Intraoperative Neurophysiological Monitoring Modalities Research Articles

The application value and improved warning criterion of D-wave monitoring in intramedullary spinal cord tumor surgery

BACKGROUND CONTEXTThe primary treatment method for intramedullary spinal cord tumor (IMSCT) is surgical resection, but this procedure carries a significant risk of neurological damage. Intraoperative neurophysiological monitoring (IONM) has become a necessary adjunctive tool for IMSCT resection. PURPOSEThe current study aimed to explore the application value of D-wave monitoring in IMSCT surgery, and tried to investigate a tailored criterion for its early warning. STUDY DESIGNA retrospective clinical study. PATIENT SAMPLEA retrospective analysis was conducted based on the data of patients who underwent IMSCT surgeries performed by the same neurosurgical team at our hospital. IONM was applied in all surgeries. According to inclusion and exclusion criteria, ultimately 90 patients were enrolled in the study. OUTCOME MEASURESThe McCormick Scale (MMS) was applied to assess the functional outcome through outpatient visits or telephone follow-up at one month and six months postoperatively. Patients with an MMS grade over II one month after surgery were considered to have newly developed postoperative motor dysfunction (PMD). If the MMS grade could be restored to I or II six months after surgery, it was defined as a short-term PMD. Otherwise, it was defined as a long-term PMD. METHODSThe predictive value of different IONM modalities, including somatosensory evoked potential (SEP), muscle motor evoked potential (MEP), and D-wave for PMD, was assessed with sensitivity, specificity, positive predictive value, negative predictive value, and subsequent logistic regression analysis. At last, the cut-off value of the D-wave amplitude reduction ratio for predicting PMD was obtained through the receiver operating characteristic (ROC) curve analysis. RESULTSSEP showed the worst performance in predicting short-term and long-term PMD. Significant MEP changes were indicated as an independent predictive factor for short-term PMD (OR 5.062, 95% CI 1.947–13.166, p=.001), while D-wave changes were demonstrated as an independent predictor for long-term PMD (OR 339.433, 95% CI 11.337–10770.311, p=.001). The optimum cut-off value of the D-wave amplitude reduction ratio for predicting long-term PMD was 42.18%, with a sensitivity of 100% and a specificity of 93.8% (AUC=0.981, p<.001). CONCLUSIONSD-wave monitoring showed extremely high specificity in predicting PMD compared to SEP and MEP monitoring. Moreover, the authors suggested that a D-wave amplitude reduction of over 40% during IMSCT surgery generally indicates long-term PMD for patients.

Intraoperative neuromonitoring as real-time diagnostic for cerebral ischemia in endovascular treatment of ruptured brain aneurysms

ObjectiveTo evaluate the diagnostic accuracy of intraoperative neurophysiological monitoring (IONM) during endovascular treatment (EVT) of ruptured intracranial aneurysms (rIA). MethodsIONM and clinical data from 323 patients who underwent EVT for rIA from 2014-2019 were retrospectively reviewed. Significant IONM changes and outcomes were evaluated based on visual review of data and clinical documentation. ResultsOf the 323 patients undergoing EVT, significant IONM changes were noted in 30 patients (9.29%) and 46 (14.24%) experienced postprocedural neurological deficits (PPND). 22 out of 30 (73.33%) patients who had significant IONM changes experienced PPND. Univariable analysis showed changes in somatosensory evoked potential (SSEP) and electroencephalogram (EEG) were associated with PPND (p-values: <0.001 and <0.001, retrospectively). Multivariable analysis showed that IONM changes were significantly associated with PPND (Odd ratio (OR) 20.18 (95%CI:7.40–55.03, p-value: <0.001)). Simultaneous changes in both IONM modalities had specificity of 98.9% (95% CI: 97.1%–99.7%). While sensitivity when either modality had a change was 47.8% (95% CI: 33.9%–62.0%) to predict PPND. ConclusionsSignificant IONM changes during EVT for rIA are associated with an increased risk of PPND. SignificanceIONM can be used confidently as a real time neurophysiological diagnostic guide for impending neurological deficits during EVT treatment of rIA.

Removal of schwannoma from the psoas muscle with intraoperative neurophysiological monitoring: A case report.

