Intracarotid Etomidate Decreases the Interhemispheric Synchronization in Electroencephalogram (EEG) During the Wada Test

Evaluating a Novel EEG-Based Index for Stroke Detection Under Anesthesia During Mechanical Thrombectomy

BACKGROUND

The rapid identification of acute stroke (AS) during and after anesthesia might lead to early interventions and improved outcomes. We investigated a novel 2-channel electroencephalogram (EEG)-based marker for stroke detection-the lateral interconnection ratio (LIR)-in AS patients having endovascular thrombectomy (EVT) with general anesthesia (GA) or sedation. The LIR in 2 reference groups of patients without postoperative neurological complications was used for comparison.

METHODS

The National Institutes of Health stroke scale score was assessed before and after thrombectomy in 100 patients having EVT with GA or sedation. The EEG was monitored during and for 4 hours following EVT in the AS group and during surgery in the 2 reference groups. We compared: (1) LIR between AS and reference groups; (2) LIR and stroke dynamics (clinical improvement or deterioration after EVT assessed by the National Institutes of Health stroke scale score); (3) the impact of stroke site (anterior vs. posterior circulation) and anesthesia type (GA vs. sedation) on the LIR.

RESULTS

Median (interquartile range) LIR was lower in patients with AS compared with reference patients (0.09, 0.05 to 0.16 vs. 0.39, 0.24 to 0.52, respectively; P <0.000002), and LIR increased in AS patients whose clinical status recovered after EVT compared with nonrecovered patients (0.20, 0.12 to 0.29 vs. 0.09, 0.05 to 0.11, respectively; P <0.007). The LIR might be more sensitive to anterior circulation stroke but is not impacted by anesthesia type.

CONCLUSIONS

We demonstrated the utility of using AS patients undergoing EVT as a platform for assessing a novel EEG marker for the identification of stroke during anesthesia. Further, large-scale studies in AS patients during EVT and in patients undergoing different surgeries and anesthesia are required to validate the LIR.

Association Between Risk of Stroke and Delirium After Cardiac Surgery and a New Electroencephalogram Index of Interhemispheric Similarity

OBJECTIVES

Neurologic complications after surgery (stroke, delirium) remain a major concern despite advancements in surgical and anesthetic techniques. The authors aimed to evaluate whether a novel index of interhemispheric similarity, the lateral interconnection ratio (LIR), between 2 prefrontal electroencephalogram (EEG) channels could be associated with stroke and delirium following cardiac surgery.

DESIGN

Retrospective observational study.

SETTING

Single university hospital.

PARTICIPANTS

A total of 803 adult patients without documentation of a previous stroke, who underwent cardiac surgery with cardiopulmonary bypass (CPB) between July 2016 and January 2018.

INTERVENTIONS

The LIR index was calculated retrospectively from the patients' EEG database.

MEASUREMENTS AND MAIN RESULTS

LIR was analyzed intraoperatively every 10 seconds and compared among patients with postoperative stroke, patients with delirium, and patients without documented neurologic complications, during 5 key periods, each lasting10 minutes: (1) surgery start, (2) before CPB, (3) on CPB, (4) after CPB, and (5) surgery end. After cardiac surgery, 31 patients suffered from stroke; 48 patients were diagnosed with delirium; and 724 had no documented neurologic complications. Patients with stroke demonstrated a decrease in LIR index between the start of surgery and the postbypass period of 0.08 (0.01, 0.36 [21]; median and [interquartile range {IQR}]; valid EEG samples); whereas there was no similar decrease in the no-dysfunction group (-0.04 [-0.13, 0.04; {551}], p < 0.0001). Patients with delirium showed a decrease in LIR index between the start of surgery and the end of the surgery by 0.15 (0.02, 0.30 [12]), compared with no such decrease in the no-dysfunction group (-0.02 [-0.12, 0.08 {376}], p ≈ 0.001).

CONCLUSIONS

After improvement of SNR, it might be of value to further study the index decrease as an indication for risk for brain injury after surgery. The timing of decrease (after CPB or end of surgery) may provide hints regarding the injury pathophysiology and its onset.

Changes in measures of consciousness during anaesthesia of one hemisphere (Wada test)

BACKGROUND

In the Wada test, one hemisphere is selectively anaesthetised by unilateral intracarotid injection of a fast-acting anaesthetic agent. This gives a unique opportunity to observe the functions and physiological activity of one hemisphere while anaesthetising the other, allowing direct comparisons between brain states and hemispheres that are not possible in any other setting.

AIM

To test whether potential measures of consciousness would be affected by selective anaesthesia of one hemisphere, and reliably distinguish the states of the anesthetised and non-anesthetised hemispheres.

METHODS

We analysed EEG data from 7 patients undergoing Wada-tests in preparation for neurosurgery and computed several measures reported to correlate with the state of consciousness: power spectral density, functional connectivity, and measures of signal diversity. These measures were compared between conditions (normal rest vs. unilateral anaesthesia) and hemispheres (injected vs. non-injected), and used with a support vector machine to classify the state and site of injection objectively from individual patient's recordings.

