Nerve SEPs Research Articles

Feasibility of Saphenous Nerve Somatosensory-Evoked Potential Intraoperative Monitoring during Lumbar Spine Surgery: Early Results.

Retrospective review. Assess the feasibility of saphenous nerve somatosensory evoked potentials (SN-SSEP) monitoring in lumbar spine surgeries. SN-SSEPs have been proposed for detecting lumbar plexus and femoral nerve injury during lateral lumbar surgery where tibial nerve (TN)SSEPs alone are insufficient. SN-SSEPs may also be useful in other types of lumbar surgery, as stimulation of SN below the knee derives solely from the L4 root and provides a means of L4 monitoring, whereas TN-SSEPs often do not detect single nerve root injury. The feasibility of routine SN-SSEP monitoring has not been established. A total of 563 consecutive cases using both TN and SN-SSEP monitoring were included. Anesthesia was at the discretion of the anesthesiologist, using an inhalant in 97.7% of procedures. SN stimulation was performed using 13mm needle electrodes placed below the knee using 200-400μsec pulses at 15-100mA. Adjustments to stimulation parameters were made by the neurophysiology technician while obtaining baselines. Data were graded retrospectively for monitorability and cortical response amplitudes were measured by two independent reviewers. 98% of TN-SSEPs and 92.5% of SN-SSEPs were monitorable at baseline, with a mean response amplitude of 1.35μV for TN-SSEPs and 0.71μV for SN-SSEPs. A significant difference between the stimulation parameters used to obtain reproducible TN and SN-SSEPs at baseline was observed, with SN-SSEPs requiring greater stimulation intensities. Body mass index (BMI) is not associated with baseline monitorability. Out of 20 signal changes observed, 11 involved SN while TN-SSEPs were unaffected. With adjustments to stimulation parameters, SN-SSEP monitoring is feasible within a large clinical cohort without modifications to the anesthetic plan. Incorporating SN into standard intraoperative neurophysiological monitoring (IONM) protocols for lumbar spine procedures may expand the role of SSEP monitoring to include detecting injury to the lumbar plexus. 3.

Enhanced analysis of somatosensory evoked potentials at 20–30 milliseconds can predict neurological outcome after cardiac arrest

ObjectiveThis study attempted to test the effectiveness of an enhanced analysis of the 20–30 ms complex of somatosensory evoked potentials, in predicting the short-term outcome of comatose survivors of out of hospital cardiac arrest and compare it with the current clinical practice. MethodsSingle-centre, prospective, observational study. Median nerve SSEP recording performed at 24–36 h post-return of spontaneous circulation. Recording was analysed using amplitude measurements of P25/30 and Peak-To-Trough of 20–30 ms complex and thresholds to decide P25/30 presence. Neurological outcome was dichotomised into favourable and unfavourable. Results89 participants were analysed. 43.8% had favourable and 56.2% unfavourable outcome. The sensitivity, specificity, positive and negative predictive values of the present SSEP and favourable outcome were calculated. P25/30 presence and size of PTT improved positive predictive value and specificity, while maintained similar negative predictive value and sensitivity, compared to the current practice. Inter-interpreter agreement was also improved. ConclusionsEnhanced analysis of the SSEP at 20–30 ms complex could improve the short-term prognostic accuracy for short-term neurological outcome in comatose survivors of cardiac arrest. SignificancePeak-To-Trough analysis of the 20–30 ms SSEP waveform appears to be the best predictor of neurological outcome following out of hospital cardiac arrest. It is also the easiest and most reliable to analyse.

Predictors of Functional Recovery of Upper Limb Following acute Ischemic Stroke

Background: Although age-standardised rates of stroke mortality have decreased worldwide, overall stroke burden has significantly increased over the last two and half decades especially in developing countries.Objectives: To predict the functional recovery of upper limb potential after acute ischemic stroke.Methods: 51 people were recruited and studied. SAFE, NIHS Score, Median nerve SSEP, Conventional MRI brain imaging are done for all 51 patients. 40 patients were cooperative for further DTI neuroimaging & FA value analysis done within 1wk of stroke onset. Standard care & rehabilitation given. Followed up for upper limb recovery with ARAT scores at 1st, 2nd & 3rd months. Clinical, electrophysiological and neuroimaging recovery variables of upper limb were analyzed between two groups.Results: FA asymmetry index of posterior limb of internal capsule (PLIC) suggest more structural asymmetry of PLIC and poor recovery. There is a significant negative correlation between fractional anisotropy asymmetry index and ARAT III score. Correlation coefficient (r) is -0.319.Conclusion: With initial simple clinical assessment scales most of the recovery can be predicted and thereby patient expectations can be managed and use effective targeted rehabilitation strategies, time & resources to bring the best outcome

