Intraoperative EEG-based monitors: are we looking under the lamppost?

PURPOSE OF REVIEW: While electroencephalogram (EEG)-based depth of anesthesia monitors have been in use clinically for decades, there is still a major debate concerning their efficacy for detecting awareness under anesthesia (AUA). Further utilization of these monitors has also been discussed vividly, for example, reduction of postoperative delirium (POD).It seems that with regard to reducing AUA and POD, these monitors might be applicable, under specific anesthetic protocols. But in other settings, such monitoring might be less contributive and may have a 'built-it glass ceiling'.Recent advances in other venues of electrophysiological monitoring might have a strong theoretical rationale, and early supporting results, to offer a breakthrough out of this metaphorical glass ceiling. The purpose of this review is to present this possibility. RECENT FINDINGS: Following previous findings, it might be concluded that for some anesthesia protocols, the prevailing depth of anesthesia monitors may prevent incidences of AUA and POD. However, in other settings, which may involve other anesthesia protocols, or specifically for POD - other perioperative causes, they may not. Attention-related processes measured by easy-to-use real-time electrophysiological markers are becoming feasible, also under anesthesia, and might be applicable for more comprehensive prevention of AUA, POD and possibly other perioperative complications. SUMMARY: Attention-related monitoring might have a strong theoretical basis for the prevention of AUA, POD, and potentially other distressing postoperative outcomes, such as stroke and postoperative neurocognitive disorder. There seems to be already some initial supporting evidence in this regard.

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.

Self-reported pain during the initial postoperative period following open lumbar spine fusion surgery does not correlate with the number of levels fused: A prospective trial of 40 patients.

BACKGROUND: Current spine postoperative pain control protocols consider the expected pain following spine fusion surgery to correlate with surgical extent, that is, the greater the number of operated vertebrae, the greater the postoperative pain. Due to this assumption, Enhanced Recovery After Surgery (ERAS) protocols are principally applied to minimally invasive and percutaneous spine surgery and less to open extensive spine fusion operations. The aim of this study was to determine whether postoperative pain does in fact correlate with the surgical extent, potentially opening the door to non-narcotic postoperative pain protocols for this patient subset. MATERIALS AND METHODS: Forty consecutive patients, undergoing open posterior spine surgery, were evaluated for postoperative pain during the first 72 after surgery. All patients were then divided into two groups according to the number of spine levels fused, and the correlation between the number of fusion levels and self-reported pain was analyzed statistically. RESULTS: Self-reported pain levels were not found to correlate with the extent of the spine operation. CONCLUSIONS: As "bigger operation" does not necessarily equate with "bigger pain," adequate postoperative pain control after extensive spine fusion surgery might be achieved without the routine use of narcotic medication, as practiced after minimally invasive and percutaneous surgery. Additional prospective randomized trials are needed to further substantiate this conclusion.

Identifying Recall Under Sedation by a Novel EEG Based Index of Attention-A Pilot Study.

Overview: Recall is an accepted consequence of sedation. But due to the very low prevalence of the more devastating awareness under anesthesia (AUA), it might be of value to assess first the efficacy of new markers for AUA by their efficacy in discovering the more prevalent recall under sedation (RUS). In this pilot study we assessed whether a novel index for attentional effort, the cognitive effort index (CEI), derived in real-time from one forehead EEG channel, could differentiate between patients with or without RUS. Methods: EEG was sampled from 2 groups: (1) Patients who underwent deep sedation (n = 25) (using drugs according to the anesthesiologist preference, but generally combining either Midazolam or Propofol together with either Fentanyl or Remifentanil). (2) Patients who underwent general anesthesia (GA, n = 13, a negative control for recall). In recovery, recall was assessed using the BRICE questionnaire. Results: Of the 25 sedated patients, 11 experienced recall. The CEI marker was high during significantly longer periods in patients with recall, compared to sedated patients, or patients under GA, without recall. Moreover, the increase in CEI was evident mainly toward the end of the procedure. Conclusion: RUS seems to associate with higher level of attention, which is identified in real-time by the easy-to-extract CEI marker.

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.

A New Index of Coordinated Posterior and Anterior Evoked EEG to Detect Recall Under Sedation - A Pilot Study.

EEG-based technologies may be limited in identifying recall under sedation (RUS). We developed a novel index, posteriorization/anteriorization (P/A) index, based on auditory evoked EEG signal and assessed whether it could differentiate between patients with or without RUS. Methods: EEG and BIS were sampled from 3 groups: 1. Patients undergoing sedation (n = 26); 2. Awake volunteers (n = 13, positive control for recall) 3. Patients undergoing general anesthesia (GA, n = 12, negative control for recall). In recovery, recall was assessed using the BRICE questionnaire. Of the 26 sedated patients, 12 experienced recall. Both The P/A index and BIS differentiated between patients with recall and no recall. However, BIS differentiation may have been sensitive to the main drug used for sedation (midazolam vs. propofol) and the P/A index did not show similar drug-based sensitivity. Furthermore, only BIS results were correlated with EMG. Conclusion: This pilot study provided support for the association between P/A index and recall after sedation. Further research is needed in integrating the index into clinical use: (1) it should be derived by an easy-to-use EEG system with a better signal-to-noise ratio; (2) its applicability to other drugs must be shown.

Unscheduled adolescents return to the emergency department following acute concussion.

OBJECTIVE: Emergency department (ED) visits due to concussion have increased over recent years. We aimed to identify variables associated with unscheduled adolescents return to the ED. METHODS: A retrospective cohort study was conducted. All children aged 11 to 18 years who were admitted to the ED due to concussion between 2011 and 2016 were included. Multivariable logistic regression was performed to identify predictors of ED return. RESULTS: Overall, 616 adolescents were admitted to the ED due to concussion. Within the first week from discharge, 37/616 (6%) patients returned unscheduled to the ED, 21 (3.4%) during the first 48 hours and 16 (2.6%) during the following 3-7 days. Age, gender, ethnicity, diagnosis of concussion on first visit and length-of-stay in the ED were not associated with unscheduled ED returns. Variables that were independently associated with increased odds for an unscheduled ED return included two or more symptoms of concussion [odds ratio (OR): 2.81; 95% confidence interval (CI): (1.16-6.82)], bicycle or motor vehicle accident (OR: 3.48; 95% CI: 1.29-9.4), and performance of CT scan on first visit (OR: 2.47; 95% CI: 1.12-5.48). CONCLUSIONS: The findings suggest that certain variables on the first ED visit can predict an unscheduled return visit in adolescents. ABBREVIATIONS: Emergency department (ED); Length of stay (LOS); computerised tomography (CT).

A Call of Alert for the Ambu AuraStraight Disposable Laryngeal Mask.

One day after removal of an AuraStraight disposable laryngeal mask, a plastic laryngeal mask airway cuff shield was retrieved from the oropharynx of a 5-year-old child refusing to eat, drooling, and pointing to her throat. We discuss the reasons why this occurred and suggest how it can be prevented in the future.