Clinical Electroencephalography for Anesthesiologists: Part I: Background and Basic Signatures

Nitrous oxide induces hypothermia and TrkB activation: Maintenance of body temperature abolishes antidepressant-like effects in mice

Recent studies indicate that nitrous oxide (N2O), a gaseous anesthetic and an NMDA (N-methyl-D-aspartate) receptor antagonist, produces rapid antidepressant effect in patients suffering from treatment-resistant depression. Our recent work implies that hypothermia and reduced energy expenditure are connected with antidepressant-induced activation of TrkB neurotrophin receptors - a key regulator of synaptic plasticity. In this study, we demonstrate that a brief exposure to N2O leads to a drop in body temperature following the treatment, which is linked to decreased locomotor activity; enhanced slow-wave electroencephalographic activity; reduced brain glucose utilization; and increased phosphorylation of TrkB, GSK3β (glycogen synthase kinase 3β), and p70S6K (a kinase downstream of mTor (mammalian target of rapamycin)) in the medial prefrontal cortex of adult male mice. Moreover, preventing the hypothermic response in a chronic corticosterone stress model of depression attenuated the antidepressant-like behavioral effects of N2O in the saccharin preference test. These findings indicate that N2O treatment modulates TrkB signaling and related neurotrophic signaling pathways in a temperature-dependent manner, suggesting that the phenomenon driving TrkB activation - altered thermoregulation and energy expenditure - is linked to antidepressant-like behavioral responses.

Changes in brain connectivity and neurovascular dynamics during dexmedetomidine-induced loss of consciousness

Understanding the neurophysiological changes that occur during loss and recovery of consciousness is a fundamental aim in neuroscience and has marked clinical relevance. Here, we utilize multimodal magnetic resonance neuroimaging to investigate changes in regional network connectivity and neurovascular dynamics as the brain transitions from wakefulness to dexmedetomidine-induced unconsciousness, and finally into early-stage recovery of consciousness. We observed widespread decreases in functional connectivity strength across the whole brain, and targeted increases in structure-function coupling (SFC) across select networks- especially the cerebellum-as individuals transitioned from wakefulness to hypnosis. We also observed robust decreases in cerebral blood flow (CBF) across the whole brain-especially within the brainstem, thalamus, and cerebellum. Moreover, hypnosis was characterized by significant increases in the amplitude of low-frequency fluctuations (ALFF) of the resting-state blood oxygen level-dependent signal, localized within visual and somatomotor regions. Critically, when transitioning from hypnosis to the early stages of recovery, functional connectivity strength and SFC-but not CBF-started reverting towards their awake levels, even before behavioral arousal. By further testing for a relationship between connectivity and neurovascular alterations, we observed that during wakefulness, brain regions with higher ALFF displayed lower functional connectivity with the rest of the brain. During hypnosis, brain regions with higher ALFF displayed weaker coupling between structural and functional connectivity. Correspondingly, brain regions with stronger functional connectivity strength during wakefulness showed greater reductions in CBF with the onset of hypnosis. Earlier recovery of consciousness was associated with higher baseline (awake) levels of functional connectivity strength, CBF, and ALFF, as well as female sex. Across our findings, we also highlight the role of the cerebellum as a recurrent marker of connectivity and neurovascular changes between states of consciousness. Collectively, these results demonstrate that induction of, and emergence from dexmedetomidine-induced unconsciousness are characterized by widespread changes in connectivity and neurovascular dynamics.

SIGNIFICANCE STATEMENT

Elucidating the neurophysiological changes underlying loss and recovery of consciousness is a fundamental question in neuroscience. Here, we analyze magnetic resonance imaging data collected across multiple time-points to characterize how the human brain's connectivity and neurovascular dynamics change as it transitions from wakefulness to dexmedetomidine-induced unconsciousness, and early-stage recovery of consciousness. During hypnosis, brain regions become less functionally synchronized to each other; they attain a smaller number of functional configurations compared to wakefulness, and display functional connectivity patterns that are more similar to the underlying structural connectivity. Furthermore, cerebral blood flow significantly decreases across the whole brain, and less metabolically demanding low frequency fluctuations in the hemodynamic signal become more prominent. Collectively, loss of consciousness is accompanied by widespread connectivity and neurovascular changes in the brain, characteristic of less metabolically demanding dynamics.

Electroencephalographic Features of Elderly Patients during Anesthesia Induction with Remimazolam: A Substudy of a Randomized Controlled Trial

BACKGROUND

Although remimazolam is used as a general anesthetic in elderly patients due to its hemodynamic stability, the electroencephalogram characteristics of remimazolam are not well known. The purpose of this study was to identify the electroencephalographic features of remimazolam-induced unconsciousness in elderly patients and compare them with propofol.

METHODS

Remimazolam (n = 26) or propofol (n = 26) were randomly administered for anesthesia induction in surgical patients. The hypnotic agent was blinded only to the patients. During the induction of anesthesia, remimazolam was administered at a rate of 6 mg · kg-1 · h-1, and propofol was administered at a target effect-site concentration of 3.5 μg/ml. The electroencephalogram signals from eight channels (Fp1, Fp2, Fz, F3, F4, Pz, P3, and P4, referenced to A2, using the 10 to 20 system) were acquired during the induction of anesthesia and in the postoperative care unit. Power spectrum analysis was performed, and directed functional connectivity between frontal and parietal regions was evaluated using normalized symbolic transfer entropy. Functional connectivity in unconscious processes induced by remimazolam or propofol was compared with baseline. To compare each power of frequency over time of the two hypnotic agents, a permutation test with t statistic was conducted.

RESULTS

Compared to the baseline in the alpha band, the feedback connectivity decreased by averages of 46% and 43%, respectively, after the loss of consciousness induced by remimazolam and propofol (95% CI for the mean difference: -0.073 to -0.044 for remimazolam [P < 0.001] and -0.068 to -0.042 for propofol [P < 0.001]). Asymmetry in the feedback and feedforward connectivity in the alpha band was suppressed after the loss of consciousness induced by remimazolam and propofol. There were no significant differences in the power of each frequency over time between the two hypnotic agents (minimum q value = 0.4235).

CONCLUSIONS

Both regimens showed a greater decrease in feedback connectivity compared to a decrease in feedforward connectivity after loss of consciousness, leading to a disruption of asymmetry between the frontoparietal connectivity.

EDITOR’S PERSPECTIVE

Changes in the Term Neonatal Electroencephalogram with General Anesthesia: A Systematic Review with Narrative Synthesis

BACKGROUND

Although effects of general anesthesia on neuronal activity in the human neonatal brain are incompletely understood, electroencephalography provides some insight and may identify age-dependent differences.

METHODS

A systematic search (MEDLINE, Embase, PubMed, and Cochrane Library to November 2023) retrieved English language publications reporting electroencephalography during general anesthesia for cardiac or noncardiac surgery in term neonates (37 to 44 weeks postmenstrual age). Data were extracted, and risk of bias (ROBINS-I Cochrane tool) and quality of evidence (Grading of Recommendations Assessment, Development, and Evaluation [GRADE] checklist) were assessed.

RESULTS

From 1,155 abstracts, 9 publications (140 neonates; 55% male) fulfilled eligibility criteria. Data were limited, and study quality was very low. The occurrence of discontinuity, a characteristic pattern of alternating higher and lower amplitude electroencephalography segments, was reported with general anesthesia (94 of 119 neonates, 6 publications) and with hypothermia (23 of 23 neonates, 2 publications). Decreased power in the delta (0.5 to 4 Hz) frequency range was also reported with increasing anesthetic dose (22 neonates; 3 publications).

CONCLUSION

Although evidence gaps were identified, both increasing sevoflurane concentration and decreasing temperature are associated with increasing discontinuity.

EDITOR’S PERSPECTIVE

Recovery of consciousness after acute brain injury: a narrative review

BACKGROUND

Disorders of consciousness (DoC) are frequently encountered in both, acute and chronic brain injuries. In many countries, early withdrawal of life-sustaining treatments is common practice for these patients even though the accuracy of predicting recovery is debated and delayed recovery can be seen. In this review, we will discuss theoretical concepts of consciousness and pathophysiology, explore effective strategies for management, and discuss the accurate prediction of long-term clinical outcomes. We will also address research challenges.

MAIN TEXT

DoC are characterized by alterations in arousal and/or content, being classified as coma, unresponsive wakefulness syndrome/vegetative state, minimally conscious state, and confusional state. Patients with willful modulation of brain activity detectable by functional MRI or EEG but not by behavioral examination is a state also known as covert consciousness or cognitive motor dissociation. This state may be as common as every 4th or 5th patient without behavioral evidence of verbal command following and has been identified as an independent predictor of long-term functional recovery. Underlying mechanisms are uncertain but intact arousal and thalamocortical projections maybe be essential. Insights into the mechanisms underlying DoC will be of major importance as these will provide a framework to conceptualize treatment approaches, including medical, mechanical, or electoral brain stimulation.

