Somatosensory Evoked Potentials Research Articles

Multimodal Intraoperative Neurophysiological Monitoring in Intramedullary Spinal Cord Tumors: A 10-Year Single Center Experience.

The study aimed at evaluating the efficacy and the ability of D-wave monitoring combined with somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) to predict functional outcomes in intramedullary spinal cord tumor (IMSCT) surgery. Between December 2011 and December 2020, all patients harboring IMSCT who underwent surgery at our institution were prospectively collected in a surgical spinal registry and retrospectively analyzed. Patient charts and surgical and histological reports were analyzed. The multimodal IONM included SSEPs, MEPs, and-whenever possible-D-waves. All patients were evaluated using the modified McCormick and Frankel grade at admission and 3, 6, and 12 months of follow-up. Sixty-four patients were enrolled in the study. SSEP and MEP monitoring was performed in all patients. The D-wave was not recordable in seven patients (11%). Significant IONM changes (at least one evoked potential modality) were registered in 26 (41%) of the 64 patients. In five cases (8%) where the SSEPs and MEPs lost and the D-wave permanently dropped by about 50%, patients experienced a permanent deterioration of their neurological status. Multimodal IONM (SSEP, MEP, and D-wave neuromonitoring) significantly predicted postoperative deficits (p = 0.0001), with a sensitivity of 100.00% and a specificity of 95.65%. However, D-waves demonstrated significantly higher sensitivity (100%) than MEPs (62.5%) and SSEPs (71.42%) alone. These tests' specificities were 85.10%, 13.89%, and 17.39%, respectively. Comparing the area under ROC curves (AUCs) of these evoked potentials in 53 patients (where all three modalities of IONM were registered) using the pairwise t-test, D-wave monitoring appeared to have higher accuracy and ability to predict postoperative deficits with strong statistical significance compared with MEP and SSEP alone (0.992 vs. 0.798 vs. 0.542; p = 0.018 and p < 0.001). The use of multimodal IONM showed a statistically significant greater ability to predict postoperative deficits compared with SSEP, MEP, and D-wave monitoring alone. D-wave recording significantly increased the accuracy and clinical value of neurophysiological monitoring in IMSCT tumor resection.

Temporal Electroencephalography Traits Dissociating Tactile Information and Cross-Modal Congruence Effects.

To explore whether temporal electroencephalography (EEG) traits can dissociate the physical properties of touching objects and the congruence effects of cross-modal stimuli, we applied a machine learning approach to two major temporal domain EEG traits, event-related potential (ERP) and somatosensory evoked potential (SEP), for each anatomical brain region. During a task in which participants had to identify one of two material surfaces as a tactile stimulus, a photo image that matched ('congruent') or mismatched ('incongruent') the material they were touching was given as a visual stimulus. Electrical stimulation was applied to the median nerve of the right wrist to evoke SEP while the participants touched the material. The classification accuracies using ERP extracted in reference to the tactile/visual stimulus onsets were significantly higher than chance levels in several regions in both congruent and incongruent conditions, whereas SEP extracted in reference to the electrical stimulus onsets resulted in no significant classification accuracies. Further analysis based on current source signals estimated using EEG revealed brain regions showing significant accuracy across conditions, suggesting that tactile-based object recognition information is encoded in the temporal domain EEG trait and broader brain regions, including the premotor, parietal, and somatosensory areas.

Assessment of neurofunctional activity in patients with vibration disease caused of local vibration

