Intraoperative Neurophysiological Monitoring for Endoscopic Endonasal Approaches to the Skull Base: A Technical Guide.

Intraoperative neurophysiological monitoring during endoscopic, endonasal approaches to the skull base is both feasible and safe. Numerous reports have recently emerged from the literature evaluating the efficacy of different neuromonitoring tests during endonasal procedures, making them relatively well-studied. The authors report on a comprehensive, multimodality approach to monitoring the functional integrity of at risk nervous system structures, including the cerebral cortex, brainstem, cranial nerves, corticospinal tract, corticobulbar tract, and the thalamocortical somatosensory system during endonasal surgery of the skull base. The modalities employed include electroencephalography, somatosensory evoked potentials, free-running and electrically triggered electromyography, transcranial electric motor evoked potentials, and auditory evoked potentials. Methodological considerations as well as benefits and limitations are discussed. The authors argue that, while individual modalities have their limitations, multimodality neuromonitoring provides a real-time, comprehensive assessment of nervous system function and allows for safer, more aggressive management of skull base tumors via the endonasal route

Usefulness of time-frequency patterns of somatosensory evoked potentials in identification of the location of spinal cord injury

postprin

Signal-to-noise ratio of intraoperative tibial nerve somatosensory-evoked potentials

To reveal the intrinsic signal-to-noise ratio (SNR) of single-trial somatosensory-evoked potentials (SEP). SEP was recorded from 13 scoliosis patients during surgery. The power of SEP was estimated with least-square fitting to obtain the most accurate value and then to estimate the SNR of every trial of SEP. The SNR of cortical SEP from 13 cases presented individual difference among each other. According to the mean and standard deviation, the coefficients of variation of cortical and subcortical SEP were 4.2% and 23%, respectively. The SNR of SEP was estimated to be -24 ± 1 dB in cortical SEP and -22 ± 5 dB in subcortical SEP. The lowest SNR of individual case was found to be -30 dB in cortical SEP and -53 dB in subcortical SEP. The results showed that SNR of intraoperative SEP recordings varies from person to person and presents a higher variability in subcortical than that in cortical, with a broad range from -53 to -5 dB. The results from this study can be used to understand the nature of SEP signals, which could guide researchers and designers on SEP denoising method selection, extraction, and measurement, as well as equipment development. © 2010 by the American Clinical Neurophysiology Society.postprin

Time-frequency analysis of somatosensory evoked potentials for intraoperative spinal cord monitoring

PURPOSE: To evaluate the potential use of time-frequency analysis and its reliability in intraoperative somatosensory evoked potential (SEP) monitoring. METHODS: One hundred ninety-one patients undergoing thoracic and/or lumbar spinal surgery were studied retrospectively. The SEP signals were recorded during different stages of surgery. Averaged SEP was analyzed by short-time Fourier transform. The main peak in the time-frequency interpretation of SEP was measured in peak power, peak time, and peak frequency. The variability of these parameters was compared with that of amplitude and latency during different stages of surgery. The reliability of these parameters was also compared in true-positive and false-positive cases. RESULTS: During different surgical stages for the posterior tibial nerve SEP, the intrasubject variability of peak power was found to be more stable than that of amplitude, while the intrasubject variability of peak time did not show any difference compared with that of latency. The peak frequency presented stable during surgery. Moreover, the true-positive SEP case showed that peak power may detect the potential injury earlier than amplitude does. The false-positive outcomes could be reduced by the proposed method. CONCLUSIONS: The SEP peak component was found stable and reliable during the different stages of surgery. For clinical application purpose, time-frequency analysis was suggested to be an additional monitoring method besides the conventional amplitude/latency measurement since it provided a more reproducible and prompt response to the potential injury in intraoperative SEP monitoring. Copyright © 2011 by the American Clinical Neurophysiology Society.postprin

Identification of detailed time-frequency components in somatosensory evoked potentials

Somatosensory evoked potential (SEP) usually contains a set of detailed temporal components measured and identified in time domain, providing meaningful information on physiological mechanisms of the nervous system. The purpose of this study is to reveal complex and fine time-frequency features of SEP in time-frequency domain using advanced time-frequency analysis (TFA) and pattern classification methods. A high-resolution TFA algorithm, matching pursuit (MP), was proposed to decompose a SEP signal into a string of elementary waves and to provide a time-frequency feature description of the waves. After a dimension reduction by principle component analysis (PCA), a density-guided K-means clustering was followed to identify typical waves existed in SEP. Experimental results on posterior tibial nerve SEP signals of 50 normal adults showed that a series of typical waves were discovered in SEP using the proposed MP decomposition and clustering methods. The statistical properties of these SEP waves were examined and their representative waveforms were synthesized. The identified SEP waves provided a comprehensive and detailed description of time-frequency features of SEP. © 2006 IEEE.published_or_final_versio