CONCLUSIONS

We are beginning to gain insights into the underlying mechanisms of DoC, identifying novel advanced prognostication tools to improve the accuracy of recovery predictions, and are starting to conceptualize targeted treatments to support the recovery of DoC patients. It is essential to determine how these advancements can be implemented and benefit DoC patients across a range of clinical settings and global societal systems. The Curing Coma Campaign has highlighted major gaps knowledge and provides a roadmap to advance the field of coma science with the goal to support the recovery of patients with DoC.

Unconscious classification of quantitative electroencephalogram features from propofol versus propofol combined with etomidate anesthesia using one-dimensional convolutional neural network

Objective

Establishing a convolutional neural network model for the recognition of characteristic raw electroencephalogram (EEG) signals is crucial for monitoring consciousness levels and guiding anesthetic drug administration.

Methods

This trial was conducted from December 2023 to March 2024. A total of 40 surgery patients were randomly divided into either a propofol group (1% propofol injection, 10 mL: 100 mg) (P group) or a propofol-etomidate combination group (1% propofol injection, 10 mL: 100 mg, and 0.2% etomidate injection, 10 mL: 20 mg, mixed at a 2:1 volume ratio) (EP group). In the P group, target-controlled infusion (TCI) was employed for sedation induction, with an initial effect site concentration set at 5-6 μg/mL. The EP group received an intravenous push with a dosage of 0.2 mL/kg. Six consciousness-related EEG features were extracted from both groups and analyzed using four prediction models: support vector machine (SVM), Gaussian Naive Bayes (GNB), artificial neural network (ANN), and one-dimensional convolutional neural network (1D CNN). The performance of the models was evaluated based on accuracy, precision, recall, and F1-score.

Results

The power spectral density (94%) and alpha/beta ratio (72%) demonstrated higher accuracy as indicators for assessing consciousness. The classification accuracy of the 1D CNN model for anesthesia-induced unconsciousness (97%) surpassed that of the SVM (83%), GNB (81%), and ANN (83%) models, with a significance level of p < 0.05. Furthermore, the mean and mean difference ± standard error of the primary power values for the EP and P groups during the induced period were as follows: delta (23.85 and 16.79, 7.055 ± 0.817, p < 0.001), theta (10.74 and 8.743, 1.995 ± 0.7045, p < 0.02), and total power (24.31 and 19.72, 4.588 ± 0.7107, p < 0.001).

Conclusion

Large slow-wave oscillations, power spectral density, and the alpha/beta ratio are effective indicators of changes in consciousness during intravenous anesthesia with a propofol-etomidate combination. These indicators can aid anesthesiologists in evaluating the depth of anesthesia and adjusting dosages accordingly. The 1D CNN model, which incorporates consciousness-related EEG features, represents a promising tool for assessing the depth of anesthesia.

Clinical Trial Registration

https://www.chictr.org.cn/index.html.

Accurate Machine Learning-based Monitoring of Anesthesia Depth with EEG Recording

General anesthesia, pivotal for surgical procedures, requires precise depth monitoring to mitigate risks ranging from intraoperative awareness to postoperative cognitive impairments. Traditional assessment methods, relying on physiological indicators or behavioral responses, fall short of accurately capturing the nuanced states of unconsciousness. This study introduces a machine learning-based approach to decode anesthesia depth, leveraging EEG data across different anesthesia states induced by propofol and esketamine in rats. Our findings demonstrate the model's robust predictive accuracy, underscored by a novel intra-subject dataset partitioning and a 5-fold cross-validation method. The research diverges from conventional monitoring by utilizing anesthetic infusion rates as objective indicators of anesthesia states, highlighting distinct EEG patterns and enhancing prediction accuracy. Moreover, the model's ability to generalize across individuals suggests its potential for broad clinical application, distinguishing between anesthetic agents and their depths. Despite relying on rat EEG data, which poses questions about real-world applicability, our approach marks a significant advance in anesthesia monitoring.

The evolving role of the modern perfusionist: Insights from processed electro-encephalography

Introduction: Since its origin in the 1920s, electroencephalography (EEG) has become a viable option for anesthesia and perfusion teams to monitor anesthetic delivery, optimizing drug dosage and enhancing patient safety. Patients undergoing cardiopulmonary bypass (CPB) are at particular high risk for excessive or inadequate anesthetic doses. During CPB, traditional physiological indicators such as heart rate and blood pressure can be significantly altered. These abnormalities are compounded by rapid changes in anesthetic concentration from hemodilution, circuit absorption, and altered pharmacokinetics. Method: This narrative highlights the use of processed EEG with spectral analysis for anesthetic management during CPB. Conclusion: We emphasize that neuromonitoring using processed EEG during CPB can assess adequacy of anesthesia delivery and monitor for pathologic conditions that can compromise brain function such as inadequate cerebral blood flow, emboli, and seizures. This information is highly valuable for the clinical team including the perfusionist, who regularly diagnose and manage these pathological conditions.

EEG reactivity in neurologic prognostication in post-cardiac arrest patients: A narrative review

Electroencephalographic reactivity (EEG-R) is a promising early predictor of arousal in comatose patients after cardiac arrest. Despite recent guidelines advocating for the integration of EEG-R into the multimodal prognostication model, EEG-R testing methods remain heterogeneous across studies. While efforts towards standardization have been made to reduce interrater variability by the development of quantitative approaches and machine learning models, future validation studies are needed to increase clinical applicability. Furthermore, the specific neurophysiological mechanisms and neuroanatomical correlates underlying EEG-R are not fully understood. In this narrative review, we explore the value and possible mechanisms of EEG-R, focusing on post-cardiac arrest comatose patients. We aim to discuss the current standard of knowledge and future directions, as well as elucidate possible implications for patient care and research.

A Retrospective Comparative Study of the Frequency of Hypotension in Pediatric Cardiac Catheterization under General Anesthesia: Remimazolam versus Sevoflurane

OBJECTIVE

To compare the incidence of hypotension between remimazolam and sevoflurane under general anesthesia for cardiac catheterization in patients with congenital heart disease.

DESIGN

Retrospective observational study.

SETTING

A single university hospital with 300 pediatric cardiac catheterizations by general anesthesia performed annually.

PARTICIPANTS

Patients younger than 15 years who underwent cardiac catheterization under general anesthesia between March 1, 2021, and December 31, 2022. Exclusion criteria were general anesthesia maintained with other than remimazolam or sevoflurane, receipt of remifentanil, American Society of Anesthesiologists score 4 or 5, emergency procedures, and no direct arterial pressure measurement.

INTERVENTIONS

General anesthesia was maintained with remimazolam or sevoflurane.

MEASUREMENTS AND MAIN RESULTS

A total of 309 patients were analyzed, including 28 in the remimazolam group and 281 in the sevoflurane group. Propensity score matching adjusted for confounding factors resulted in 28 patients in each arm, with no apparent differences in background factors. Hypotension was defined as a time-averaged area > 1, in which systolic arterial pressure fell below 80% of the baseline from the start of anesthesia to the end of procedure. The significance level was set at P < .05. The incidence of hypotension was 39.3% in the remimazolam arm and 46.4% in the sevoflurane arm, with no significant difference (P = .79), although the ratio of the median systolic arterial pressure to the baseline value was significantly higher in the remimazolam arm (91.4 ± 15.2% vs 83.2 ± 11.4% in the sevoflurane arm; P = .03).

CONCLUSIONS

Remimazolam was not associated with a lower incidence of hypotension compared to sevoflurane during pediatric cardiac catheterization for congenital heart disease while maintaining significantly higher blood pressure overall.

Recommendation for the practice of total intravenous anesthesia

This Recommendation was developed by the Japanese Society of Intravenous Anesthesia Recommendation Making Working Group (JSIVA-WG) to promote the safe and effective practice of total intravenous anesthesia (TIVA), tailored to the current situation in Japan. It presents a policy validated by the members of JSIVA-WG and a review committee for practical anesthesia management. Anesthesiologists should acquire and maintain the necessary knowledge and skills to be able to administer TIVA properly. A secure venous access is critically important for TIVA. To visualize and understand the pharmacokinetics of intravenous anesthetics, use of real-time pharmacokinetic simulations is strongly recommended. Syringe pumps are essential for the infusion of intravenous anesthetics, which should be prepared according to the rules of each individual anesthesia department, particularly with regard to dilution. Syringes should be clearly labeled with content and drug concentration. When managing TIVA, particularly with the use of muscle relaxants, monitoring processed electroencephalogram (EEG) is advisable. However, the depth of sedation/anesthesia must be assessed comprehensively using various parameters, rather than simply relying on a single EEG index. TIVA should be swiftly changed to an alternative method that includes inhalation anesthesia if necessary. Use of antagonists at emergence may be associated with re-sedation risk. Casual administration of antagonists and sending patients back to surgical wards without careful observation are not acceptable.