Introduction. The stressful effect of local vibration contributes to the development of cerebral dysfunction with the formation of a sensorineural deficit in patients with vibration disease associated with exposure to local vibration.&#x0D; The study aims to identify the features of changes in somatosensory evoked potentials, neuroenergocarting and neuropsychological testing in patients with local vibration.&#x0D; Materials and methods. Scientists examined 103 patients with local vibration (group one), 35 healthy men (comparison group). We used methods of registration of somatosensory evoked potentials (SSEP), constant potential level (CPL), neuropsychological testing.&#x0D; Results. The authors revealed in the first group, in comparison with the other group, a significant increase in cerebral energy metabolism in the form of an increase in the level of constant potential in the frontal right and left (Fd, Fs), central (Cd, Cz, Cs), parietal (Pd, Pz, Ps), occipital (Oz), right and central temporal (Td, Tz) brain regions, increased latency of peaks N10, N11, N13, N30, peak interval N13–N18 at p&lt;0.04, cognitive dysfunction with mild damage to prefrontal frontal lobes, inferior temporal and inferior parietal regions, parietal-temporal-occipital zone of the left hemisphere, as well as subcortical structures. The data of the correlation analysis indicate that the slowing down of the ascending somatosensory flow from the level of the brachial plexus ganglia to the ventroposterolateral nucleus of the thalamus contributes to the emergence of a compensatory state in the form of an increase in energy processes in the frontal-central and parietal parts of the cerebral cortex, causing the development of cognitive disorders.&#x0D; Limitations. The limitations of the study were the lack of studying the effects of local vibration on cerebral hemodynamics and the state of efferent pathways of the central nervous system in patients with local vibration.&#x0D; Conclusion. Signs of impaired neurofunctional activity in local vibration are an increase in the duration of peak intervals N10–N13 and N11–N13, the latency of peak N10, the level of constant potential of the frontal right and central left leads, the level of constant potential of interhemispheric relations in the central department, a decrease in categorical and conceptual thinking, short-term (auditory) memory, visual gnosis, expressive speech.&#x0D; Ethics. The study was conducted in compliance with Ethical standards developed in accordance with the Helsinki Declaration of the World Medical Association "Ethical principles of conducting scientific medical research with human participation" as amended in 2000 and "Rules of Clinical Practice in the Russian Federation" approved by Order of the Ministry of Health of the Russian Federation No. 266 dated 06/19/2003. Informed consent was received from each person to participate in the survey, approved in accordance with the established procedure by the Local Ethics Committee.

Additional predictive value of optic nerve sheath diameter for neurological prognosis after cardiac arrest: a prospective cohort study

BackgroundThe goal is to estimate the additional value of ultrasonographic optic nerve sheath diameter (ONSD) measurement on days 1–3, on top of electroencephalography (EEG), pupillary light reflexes (PLR), and somatosensory evoked potentials (SSEP), for neurological outcome prediction of comatose cardiac arrest patients. We performed a prospective longitudinal cohort study in adult comatose patients after cardiac arrest. ONSD was measured on days 1–3 using ultrasound. Continuous EEG, PLR, and SSEP were acquired as standard care. Poor outcome was defined as cerebral performance categories 3–5 at 3–6 months. Logistic regression models were created for outcome prediction based on the established predictors with and without ONSD. Additional predictive value was assessed by increase in sensitivity for poor (at 100% specificity) and good outcome (at 90% specificity).ResultsWe included 100 patients, 54 with poor outcome. Mean ONSD did not differ significantly between patients with good and poor outcome. Sensitivity for predicting poor outcome increased by adding ONSD to EEG and SSEP from 25% to 41% in all patients and from 27% to 50% after exclusion of patients with non-neurological death.ConclusionsONSD on days 1–3 after cardiac arrest holds potential to add to neurological outcome prediction.Trialregistration: clinicaltrials.gov, NCT04084054. Registered 10 September 2019, https://www.clinicaltrials.gov/study/NCT04084054.

Can NIRS be a surrogate indicator of elective shunt in carotid endarterectomy? A single-center observational retrospective study says no.

Neuromonitoring during carotid endarterectomy (CEA) under general anesthesia is desirable and may be useful for preventing brain ischemia, but the selection of the most appropriate method remains controversial. To determine the effectiveness of near infrared spectroscopy (NIRS) compared to multimodality intraoperative neuromonitoring (IONM) in indicating elective shunts and predicting postoperative neurological status. This is a retrospective observational study including 86 consecutive patients with CEA under general anesthesia. NIRS and multimodality IONM were performed during the procedure. IONM included electroencephalography (EEG), somatosensory evoked potentials (SSEPs) and transcranial motor-evoked potentials (TcMEPs). Sensitivity, specificity, and positive and negative predictive values (PPV and NPV) were calculated for each neuromonitoring modality. NIRS presented a sensitivity and a specificity for detecting brain ischemia of 77.7% and 89.6%, respectively (PPV = 46.6% and NPV = 97.2%). In contrast, a 100% sensitivity and specificity for multimodality IONM was determined (PPV and NPV = 100%). No significant difference (in demographical or clinical data) between "true positive" and "false-positive" patients was identified. Among the methods included in multimodality IONM, EEG showed the best results for predicting postoperative outcome after CEA (PPV and NPV=100%). NIRS is inferior to multimodality IONM in detecting brain ischemia and predicting postoperative neurological status during CEA under general anesthesia.