The incidence of a schwannoma within the psoas muscle is rare, and only a few cases have been reported. The surgical approach to removing schwannomas present in the psoas muscle is challenging because of its anatomical proximity to the lumbar plexus. A 31-year-old man experienced right lower back pain and anterolateral thigh numbness for 2 months. Magnetic resonance imaging of the patient's lumbar spine revealed a mass lesion, which was radiologically diagnosed as a well-demarcated schwannoma. The patient underwent surgery for excision of the schwannoma in the right psoas muscle at the second to fourth lumbar vertebrae levels. During surgery, intraoperative neurophysiological monitoring modalities, free-running and triggered electromyography and evoked potentials, from the target muscles were recorded. There was no neurotonic discharge corresponding to neuronal injury. Compound motor nerve action potential was detected in the triggered electromyography of muscles around the medial margin of the tumor. However, direct integration of the motor nerve was not observed in the intra-tumor region. We report that schwannoma removal in the psoas muscle, which is adjacent to the lumbar plexus, can be safely performed using intraoperative neurophysiological monitoring.

Pediatric Intraoperative Neurophysiological Monitoring and Long-Term Outcomes in a Developing Country.

Pediatric intraoperative neurophysiological monitoring (IONM) has been shown to be effective in preventing and reversing postoperative neurological deficits in developed countries. There are currently no published studies from developing countries that describe neurophysiological findings and postoperative outcomes. Our study aims to address these gaps in children undergoing neurosurgical procedures in a single center. We conducted a retrospective study of case series of children who underwent IONM (2014-2020) in the State of Mexico, Mexico. Sociodemographic characteristics, IONM modalities, changes during procedures, and short-term and long-term postoperative results were recorded. Descriptive statistics were used. We included 35 patients (≤18 years of age), 57% (20/35) boys. A relative increase of up to 5 times in the use of IONM is observed from 2014 (5.7%) to 2020 (25.7%) in our center. The most frequent preoperative pathologies were located at the infratentorial cranium (40%), followed by the spine and spinal cord (37.1%). The IONM modalities were as follows: free-running EMG 94.3%, transcranial electrical stimulation motor-evoked potentials 91.4%, somatosensory-evoked potentials 85.7%, triggered EMG 28.6%, EEG 25.7%, and visual-evoked potentials 5.7%. Only in 8.3%, we did not obtain sufficient evoked potential baseline signals. At 24 hours postoperatively true negatives were 100%. Long-term follow-up was completed in 22/35 (63%) at 3 months, 12/35 (34.2%) at 6 months, and 5/35 (14.3%) at 12 months with progressive motor and sensory improvement. Pediatric multimodal IONM in neurosurgeries from a single center in a developing country is mainly used in pathologies of the posterior fossa, spine, and spinal cord, with true negatives in 100% of those monitored, preventing and avoiding postoperative sequelae.

Confirming a C5 Palsy with a Motor Evoked Potential Trending Algorithm during Insertion of Cervical Facet Spacers: A Case Study

ABSTRACT The use of cervical facet spacers has shown favorable clinical results in the treatment of cervical spondylotic disease; however, there are limited data regarding neurological complications associated with the procedure. This case report demonstrates the specificity of multi-myotomal motor evoked potentials (MEPs) in detecting acute postoperative C5 palsy following placement of facet spacers. A posterior cervical fusion with decompression and instrumentation involving DTRAX (Providence Medical Technology; Lafayette, CA) was used to treat a patient with cervical stenosis and myelopathy. Intraoperative neurophysiological monitoring (IONM) consisting of MEPs, somatosensory evoked potentials (SSEPs), and free-run electromyography (EMG), was used throughout the procedure. Immediately following the placement of the DTRAX spacers at C4-5, a decrease in amplitudes from the right deltoid and biceps MEP recordings (>65%) was detected. All other IONM modalities remained stable; it is noteworthy that there was an absence of mechanically elicited EMG. A novel post-alert regression analysis trending algorithm of MEP amplitudes confirmed the visual alert. This warning along with an intraoperative computed tomography (CT) scan of the cervical spine subsequently resulted in the decision to remove one of the facet spacers. Surgical intervention did not result in recovery of the aforementioned MEP recordings, which remained attenuated at the time of wound closure. Postoperatively, the patient exhibited an immediate right C5 palsy (2/5). A post-surgery application of the trending algorithm demonstrated that it correlated to the visual alert until the end of monitoring.