State-specific Regulation of Electrical Stimulation in the Intralaminar Thalamus of Macaque Monkeys: Network and Transcriptional Insights into Arousal

Long-range thalamocortical communication is central to anesthesia-induced loss of consciousness and its reversal. However, isolating the specific neural networks connecting thalamic nuclei with various cortical regions for state-specific anesthesia regulation is challenging, with the biological underpinnings still largely unknown. Here, simultaneous electroencephalogram-fuctional magnetic resonance imaging (EEG-fMRI) and deep brain stimulation are applied to the intralaminar thalamus in macaques under finely-tuned propofol anesthesia. This approach led to the identification of an intralaminar-driven network responsible for rapid arousal during slow-wave oscillations. A network-based RNA-sequencing analysis is conducted of region-, layer-, and cell-specific gene expression data from independent transcriptomic atlases and identifies 2489 genes preferentially expressed within this arousal network, notably enriched in potassium channels and excitatory, parvalbumin-expressing neurons, and oligodendrocytes. Comparison with human RNA-sequencing data highlights conserved molecular and cellular architectures that enable the matching of homologous genes, protein interactions, and cell types across primates, providing novel insight into network-focused transcriptional signatures of arousal.

Cyclic Alternating EEG Patterns: From Sleep to Encephalopathy

SUMMARY

In the 2021 version of the Standardized Critical Care EEG Terminology, the American Clinical Neurophysiology Society introduced new definitions, including for the cyclic alternating pattern of encephalopathy (CAPE). CAPE refers to changes in background EEG activity, with two patterns alternating spontaneously in a regular manner. CAPE shares remarkable similarities with the cyclic alternating pattern, a natural EEG phenomenon occurring in normal non-rapid eye movement sleep, considered the main electrophysiological biomarker of sleep instability. This review explores similarities and differences between cyclic alternating pattern and CAPE and, leveraging the existing expertise on cyclic alternating pattern, aims to extend knowledge on CAPE. A standardized assessment of CAPE features is key to ascertain its prevalence and clinical significance among critically ill patients and to encompass the impact of confounding factors such as anesthetic and sedative agents. Although the preservation of non-rapid eye movement sleep-related elements has a well-known prognostic value in the critical care setting, the clinical importance of cyclic oscillating patterns and the prognostic significance of CAPE remain to be elucidated.

Nociception level index variations in ICU: curarized vs non-curarized patients - a pilot study

PURPOSE

Pain is a major physiological stressor that can worsen critical medical conditions in many ways. Currently, there is no reliable monitoring tool which is available for pain monitoring in the deeply sedated ± curarized critically ill patients. This study aims to assess the effectiveness of the multiparameter nociception index (NOL®) in the critical care setting. We compared NOL with traditionally used neurovegetative signs and examined its correlation with sedation depth measured by bispectral index (BIS®) electroencephalographic (EEG) monitoring.

METHODS

This retrospective monocentric cohort study was conducted in a general intensive care unit, including patients who required moderate-to-deep levels of sedation with or without continuous neuromuscular blockade. The performance of NOL was evaluated both in the entire studied population, as well as in two subgroups: curarized and non-curarized patients.

RESULTS

NOL demonstrated greater accuracy than all other indicators in pain detection in the overall population. In the non-curare subgroup, all indices correctly recognized painful stimulation, while in the patients subjected to neuromuscular blocking agent's infusion, only NOL properly identified nociception. In the former group, EEG's relation to nociception was on the border of statistical significance, whereas in the latter BIS showed no correlation with NOL.

CONCLUSION

NOL emerges as a promising device for pain assessment in the critical care setting and exhibits its best performance precisely in the clinical context where reliable pain assessment methods are most lacking. Furthermore, our research confirms the distinction between sedation and analgesia, highlighting the necessity for distinct monitoring instruments to accurately assess them.

Electroencephalogram-Based Anesthesia Indices Differently React to Modulations of Alpha-Oscillatory Activity

BACKGROUND

The electroencephalographic (EEG) provides the anesthesiologist with information regarding the level of anesthesia. Processed EEG indices are available that reflect the level of anesthesia as a single number. Strong oscillatory EEG activity in the alpha-band may be associated with an adequate level of anesthesia and a lower incidence of cognitive sequelae. So far, we do not know how the processed indices would react to changes in the alpha-band activity. Hence, we modulated the alpha-oscillatory activity of intraoperative EEG to assess possible index changes.

METHODS

We performed our analyses based on data from 2 studies. Intraoperative EEG was extracted, and we isolated the alpha-band activity by band-pass filtering (8-12 Hz). We added or subtracted this activity to the original EEG in different steps with different amplifications of the alpha signal. We then replayed these signals to the bispectral index (BIS), the Entropy Module (state entropy [SE]), the CONOX (qCON), and the SEDLine (patient state index [PSI]); and evaluated the alpha-band modulation's impact on the respective index.

RESULTS

The indices behaved differently to the modulation. In general, indices decreased with stronger alpha-band activity, but the rate of change was different with SE showing the strongest change (9% per step) and PSI and BIS (<5% per step) showing the weakest change. A simple regression analysis revealed a decrease of 0.02 to 0.09 index points with increasing alpha amplification.

CONCLUSIONS

While the alpha-band in the intraoperative EEG seems to carry information regarding the quality of anesthesia, changes in the alpha-band activity do neither strongly nor uniformly influence processed EEG indices. Hence, to assess alpha-oscillatory activity's strength, the user needs to focus on the raw EEG or its spectral representation also displayed on the monitoring systems.

Non-invasive technology for brain monitoring: definition and meaning of the principal parameters for the International PRactice On TEChnology neuro-moniToring group (I-PROTECT)

Technologies for monitoring organ function are rapidly advancing, aiding physicians in the care of patients in both operating rooms (ORs) and intensive care units (ICUs). Some of these emerging, minimally or non-invasive technologies focus on monitoring brain function and ensuring the integrity of its physiology. Generally, the central nervous system is the least monitored system compared to others, such as the respiratory, cardiovascular, and renal systems, even though it is a primary target in most therapeutic strategies. Frequently, the effects of sedatives, hypnotics, and analgesics are entirely unpredictable, especially in critically ill patients with multiple organ failure. This unpredictability exposes them to the risks of inadequate or excessive sedation/hypnosis, potentially leading to complications and long-term negative outcomes. The International PRactice On TEChnology neuro-moniToring group (I-PROTECT), comprised of experts from various fields of clinical neuromonitoring, presents this document with the aim of reviewing and standardizing the primary non-invasive tools for brain monitoring in anesthesia and intensive care practices. The focus is particularly on standardizing the nomenclature of different parameters generated by these tools. The document addresses processed electroencephalography, continuous/quantitative electroencephalography, brain oxygenation through near-infrared spectroscopy, transcranial Doppler, and automated pupillometry. The clinical utility of the key parameters available in each of these tools is summarized and explained. This comprehensive review was conducted by a panel of experts who deliberated on the included topics until a consensus was reached. Images and tables are utilized to clarify and enhance the understanding of the clinical significance of non-invasive neuromonitoring devices within these medical settings.

Processed electroencephalography-guided general anesthesia and norepinephrine requirements: A randomized trial in patients having vascular surgery

STUDY OBJECTIVE

Processed electroencephalography (pEEG) may help clinicians optimize depth of general anesthesia. Avoiding excessive depth of anesthesia may reduce intraoperative hypotension and the need for vasopressors. We tested the hypothesis that pEEG-guided - compared to non-pEEG-guided - general anesthesia reduces the amount of norepinephrine needed to keep intraoperative mean arterial pressure above 65 mmHg in patients having vascular surgery.

DESIGN

Randomized controlled clinical trial.

SETTING

University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

PATIENTS

110 patients having vascular surgery.

INTERVENTIONS

pEEG-guided general anesthesia.

MEASUREMENTS

Our primary endpoint was the average norepinephrine infusion rate from the beginning of induction of anesthesia until the end of surgery.

MAIN RESULT

96 patients were analyzed. The mean ± standard deviation average norepinephrine infusion rate was 0.08 ± 0.04 μg kg-1 min-1 in patients assigned to pEEG-guided and 0.12 ± 0.09 μg kg-1 min-1 in patients assigned to non-pEEG-guided general anesthesia (mean difference 0.04 μg kg-1 min-1, 95% confidence interval 0.01 to 0.07 μg kg-1 min-1, p = 0.004). Patients assigned to pEEG-guided versus non-pEEG-guided general anesthesia, had a median time-weighted minimum alveolar concentration of 0.7 (0.6, 0.8) versus 0.8 (0.7, 0.8) (p = 0.006) and a median percentage of time Patient State Index was <25 of 12 (1, 41) % versus 23 (3, 49) % (p = 0.279).