Descending Neurogenic Evoked Potentials Monitoring Is an Effective Alternative in Spinal Deformity Surgery Under Inhaled Anesthesia

To evaluate the reliability of descending neurogenic evoked potentials (DNEP) monitoring in spinal deformity surgery under inhaled anesthesia. A total of 180 consecutive patients who underwent spinal deformity surgery in our scoliosis center from July 2014 to August 2016 were reviewed. Intraoperative monitoring including somatosensory evoked potentials (SEP), motor evoked potentials (MEP), and DNEP was conducted routinely throughout operation. Patients were divided into 2 groups according to anesthesia methods: group A (n= 72, inhaled anesthesia, SEP/DNEP) and group B (n= 108, total intravenous anesthesia, SEP/MEP/DNEP). Intraoperative monitoring data were collected and analyzed. Positive alerts were observed in 26 patients (14.5%), of whom 18 (10%) were confirmed as true-positive events in the study population. No false-negative events were recorded. In group A, the sensitivity and specificity of SEP and DNEP were 100% and 93.8% and 100% and 98.5%, respectively. For group B, the sensitivity and specificity of SEP/MEP and DNEP were 100% and 95.9% and 100% and 98%, respectively. DNEP monitoring seemed to be effective for the detection and prevention of iatrogenic neurologic deficits during spinal deformity surgery. This study indicates that DNEP was an effective alternative in spinal deformity surgery under inhaled anesthesia.

Soft, conformal PDMS-based ECoG electrode array for long-term in vivo applications

Electrocorticogram (ECoG) electrode arrays based on soft materials, such as polydimethylsiloxane (PDMS), are preferable because they can be implanted with better conformal contact and have physical properties close to biological tissues; thus, the adverse effects on tissues are minimal. However, the realization of electrodes in the micrometer scale on PDMS is challenging. Previously, parylene-treated PDMS was suggested as a solution and proven to be successful in acute in vivo applications. In this study, PDMS-based ECoG electrode arrays fabricated using parylene-treated PDMS (parylene-deposited PDMS and parylene-filled PDMS) are evaluated for the first time in terms of stability and reliability for long-term use. The mechanical and electrochemical properties are investigated over time for up to 8 months through accelerated aging. The ECoG electrode array, implanted in the primary somatosensory area of the brain, can successfully record somatosensory evoked potentials (SEPs) upon mechanical stimulus of the paws with sufficient spatial resolution to distinguish between forepaw and hindpaw stimulations. Finally, the PDMS-based electrodes demonstrate the feasibility of chronic recording for up to 3 months in non-human primates. Based on theses results, it is concluded that they can be used as promising materials and methods to develop various bio-integrated electronic devices that require softness, flexibility, conformability, and robustness over long-term.

Detection And Management of Lower Body Deformity And Ulceration Extremity In People With A Lived Experience of Diabetes

Background: Diabetes is a silent killer, wherein prolonged poor glucose control could lead to acute diabetic ulcers that are responsible for foot ulcers in the lower body extremities. A diabetic foot is a skin sore formed as a result of skin tissue breaking down and exposing the tissue layers underneath. Chronic conditions of the disease lead to amputation of the limb which is a lifelong disability as well as morbidity. Objective: We have compiled an interesting and informative review on diabetic foot ulceration. Topics and subtopics discussed in the article have scientific relevance for the readers of health management journals. Main Outcome and Results: The cascade of events that lead to ulceration is responsible for degrading vascular changes in nerve fibers, resulting in poor motor neuropathy in the lower extremities. Therefore, detection of diabetic foot and ulceration in the early stage is crucial for proper disease management. Various tools in this regard have been used to detect and monitor diabetic foot occurrence apart from a conventional assessment such as the severity of the infection, infection of the skin, extent or size of the ulcer, depth of tissue infection, and loss of sensation from various parts of the lower body. Furthermore, recent advancement in medical technology has also given some critical diagnostic tools EMG (Electromyography), NCV (Nerve Conduction Velocity), PPG (Photoplethysmography), and SSEP (Somatosensory Evoked Potential). Conclusion: The review discusses various complications related to people with a lived experience of diabetic foot ulcers and some advanced tools to diagnose them. Furthermore, a conclusive discussion on a holistic view of diabetic foot diagnosis methods and available treatments has been summarized which could be more explored for better detection/management of the disease.