Utility of Intraoperative Neurophysiologic Monitoring in Routine Anterior Cervical Spine Surgery

Introduction: Intraoperative neurophysiologic monitoring (IOM) is commonly used in spine surgery; advantages include identification of intraoperative neurologic decline that may be related to a remediable cause. Disadvantages include increased time and cost, morbidity associated with the monitoring procedure, and the potential for false positive alerts prompting unnecessary action. The study’s goal was to assess whether use of IOM in routine, uncomplicated cases of anterior cervical discectomy and fusion (ACDF) surgery was of demonstrable benefit. Methods: 50 consecutive patients were identified who underwent one-level ACDF with anterior instrumentation for cervical disc herniation with radiculopathy without myelopathy. For all cases, a NIMS tube was used to monitor laryngeal nerve function, and EMG, SSEP, and MEP modalities were monitored. Hospital and postoperative records were investigated for the presence of IOM alerts, whether corrective action was taken during surgery, and the presence of any postoperative neurologic deficits. Results: In all cases, there were no alerts of laryngeal nerve dysfunction, or SSEP/ MEP abnormality. In 12 cases, transient EMG irritation activity was documented; in no cases was there any change to the surgical procedure, such as abandonment of surgery, removal of implant, etc. There were no instances of new or worsened postoperative neurologic deficit, and clinical findings of vocal cord dysfunction. Conclusion: In ACDF with anterior instrumentation for cervical disc herniation with radiculopathy without myelopathy, IOM use did not convey any identifiable advantage. Therefore, the data does not support considering IOM to be required or standard of care for routine, uncomplicated ACDF surgery.

Somatosensory evoked potentials and magnetic resonance imaging of the central nervous system in early multiple sclerosis

BackgroundSomatosensory evoked potentials (SSEP) are still broadly used, although not explicitly recommended, for the diagnostic work-up of suspected multiple sclerosis (MS).ObjectiveTo relate disability, SSEP, and lesions on T2-weighted magnetic resonance imaging (MRI) in patients with early MS.MethodsIn this monocentric retrospective study, we analyzed a cohort of patients with relapsing–remitting MS or clinically isolated syndrome, with a maximum disease duration of two years, as well as with available data on the score at the expanded disability status scale (EDSS), on SSEP, on whole spinal cord (SC) MRI, and on brain MRI.ResultsComplete data of 161 patients were available. Tibial nerve SSEP (tSSEP) were less frequently abnormal than SC MRI (22% vs. 68%, p < 0.001). However, higher EDSS scores were significantly associated with abnormal tSSEP (median, 2.0 vs. 1.0; p = 0.001) but not with abnormal SC MRI (i.e., at least one lesion; median, 1.5 vs. 1.5; p = 0.7). Of the 35 patients with abnormal tSSEP, 32 had lesions on SC MRI, and 2 had corresponding lesions on brain MRI.ConclusionCompared to tSSEP, SC MRI is the more sensitive diagnostic biomarker regarding SC involvement. In early MS, lesions as detectable by T2-weighted MRI are the main driver of abnormal tSSEP. However, tSSEP were more closely associated with disability, which is compatible with a potential role of tSSEP as prognostic biomarker in complementation of MRI.

Short-Acting Neuromuscular Blockade Improves Inter-rater Reliability of Median Somatosensory Evoked Potentials in Post-cardiacarrest Prognostication.