Fosaprepitant Does Not Interfere With Commonly Used Intraoperative Neuromonitoring Modalities Under General Anesthesia: A Preliminary Study.

Fosaprepitant [Emend®], a neurokinin type-1 [NK-1] receptor antagonist, is a highly effective for the prophylaxis of postoperative nausea and vomiting [PONV] after general anesthesia; it is particularly effective in patients undergoing neurosurgical procedures. Based on the widespread distribution of NK-1 receptors in the central and peripheral nervous systems, we sought to determine whether fosaprepitant administration would interfere with commonly used intraoperative neurophysiologic monitoring modalities during general anesthesia. Eleven patients having propofol-based general anesthesia for interventional neuroradiology procedures were administered 150mg fosaprepitant intravenously after baseline electroencephalogram [EEG], transcranial motor evoked potential [TcMEP], and somatosensory evoked potential [SSEP] recordings were obtained. Recordings of these neuromonitoring modalities at 30, 60, and 90 min after fosaprepitant administration were compared to baseline. Fosaprepitant did not have a significant effect on SSEP/TcMEP amplitudes or latencies, or on TcMEP morphology. There were also no changes in EEG voltage, frequency, or symmetry. Fosaprepitant does not appear to markedly interfere with SSEP, TcMEP, or EEG neuromonitoring modalities during propofol-based general anesthesia.

Relevance of intraoperative motor evoked potentials and D-wave monitoring for the resection of intramedullary spinal cord tumors in children.

The purpose of this study was to evaluate the reliability of motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), and D-wave monitoring as predictors of postoperative neurological deficits in pediatric patients undergoing resection of intramedullary spinal cord tumors (IMSCTs). Additionally, we aimed to determine whether alerts in the intraoperative neurophysiological monitoring (IONM) influenced the extent of resection (EOR). A retrospective analysis of the pediatric patients who underwent resection of IMSCT between March 2010 and April 2021 with an IONM guidance was performed. IONM alerts were recorded and correlated with patients' clinical status at discharge. Twenty three pediatric patients were included. MEP and SSEP were successfully elicited in all patients, while D-wave monitoring was feasible for 14 of them (60.9%). Significant IONM alerts occurred in 6 individuals (26.1%) with monitorable MEP and SSEP and 2 patients with monitorable D-waves (14.3%). The sensitivity, specificity, positive predictive value, and negative predictive value accounted for 100%, 81.8%, 20%, 100% for MEP, 100%, 92.3%, 50%, 100% for D-wave, and 50%, 81%, 20%, 94.44% for SSEP, respectively. Both MEP (p < 0.001) and D-wave monitoring (p < 0.001) accurately predicted postoperative motor deficits, while SSEP failed to provide significant accuracy regarding sensory deficits (p = 0.491). Gross-total tumor resection was performed in 29.4% of patients without IONM alerts and 33.3% of patients with IONM alerts, indicating that IONM alerts did not limit the EOR (p = 0.0857). MEP and D-wave monitoring can be perceived as reliable IONM modalities in pediatric IMSCTs surgery. Caution is needed with the implementation of SSEP to guide surgical decisions.

OC19: Visual evoked potentials monitoring during neurosurgical operations: optimizing the protocol

Visual evoked potentials (VEPs) are used for intraoperative neurophysiological monitoring (IONM) during surgeries involving visual system. But unlike other IONM modalities, no standards have been yet developed for the intreoperative VEPs monitoring. Here we consider VEPs registration parameters contributing to their successful and useful monitoring. Methods. 144 consecutive surgeries (288 eyes) performed using VEPs monitoring were analyzed retrospectively. Stimulation: flash intensity 25000 lx, duration 10 ms, frequency ∼1 Hz, 20–100 responses averaged. 7 electrodes placed, three pairs chosen. Bandpass filtering: [10-20] – [200-400] Hz (chosen individually). Alarm: standard 10–50% criteria. Anesthesia: propofol – 110 surgeries, sevoflurane – 14, combined – 20. In 27 surgeries, propofol-to-sevoflurane transition performed after dura closure. Results. Chosen electrode pairs: Oz-A1&Oz-A2 in 45% of surgeries, O1/O2/Oz-CPz in 25%, O1/O2/Oz-Fz in 24%. Chosen frequency filters: 100–400 Hz (200 Hz in 67%) low-pass, 5–20 Hz (10 Hz in 59%) high-pass. Anesthesia effects: 5,9% unresponsive non-blind eyes for propofol and 18,5% for sevoflurane anesthesia. After propofol-to-sevoflurane transition VEPs disappeared in 22% of cases. Alarm criteria had been reached for 73 eyes. Full recovery observed later in 62%, partial in 23%, no recovery in 15% of cases. Postoperative visual impairments among eyes with: successful VEPs monitoring without alarms – 3%, full recovery after alarms – 7%, incomplete or no recovery – 23%, unobtainable VEPs – 14%. Conclusions. Optimal parameters of VEPs recording for IONM should be selected individually and differs from the standards for clinical diagnostics. VEPs recording under (low-to-moderate-dose) sevoflurane is often possible, but the propofol anesthesia is preferable.