Anodal transcutaneous spinal direct current stimulation influences the amplitude of pain-related evoked potentials in healthy subjects

It has already been described that transcutaneous spinal direct current stimulation (tsDCS) can selectively influence nociceptive evoked potentials. This study is the first aiming to prove an influence of tsDCS on pain-related evoked potentials (PREP) using concentric surface electrodes (CE), whose nociceptive specificity is still under discussion. 28 healthy subjects participated in this sham-controlled, double-blind cross-over study. All subjects underwent one session of anodal and one session of sham low-thoracic tsDCS. Before and after the intervention, PREP using CE, PREP-induced pain perception and somatosensory evoked potentials (SEP) were assessed on the right upper and lower limb. We found a decrease in PREP amplitude at the lower limb after sham stimulation, but not after anodal tsDCS, while SEP remained unchanged under all studied conditions. There was no difference between the effects of anodal tsDCS and sham stimulation on the studied parameters assessed at the upper limb. PREP-induced pain of the upper and lower limb increased after anodal tsDCS. The ability of influencing PREP using a CE at the spinal level in contrast to SEP suggests that PREP using CE follows the spinothalamic pathway and supports the assumption that it is specifically nociceptive. However, while mainly inhibitory effects on nociceptive stimuli have already been described, our results rather suggest that anodal tsDCS has a sensitizing effect. This may indicate that the mechanisms underlying the elicitation of PREP with CE are not the same as for the other nociceptive evoked potentials. The effects on the processing of different types of painful stimuli should be directly compared in future studies.

Multimodal Intraoperative Neurophysiological Monitoring in Cranial and Spinal Tumour Surgeries: A Descriptive Observational Study.

Intraoperative neurophysiological monitoring (IONM) involves monitoring the functional integrity of critical brain regions and pathways as well as identifying and preserving functionally viable neural tissues (mapping) during surgery using electrophysiological techniques. Multimodality combines various neurophysiological techniques to optimise diagnostic effectiveness and to improve the outcomes of the surgeries. The present study is a case series with comprehensive and illustrative descriptions of the neurophysiological changes in five neuromonitored cases of cranial and spinal cord tumour surgeries conducted with a multimodal approach. The cases were monitored with somatosensory evoked potentials (SSEP), transcranial motor evoked potentials (TcMEP), and both free run and triggered electromyography (fEMG and tEMG). No false negative outcomes were identified in the cases studied as there was an association of absence of change in SSEP and TcMEP both, with no neurological deficit postoperatively.Two cases were identified as having true positive neuromonitoring alerts.No false positive alerts were found in any case. Multimodal monitoring using SSEP, TcMEP, and EMG (fEMG and tEMG) in cranial and spinal tumour surgeries can improve performance with fewer false-negative and false-positive results. Neuromonitoring approaches used in combination can provide reliable information regarding postoperative neurological outcomes.

Visual objects approaching the body modulate subsequent somatosensory processing at 4 months of age

We asked whether, in the first year of life, the infant brain can support the dynamic crossmodal interactions between vision and somatosensation that are required to represent peripersonal space. Infants aged 4 (n = 20, 9 female) and 8 (n = 20, 10 female) months were presented with a visual object that moved towards their body or receded away from it. This was presented in the bottom half of the screen and not fixated upon by the infants, who were instead focusing on an attention getter at the top of the screen. The visual moving object then disappeared and was followed by a vibrotactile stimulus occurring later in time and in a different location in space (on their hands). The 4-month-olds’ somatosensory evoked potentials (SEPs) were enhanced when tactile stimuli were preceded by unattended approaching visual motion, demonstrating that the dynamic visual-somatosensory cortical interactions underpinning representations of the body and peripersonal space begin early in the first year of life. Within the 8-month-olds’ sample, SEPs were increasingly enhanced by (unexpected) tactile stimuli following receding visual motion as age in days increased, demonstrating changes in the neural underpinnings of the representations of peripersonal space across the first year of life.

EEG Investigation on the Tactile Perceptual Performance of a Pneumatic Wearable Display of Softness