Although median nerve somatosensory evoked potentials are routinely used for prognostication in comatose cardiac arrest survivors, myogenic artifact can reduce inter-rater reliability, leading to unreliable or inaccurate results. To minimize this risk, we determined the benefit of neuromuscular blockade agents in improving the inter-rater reliability and signal-to-noise ratio of SSEPs in the context of prognostication. Thirty comatose survivors of cardiac arrest were enrolled in the study, following the request from an intensivist to complete an SSEP for prognostication. Right and left median nerve SSEPs were obtained from each patient, before and after administration of an NMB agent. Clinical histories and outcomes were retrospectively reviewed. The SSEP recordings before and after NMB were randomized and reviewed by five blinded raters, who assessed the latency and amplitude of cortical and noncortical potentials (vs. absence of response) as well as the diagnostic quality of cortical recordings. The inter-rater reliability of SSEP interpretation before and after NMB was compared via Fleiss' κ score. Following NMB administration, Fleiss' κ score for cortical SSEP interpretation significantly improved from 0.37 to 0.60, corresponding to greater agreement among raters. The raters were also less likely to report the cortical recordings as nondiagnostic following NMB (40.7% nondiagnostic SSEPs pre-NMB; 17% post-NMB). The SNR significantly improved following NMB, especially when the pre-NMB SNR was low (< 10dB). Across the raters, there were three patients whose SSEP interpretation changed from bilaterally absent to bilaterally present after NMB was administered (potential false positives without NMB). NMB significantly improves the inter-rater reliability and SNR of median SSEPs for prognostication among comatose cardiac arrest survivors. To ensure the most reliable prognostic information in comatose post-cardiacarrest survivors, pharmacologic paralysis should be consistently used before recording SSEPs.

Distal Stimulation Site at the Medial Tibia for Saphenous Nerve Somatosensory Evoked Potentials (DSn-SSEPs) in Lateral Lumbar Spine Procedures

ABSTRACT Lateral lumbar interbody fusion procedures are performed with multimodality neuromonitoring of the femoral nerve to prevent lumbosacral plexus and peripheral nerve injury from positioning, dilation, retraction, and hardware implantation. The integrity of the femoral nerve can be continuously assessed during these procedures by Somatosensory Evoked Potentials of the Saphenous nerve (Sn-SSEPs). Sn-SSEPs are technically challenging to acquire and necessitate advanced troubleshooting skills with a more rigid anesthetic regimen and physiological parameters. We performed a retrospective analysis of Sn-SSEP data for 100 consecutive lateral lumbar surgeries where the stimulation electrodes were placed distally below the knee and medial to the tibia bone (i.e., DSn-SSEPs). Monitorable baseline responses were present in 87% of patients after the exclusion of fourteen cases where the tibial nerve SSEP was absent, quadriceps transcranial electrical motor evoked potentials (TCeMEPs) were absent or not utilized. Sex, age, body mass index (BMI), diagnosis, mean arterial pressure (MAP), inhalational anesthetic levels, reliability of ulnar and posterior tibial nerve SSEPs, and the reliability of femoral nerve innervated quadriceps TCeMEPs were evaluated but were not of statistically significant consequence between cases where the DSn-SSEP was present or absent in this study. We found the utilization of DSn-SSEPs to be a valuable adjunct to femoral nerve monitoring. Stimulation electrode placement is easy to palpate with clear anatomical borders. Significant muscle artifact and patient movement from stimulation do not affect waveform morphology, allowing for continuous and reliable monitoring. We recommend including DSn-SSEPs to optimize recordings during lateral lumbar procedures.

Evaluation of Neurological Examination, SEP Results, MRI Results, and Lesion Levels in Patients Who Had Been Operated for Myelomeningocele.

Objective:Myelomeningocele is the most severe and the most frequent form of spina bifida. Most of the myelomeningocele patients undergo operations in new-born age. In terms of life quality and rehabilitation, follow-up’s of these patients in the growth and development period after the operation is critical. In our study, our aim is to emphasize the correlation of SEP results with MRI results and clinical features of the myelomeningocele patients.Materials and Methods:In our study, we included 36 patients who had undergone myelomeningocele operation and have been followed-up in Istanbul Bilim University Florence Nightingale Hospital, Spina Bifida Research and Treatment Centre. Posterior tibial nerve SEP was performed on each patient and neurological examinations were done in the same session. Results were compared with clinical functional lesion levels, levels of fusion defect and ambulation levels. In order to evaluate SEP results, we used age-related reference values from Boor et al.’s study in 2008. Patients were grouped as normal, unilaterally prolonged, bilaterally prolonged, unilaterally lost, and bilaterally lost.Results:The correlations of posterior tibial nerve SEP results were significant with ambulation levels (r = 0.428, P < 0.01), clinical functional lesion levels (r = 0.477, P < 0.01) and fusion defect levels (r = −0.528 P < 0.05). The lumbar SEP results were only significantly correlated with functional lesion levels (r = 0.443 P < 0.05).Conclusions:Radiological studies are insufficient when evaluating the functionality of the central nervous system. To fully evaluate the functionality and watch the neurological development with accuracy, especially in operated patients, electrophysiological studies should be an indispensable part of myelomeningocele follow-ups.