PRACTICAL ASPECTS OF INTRAOPERATIVE NEUROMONITORING IN PATIENTS WITH DIFFERENT SPINAL PATHOLOGIES

Objective. To study the operating parameters and phenomena of intraoperative monitoring and to identify the specificity and sensitivityof its different modalities associated with postoperative neurological complications in patients with different spinal pathologies.Methods. The intraoperative neurophysiological monitoring (IOM) protocols of 88 patients who underwent spinal surgeries were analyzed:kyphoscoliotic spinal deformities — 58 (68 %), traumatic — 12 (13.3 %), degenerative diseases — 10 (11.7 %), neoplasms — 6 (6.7 %). In 33 (38.4 %) cases, a combination of modalities of motor evoked potentials (MEP) and transpedicular screws stimulation (TSS) was used, in 36 (41.9%) — only MEP, 17 (19.8 %) — TSS. In all cases, freerun and triggered EMG was used. Results. The most stable MEPs were recorded at mm. tibibalis anterior, mm. abductor hallucis longus. It has been proven that an unfavorable and reliable factor of the anxiety sign is a unilateral sustained decrease in the MEP amplitude by more than 80 %. According to the TSS results 424 (97.5 %) screws are installed correctly, 1 (0.2 %) false negative case of incorrect installation. False positive results for the TSS test ranged from 34.7 to 15.4 %, depending on the chosen critical threshold of the current applied to the pedicle screw. We consider the threshold of the TSS test at 13 mA satisfactory, and below it, unsatisfactory. A group of patients was identified who had 72 screws (16.6% of all analyzed) who, according to the results of the TSS test, received an unsatisfactory assessment, and X-ray did not reveal any deviations in the position of the screws.Conclusions. IOM modalities are highly sensitive and specific to damage to the structures of the spinal cord and spinal nerves, but dependence on a number of external factors reduces their information content, which leads to false positive and false negative results. It was established, that the dynamics of the MEP amplitudes of the target muscles differs in information content and efficiency during surgery due to individual morphological and motor characteristics.

Roles of multimodal intra-operative neurophysiological monitoring (IONM) in percutaneous endoscopic transforaminal lumbar interbody fusion: a case series of 113 patients

BackgroundDespite the wide use of intraoperative neurophysiological monitoring (IONM) in spinal surgeries, the efficacy of IONM during percutaneous endoscopic transforaminal lumbar interbody fusion (PE-TLIF) surgery in detecting postoperative neurological deficits has not been well characterized.MethodsMIONM data from 113 consecutive patients who underwent PE-TLIF surgeries between June 2018 and April 2020 were retrospectively reviewed. Postoperative neurological deficits were documented and analyzed, and the efficacy and specificity of various IONM techniques were compared.ResultsOf the 113 consecutive patients, 12 (10.6%) with IONM alerts were identified. The MIONM sensitivity and specificity were 100 and 96.2%, respectively. The frequency of neurological complications, including minor deficits, was 6.2% (n = 7); all of the neurological complications were temporary. The ability of single IONM modalities to detect neurological complications varied between 25.0 and 66.6%, whereas that of all modalities was 100%.ConclusionsMIONM is more effective and accurate than unimodal monitoring in assessing nerve root function during PE-TLIF surgeries, reducing both neurological complications and false-negative findings. We recommend MIONM in PE-TLIF surgeries.