Multisensory human–machine interfaces for virtual- or augmented-reality systems are lacking wearable actuated devices that can provide users with tactile feedback on the softness of virtual objects. They are needed for a variety of uses, such as medical simulators, tele-operation systems and tele-presence environments. Such interfaces require actuators that can generate proper tactile feedback, by stimulating the fingertips via quasi-static (non-vibratory) forces, delivered through a deformable surface, so as to control both the contact area and the indentation depth. The actuators should combine a compact and lightweight structure with ease and safety of use, as well as low costs. Among the few actuation technologies that can comply with such requirements, pneumatic driving appears to be one of the most promising. Here, we present an investigation on a new type of pneumatic wearable tactile displays of softness, recently described by our group, which consist of small inflatable chambers arranged at the fingertips. In order to objectively assess the perceptual response that they can elicit, a systematic electroencephalographic study was conducted on ten healthy subjects. Somatosensory evoked potentials (SEPs) were recorded from eight sites above the somatosensory cortex (Fc2, Fc4, C2 and C4, and Fc1, Fc3, C1 and C3), in response to nine conditions of tactile stimulation delivered by the displays: stimulation of either only the thumb, the thumb and index finger simultaneously, or the thumb, index and middle finger simultaneously, each repeated at tactile pressures of 10, 20 and 30 kPa. An analysis of the latency and amplitude of the six components of SEP signals that typically characterise tactile sensing (P50, N100, P200, N300, P300 and N450) showed that this wearable pneumatic device is able to elicit predictable perceptual responses, consistent with the stimulation conditions. This proved that the device is capable of adequate actuation performance, which enables adequate tactile perceptual performance. Moreover, this shows that SEPs may effectively be used with this technology in the future, to assess variable perceptual experiences (especially with combinations of visual and tactile stimuli), in objective terms, complementing subjective information gathered from psychophysical tests.

Movement predictability modulates sensorimotor processing.

An important factor for optimal sensorimotor control is how well we are able to predict sensory feedback from internal and external sources during movement. If predictability decreases due to external disturbances, the brain is able to adjust muscle activation and the filtering of incoming sensory inputs. However, little is known about sensorimotor adjustments when predictability is increased by availability of additional internal feedback. In the present study we investigated how modifications of internal and external sensory feedback influence the control of muscle activation and gating of sensory input. Co-activation of forearm muscles, somatosensory evoked potentials (SEP) and short afferent inhibition (SAI) were assessed during three object manipulation tasks designed to differ in the predictability of sensory feedback. These included manipulation of a shared object with both hands (predictable coupling), manipulation of two independent objects without (uncoupled) and with external interference on one of the objects (unpredictable coupling). We found a task-specific reduction in co-activation during the predictable coupling compared to the other tasks. Less sensory gating, reflected in larger subcortical SEP amplitudes, was observed in the unpredictable coupling task. SAI behavior was closely linked to the subcortical SEP component indicating an important function of subcortical sites in predictability related SEP gating and their direct influence on M1 inhibition. Together, these findings suggest that the unpredictable coupling task cannot only rely on predictive forward control and is compensated by enhancing co-activation and increasing the saliency for external stimuli by reducing sensory gating at subcortical level. This behavior might serve as a preparatory step to compensate for external disturbances and to enhance processing and integration of all incoming external stimuli to update the current sensorimotor state. In contrast, predictive forward control is accurate in the predictable coupling task due to the integrated sensory feedback from both hands where sensorimotor resources are economized by reducing muscular co-activation and increasing sensory gating.

Somatosensory evoked potentials amplitude is enhanced after non-invasive brain stimulation in chronic ischemic stroke: Preliminary results from a randomised control trial

ObjectiveTo investigate the effects of transcranial electrical and magnetic non-invasive brain stimulation (NIBS) protocols on somatosensory evoked potential (SEP) in chronic ischemic stroke. Methods33 patients were randomly assigned to one of the four treatment groups of the transcranial direct current stimulation (tDCS) and/or repetitive transcranial magnetic stimulation (rTMS) protocol. SEP parameters were recorded before and after ten days of the treatment session. All the statistical analyses were carried out using SPSS version 19. ResultsIt was found that there is a statistically significant improvement in the N20-P22 mean amplitude after treatment sessions in all groups except the group where tDCS and rTMS groups were sham. On paired t-tests, the difference betweeen post and pre-stimulation SEP amplitudes for the real tDCS and real rTMS coupled group was 1.045 ± 0.732 (p value = 0.005). For sham tDCS+real rTMS group, 1.05 ± 0.96 (P = 0.04); for real tDCS+sham rTMS 0.543 ± 0.332 (P = 0.01) and for double sham stimulation, 0.204 ± 0.648 (P = 0.4) respectively ConclusionIn ischemic stroke patients, either or coupled true transcranial tDCS and rTMS was found to be safe and significantly enhanced the amplitude of cortical somatosensory potentials when combined with standard physiotherapy, in the interim analysis of an ongoing randomised controlled trial. Clinical Trial Registry of IndiaCTRI/2019/11/022009 SignificanceThe results of this research indicates the importance of RCTs in developing robust improved NIBS protocols coupled to physiotherapy to enhance the sensory-motor functional recovery following ischemic stroke.