P2-08-01. The influence of right-left error of the placement of Cc electrode in tibial nerve SEPs

P2-08-01. The influence of right-left error of the placement of Cc electrode in tibial nerve SEPs

P10-T Correlation of various EEG patterns with multimodal prognostic factors in patients with post-anoxic coma

Bilateral absence of N20, elevated NSE levels and anoxic brain injury signs in neuroimaging, are noted as predictors of poor outcome in comatose patients after cardiac arrest (CA). We evaluated the association of various EEG patterns with these prognostic factors in comatose patients post AC. In our study, 166 patients with cardiac arrest in coma were stratified according to 4 independent EEG patterns: benign, RSE, generalized periodic discharges [GPDs], malignant non-epileptiform. NSE level > 68 ng/mL, bilateral absence of median nerve SEP and moderate to severe anoxic brain injury on neuroimaging, were considered indicators of poor prognosis. Of 166 patients that were included, a benign EEG pattern was recorded in 76 patients (45.8%); RSE occurred in 36 patients, a periodic pattern (GPDs) was seen in 13 patients (7.8%); and a malignant non epileptiform EEG pattern was recorded in 41 patients (24.7%). The four EEG patterns were highly associated with different prognostic indicators. Patients with benign EEG pattern and RSE showed lower NSE levels and were less likely to show bilateral absence N20 responses and severe anoxic brain injury on neuroimaging. On the other side, patients with GPDs and malignant pattern were associated more frequently with bilateral absence of N20 responses, higher NSE levels and severe anoxic brain injury on neuroimaging. These data show that the a benign EEG pattern and RSE without periodisms, may be a predictor of a good outcome and a more aggressive treatment may be indicated in this patients, given the possibility of a better prognosis.

Lower Extremity Somatosensory Evoked Potential P37 Waveform Optimization

ABSTRACTSomatosensory evoked potentials (SEPs) using tibial nerve stimulation are used during neurophysiologic intraoperative monitoring (NIOM). These SEPs produce a P37 waveform that is recorded from scalp electrodes. In this study, we attempted to determine the best derivation for recording the P37 waveform. Surgical cases using tibial nerve SEP NIOM were reviewed. Only cases in which the P37 was recorded using all of the following derivations were analyzed: centroparietal ipsilateral–centroparietal contralateral (CPi-CPc), centroparietal midline–frontopolar midline (CPz-Fpz), and CPz-CPc. The amplitude of the P37 waveform was measured in each derivation. Descriptive statistics were obtained for the P37 waveform amplitude. The mean amplitude in each of the derivations was compared using a chi-square test. Data from 39 patients (78 lower limbs) were available for analysis. The mean age of the patients was 49.64 years (range: 4–87 years); 18 were female. The highest amplitude P37 waveform was recorded from the CPz-Fpz derivation in 29 (35.4%) limbs, whereas the CPz-CPc and CPi-CPc derivations showed the highest amplitude in 29 (35.4%) and 20 (24.4%) limbs, respectively. The mean amplitudes were not significantly different between the various derivations. In only 10 (24.4%) of patients was the best derivation the same for both left and right limbs. A single best derivation was not found for recording the P37 waveform. Multiple derivations should be used to record cortical channels whenever possible. If the number of available channels is limited, using at least the CPz-Fpz and CPz-CPc derivations is recommended.