Intraoperative Neurophysiology and Transcranial Doppler for Detection of Cerebral Ischemia and Hyperperfusion During Carotid Endarterectomy

To evaluate and compare efficacy of intraoperative neurophysiological monitoring (IONM) and intraoperative transcranial Doppler (TCD) techniques for identification of hypoperfusion during carotid artery clamp and hyperperfusion after release of occlusion during carotid endarterectomy. This was a retrospective, consecutive case series of 152 patients undergoing carotid endarterectomy between June 2018 and March 2020. Somatosensory evoked potentials, motor evoked potentials, electroencephalogram, and TCD were obtained. Three patient cohorts were observed after clamping the carotid artery: A, in 132 of 152 patients (87%), TCD blood flow velocity decreased by <50% and there were no changes in IONM; B, in 5 of 152 (3%) patients, TCD blood flow rate was reduced 50%-100% with no changes in IONM; C, in 15 patients (10%), blood flow velocity was reduced by 50%-100% and all IONM modalities met warning criteria. With increased blood pressure, IONM and blood flow velocities improved to less than warning criteria in 8 of 15 patients. In 6 of the 7 remaining patients, IONM modalities recovered to baseline immediately after clamps were removed from the carotid artery. The 1 patient with persistent motor evoked potential deterioration experienced postoperative proximal muscle weakness, which recovered 48 hours later. In 22 patients, TCD detected hyperperfusion at the moment of clamp release. TCD blood flow velocity is correlated with motor evoked potential and somatosensory evoked potential amplitude changes after clamping. After declamping, TCD can detect hyperperfusion and help regulate blood pressure to prevent hyperperfusion.

Mapping of the Motor Cortex.

The resection of brain tumors located within or near the eloquent tissue has a higher risk of postoperative neurological deficits. The primary concerns include loss of sensory and motor functions in the contralateral face, upper and lower extremities, as well as speech deficits. Intraoperative neurophysiological monitoring (IONM) techniques are performed routinely for the identification and preservation of the functional integrity of the eloquent brain areas during neurosurgical procedures. The IONM modalities involve sensory, motor, and language mapping, which helps in the identification of the boundaries of these areas during surgical resection. Cortical motor Mapping (CmM) technique is considered as a gold-standard technique for mapping of the brain. We present the intraoperative CmM technique, including anesthesia recommendations, types of electrodes, as well as stimulation and recording parameters for successful monitoring.

Multimodality Intraoperative Neurophysiological Monitoring (IONM) During Shoulder Surgeries

ABSTRACT Introduction: The purpose of this study is to identify the advancing role of Intraoperative Neurophysiological Monitoring (IONM) in detecting and preventing nerve injuries during shoulder surgery procedures. Methods: We performed a retrospective analysis of IONM data from ten shoulder procedures. The patients consisted of nine females and one male with ages ranging from 67 to 81 years (median: 74 years). IONM modalities utilized were bilateral Somatosensory Evoked Potentials (SSEP), Transcranial Motor Evoked Potentials (TCeMEP), ipsilateral Electromyogram (EMG) from upper extremity muscles and Train of four (TOF) recordings. Results: A decrease in signals was noted in three patients (30%). Only upper SSEP amplitude decreased in one patient; both upper extremity SSEP and TCeMEP decreased in two patients. Only one patient had poor baseline radial nerve SSEP that improved during the surgery. We performed spontaneous EMG (s-EMG) in all ten patients and successfully recorded triggered (t-EMG) in seven patients (71.4%). In one patient, SSEP and TCeMEP did not improve, and the patient woke up with deficits. Conclusions: In this small series, we were able to identify real-time impending nerve injury. The use of IONM alerted and may have prevented intraoperative nerve injury in 30% of the patients in this series. In one patient, SSEP and TCeMEP did not recover even after the intervention due to severe blood loss. The patient woke up with sensory and motor deficits. The utilization of multimodality IONM can be helpful due to signal changes, therefore minimizing the frequency of nerve injury and deficits.

P41. Intraoperative neurophysiologic monitoring and neurologic outcomes in orthopedic spine surgery patients without preoperative neurologic deficits

P41. Intraoperative neurophysiologic monitoring and neurologic outcomes in orthopedic spine surgery patients without preoperative neurologic deficits

The impact and value of uni- and multimodal intraoperative neurophysiological monitoring (IONM) on neurological complications during spine surgery: a prospective study of 2728 patients.