Effectiveness of MEP and SSEP Monitoring in the Diagnosis of Neurological Dysfunction Immediately After Craniotomy Aneurysm Clipping.

To explore the diagnostic accuracy of motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring in predicting immediate neurological dysfunction after craniotomy aneurysm clipping. A total of 184 patients with neurosurgery aneurysms in the Affiliated Hospital of Qingdao University from April 2019 to December 2021 were retrospectively included. All patients underwent craniotomy aneurysm clipping, and MEP and SSEP were used to monitor during the operation. Receiver operating characteristic (ROC) curve analysis was used to determine the optimal cutoff value for early warning of MEP and SSEP amplitude decline and to evaluate the effectiveness of MEP and SSEP changes in predicting immediate postoperative neurological dysfunction. Among the 184 patients with intracranial aneurysms, the incidences of immediate postoperative neurological dysfunction were 44.4% (12/27) and 3.2% (5/157) in patients with intraoperative MEP changes and without changes, respectively. For SSEP, The incidence rates were 52.6% (10/19) and 4.2% (7/165), respectively, and the differences were statistically significant ( P <0.001). Significant changes in intraoperative MEP and SSEP were significantly associated with the development of immediate postoperative neurological deficits ( P <0.05). The critical values for early warning of MEP and SSEP amplitude decrease were: 61.6% ( P < 0.001, area under the curve 0.803) for MEP amplitude decrease and 54.6% ( P <0.001, area under the curve 0.770) for SSEP amplitude decrease. The sensitivity and specificity of MEP amplitude change in predicting immediate postoperative neurological dysfunction were 70.6% and 91.0%, respectively. For SSEP amplitude changes, the sensitivity and specificity were 58.8% and 95.8%, respectively. Motor-evoked potential and SSEP monitoring have moderate sensitivity and high specificity for immediate postoperative neurological dysfunction after craniotomy aneurysm clipping. Motor-evoked potential is more accurate than SSEP. Patients with changes in MEP and SSEP are at greatly increased risk of immediate postoperative neurologic deficits.

Application of Machine Learning Strategies to Model the Effects of Sevoflurane on Somatosensory-Evoked Potentials during Spine Surgery

In this study, a small sample of patients’ neuromonitoring data was analyzed using machine learning (ML) tools to provide proof of concept for quantifying complex signals. Intraoperative neurophysiological monitoring (IONM) is a valuable asset for monitoring the neurological status of a patient during spine surgery. Notably, this technology, when operated by neurophysiologists and surgeons familiar with proper alarm criteria, is capable of detecting neurological deficits. However, non-surgical factors, such as volatile anesthetics like sevoflurane, can negatively influence robust IONM signal generation. While sevoflurane has been shown to affect the latency and amplitude of somatosensory evoked potential (SSEP), a more complex and nuanced analysis of the SSEP waveform has not been performed. In this study, signal processing and machine learning techniques were used to more intricately characterize and predict SSEP waveform changes as a function of varying end-tidal sevoflurane concentration. With data from ten patients who underwent spinal procedures, features describing the SSEP waveforms were generated using principal component analysis (PCA), phase space curves (PSC), and time-frequency analysis (TFA). A minimum redundancy maximum relevance (MRMR) feature selection technique was then used to identify the most important SSEP features associated with changing sevoflurane concentrations. Once the features carrying the maximum amount of information about the majority of signal waveform variability were identified, ML models were used to predict future changes in SSEP waveforms. Linear regression, regression trees, support vector machines, and neural network ML models were then selected for testing. Using SSEP data from eight patients, the models were trained using a range of features selected during MRMR calculations. During the training phase of model development, the highest performing models were identified as support vector machines and regression trees. After identifying the highest performing models for each nerve group, we tested these models using the remaining two patients’ data. We compared the models’ performance metrics using the root mean square error values (RMSEs). The feasibility of the methodology described provides a general framework for the applications of machine learning strategies to further delineate the effects of surgical and non-surgical factors affecting IONM signals.