S79. The utility of tibial nerve SEPs in diagnosing lumbar spinal stenosis, comparison with NCS and F-Waves

Introduction Lumbar spinal stenosis (LSS) is a popular cause of lower limb motor and sensory impairments and gait disturbance. SEPs can be a tool to evaluate LSS, and there have been considerable number of studies investigating the utility of dermatomal SEP in evaluating LSS or lumbar radiculopathy. However, few studies investigated the utility of tibial nerve SEPs. Tibial nerve SEPs have an advantage that they can evaluate plural points along the whole course of the peripheral nerve and can localize the lesion site. Three segments of ankle-knee, knee-pelvis, and pelvis-spinal entry can be evaluated by N8o latency, N8o-P15 interval, and P15-N21 interval. In this study, we compared the utility of tibial nerve SEPs with nerve conduction studies (NCS) and F-waves. Methods We searched our EMG database from 2012 to 2017 with the keyword of “LSS” or “lumbar” and SEP examinations. For extracted cases, we retrospectively reviewed clinical and EMG records and MRI images. The entry criteria were as follows: (1) presence of sensory, motor, or gait (typically, intermittent claucication) complaints, (2) unequivocal LSS in lumbar MRI, (3) final diagnosis that the chief complaint was caused by the MRI-documented LSS, (4) Tibial nerve SEPs, motor conduction study (MCS) and F waves of the tibial nerve, and sensory conduction study (SCS) of the sural nerve were conducted for the same lower-limb that was the more affected, (5) no other causes that can explain his or her symptoms, especially neuropathies and diabetes, (6) no prior lumbar surgery. Results Among 39 patients initially extracted, many have been excluded by the strict inclusion criteria. Finally enrolled were 8 patients (53–82 years, all men). The clinical features of these patients were as follows. Weakness was present in 7 (absent in 1). Sensory symptoms or signs were present in 4 (absent in 4). Intermittent claucication was present in 3 patients. Tibial nerve SEPs were abnormal in 7, and could localize the lesion at the lumbar segment (P15-N21) in 6. Notably, in 3 out of 4 patients without sensory symptoms or signs, tibial nerve SEPs localized the lesion at lumbar segment. The amplitude of the compound muscle action potential (CMAP) of the tibial MCS was reduced in 2 cases, and F-wave latency was prolonged in the same 2 cases. In no cases, F-waves were abnormal despite normal SEPs. Sural SCS was normal for all cases. In two patients in which tibial nerve SEPs could not localize the lesion, needle EMG confirmed the diagnosis of LSS. Conclusion Tibial nerve SEPs are useful in diagnosing LSS by localizing the lesion at the lumbar segments. Especially the fact that they documented lumbar lesions in patients lacking sensory symptoms or signs would contribute to the differentiation from amyotrophic lateral sclerosis. The sensitivity of F-waves was much lower than tibial nerve SEPs and added no value to the amplitude of the tibial CMAP.

P 105 Spatio-temporal characteristics of somatosensory-evoked high-gamma activity of the EEG

Introduction There is enlarging interest in the cortical function of high gamma band (HGB) changes related to different sensory modalities, movement tasks, and higher cognitive processes. EEG experiments have shown visually-evoked, auditory-evoked, and movement-related HGB changes, including the range of 50–70 Hz ( Tallon-Baudry et al., 1997 , Ball et al., 2008 ). While HGB activity in this frequency range associated to peripheral somatosensory stimulation was reported for intracranial recordings in neurological patients ( Fukuda et al., 2008 ), it has received little attention in EEG studies. Here the focus was on very high frequency somatosensory responses above 600 Hz ( Curio et al., 1994 ). In the present study, we implemented an experimental setup, optimized to measure high frequencies in the EEG, to investigate if robust 50–70 Hz HGB activity in noninvasive EEG could be identified during median nerve SEP stimulation and what the spatio-temporal characteristics of these changes are. Methods In an electromagnetically-shielded cabin, EEG data of 15 healthy subjects was obtained with 128 Ag/AgCl scalp electrodes and with NeurOne amplifiers (24-bit digital resolution and 5 kHz sampling rate). 1200 SEPs per subject were evoked by stimulation of the left median nerve with a SEP-stimulator. Simultaneous eye-tracking data from 7 of these subjects was attained to examine the influence of ocular movements on the neuronal recordings. Data analysis included preprocessing, short-time Fourier transformation algorithm, normalization, calculation of induced and evoked responses and a false discovery rate corrected sign test. Results All analyzed subjects showed a significant spectral power increase in the HGB range at 50–70 Hz after median nerve stimulation ( p Conclusion Using our purpose-build experimental set up, we were able to demonstrate a specific contralateral somatosensory-evoked response pattern in the 50–70-Hz frequency range of the noninvasive EEG. Our results agree with the findings of previous intracranial SEP studies and open up new possibilities to noninvasively study sensory related brain functions, both in healthy subjects and neurological patients.