CONCLUSION

pEEG-guided - compared to non-pEEG-guided - general anesthesia reduced the amount of norepinephrine needed to keep mean arterial pressure above 65 mmHg by about a third in patients having vascular surgery. Whether reduced intraoperative norepinephrine requirements resulting from pEEG-guided general anesthesia translate into improved patient-centered outcomes remains to be determined in larger trials.

Parabrachial nucleus Vglut2 expressing neurons projection to the extended amygdala involved in the regulation of wakefulness during sevoflurane anesthesia in mice

AIMS

The parabrachial nucleus (PBN) promotes wakefulness states under general anesthesia. Recent studies have shown that glutamatergic neurons within the PBN play a crucial role in facilitating emergence from anesthesia. Our previous study indicates that vesicular glutamate transporter 2 (vglut2) expression neurons of the PBN extend into the extended amygdala (EA). However, the modulation of PBNvglut2-EA in general anesthesia remains poorly understood. This study aims to investigate the role of PBNvglut2-EA in alterations of consciousness during sevoflurane anesthesia.

METHODS

We first validated vglut2-expressing neuron projections from the PBN to the EA using anterograde tracing. Then, we conducted immunofluorescence staining of c-Fos to investigate the role of the EA involved in the regulation of consciousness during sevoflurane anesthesia. After, we performed calcium fiber photometry recordings to determine the changes in PBNvglut2-EA activity. Lastly, we modulated PBNvglut2-EA activity under sevoflurane anesthesia using optogenetics, and electroencephalogram (EEG) was recorded during specific optogenetic modulation.

RESULTS

The expression of vglut2 in PBN neurons projected to the EA, and c-Fos expression in the EA was significantly reduced during sevoflurane anesthesia. Fiber photometry revealed that activity in the PBNvglut2-EA pathway was suppressed during anesthesia induction but restored upon awakening. Optogenetic activation of the PBNvglut2-EA delayed the induction of anesthesia. Meanwhile, EEG recordings showed significantly decreased δ oscillations and increased β and γ oscillations compared to the EYFP group. Furthermore, optogenetic activation of the PBNvglut2-EA resulted in an acceleration of awakening from anesthesia, accompanied by decreased δ oscillations on EEG recordings. Optogenetic inhibition of PBNvglut2-EA accelerated anesthesia induction. Surprisingly, we found a sex-specific regulation of PBNvglut2-EA in this study. The activity of PBNvglut2-EA was lower in males during the induction of anesthesia and decreased more rapidly during sevoflurane anesthesia compared to females. Photoactivation of the PBNvglut2-EA reduced the sensitivity of males to sevoflurane, showing more pronounced wakefulness behavior and EEG changes than females.

CONCLUSIONS

PBNvglut2-EA is involved in the promotion of wakefulness under sevoflurane anesthesia. Furthermore, PBNvglut2-EA shows sex differences in the changes of consciousness induced by sevoflurane anesthesia.

Artificial intelligence and nonoperating room anesthesia

PURPOSE OF REVIEW

The integration of artificial intelligence (AI) in nonoperating room anesthesia (NORA) represents a timely and significant advancement. As the demand for NORA services expands, the application of AI is poised to improve patient selection, perioperative care, and anesthesia delivery. This review examines AI's growing impact on NORA and how it can optimize our clinical practice in the near future.

RECENT FINDINGS

AI has already improved various aspects of anesthesia, including preoperative assessment, intraoperative management, and postoperative care. Studies highlight AI's role in patient risk stratification, real-time decision support, and predictive modeling for patient outcomes. Notably, AI applications can be used to target patients at risk of complications, alert clinicians to the upcoming occurrence of an intraoperative adverse event such as hypotension or hypoxemia, or predict their tolerance of anesthesia after the procedure. Despite these advances, challenges persist, including ethical considerations, algorithmic bias, data security, and the need for transparent decision-making processes within AI systems.

SUMMARY

The findings underscore the substantial benefits of AI in NORA, which include improved safety, efficiency, and personalized care. AI's predictive capabilities in assessing hypoxemia risk and other perioperative events, have demonstrated potential to exceed human prognostic accuracy. The implications of these findings advocate for a careful yet progressive adoption of AI in clinical practice, encouraging the development of robust ethical guidelines, continual professional training, and comprehensive data management strategies. Furthermore, AI's role in anesthesia underscores the need for multidisciplinary research to address the limitations and fully leverage AI's capabilities for patient-centered anesthesia care.

Effect of transcranial direct current stimulation and narrow-band auditory stimulation on the intraoperative electroencephalogram: an exploratoratory feasibility study

Introduction

During general anesthesia, frontal electroencephalogram (EEG) activity in the alpha frequency band (8-12 Hz) correlates with the adequacy of analgesia. Transcranial direct current stimulation (tDCS) and auditory stimulation, two noninvasive neuromodulation techniques, can entrain alpha activity in awake or sleeping patients. This study evaluates their effects on alpha oscillations in patients under general anesthesia.

Methods

30 patients receiving general anesthesia for surgery were enrolled in this two-by-two randomized clinical trial. Each participant received active or sham tDCS followed by auditory stimulation or silence according to assigned group (TDCS/AUD, TDCS/SIL, SHAM/AUD, SHAM/SIL). Frontal EEG was recorded before and after neuromodulation. Patients with burst suppression, mid-study changes in anesthetic, or incomplete EEG recordings were excluded from analysis. The primary outcome was post-stimulation change in oscillatory alpha power, compared in each intervention group against the change in the control group SHAM/SIL by Wilcoxon Rank Sum testing.

Results

All 30 enrolled participants completed the study. Of the 22 included for analysis, 8 were in TDCS/AUD, 4 were in TDCS/SIL, 5 were in SHAM/AUD, and 5 were in SHAM/SIL. The median change in oscillatory alpha power was +4.7 dB (IQR 4.4, 5.8 dB) in SHAM/SIL, +2.8 dB (IQR 1.5, 8.9 dB) in TDCS/SIL (p = 0.730), +5.5 dB in SHAM/AUD (p = 0.421), and -6.1 dB (IQR -10.2, -2.2 dB) in TDCS/AUD (p = 0.045).

Conclusion

tDCS and auditory stimulation can be administered safely intraoperatively. However, these interventions did not increase alpha power as administered and measured in this pilot study.

Developmental trajectories of EEG aperiodic and periodic components in children 2-44 months of age

The development of neural circuits has long-lasting effects on brain function, yet our understanding of early circuit development in humans remains limited. Here, periodic EEG power features and aperiodic components were examined from longitudinal EEGs collected from 592 healthy 2-44 month-old infants, revealing age-dependent nonlinear changes suggestive of distinct milestones in early brain maturation. Developmental changes in periodic peaks include (1) the presence and then absence of a 9-10 Hz alpha peak between 2-6 months, (2) nonlinear changes in high beta peaks (20-30 Hz) between 4-18 months, and (3) the emergence of a low beta peak (12-20 Hz) in some infants after six months of age. We hypothesized that the emergence of the low beta peak may reflect maturation of thalamocortical network development. Infant anesthesia studies observe that GABA-modulating anesthetics do not induce thalamocortical mediated frontal alpha coherence until 10-12 months of age. Using a small cohort of infants (n = 23) with EEG before and during GABA-modulating anesthesia, we provide preliminary evidence that infants with a low beta peak have higher anesthesia-induced alpha coherence compared to those without a low beta peak.

Electroencephalography-Guided Anesthesia and Delirium in Older Adults After Cardiac Surgery: The ENGAGES-Canada Randomized Clinical Trial

Importance

Intraoperative electroencephalogram (EEG) waveform suppression, suggesting excessive general anesthesia, has been associated with postoperative delirium.

Objective

To assess whether EEG-guided anesthesia decreases the incidence of delirium after cardiac surgery.

Design, Setting, and Participants

Randomized, parallel-group clinical trial of 1140 adults 60 years or older undergoing cardiac surgery at 4 Canadian hospitals. Recruitment was from December 2016 to February 2022, with follow-up until February 2023.

Interventions

Patients were randomized in a 1:1 ratio (stratified by hospital) to receive EEG-guided anesthesia (n = 567) or usual care (n = 573). Patients and those assessing outcomes were blinded to group assignment.

Main Outcomes and Measures

The primary outcome was delirium during postoperative days 1 through 5. Intraoperative measures included anesthetic concentration and EEG suppression time. Secondary outcomes included intensive care and hospital length of stay. Serious adverse events included intraoperative awareness, medical complications, and 30-day mortality.