RESULTS

Although brain function, assessed behaviourally, appeared to be substantially altered only on the injected side, we found large bilateral changes in power spectral density for all frequency bands tested, and functional connectivity changed significantly both between and within both hemispheres. Surprisingly, we found no statistically significant differences in the measures of signal diversity between hemispheres or states, for the group of 7 patients, although 4 of the individual patients showed a significant decrease in signal diversity on the injected side. Nevertheless, including signal diversity measures improved the classification results, indicating that these measures carry at least some non-redundant information about the condition and injection site. We propose that several of these results may be explained by conduction of activity, via the corpus callosum, from the injected to the contralateral hemisphere and vice versa, without substantially affecting the function of the receiving hemisphere, thus reflecting what we call "cross-state unreceptiveness".

The Effects of Anesthetics on the Cortex-Lessons From Event-Related Potentials

Consciousness while under general anesthesia is a dreadful condition. Various electroencephalogram (EEG)-based technologies have been developed, on the basis of empirical evidence, in order to identify this condition. However, certain electrophysiological phenomena, which seem strongly related with depth of anesthesia in some drugs, appear less consistent with those of other anesthetic drugs. There is a gap between the complexity of the phenomenon of consciousness and its behavioral manifestations, on the one hand, and the empirical nature of the reported electrophysiological markers, which are associated with it, on the other hand. In fact, such a gap might prevent us from progressing toward unified electrophysiological markers of consciousness while under anesthesia, which are applicable to all anesthetic drugs. We believe that there is a need to bridge this conceptual gap. Therefore, in this work, we will try to present a theoretical framework for such bridging. First, we suggest focusing on neuropsychological processes, which seem to have a clear role in the behavioral manifestations of consciousness while under anesthesia but seem, nevertheless, better defined than consciousness itself-such as perception and attention. Then, we suggest analyzing the effects of anesthesia upon these neuropsychological processes, as they are manifested in the EEG signal. Specifically, we will focus on the effects of anesthesia on event-related potentials (ERPs), which seem more easily associable with neuropsychological modeling.

Epileptic foci localization based on mapping the synchronization of dynamic brain network

BACKGROUND

Characterizing the synchronous changes of epileptic seizures in different stages between different regions is profound to understand the transmission pathways of epileptic brain network and epileptogenic foci. There is currently no adequate quantitative calculation method for describing the propagation pathways of electroencephalogram (EEG) signals in the brain network from the short and long term. The goal of this study is to explore the innovative method to locate epileptic foci, mapping synchronization in the brain networks based on EEG.

METHODS

Mutual information was used to analyze the short-term synchronization in the full electrodes; while nonlinear dynamics quantifies the statistical independencies in the long -term among all electrodes. Then graph theory based on the complex network was employed to construct a dynamic brain network for epilepsy patients when they were awake, asleep and in seizure, analyzing the changing topology indexes.

RESULTS

Epileptic network achieved a high degree of nonlinear synchronization compared to awake time. and the main path of epileptiform activity was revealed by searching core nodes. The core nodes of the brain network were in connection with the onset zone. Seizures always happened with a high degree of distribution.

CONCLUSIONS

This study indicated the path of EEG synchronous propagation in seizures, and core nodes could locate the epileptic foci accurately in some epileptic patients.

An EEG Tool for Monitoring Patient Engagement during Stroke Rehabilitation: A Feasibility Study

Objective

Patient engagement is of major significance in neural rehabilitation. We developed a real-time EEG marker for attention, the Brain Engagement Index (BEI). In this work we investigate the relation between the BEI and temporary functional change during a rehabilitation session.

Methods

First part: 13 unimpaired controls underwent BEI monitoring during motor exercise of varying levels of difficulty. Second part: 18 subacute stroke patients underwent standard motor rehabilitation with and without use of real-time BEI feedback regarding their level of engagement. Single-session temporary functional changes were evaluated based on videos taken before and after training on a given task. Two assessors, blinded to feedback use, assessed the change following single-session treatments.

Results

First part: a relation between difficulty of exercise and BEI was identified. Second part: temporary functional change was associated with BEI level regardless of the use of feedback.

Conclusions

This study provides preliminary evidence that when BEI is higher, the temporary functional change induced by the treatment session is better. Further work is required to expand this preliminary study and to evaluate whether such temporary functional change can be harnessed to improve clinical outcome.

Clinical Trial Registration

Registered with clinicaltrials.gov, unique identifier: NCT02603718 (retrospectively registered 10/14/2015).

A Pilot Study of Possible Easy-to-Use Electrophysiological Index for Early Detection of Antidepressive Treatment Non-Response

INTRODUCTION

The evaluation of response to pharmacological treatment in MDD requires 4-8 weeks. Therefore, the ability to predict response, and especially lack of response to treatment, as early as possible after treatment onset or change, is of prime significance. Many studies have demonstrated significant results regarding the ability to use EEG and ERP markers, including attention-associated markers such as P300, for early prediction of response to treatment. But these markers are derived from long EEG/ERP samples, often from multiple channels, which render them impractical for frequent sampling.

METHODS AND RESULTS

We developed a new electrophysiological attention-associated marker from a single channel (two electrodes), using 1-min samples with auditory oddball stimuli. This work presents an initial evaluation of the ability to use this marker's dynamics between repetitive measures for early (<2 weeks) differentiation between responders and non-responders to antidepressive treatment, in 26 patients with various levels of depression and heterogeneous treatment interventions. The slope of change in the marker between early consecutive samples was negative in the non-responders, but not in the responders. This differentiation was stronger for patients suffering from severe depression (p < 0.001).

CONCLUSION

This pilot study supports the feasibility of the EEG marker for early recognition of treatment-resistant depression. If verified in large-scale prospective studies, it can contribute to research and clinical work.