Evoked potentials recorded during routine EEG predict outcome after perinatal asphyxia.

To evaluate the added value of somatosensory (SEPs) and visual evoked potentials (VEPs) recorded simultaneously with routine EEG in early outcome prediction of newborns with hypoxic-ischemic encephalopathy under modern intensive care. We simultaneously recorded multichannel EEG, median nerve SEPs, and flash VEPs during the first few postnatal days in 50 term newborns with hypoxic-ischemic encephalopathy. EEG background was scored into five grades and the worst two grades were considered to indicate poor cerebral recovery. Evoked potentials were classified as absent or present. Clinical outcome was determined from the medical records at a median age of 21months. Unfavorable outcome included cerebral palsy, severe mental retardation, severe epilepsy, or death. The accuracy of outcome prediction was 98% with SEPs compared to 90% with EEG. EEG alone always predicted unfavorable outcome when it was inactive (n=9), and favorable outcome when it was normal or only mildly abnormal (n=17). However, newborns with moderate or severe EEG background abnormality could have either favorable or unfavorable outcome, which was correctly predicted by SEP in all but one newborn (accuracy in this subgroup 96%). Absent VEPs were always associated with an inactive EEG, and an unfavorable outcome. However, presence of VEPs did not guarantee a favorable outcome. SEPs accurately predict clinical outcomes in newborns with hypoxic-ischemic encephalopathy and improve the EEG-based prediction particularly in those newborns with severely or moderately abnormal EEG findings. SEPs should be added to routine EEG recordings for early bedside assessment of newborns with hypoxic-ischemic encephalopathy.

24. Dorsal column nuclei evoked activity recorded from the human Pedunculopontine nucleus

This study aimed to verify the hypothesis that somatosensory activity recorded from the Pedunculopontine nucleus (PPTg) comes from the dorsal column nuclei (DCN) (Insola et al., 2015). In one parkinsonian patient implanted in the PPTg for DBS, both tibial and median nerve SEPs were recorded from the PPTg electrode. The finding obtained from this patient was compared with that issued from another patient implanted with an epidural electrode at Cv2 level for pain relief. The triphasic waform and HFOs recorded from the PPTg after tibial nerve stimulation were very similar to the low- and high-frequency components recorded from the Cv2 epidural electrode, known to be generated in the DCN (Insola et al., 2010). Therefore, the present results suggest that both the low-frequency triphasic waveform and the HFOs recorded from the PPTg are generated from the DCN.

40. Brachial plexopathy: What to monitor?

The utility of IONM in the surgical treatment of peripheral nerve disorders is well established and described in the literature. The purpose of this presentation is to demonstrate the utility of IONM in brachial plexus surgery and review how the different clinical neurophysiologic testing modalities, such as nerve action potentials, EMG, SSEPs and TcMEPs can be used to assess different regions of this complex structure. Amongst other things, IONM can assist in identifying the different brachial plexus structures, determine areas of abnormality or injury, evaluate for peripheral nerve continuity and evaluate for possible root avulsion. However, in order to do this the IONM physician must have a clear understanding of the brachial plexus anatomy and of the specialized techniques used in assessing these structures. Thus, the following will be described in detail: 1. The technique used to obtain nerve action potentials; 2. Techniques used to determine peripheral and central continuity of neural structures; and 3. How IONM can alter surgical management. Unfortunately, the short time allocated for this presentation does not allow for a full discussion of this complex subject and the attendee is directed to reviews of the subject available in the literature.

EPV 14. Non-invasive single-trial detection of human population spike responses in somatosensory evoked potentials in a realistic clinical setting