Abstract 036: Diagnostic Accuracy of IONM for Perioperative Strokes during Endovascular Treatment of Ruptured Intracranial Aneurysms

Introduction Ruptured aneurysmal SAH accounts up to 80% of nontraumatic SAH, with more than 80% located in the anterior circulation and a mortality rate upwards of 50%.1‐3 Endovascular treatment (EVT) of ruptured intracranial aneurysms (rIA) is increasingly being recognized as a standard treatment that may result in better early outcomes and independency when compared with open neurosurgical clipping in cases of appropriate equipoise.1,2,4–6 Despite this, EVT of intracranial aneurysms has its own risk of complications including intraoperative rupture and thromboembolic events.7 The complication rate is found to be higher in cases of rIA than that seen in cases of unruptured intracranial aneurysms.8 The use of somatosensory evoked potentials (SSEP) and electroencephalography (EEG) intraoperative neuromonitoring (IONM) have proven their efficacy in identifying iatrogenic neurological complications in vascular surgeries including carotid endarterectomy 9–11, EVT and microsurgical treatment of intracranial aneurysms. 11,12 rIA have their own unique challenges due to preoperative neurological deficits and perioperative vasospasm making it more difficult to identify new neurological deficits after the procedure. They are also associated with decreased vasoreactivity secondary to bleeding, and a higher rate of procedural complications that can alter the IONM signals.13,14 IONM in the form of SSEP and EEG can be utilized in anesthetized patients to indirectly monitor intraoperative cerebral perfusion as well as central and peripheral neuronal integrity.15,16 Changes in one or both modalities indicate a change in cerebral perfusion that can be related to EVT directly, for example, aneurysm perforation or coil herniation and embolism, or indirectly secondary to anesthesia and hemodynamic changes.17 (Figure1) Methods We reviewed the medical records of 323 patients who underwent EVT of ruptured aneurysms with IONM utilizing SSEP and EEG. We included all patients who had endovascular management of ruptured aneurysm and completed IONM records until the end of the procedure and excluded those with no IONM records or incomplete records. Patients were divided into 2 groups, one group with postprocedural neurological deficits (PPND) and one group without PPND. Results Total of 323 patients undergoing EVT, significant IONM changes were noted in 71 patients (21.98%) and 46 (14.24%) who experienced PPND. 22 out of 71 (30.98%) patients who had significant IONM changes experienced PPND. Univariable analysis demonstrated that persistent changes in SSEP and EEG were associated with PPND (p‐values: &lt;0.001 and &lt;0.001). Multivariable analysis showed that persistent IONM changes were significantly associated with PPND (OR: 8.28 (95%CI:2.92‐24.66, p‐value: &lt;0.001). Simultaneous changes in both modalities had a specificity of 95% (95% CI: 0.92, 0.97%) and sensitivity of 48% (95% CI: 0.33, 0.63) to predict PPND when either modality had a change. Out of 46 patients with PPND, 29 (63.04%) experienced periprocedural complications. PPND was associated with periprocedural complications with a p‐value &lt;0.001. Also, multivariable analysis showed an association between IONM changes and persistent IONM changes with PPND with OR of 7.35 (95% CI; 3.68, 15.03) and 7.25 (95% CI; 3.58, 15.00), respectively. Conclusion Significant IONM changes during EVT for rIA are associated with an increased risk of PPND.

Lower Extremity Somatosensory Evoked Potentials Predict Functional Outcomes in Complete Traumatic Cervical Spinal Cord Injury

Traumatic cervical spinal cord injury (tCSCI) is often a debilitating injury, making early prognosis important for medical and surgical planning. Currently, the best early predictors of prognosis are physical examination, imaging studies, and patient demographics. Despite these factors, patient outcomes continue to vary significantly. The purpose of this study was to evaluate the prognostic value of somatosensory evoked potentials (SSEPs) with functional outcomes in tCSCI patients. A retrospective study was conducted on prospectively collected data from 2 academic institutions. Patients 18years and older who had tCSCI and underwent posterior cervical decompression and stabilization with intraoperative neuromonitoring were reviewed. The outcomes of interest were the American Spinal Injury Association (ASIA) Impairment Scale (AIS) grade and ASIA motor score at follow-up. Outcomes measures were assessed via student t-tests, chi-squared tests, and multivariable regression analysis. A total of 79 patients were included. In complete injuries, detectable lower extremity SSEPs were associated with higher ASIA motor scores at follow-up (P= 0.002), greater increases in ASIA motor scores at follow-up (P= 0.009), and a greater likelihood of clinically important improvement in ASIA motor score (P= 0.024). Incomplete, AIS grade C injuries has higher rates of grade conversion (P= 0.019) and clinically important improvement in ASIA motor score (P= 0.010), compared to AIS grade A or B injuries. The detection of lower extremity SSEP signals during initial surgical treatment of tCSCI is associated with greater improvement in ASIA motor scores postoperatively. The association is most applicable to patients with complete injury.