Results

Of 1140 randomized patients (median [IQR] age, 70 [65-75] years; 282 [24.7%] women), 1131 (99.2%) were assessed for the primary outcome. Delirium during postoperative days 1 to 5 occurred in 102 of 562 patients (18.15%) in the EEG-guided group and 103 of 569 patients (18.10%) in the usual care group (difference, 0.05% [95% CI, -4.57% to 4.67%]). In the EEG-guided group compared with the usual care group, the median volatile anesthetic minimum alveolar concentration was 0.14 (95% CI, 0.15 to 0.13) lower (0.66 vs 0.80) and there was a 7.7-minute (95% CI, 10.6 to 4.7) decrease in the median total time spent with EEG suppression (4.0 vs 11.7 min). There were no significant differences between groups in median length of intensive care unit (difference, 0 days [95% CI, -0.31 to 0.31]) or hospital stay (difference, 0 days [95% CI, -0.94 to 0.94]). No patients reported intraoperative awareness. Medical complications occurred in 64 of 567 patients (11.3%) in the EEG-guided group and 73 of 573 (12.7%) in the usual care group. Thirty-day mortality occurred in 8 of 567 patients (1.4%) in the EEG-guided group and 13 of 573 (2.3%) in the usual care group.

Conclusions and Relevance

Among older adults undergoing cardiac surgery, EEG-guided anesthetic administration to minimize EEG suppression, compared with usual care, did not decrease the incidence of postoperative delirium. This finding does not support EEG-guided anesthesia for this indication.

Trial Registration

ClinicalTrials.gov Identifier: NCT02692300.

Clinical adverse events to dexmedetomidine: a real-world drug safety study based on the FAERS database

Objective

Adverse events associated with dexmedetomidine were analyzed using data from the FDA's FAERS database, spanning from 2004 to the third quarter of 2023. This analysis serves as a foundation for monitoring dexmedetomidine's safety in clinical applications.

Methods

Data on adverse events associated with dexmedetomidine were standardized and analyzed to identify clinical adverse events closely linked to its use. This analysis employed various signal quantification analysis algorithms, including Reporting Odds Ratio (ROR), Proportional Reporting Ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), and Multi-Item Gamma Poisson Shrinker (MGPS).

Results

In the FAERS database, dexmedetomidine was identified as the primary suspect in 1,910 adverse events. Our analysis encompassed 26 organ system levels, from which we selected 346 relevant Preferred Terms (PTs) for further examination. Notably, adverse drug reactions such as diabetes insipidus, abnormal transcranial electrical motor evoked potential monitoring, acute motor axonal neuropathy, and trigeminal cardiac reflex were identified. These reactions are not explicitly mentioned in the drug's specification, indicating the emergence of new signals for adverse drug reactions.

Conclusion

Data mining in the FAERS database has elucidated the characteristics of dexmedetomidine-related adverse drug reactions. This analysis enhances our understanding of dexmedetomidine's drug safety, aids in the clinical management of pharmacovigilance studies, and offers valuable insights for refining drug-use protocols.

Do all sedatives promote biological sleep electroencephalogram patterns? A machine learning framework to identify biological sleep promoting sedatives using electroencephalogram

BACKGROUND

Sedatives are commonly used to promote sleep in intensive care unit patients. However, it is not clear whether sedation-induced states are similar to the biological sleep. We explored if sedative-induced states resemble biological sleep using multichannel electroencephalogram (EEG) recordings.

METHODS

Multichannel EEG datasets from two different sources were used in this study: (1) sedation dataset consisting of 102 healthy volunteers receiving propofol (N = 36), sevoflurane (N = 36), or dexmedetomidine (N = 30), and (2) publicly available sleep EEG dataset (N = 994). Forty-four quantitative time, frequency and entropy features were extracted from EEG recordings and were used to train the machine learning algorithms on sleep dataset to predict sleep stages in the sedation dataset. The predicted sleep states were then compared with the Modified Observer's Assessment of Alertness/ Sedation (MOAA/S) scores.

RESULTS

The performance of the model was poor (AUC = 0.55-0.58) in differentiating sleep stages during propofol and sevoflurane sedation. In the case of dexmedetomidine, the AUC of the model increased in a sedation-dependent manner with NREM stages 2 and 3 highly correlating with deep sedation state reaching an AUC of 0.80.

CONCLUSIONS

We addressed an important clinical question to identify biological sleep promoting sedatives using EEG signals. We demonstrate that propofol and sevoflurane do not promote EEG patterns resembling natural sleep while dexmedetomidine promotes states resembling NREM stages 2 and 3 sleep, based on current sleep staging standards.

Depth of anesthesia monitoring in Norway-A web-based survey

BACKGROUND

The bispectral index (BIS) monitor is the most frequently used electroencephalogram (EEG)-based depth of anesthesia (DoA) technology in Norwegian hospitals. However, there is limited knowledge regarding the extent and clinical impact of its use and how anesthesiologists and nurse anesthetists use the information provided by the DoA monitors in their clinical practice.

METHODS

This cross-sectional survey on the use of DoA monitors in Norway used a web-based questionnaire distributed to anesthesia personnel in all hospitals in Norway. Participation was voluntary and anonymized, and the web form could not track IP sources or respondents' locations.

RESULTS

Three hundred and ninety-one nurse anesthetists (n = 324) and anesthesiologists (n = 67) responded. Among the EEG-based DoA monitoring tools, BIS was most often used to observe and assess patients' DoA (98%). Raw EEG waveform analysis (10%), EEG-spectrogram (9%), and suppression rate (10%) were seldom used. Twenty-seven percent of the anesthesia personnel were able to recognize a burst suppression pattern on EEG and its significance. Fifty-eight percent of the respondents considered clinical observations more reliable than BIS. Almost all respondents reported adjusting anesthetic dosage based on the BIS index values (80%). However, the anesthetic dose was more often increased (90%) because of high BIS index values than lowered (55%) because of low BIS index values.

CONCLUSION

Despite our respondents' extensive use of DoA monitoring, the anesthesia personnel in our survey did not use all the information and the potential to guide the titration of anesthetics the DoA monitors provide. Thus, anesthesia personnel could generally benefit from increased knowledge of how EEG-based DoA monitoring can be used to assess and determine individual patients' need for anesthetic medication.

Intraoperative use of processed electroencephalogram in a quaternary center: a quality improvement audit

Although intraoperative electroencephalography (EEG) is not consensual among anesthesiologists, growing evidence supports its use to titrate anesthetic drugs, assess the level of arousal/consciousness, and detect ischemic cerebrovascular events; in addition, intraoperative EEG monitoring may decrease the incidence of postoperative neurocognitive disorders. Based on the known and potential benefits of intraoperative EEG monitoring, an educational program dedicated to staff anesthesiologists, residents of Anesthesiology and anesthesia technicians was started at Cleveland Clinic Abu Dhabi in May 2022 and completed in June 2022, aiming to have all patients undergoing general anesthesia with adequate brain monitoring and following international initiatives promoting perioperative brain health. All the surgical cases performed under General Anesthesia at 24 daily locations were prospectively inspected during 15 consecutive working days in March 2023. The use or absence of a processed EEG monitor was registered. Of 379 surgical cases distributed by 24 locations under General Anesthesia, 233 cases (61%) had processed EEG monitoring. The specialty with the highest use of EEG monitoring was Cardiothoracic Surgery, with 100% of cases, followed by interventional Cardiology (90%) and Vascular Surgery (75%). Otorhinolaryngology (29%), Gastrointestinal Endoscopy (25%), and Interventional Pulmonology (20%) were the areas with the lowest use of EEG monitoring. Of note, in the Neuroradiology suite, no processed EEG monitor was used in cases under General Anesthesia. We identified a reasonable use of EEG monitoring during general anesthesia, unfortunately not reaching our target of 100%. The educational and support program previously implemented within the Anesthesiology Institute needs to be continued and improved, including workshops, online discussions, and journal club sessions, to increase the use of EEG monitoring in underused areas.

Electroencephalographic insights into the pathophysiological mechanisms of emergence delirium in children and corresponding clinical treatment strategies

Emergence delirium is a common postoperative complication in patients undergoing general anesthesia, especially in children. In severe cases, it can cause unnecessary self-harm, affect postoperative recovery, lead to parental dissatisfaction, and increase medical costs. With the widespread use of inhalation anesthetic drugs (such as sevoflurane and desflurane), the incidence of emergence delirium in children is gradually increasing; however, its pathogenesis in children is complex and unclear. Several studies have shown that age, pain, and anesthetic drugs are strongly associated with the occurrence of emergence delirium. Alterations in central neurophysiology are essential intermediate processes in the development of emergence delirium. Compared to adults, the pediatric nervous system is not fully developed; therefore, the pediatric electroencephalogram may vary slightly by age. Moreover, pain and anesthetic drugs can cause changes in the excitability of the central nervous system, resulting in electroencephalographic changes. In this paper, we review the pathogenesis of and prevention strategies for emergence delirium in children from the perspective of brain electrophysiology-especially for commonly used pharmacological treatments-to provide the basis for understanding the development of emergence delirium as well as its prevention and treatment, and to suggest future research direction.

