimulation of the cerebral cortex in the intact human subject. Nature 1980;285:227. Nelson KR, Vasconez HC. Nerve transection without neurotonic discharges during intraoperative electromyographic monitoring. Muscle Nerve 1995;18:236–238. Nichols GS, Manafov E. Utility of electromyography for nerve root monitoring during spinal surgery. J Clin Neurophysiol 2012;29:140–148. Nuwer MR. Intraoperative monitoring of neural function. Amsterdam: Elsevier, 2008. Nuwer MR, Dawson E. Intraoperative evoked potential monitoring of the spinal cord: enhanced stability of cortical recordings. Electroencephalogr Clin Neurophysiol 1984;59:318–327. Nuwer MR, Dawson EG, Carlson LG, et al. Somatosensory evoked potential spinal cord monitoring reduces neurologic deficits after scoliosis surgery: results of a large multicenter survey. Electroencephalogr Clin Neurophysiol 2003;96:6–11.

Nuwer MR, Emerson RG, Galloway G, et al. Evidence-based guideline update: intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials*. J Clin Neurophysiol 2012;29:101–108. Owen JH, Bridwell KH, Lenke LG. Innervation pattern of dorsal roots and their effects on the specificity of dermatomal somatosensory evoked potentials. Spine (Phila Pa 1976) 1993;18:748–754. Owen JH, Bridwell KH, Grubb R, et al. The clinical application of neurogenic motor evoked potentials to monitor spinal cord function during surgery. Spine (Phila Pa 1976) 1991;16(6 suppl 1):S201–S205. Parker SL, Amin AG, Farber SH, et al. Ability of electromyographic monitoring to determine the presence of malpositioned pedicle screws in the lumbosacral spine: analysis of 2450 consecutively placed screws. J Neurosurg Spine 2011;15:130–135. Penfield W, Boldrey E. Somatic Motor and Sensory Representation in the Cerebral Cortex of Man as studied by Electrical Stimulation. Brain 1937;60:389–443. Porkkala T, Kaukinen S, Häkkinen V, Jäntti V. Effects of hypothermia and sternal retractors on median nerve somatosensory evoked potentials. Acta Anaesthesiol Scand 1997;41:843–848. Quinones-Hinojosa A, Lyon R, Zada G. Changes in transcranial motor evoked potentials during intramedullary spinal cord tumor resection correlate with postoperative motor function. Neurosurgery 2005;56:982–993. Raynor BL, Lenke LG, Bridwell KH, et al. Correlation between low triggered electromyographic thresholds and lumbar pedicle screw malposition: analysis of 4857 screws. Spine (Phila Pa 1976) 2007;32:2673–2678. Sala F, Palandri G, Basso E, et al. Motor evoked potential monitoring improves outcome after surgery for intramedullary spinal cord tumors: a historical control study. Neurosurgery 2006;58:1129–1143; discussion 1129–1143. Sloan TB, Heyer EJ. Anesthesia for intraoperative neurophysiologic monitoring of the spinal cord. J Clin Neurophysiol 2002;19:430–443. Sutter M, Eggspuehler A, Grob D, et al. The diagnostic value of multimodal intraoperative monitoring (MIOM) during spine surgery: a prospective study of 1,017 patients. Eur Spine J 2007;16(Suppl 2):S162–S170. Tsai RY, Yang RS, Nuwer MR, et al. Intraoperative dermatomal evoked potential monitoring fails to predict outcome from lumbar decompression surgery. Spine (Phila Pa 1976) 1997;22:1970–1975. Vauzelle C, Stagnara P, Jouvinroux P. Functional monitoring of spinal cord activity during spinal surgery. Clin Orthop Relat Res 1973;173–178. Wiedemayer H, Sandalcioglu IE, Armbruster W, et al. False negative findings in intraoperative SEP monitoring: analysis of 658 consecutive neurosurgical cases and review of published reports. J Neurol Neurosurg Psychiatr 2004;75:280–286.

APPENDIX 1 TABLE 1.

Typical intraoperative Neuromonitoring Settings at Our Institution Stimulation Parameters

Modality SSEP TcMEP EMG

Recording Parameters

Stimulation Rate

Stimulation Type

Pulse Width

Intensity

Number of Averages

Low-Frequency Filter

High-Frequency Filter

4–5 (avoiding multiples of 60) 250–500 Hz (5–7 pulses) 2.79 Hz

Constant current Constant voltage Constant current

100–200 ms 50–75 ms 100 ms

20–60 mA* 100–400 V 2–40 mA

250–500 None None

30 Hz 30 Hz 10 Hz

500–1500 Hz 3000 Hz 3000 Hz

*Adjusted to produce adequate muscle twitch.

TABLE 2.

Typical Channel Setting Used at Our Institution

Modality Upper SSEP Lower SSEP TcMEP spEMG tEMG

Recording Channels CPc-CPi, Cz-FPz, A1/C5s-FPz CpPi-CPc, CPi-FPz, Cz-FPz, A1-FPz Various muscles in all extremities Various muscles in all extremities Various muscles in all extremities

c, contralateral; i, ipsilateral.

clinicalneurophys.com

Journal of Clinical Neurophysiology Volume 33, Number 4, August 2016

339

Overview of Intraoperative Neurophysiological Monitoring During Spine Surgery.

Intraoperative neurophysiologic monitoring has had major advances in the past few decades. During spine surgery, the use of multimodality monitoring e...
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