Abstract 242: Clinical Validation Trial Of BraiN20® Medical Device. PROMISE20 Study Protocol

Introduction N20 somatosensory evoked potential (SEP) response shows high predictive accuracy of functional recovery in patients with Acute Ischemic Stroke (AIS) undergoing endovascular thrombectomy (https://www.clinicaltrials.gov/ct2/show/NCT04099615; SVIN Journal, in press). This capacity is independent and even higher than clinical and advanced imaging variables. This study aims to validate BraiN20®, a portable, non‐invasive, AI‐based device to monitor in real‐time the presence and characteristics of N20 in AIS. Methods 65 patients with AIS and anterior Large Vessel Occlusion (LVO) undergoing EVT within 24 hours from onset are included in three comprehensive stroke centers of Catalonia, Spain. Eligibility criteria are no significant pre‐stroke functional dependence, baseline NIHSS score equal or higher than 6 points, occlusion (mTICI 0‐1) of the intracranial ICA, MCA‐M1 or M2 suitable for EVT per local protocols, without infarct volume restrictions measured by ASPECT score or by CTP/DWI‐MRI prior to EVT . The primary objective is to confirm an optimal/good reliability of N20 registration before EVT higher than 75% by two blind expert neurophysiologists, assuming a true proportion equal to 87.5%. Secondary endpoints are the predictive accuracy of N20 response recorded by BraiN20® before and after EVT on functional outcome evaluated by the mRS at 7 and 90 days and analyzed by using Receiving Operating Characteristic curves. A futility interim analysis is planned after the inclusion of 25% of the sample. Results The trial is sponsored by Time is Brain S.L. and will start early September 2023. Primary endpoint results are expected by the end of this year. Conclusion BraiN20® could be a useful medical device to predict salvageable brain and functional recovery of patients along the stroke chain.

Abstract 062: N20 Potential And Imaging Biomarkers Of Functional Recovery In Acute Ischemic Stroke Patients And EVT

Introduction PROMISE trial has shown high predictive accuracy of the N20 somatosensory evoked potential (SEP) response on functional recovery in patients with AIS undergoing endovascular thrombectomy (EVT). This secondary study aims to describe the association between the N20 response and imaging biomarkers of ischemic penumbra, infarct volume and collateral flow. Methods Presence and amplitude of the N20 response was recorded before EVT. At baseline, infarct core was automatically calculated establishing a threshold value of ADC&lt;620x10‐6mm2/s in MR and of rCBF&lt;30% in CTP; ischemic volume was estimated as Tmax &gt;6 sec; and hypoperfusion intensity ratio (HIR) as the proportion of ischemic volume that also has a delay in Tmax&gt;10s. Leptomeningeal collaterals were classified according to the Arterial Collateral Grading Scale in CTA as "poor" (absence and &lt;50%) and optimal (&gt;50%, equal to and greater than the contralateral), or according to the American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology scale when the acquired image was dynamic MR angiography, dichotomized as incomplete collateral fill (poor collateral) (grades 0 to 2) and complete collateral fill (optimal collateral) (grades 3 and 4). Collaterals were not evaluated in the conventional angiography since we did not perform a full study to shorten the time to thrombus access. The adjusted predictive value of N20 for functional recovery was analyzed by logistic regression and compared with imaging variables by using receiver operating characteristic curves. Results From 223 patients studied, 99 patients had multimodal imaging with perfusion studies and N20 assessable recordings at baseline (mean age, 70y; median NIHSS, 18), 63 patients with present (N20+) and 36 with absent N20 response (N20‐). Median infarct core was 12 (0‐25) and 16 (3‐60) cc (p= 0,193), ischemic volume 81 (39‐132) and 111 (54‐188) cc (p=0,082) and the HIR 0,4 (0,2‐0,6) 0,4 (0,3‐0,6) (p=0,572), respectively. N20+ was associated to a better collateral flow (OR 2,5; [1,2‐5,3]; p=0,01). N20+ showed the highest predictive capacity of functional recovery at day 7 compared to imaging variables (Table 1) and increased 15 (4‐103) fold the likelihood of good outcome after adjusting for collateral flow 2.94 (1.10‐8.40), ASPECT score (1,17 (0,74 ‐ 1,87) and infarct core 0.98 (0.95‐1.01). Conclusion N20 SEP response is a powerful biomarker of functional recovery that might surrogate advanced imaging in patients with AIS evaluated for endovascular thrombectomy.