The Effect of Different Propofol-Ketamine Combinations on Emergence Delirium in Children Undergoing Adenoidectomy and Tonsillectomy Surgery

PURPOSE

Emergence delirium (ED) after sevoflurane anesthesia remains a serious issue in children. We aimed to compare different ratios of propofol-ketamine combinations to determine a better option for preventing ED.

DESIGN

A prospective, randomized clinical trial.

METHODS

In this study, 112 children aged between 3 and 12 years who underwent adenoidectomy and tonsillectomy were recruited. Propofol 1 mg kg-1 + ketamine 1 mg kg-1 (1:1 ratio), propofol 1.5 mg kg-1 + ketamine 0.75 mg kg-1 (2:1 ratio), propofol 2 mg kg-1 + ketamine 0.66 mg kg-1 (3:1 ratio), and propofol 3 mg kg-1 were applied at induction of anesthesia for Groups I, II, III, and IV, respectively. Fentanyl 1 mcg kg-1 and rocuronium 0.6 mg kg-1 were applied at induction, and anesthesia was maintained with sevoflurane and O2/N2O mixture for all participants. Intravenous morphine 0.1 mg kg-1 was applied for postoperative analgesia in the last 10 minutes of surgery. ED was defined as a Watcha score of ≥3. Demographics, hemodynamics, extubation time, Watcha scores, the Face, Legs, Activity, Cry, and Consolability scores, length of stay in the postanesthesia care unit (PACU), rescue analgesic requirement, and postoperative complications were recorded.

FINDINGS

ED was significantly higher at 10 and 20 minutes in Group IV. Eighteen children experienced ED in PACU, (3, 2, 2, and 11 children in Groups I, II, III, and IV, respectively). Face, Legs, Activity, Cry, and Consolability scores were significantly different at all times. Rescue analgesics were required by 3 children (10.7%) in Group I, 2 (7.1%) in Group II, 2 (7.1%) in Group III, and 10 (35.7%) in Group IV (P = .012). The PACU stay was 21.9 ± 6.4 in Group I, 18.7 ± 6.3 in Group II, 16.7 ± 5.8 in Group III, and 17.4 ± 5.8 in Group IV. Nystagmus was observed in three children in Group I.

CONCLUSIONS

To addition of ketamine to propofol during the induction of sevoflurane anesthesia can reduce the ED and analgesic requirements in children. A propofol-to-ketamine ratio of 3:1 provided better postoperative recovery with less pain and ED, without prolonging the PACU length of stay.

Globus pallidus externus drives increase in network-wide alpha power with propofol-induced loss-of-consciousness in humans

States of consciousness are likely mediated by multiple parallel yet interacting cortico-subcortical recurrent networks. Although the mesocircuit model has implicated the pallidocortical circuit as one such network, this circuit has not been extensively evaluated to identify network-level electrophysiological changes related to loss of consciousness (LOC). We characterize changes in the mesocircuit in awake versus propofol-induced LOC in humans by directly simultaneously recording from sensorimotor cortices (S1/M1) and globus pallidus interna and externa (GPi/GPe) in 12 patients with Parkinson disease undergoing deep brain stimulator implantation. Propofol-induced LOC is associated with increases in local power up to 20 Hz in GPi, 35 Hz in GPe, and 100 Hz in S1/M1. LOC is likewise marked by increased pallidocortical alpha synchrony across all nodes, with increased alpha/low beta Granger causal (GC) flow from GPe to all other nodes. In contrast, LOC is associated with decreased network-wide beta coupling and beta GC from M1 to the rest of the network. Results implicate an important and possibly central role of GPe in mediating LOC-related increases in alpha power, supporting a significant role of the GPe in modulating cortico-subcortical circuits for consciousness. Simultaneous LOC-related suppression of beta synchrony highlights that distinct oscillatory frequencies act independently, conveying unique network activity.

Substance-dependent EEG during recovery from anesthesia and optimization of monitoring

The electroencephalographic (EEG) activity during anesthesia emergence contains information about the risk for a patient to experience postoperative delirium, but the EEG dynamics during emergence challenge monitoring approaches. Substance-specific emergence characteristics may additionally limit the reliability of commonly used processed EEG indices during emergence. This study aims to analyze the dynamics of different EEG indices during anesthesia emergence that was maintained with different anesthetic regimens. We used the EEG of 45 patients under general anesthesia from the emergence period. Fifteen patients per group received sevoflurane, isoflurane (+ sufentanil) or propofol (+ remifentanil) anesthesia. One channel EEG and the bispectral index (BIS A-1000) were recorded during the study. We replayed the EEG back to the Conox, Entropy Module, and the BIS Vista to evaluate and compare the index behavior. The volatile anesthetics induced significantly higher EEG frequencies, causing higher indices (AUC > 0.7) over most parts of emergence compared to propofol. The median duration of "awake" indices (i.e., > 80) before the return of responsiveness (RoR) was significantly longer for the volatile anesthetics (p < 0.001). The different indices correlated well under volatile anesthesia (rs > 0.6), with SE having the weakest correlation. For propofol, the correlation was lower (rs < 0.6). SE was significantly higher than BIS and, under propofol anesthesia, qCON. Systematic differences of EEG-based indices depend on the drugs and devices used. Thus, to avoid early awareness or anesthesia overdose using an EEG-based index during emergence, the anesthetic regimen, the monitor used, and the raw EEG trace should be considered for interpretation before making clinical decisions.

Intraoperative pediatric electroencephalography monitoring: an updated review

Intraoperative electroencephalography (EEG) monitoring under pediatric anesthesia has begun to attract increasing interest, driven by the availability of pediatric-specific EEG monitors and the realization that traditional dosing methods based on patient movement or changes in hemodynamic response often lead to imprecise dosing, especially in younger infants who may experience adverse events (e.g., hypotension) due to excess anesthesia. EEG directly measures the effects of anesthetics on the brain, which is the target end-organ responsible for inducing loss of consciousness. Over the past ten years, research on anesthesia and computational neuroscience has improved our understanding of intraoperative pediatric EEG monitoring and expanded the utility of EEG in clinical practice. We now have better insights into neurodevelopmental changes in the developing pediatric brain, functional connectivity, the use of non-proprietary EEG parameters to guide anesthetic dosing, epileptiform EEG changes during induction, EEG changes from spinal/regional anesthesia, EEG discontinuity, and the use of EEG to improve clinical outcomes. This review article summarizes the recent literature on EEG monitoring in perioperative pediatric anesthesia, highlighting several of the topics mentioned above.

The Influence of Electromyographic on Electroencephalogram-Based Monitoring: Putting the Forearm on the Forehead

BACKGROUND

Monitoring the electroencephalogram (EEG) during general anesthesia can help to safely navigate the patient through the procedure by avoiding too deep or light anesthetic levels. In daily clinical practice, the EEG is recorded from the forehead and available neuromonitoring systems translate the EEG information into an index inversely correlating with the anesthetic level. Electrode placement on the forehead can lead to an influence of electromyographic (EMG) activity on the recorded signal in patients without neuromuscular blockade (NMB). A separation of EEG and EMG in the clinical setting is difficult because both signals share an overlapping frequency range. Previous research showed that indices decreased when EMG was absent in awake volunteers with NMB. Here, we investigated to what extent the indices changed, when EEG recorded during surgery with NMB agents was superimposed with EMG.

METHODS

We recorded EMG from the flexor muscles of the forearm of 18 healthy volunteers with a CONOX monitor during different activity settings, that is, during contraction using a grip strengthener and during active diversion (relaxed arm). Both the forehead and forearm muscles are striated muscles. The recorded EMG was normalized by z -scoring and added to the EEG in different amplification steps. The EEG was recorded during anesthesia with NMB. We replayed these combined EEG and EMG signals to different neuromonitoring systems, that is, bispectral index (BIS), CONOX with qCON and qNOX, and entropy module with state entropy (SE) and response entropy (RE). We used the Friedman test and a Tukey-Kramer post hoc correction for statistical analysis.

RESULTS

The indices of all neuromonitoring systems significantly increased when the EEG was superimposed with the contraction EMG and with high EMG amplitudes, the monitors returned invalid values, representative of artifact contamination. When replaying the EEG being superimposed with "relaxed" EMG, the qCON and BIS showed significant increases, but not SE and RE. For SE and RE, we observed an increased number of invalid values.