We compared the value of different uni- and multimodal intraoperative neurophysiological monitoring (IONM) methods on the detection of neurological complications during spine surgery. IONM data derived from sensory spinal and cortical evoked potentials combined with continuous electromyography monitoring, motor evoked potentials and spinal recording were evaluated in relation to subsequent post-operative neurological changes. Patients were categorised based on their true-positive or true-negative post-operative neurological status. In 2728 consecutive patients we had 909 (33.3%) IONM alerts. We had 8 false negatives (0.3%) with post-operative radicular deficit that completely recovered within 3months, except for one. There was no false negative for spinal cord injury. 107 were true positives, and 23 were false positives. Multimodal IONM sensitivity and specificity were 93.0% and 99.1%, respectively. The frequency of neurological complications including minor deficits was 4.2% (n = 115), of which 0.37% (n = 10) were permanent. Analysis of the single IONM modalities varied between 13 and 81% to detect neurological complications compared with 93% when using all modalities. Multimodal IONM is more effective and accurate in assessing spinal cord and nerve root function during spine surgeries to reduce both neurological complications and false-negative findings compared to unimodal monitoring. We recommend multimodal IONM in all complex spine surgeries. These slides can be retrieved from Electronic Supplementary Material.

Anesthetic considerations during intraoperative neurophysiological monitoring in spine surgery

Objective We conducted an overview of the intraoperative neurophysiological monitoring (IONM) modalities in spine surgeries and effects of anesthesia and physiological factors on these modalities. Background The development of IONM minimizes iatrogenic neurological complications. All anesthetic agents impact on the modalities of IONM. Materials and methods Medline, articles in Medscape, ScienceDirect, and PubMed were searched. The search was performed in January 2016 and included all articles with no language restriction. The initial search presented 50 articles. The articles studied the types of IONM modalities and effects of anesthesia on these modalities. Data from each study were independently abstracted to capture information on study characteristics, interventions, and quantitative results reported for each outcome of interest. Significant data were collected and thus a structured review was performed. Results A close working relationship of the monitoring team, the anesthesiologist, and the surgeon is a key to the successful conduct and interpretation of IONM, prevention of complications of spinal surgeries, and early detection of these complications. On the basis of the monitoring modalities involved, the basic anesthetic constraints can be identified. Conclusion Using IONM such as somatosensory and motor-evoked potentials has become common to minimize neural risk and to improve intraoperative decision making for any spine surgery. IONM is affected by the choice of the different anesthetic agents and skeletal muscle relaxants, because anesthetic agents have effects on neural synaptic and skeletal muscle relaxants have effects on neuromuscular junctions.

Perils of intraoperative neurophysiological monitoring: analysis of “false-negative” results in spine surgeries

Background ContextAlthough some authors have published case reports describing false negatives in intraoperative neurophysiological monitoring (IONM), a systematic review of causes of false-negative IONM results is lacking. PurposeThe objective of this study was to analyze false-negative IONM findings in spine surgery. Study designThis is a retrospective cohort analysis. Patient sampleA cohort of 109 patients with new postoperative neurologic deficits was analyzed for possible false-negative IONM reporting. Outcome MeasuresThe causes of false-negative IONM reporting were determined. Materials and MethodsFrom a cohort of 62,038 monitored spine surgeries, 109 consecutive patients with new postoperative neurologic deficits were reviewed for IONM alarms. ResultsIntraoperative neurophysiological monitoring alarms occurred in 87 of 109 surgeries. Nineteen patients with new postoperative neurologic deficits did not have an IONM alarm and surgeons were not warned. In addition, three patients had no interpretable IONM baseline data and no alarms were possible for the duration of the surgery. Therefore, 22 patients were included in the study. The absence of IONM alarms during these 22 surgeries had different origins: “true” false negatives where no waveform changes meeting the alarm criteria occurred despite the appropriate IONM (7); a postoperative development of a deficit (6); failure to monitor the pathway, which became injured (5); the absence of interpretable IONM baseline data which precluded any alarm (3); and technical IONM application issues (1). ConclusionsOverall, the rate of IONM method failing to predict the patient's outcome was very low (0.04%, 22/62,038). Minimizing false negatives requires the application of a proper IONM technique with the limitations of each modality considered in their selection and interpretation. Multimodality IONM provides the most inclusive information, and although it might be impractical to monitor every neural structure that can be at risk, a thorough preoperative consideration of available IONM modalities is important. Delayed development of postoperative deficits cannot be predicted by IONM. Absent baseline IONM data should be treated as an alarm when inconsistent with the patient's preoperative neurologic status. Alarm criteria for IONM may need to be refined for specific procedures and deserves continued study.