Introduction High-frequency EEG oscillations ( ≈ 600 Hz; HFO) evoked by median nerve stimulation and recorded above the human somatosensory cortex are non-invasive correlates of cortical population spikes. Recently, it was shown that spatiotemporal filtering and multivariate classification enables single-trial HFO detection using 29-channel low-impedance ( Ω ) low-noise EEG in an electromagnetically shielded recording chamber. It is an open question, whether this can be achieved in a realistic clinical setting. Methods With a custom-built CE-certified low-noise EEG amplifier, median nerve SEPs were recorded in 10 healthy subjects using 8 electrodes (impedances ≈ 1 k Ω ) in a standard unshielded hospital environment. After band-pass filtering (500–900 Hz), a subset of the trials (N = 2000) was used to train the two-step single-trial HFO detector, which is composed of spatiotemporal filter optimization and nonlinear classification. The performance of the algorithm was assessed using an independent set of additional trials (N = 5200). Results In the present group of 10 subjects, on average the algorithm detected evoked HFOs in 64.9% of the single trials in the correct latency window (around ≈ 20 ms) with a positive predictive value (PPV) of 61.9%. Notably, in several subjects with a higher signal-plus-noise-to-noise ratio (SNNR), detection rate (DR) and PPV were above 80% (peak values: SNNR = 2.0, DR = 95.2%, PPV = 98.5%). Conclusions A non-invasive single-trial detection of human population spike responses in somatosensory evoked potentials can be achieved also in a realistic unshielded clinical setting. The increase in sensitivity brought about by combined hardware and algorithmic improvements enables the analysis of single-trial variability and might be extended also to pathological components, such as the non-invasive detection of epileptic neocortical high-frequency oscillations.

Contemporaneous Evaluation of Intraoperative Ulnar and Median Nerve Somatosensory Evoked Potentials for Patient Positioning: A Review of Four Cases

ABSTRACTSomatosensory evoked potentials (SSEPs) are a valuable tool for assessing changes in peripheral nerve pathways caused by patient positioning during spinal surgeries. These changes, when left undiagnosed, may lead to postoperative neurological sequelae. Why an upper extremity SSEP attenuates due to positioning is not necessarily clear and can be multifactorial, affecting the peripheral nerves or elements of the brachial plexus. A conduction block can occur at any point along the course of the nerve secondary to entrapment, compression, and ischemia. These mechanisms of injury may be caused by extreme body habitus, the length of the procedure, or the patient’s metabolic underpinnings. The goal of neuromonitoring for positional injury is to predict and prevent both peripheral nerve and brachial plexus injuries. Using ulnar and median nerve SSEPs contemporaneously may lead to better identification of compromised structures when an SSEP change to one or both of the nerves occurs. The investigators provide four case reports where intraoperative SSEP assessment of contemporaneous ulnar and median nerves prevented postoperative upper extremity neural deficits.

76. Intraoperative recording of saphenous nerve somatosensory evoked potentials during spine deformity surgery

Intraoperative SEPs from lower-extremity are typically elicited by stimulating the posterior tibial nerve. Recently, Silverstein et al. described the novel technique of monitoring saphenous nerve SEP (snSEP) during transpsoas approach to the spine in order to detect femoral nerve injury at the L2–L3–L4 levels. The aim of this study was to record snSEP during spine deformity surgery in order to monitor dorsal column and L2–L3–L4 roots at risk during spinal instrumentation procedures. Twenty consecutive patients were involved. Multimodal-IOM, with MEPs, SEPs (stimulating saphenous and posterior tibial nerves), EMG and pedicle screw stimulation, was employed in the patients. Saphenous nerve was stimulated through needle electrodes placed in between the vastus medialis and sartorius muscles, using a repetition rate of 2.7 Hz and a stimulus intensity of 30–45 mA. The cortical response, recorded at the CPz and Fz location, was a positive downward deflection with reproducible latencies at 30 ms. Saphenous nerve stable SEP was recorded in 18/20 patients. Changes were noted in one patient who presented a bilateral transient reduction of lower limbs MEPs and snSEPs during deformity correction. SnSEP monitoring may be a complementary technique in preserving dorsal columns and upper lumbar roots function during spine surgery.

87. Median nerve SEPs predict motor outcome in neonatal ipossic-ischemic encephalopathy treated with hypothermia

The role of SEPs in motor prognosis of hypoxic–ischemic neonatal encephalopathy has been evaluated in pre-hypothermia era (Suppiej, 2010) but their role in babies treated with hypothermia has not been studied yet. We investigated motor outcome at 12 months of age in 38 children who suffered from hypoxic–ischemic neonatal encephalopathy and were treated with hypothermia at the NICU of the Paediatric University Hospital of Padua. All performed median nerve SEPs in the neonatal period, traces were scored as bilaterally present (group1) or as bilaterally/unilaterally absent (group2) cortical N20 response. At follow up 4/38 children had the diagnosis of cerebral palsy (all of them had bilaterally absent cortical SEP). Of the remaining 34, 7 had abnormal (