CONCLUSIONS

With our approach, we could show that EMG activity during contraction and resting state can influence the neuromonitoring systems. This knowledge may help to improve EEG-based patient monitoring in the future and help the anesthesiologist to use the neuromonitoring systems with more knowledge regarding their function.

Unreported Source of Interference with the Bispectral Index During Liposuction: A Case Report

Incorrect bispectral index (BIS) values have been reported due to interference with this monitoring system. We report a case of a 46-year-old woman who underwent liposuction and breast lipofilling, where we observed a misinterpretation by the BIS algorithm that has not yet been reported. Concurrently with abdominal and thigh liposuction, an increase in the BIS value was observed. The importance of examining electroencephalogram (EEG) and density spectral array (DSA) readings during liposuction procedures is highlighted in this case report, extending our observations beyond just the numerical BIS value, which is not always reliable.

Propofol enhancement of slow wave sleep to target the nexus of geriatric depression and cognitive dysfunction: protocol for a phase I open label trial

INTRODUCTION

Late-life treatment-resistant depression (LL-TRD) is common and increases risk for accelerated ageing and cognitive decline. Impaired sleep is common in LL-TRD and is a risk factor for cognitive decline. Slow wave sleep (SWS) has been implicated in key processes including synaptic plasticity and memory. A deficiency in SWS may be a core component of depression pathophysiology. The anaesthetic propofol can induce electroencephalographic (EEG) slow waves that resemble SWS. Propofol may enhance SWS and oral antidepressant therapy, but relationships are unclear. We hypothesise that propofol infusions will enhance SWS and improve depression in older adults with LL-TRD. This hypothesis has been supported by a recent small case series.

METHODS AND ANALYSIS

SWIPED (Slow Wave Induction by Propofol to Eliminate Depression) phase I is an ongoing open-label, single-arm trial that assesses the safety and feasibility of using propofol to enhance SWS in older adults with LL-TRD. The study is enrolling 15 English-speaking adults over age 60 with LL-TRD. Participants will receive two propofol infusions 2-6 days apart. Propofol infusions are individually titrated to maximise the expression of EEG slow waves. Preinfusion and postinfusion sleep architecture are evaluated through at-home overnight EEG recordings acquired using a wireless headband equipped with dry electrodes. Sleep EEG recordings are scored manually. Key EEG measures include sleep slow wave activity, SWS duration and delta sleep ratio. Longitudinal changes in depression, suicidality and anhedonia are assessed. Assessments are performed prior to the first infusion and up to 10 weeks after the second infusion. Cognitive ability is assessed at enrolment and approximately 3 weeks after the second infusion.

ETHICS AND DISSEMINATION

The study was approved by the Washington University Human Research Protection Office. Recruitment began in November 2022. Dissemination plans include presentations at scientific conferences, peer-reviewed publications and mass media. Positive results will lead to a larger phase II randomised placebo-controlled trial.

TRIAL REGISTRATION NUMBER

NCT04680910.

Ketamine can produce oscillatory dynamics by engaging mechanisms dependent on the kinetics of NMDA receptors

Ketamine is an N-methyl-D-aspartate (NMDA)-receptor antagonist that produces sedation, analgesia, and dissociation at low doses and profound unconsciousness with antinociception at high doses. At high and low doses, ketamine can generate gamma oscillations (>25 Hz) in the electroencephalogram (EEG). The gamma oscillations are interrupted by slow-delta oscillations (0.1 to 4 Hz) at high doses. Ketamine's primary molecular targets and its oscillatory dynamics have been characterized. However, how the actions of ketamine at the subcellular level give rise to the oscillatory dynamics observed at the network level remains unknown. By developing a biophysical model of cortical circuits, we demonstrate how NMDA-receptor antagonism by ketamine can produce the oscillatory dynamics observed in human EEG recordings and nonhuman primate local field potential recordings. We have identified how impaired NMDA-receptor kinetics can cause disinhibition in neuronal circuits and how a disinhibited interaction between NMDA-receptor-mediated excitation and GABA-receptor-mediated inhibition can produce gamma oscillations at high and low doses, and slow-delta oscillations at high doses. Our work uncovers general mechanisms for generating oscillatory brain dynamics that differs from ones previously reported and provides important insights into ketamine's mechanisms of action as an anesthetic and as a therapy for treatment-resistant depression.

Spatio-temporal electroencephalographic power distribution in experimental pigs receiving propofol

INTRODUCTION

When assessing the spatio-temporal distribution of electroencephalographic (EEG) activity, characteristic patterns have been identified for several anesthetic drugs in humans. A shift in EEG power from the occipital to the prefrontal regions has been widely observed during anesthesia induction. This has been called "anteriorization" and has been correlated with loss of consciousness in humans. The spatio-temporal distribution of EEG spectral power in pigs and its modulation by anesthetics have not been described previously. The aim of the present study was to analyze EEG power across an anterior-posterior axis in pigs receiving increasing doses of propofol to 1) characterize the region of highest EEG power during wakefulness, 2) depict its spatio-temporal modification during propofol infusion, and 3) determine the region demonstrating the most significant modulations across different doses administered.

MATERIALS AND METHODS

Six pigs with a body weight of 33.3 ± 3.6 kg and aged 11.3 ± 0.5 weeks were included in a prospective experimental study. Electroencephalographic activity was collected at the occipital, parietal and prefrontal regions at increasing doses of propofol (starting at 10 mg kg-1 h-1 and increasing it by 10 mg kg-1 h-1 every 15 minutes). The EEG power was assessed using a generalized linear mixed model in which propofol doses and regions were treated as fixed effects, whereas pig was used as a random effect. Pairwise comparisons of marginal linear predictions were used to assess the change in power when the specific propofol dose (or region) was considered.

RESULTS

During both wakefulness and propofol infusion, the highest EEG power was located in the prefrontal region (p<0.001). The EEG power, both total and for each frequency band, mostly followed the same pattern, increasing from awake until propofol 20 mg kg-1 h-1 and then decreasing at propofol 30 mg kg-1 h-1. The region showing the strongest differences in EEG power across propofol doses was the prefrontal.

CONCLUSION

In juvenile pigs receiving increasing doses of propofol, the prefrontal region showed the highest EEG power both during wakefulness and propofol administration and was the area in which the largest frequency-band specific variations were observed across different anesthetic doses. The assessment of the spectral EEG activity at this region could be favorable to distinguish DoA levels in pigs.

Personalized anesthesia and precision medicine: a comprehensive review of genetic factors, artificial intelligence, and patient-specific factors

Precision medicine, characterized by the personalized integration of a patient's genetic blueprint and clinical history, represents a dynamic paradigm in healthcare evolution. The emerging field of personalized anesthesia is at the intersection of genetics and anesthesiology, where anesthetic care will be tailored to an individual's genetic make-up, comorbidities and patient-specific factors. Genomics and biomarkers can provide more accurate anesthetic protocols, while artificial intelligence can simplify anesthetic procedures and reduce anesthetic risks, and real-time monitoring tools can improve perioperative safety and efficacy. The aim of this paper is to present and summarize the applications of these related fields in anesthesiology by reviewing them, exploring the potential of advanced technologies in the implementation and development of personalized anesthesia, realizing the future integration of new technologies into clinical practice, and promoting multidisciplinary collaboration between anesthesiology and disciplines such as genomics and artificial intelligence.

Substance specific EEG patterns in mice undergoing slow anesthesia induction

The exact mechanisms and the neural circuits involved in anesthesia induced unconsciousness are still not fully understood. To elucidate them valid animal models are necessary. Since the most commonly used species in neuroscience are mice, we established a murine model for commonly used anesthetics/sedatives and evaluated the epidural electroencephalographic (EEG) patterns during slow anesthesia induction and emergence. Forty-four mice underwent surgery in which we inserted a central venous catheter and implanted nine intracranial electrodes above the prefrontal, motor, sensory, and visual cortex. After at least one week of recovery, mice were anesthetized either by inhalational sevoflurane or intravenous propofol, ketamine, or dexmedetomidine. We evaluated the loss and return of righting reflex (LORR/RORR) and recorded the electrocorticogram. For spectral analysis we focused on the prefrontal and visual cortex. In addition to analyzing the power spectral density at specific time points we evaluated the changes in the spectral power distribution longitudinally. The median time to LORR after start anesthesia ranged from 1080 [1st quartile: 960; 3rd quartile: 1080]s under sevoflurane anesthesia to 1541 [1455; 1890]s with ketamine. Around LORR sevoflurane as well as propofol induced a decrease in the theta/alpha band and an increase in the beta/gamma band. Dexmedetomidine infusion resulted in a shift towards lower frequencies with an increase in the delta range. Ketamine induced stronger activity in the higher frequencies. Our results showed substance-specific changes in EEG patterns during slow anesthesia induction. These patterns were partially identical to previous observations in humans, but also included significant differences, especially in the low frequencies. Our study emphasizes strengths and limitations of murine models in neuroscience and provides an important basis for future studies investigating complex neurophysiological mechanisms.