51. Efficacy and safety of pharmacologic provocative testing with methohexital and intraoperative neurophysiologic monitoring in endovascular embolization procedures

Objective The purpose of this study is to evaluate the efficacy and reliability of pharmacologic provocative testing with methohexital (PPTM) using intraoperative neurophysiologic monitoring (IONM) in endovascular embolization procedures (EEPs). Methods 111 EEPs cases were retrospectively reviewed between 2014 and 2015. PPTM and IONM was performed in 70 cases. The data, including cerebrovascular territory tested, PPTM dose, IONM modalities, PPTM results, and postoperative neurologic outcomes were obtained via chart review. Results Mean age was 28.2 years. 85.7% of the cases were cerebral arteriovenous malformations. Mean PPTM dose was 10.8 mg. Two positive tests were detected; one causing widespread loss of SSEPs and TcMEPs, embolization was deferred; and other with burst-suppression EEG immediately after PPTM administration, with embolization done at a different site. There were no false negative cases. Thus, the negative predictive value was 1.0. Conclusion Our results regarding PPTM and IONM indicate the following: it is safe: can aid in intraoperative management; is accurate in predicting postoperative neurologic outcome; and that it is a useful adjunct for EEPs. Significance Use of PPTM combined with IONM has not been previously described in the literature. Our study provides evidence of the utility and safety of PPTM in EPPs.

Neurophysiological monitoring and spinal cord integrity.

An integral part of a major spine surgery is the intraoperative neurophysiological monitoring (IONM). By providing continuous functional assessment of specific anatomic structures, IONM allows the rapid detection of neuronal compromise and the opportunity for corrective action before an insult causes permanent neurological damage. Thus, IONM functions not just as a diagnostic tool but may also improve surgical outcomes. Effective clinical application requires a thorough understanding of the scope and limitations of IONM modalities not only by the monitoring team but also by the surgeon and anesthesiologist. Intraoperatively, collaboration and communication between monitorist, surgeon, and anesthesiologist are critical to the effectiveness of IONM. In this study, we review specific monitoring modalities, focusing on the relevant anatomy, physiology, and mechanisms of neuronal injury during major spine surgery. We discuss how these factors interact with anesthetic and surgical management. This review concludes with the current controversies surrounding the evidence in support of IONM and directions of future research.

A Prospective Study of the Intra- and Postoperative Efficacy of Intraoperative Neuromonitoring in Spinal Cord Stimulation

Background: Accurate lead placement is critical for spinal cord stimulation (SCS) efficacy. The traditional gold standard of awake placement is often technically difficult. While there is retrospective evidence supporting the use of intraoperative neurophysiological monitoring (IOM) as an alternative, a prospective assessment has not yet been performed. Objective: To prospectively evaluate pain and functionality outcomes for IOM-guided SCS, validate two IOM modalities as a means to lateralize lead placement and assess whether IOM can be useful for postoperative programming. Methods: A total of 73 patients were implanted with SCS using electromyography (EMG) and somatosensory-evoked potential collision studies (SSEP-CS) to verify lead placement. Patient pain and function were assessed through serial administration of several validated questionnaires. Stimulation parameters at 6 months were documented. Results: Statistically significant (p < 0.05) improvements were observed in the McGill Pain Questionnaire, Oswestry Disability Index, Pain Catastrophizing Scale, and Visual Analog Scale. EMG and SSEP-CS appropriately lateralized leads in 65/73 (89.0%) and 40/58 (69.0%) cases, respectively. EMG predicted active contacts in use at follow-up with 82.7% sensitivity. Conclusions: We provide prospective evidence that IOM can be used to verify SCS placement. Additionally, EMG may help to streamline device programming and thereby improve outcomes by predicting the ideal stimulation contacts in many cases.