Single trial somatosensory evoked potential extraction with ARX filtering for a combined spinal cord intraoperative neuromonitoring technique

BACKGROUND: When spinal cord functional integrity is at risk during surgery, intraoperative neuromonitoring is recommended. Tibial Single Trial Somatosensory Evoked Potentials (SEPs) and H-reflex are here used in a combined neuromonitoring method: both signals monitor the spinal cord status, though involving different nervous pathways. However, SEPs express a trial-to-trial variability that is difficult to track because of the intrinsic low signal-to-noise ratio. For this reason single trial techniques are needed to extract SEPs from the background EEG. METHODS: The analysis is performed off line on data recorded in eight scoliosis surgery sessions during which the spinal cord was simultaneously monitored through classical SEPs and H-reflex responses elicited by the same tibial nerve electrical stimulation. The single trial extraction of SEPs from the background EEG is here performed through AutoRegressive filter with eXogenous input (ARX). The electroencephalographic recording can be modeled as the sum of the background EEG, which can be described as an autoregressive process not related to the stimulus, and the evoked potential (EP), which can be viewed as a filtered version of a reference signal related to the stimulus. The choice of the filter optimal orders is based on the Akaike Information Criterion (AIC). The reference signal used as exogenous input in the ARX model is a weighted average of the previous SEPs trials with exponential forgetting behavior. RESULTS: The moving average exponentially weighted, used as reference signal for the ARX model, shows a better sensibility than the standard moving average in tracking SEPs fast inter-trial changes. The ability to promptly detect changes allows highlighting relations between waveform changes and surgical maneuvers. It also allows a comparative study with H-reflex trends: in particular, the two signals show different fall and recovery dynamics following stressful conditions for the spinal cord. CONCLUSION: The ARX filter showed good performances in single trial SEP extraction, enhancing the available information concerning the current spinal cord status. Moreover, the comparison between SEPs and H-reflex showed that the two signals are affected by the same surgical maneuvers, even if they monitor the spinal cord through anatomically different pathways

The Effects of Filter's Class, Cutoff Frequencies, and Independent Component Analysis on the Amplitude of Somatosensory Evoked Potentials Recorded from Healthy Volunteers

Objective: The aim of this study was to investigate the effects of different preprocessing parameters on the amplitude of median nerve somatosensory evoked potentials (SEPs). Methods: Different combinations of two classes of filters (Finite Impulse Response (FIR) and Infinite Impulse Response (IIR)), three cutoff frequency bands (0.5–1000 Hz, 3–1000 Hz, and 30–1000 Hz), and independent component analysis (ICA) were used to preprocess SEPs recorded from 17 healthy volunteers who participated in two sessions of 1000 stimulations of the right median nerve. N30 amplitude was calculated from frontally placed electrode (F3). Results: The epochs classified as artifacts from SEPs filtered with FIR compared to those filtered with IIR were 1% more using automatic and 140% more using semi-automatic methods (both p < 0.001). There were no differences in N30 amplitudes between FIR and IIR filtered SEPs. The N30 amplitude was significantly lower for SEPs filtered with 30–1000 Hz compared to the bandpass frequencies 0.5–1000 Hz and 3–1000 Hz. The N30 amplitude was significantly reduced when SEPs were cleaned with ICA compared to the SEPs from which non-brain components were not removed using ICA. Conclusion: This study suggests that the preprocessing of SEPs should be done carefully and the neuroscience community should come to a consensus regarding SEP preprocessing guidelines, as the preprocessing parameters can affect the outcomes that may influence the interpretations of results, replicability, and comparison of different studies

Wyniki monitorowania neurofizjologicznego operacji kanału kręgowego

Background and purpose Spine surgery carries the risk of neurological complications. Neurophysiological intraoperative monitoring (NIOM) plays some role in preventing adverse events. NIOM is a young technique, and because of its costs and additional personnel it requires constant evaluation of indications. Nowadays, it is generally assumed that if available, NIOM should be used in every intracanal surgical procedure. This study aimed to evaluate the efficacy and indications for NIOM in spine surgery in relation to procedure location. Material and methods Effectiveness of NIOM in spinal canal surgery was evaluated by comparison of the number of neurological complications in patients treated surgically with and without NIOM. A total of 74 consecutive patients were surgically treated for spinal canal pathology at the Department of Neurosurgery, 10th Military Hospital in Bydgoszcz. Thirty-eight patients operated on with the use of NIOM were compared to a historic population of 36 patients treated before the introduction of NIOM. The number of patients with neurological complications was analyzed in three groups based on surgical location: extradural, intradural extramedullary, and intramedullary procedures. Differences between groups were tested with the Fisher exact test. Results The number of neurological complications was significantly lower in the intramedullary procedure group with NIOM. There was no significant difference in the number of complications in patients undergoing intra- or extradural extramedullary procedures with versus without NIOM. Conclusions NIOM decreases the risk of neurological complications in spinal cord surgery, but not in extramedullary spinal canal procedures.Wstęp i cel pracy Operacje kanału kręgowego są obarczone wyjątkowo dużym ryzykiem powikłań neurologicznych. Jedna z najważniejszych metod zmniejszania ryzyka powikłań operacji to śródoperacyjne monitorowanie neurofizjologiczne (neurophysiologic intraoperative monitoring – NIOM). Jest to technika młoda i ze względu na koszty aparatury oraz dodatkowego personelu konieczna jest ocena jej skuteczności i ustalenie wskazań do jej stosowania. Obecnie zakłada się, że jeżeli technika NIOM jest dostępna, to powinna być zastosowana w każdego rodzaju operacjach kanału kręgowego. Celem pracy była ocena skuteczności i zasadności NIOM w operacjach kanału kręgowego w odniesieniu do zakresu procedury. Materiał i metody Skuteczność NIOM w operacjach kanału kręgowego oceniono poprzez porównanie liczby powikłań neurologicznych po zabiegach z użyciem NIOM i bez zastosowania NIOM. Badaniem objęto 74 kolejnych chorych operowanych w zakresie kanału kręgowego w Klinice Neurochirurgii 10. Wojskowego Szpitala w Bydgoszczy. Wyniki leczenia 38 chorych operowanych z wykorzystaniem NIOM porównano z wynikami w historycznej grupie kontrolnej, którą stanowiło 36 kolejnych chorych operowanych przed wprowadzeniem tej techniki. Oceniono liczbę powikłań neurologicznych po operacjach w trzech grupach – zewnątrz-oponowych, wewnątrzoponowych, zewnątrzrdzeniowych oraz wewnątrzrdzeniowych. Istotność różnic oceniano przy zastosowaniu testu dokładnego Fishera. Wyniki Po operacjach rdzenia kręgowego stwierdzono istotnie mniejszą liczbę powikłań w grupie chorych operowanych z wykorzystaniem NIOM. Nie stwierdzono istotnej różnicy pomiędzy wynikami operacji prowadzonych zewnątrzrdze-niowo – wewnątrzoponowo ani zewnątrzoponowo. Wnioski Śródoperacyjne monitorowanie neurofizjologiczne podczas operacji rdzenia kręgowego zmniejszyło liczbę powikłań neurologicznych, ale w przypadku operacji zewnątrz-rdzeniowych nie wpłynęło istotnie na neurologiczny wynik leczenia

Time-frequency component analysis of somatosensory evoked potentials in rats

<p>Abstract</p> <p>Background</p> <p>Somatosensory evoked potential (SEP) signal usually contains a set of detailed temporal components measured and identified in a time domain, giving meaningful information on physiological mechanisms of the nervous system. The purpose of this study is to measure and identify detailed time-frequency components in normal SEP using time-frequency analysis (TFA) methods and to obtain their distribution pattern in the time-frequency domain.</p> <p>Methods</p> <p>This paper proposes to apply a high-resolution time-frequency analysis algorithm, the matching pursuit (MP), to extract detailed time-frequency components of SEP signals. The MP algorithm decomposes a SEP signal into a number of elementary time-frequency components and provides a time-frequency parameter description of the components. A clustering by estimation of the probability density function in parameter space is followed to identify stable SEP time-frequency components.</p> <p>Results</p> <p>Experimental results on cortical SEP signals of 28 mature rats show that a series of stable SEP time-frequency components can be identified using the MP decomposition algorithm. Based on the statistical properties of the component parameters, an approximated distribution of these components in time-frequency domain is suggested to describe the complex SEP response.</p> <p>Conclusion</p> <p>This study shows that there is a set of stable and minute time-frequency components in SEP signals, which are revealed by the MP decomposition and clustering. These stable SEP components have specific localizations in the time-frequency domain.</p

Improving successful rate of transcranial electrical motor-evoked potentials monitoring during spinal surgery in young children

Introduction This prospective study was to investigate the successful rate of intraoperative motor evoked potentials (MEP) monitoring for children (0.05). As well, no difference in MEP successful rates was observed in two groups with different anesthetic techniques. No wake-up test and no post-operative neurological deficits occurred in this series of patients. Conclusion Low dose anesthesia by either TIVA with propofol or sevoflurane-based mixture anesthesia protocol can help the intraoperative spinal cord monitoring to successfully elicit MEP and perform reliable monitoring for patients below 12 years of age. © 2011 Springer-Verlag.published_or_final_versio