Assessment of sedation by automated pupillometry in critically ill patients: a prospective observational study

BACKGROUND

Quantitative measurement of pupil change has not been assessed against the Richmond Agitation and Sedation Scale (RASS) and spectral edge frequency (SEF) during sedation. The aim of this study was to evaluate pupillometry against these measures in sedated critically ill adult patients.

METHODS

In ventilated and sedated patients, pupillary variables were measured by automated pupillometry at each RASS level from -5 to 0 after discontinuation of hypnotics, while processed electroencephalogram variables were displayed continuously and SEF was recorded at each RASS level. Correlations were made between percentage pupillary light reflex (%PLR) and RASS, and between %PLR and SEF. The ability of %PLR to differentiate light sedation (RASS ≥-2), moderate (RASS =-3), and deep sedation (RASS ≤-4) was assessed by areas under receiver operating characteristic (ROC) curves.

RESULTS

A total of 163 paired measurements were recorded in 38 patients. With decreasing sedation depth, median %PLR increased progressively from 20% (interquartile range 17-25%) to 36% (interquartile range 33-40%) (P<0.001). Strong correlations were found between %PLR and RASS (Rho=0.635) and between %PLR and SEF (R=0.641). Area under the curve (AUC) of 0.87 with a %PLR threshold of 28% differentiated moderate/light sedation from deep sedation with sensitivity of 83% and specificity of 83%. An AUC of 0.82 with a threshold of 31% distinguished light sedation from moderate/deep sedation with a sensitivity of 81% and a specificity of 75%.

CONCLUSIONS

Quantitative assessment of %PLR correlates with other indicators of sedation depth in critically ill patients.

The Association of Preoperative Diabetes With Postoperative Delirium in Older Patients Undergoing Major Orthopedic Surgery: A Prospective Matched Cohort Study

BACKGROUND

Postoperative delirium (POD) is a common form of postoperative brain dysfunction, especially in the elderly. However, its risk factors remain largely to be determined. This study aimed to investigate whether (1) preoperative diabetes is associated with POD after elective orthopedic surgery and (2) intraoperative frontal alpha power is a mediator of the association between preoperative diabetes and POD.

METHODS

This was a prospective matched cohort study of patients aged 60 years or more, with a preoperative diabetes who underwent elective orthopedic surgery. Nondiabetic patients were matched 1:1 to diabetic patients in terms of age, sex, and type of surgery. Primary outcome was occurrence of POD, assessed using the 3-minute Diagnostic Confusion Assessment Method (3D-CAM) once daily from 6 pm to 8 pm during the postoperative days 1-7 or until discharge. Secondary outcome was the severity of POD which was assessed for all participants using the short form of the CAM-Severity. Frontal electroencephalogram (EEG) was recorded starting before induction of anesthesia and lasting until discharge from the operating room. Intraoperative alpha power was calculated using multitaper spectral analyses. Mediation analysis was used to estimate the proportion of the association between preoperative diabetes and POD that could be explained by intraoperative alpha power.

RESULTS

A total of 138 pairs of eligible patients successfully matched 1:1. After enrollment, 6 patients in the diabetes group and 4 patients in the nondiabetes group were excluded due to unavailability of raw EEG data. The final analysis included 132 participants with preoperative diabetes and 134 participants without preoperative diabetes, with a median age of 68 years and 72.6% of patients were female. The incidence of POD was 16.7% (22/132) in patients with preoperative diabetes vs 6.0% (8/134) in patients without preoperative diabetes. Preoperative diabetes was associated with increased odds of POD after adjustment of age, sex, body mass index, education level, hypertension, arrhythmia, coronary heart disease, and history of stroke (odds ratio, 3.2; 95% confidence interval [CI], 1.4-8.0; P = .009). The intraoperative alpha power accounted for an estimated 20% (95% CI, 2.6-60%; P = .021) of the association between diabetes and POD.

CONCLUSIONS

This study suggests that preoperative diabetes is associated with an increased risk of POD in older patients undergoing major orthopedic surgery, and that low intraoperative alpha power partially mediates such association.

Differential effects of sevoflurane and desflurane on frontal intraoperative electroencephalogram dynamics associated with postoperative delirium

STUDY OBJECTIVE

Intraoperative electroencephalogram (EEG) patterns associated with postoperative delirium (POD) development have been studied, but the differences in EEG recordings between sevoflurane- and desflurane-induced anesthesia have not been clarified. We aimed to distinguish the EEG characteristics of sevoflurane and desflurane in relation to POD development.

DESIGN AND PATIENTS

We collected frontal four-channel EEG data during the maintenance of anesthesia from 148 elderly patients who received sevoflurane (n = 77) or desflurane (n = 71); 30 patients were diagnosed with delirium postoperatively. The patients were divided into four subgroups based on anesthetics and delirium status: sevoflurane delirium (n = 17), sevoflurane non-delirium (n = 60), desflurane delirium (n = 13), and desflurane non-delirium (n = 58). We compared spectral power, coherence, and pairwise phase consistency (PPC) between sevoflurane and desflurane, and between non-delirium and delirium groups for each anesthetic.

MAIN RESULTS

In patients without POD, the sevoflurane non-delirium group exhibited higher EEG spectral power across 8.5-35 Hz (99.5% CI bootstrap analysis) and higher PPC from alpha to gamma bands (p < 0.005) compared to the desflurane non-delirium group. Conversely, in patients with POD, no significant EEG differences were observed between the sevoflurane and desflurane delirium groups. For the sevoflurane-induced patients, the sevoflurane delirium group had significantly lower power within 7.5-31.5 Hz (99.5% CI bootstrap analysis), reduced coherence over 8.9-23.8 Hz (99.5% CI bootstrap analysis), and lower PPC values in the alpha band (p < 0.005) compared with the sevoflurane non-delirium group. For the desflurane-induced patients, there were no significant differences in the EEG patterns between delirium and non-delirium groups.

CONCLUSIONS

In normal patients without POD, sevoflurane demonstrates a higher power spectrum and prefrontal connectivity than desflurane. Furthermore, reduced frontal alpha power, coherence, and connectivity of intraoperative EEG could be associated with an increased risk of POD. These intraoperative EEG characteristics associated with POD are more noticeable in sevoflurane-induced anesthesia than in desflurane-induced anesthesia.

Ketamine can produce oscillatory dynamics by engaging mechanisms dependent on the kinetics of NMDA receptors

Ketamine is an NMDA-receptor antagonist that produces sedation, analgesia and dissociation at low doses and profound unconsciousness with antinociception at high doses. At high and low doses, ketamine can generate gamma oscillations (>25 Hz) in the electroencephalogram (EEG). The gamma oscillations are interrupted by slow-delta oscillations (0.1-4 Hz) at high doses. Ketamine's primary molecular targets and its oscillatory dynamics have been characterized. However, how the actions of ketamine at the subcellular level give rise to the oscillatory dynamics observed at the network level remains unknown. By developing a biophysical model of cortical circuits, we demonstrate how NMDA-receptor antagonism by ketamine can produce the oscillatory dynamics observed in human EEG recordings and non-human primate local field potential recordings. We have discovered how impaired NMDA-receptor kinetics can cause disinhibition in neuronal circuits and how a disinhibited interaction between NMDA-receptor-mediated excitation and GABA-receptor-mediated inhibition can produce gamma oscillations at high and low doses, and slow-delta oscillations at high doses. Our work uncovers general mechanisms for generating oscillatory brain dynamics that differs from ones previously reported, and provides important insights into ketamine's mechanisms of action as an anesthetic and as a therapy for treatment-resistant depression.

Effect of Repeated Exposure to Sevoflurane on Electroencephalographic Alpha Oscillation in Pediatric Patients Undergoing Radiation Therapy: A Prospective Observational Study

BACKGROUND

Pharmacological tolerance is defined as a decrease in the effect of a drug over time, or the need to increase the dose to achieve the same effect. It has not been established whether repeated exposure to sevoflurane induces tolerance in children.

METHODS

We conducted an observational study in children younger than 6 years of age scheduled for multiple radiotherapy sessions with sevoflurane anesthesia. To evaluate the development of sevoflurane tolerance, we analyzed changes in electroencephalographic spectral power at induction, across sessions. We fitted individual and group-level linear regression models to evaluate the correlation between the outcomes and sessions. In addition, a linear mixed-effect model was used to evaluate the association between radiotherapy sessions and outcomes.

RESULTS

Eighteen children were included and the median number of radiotherapy sessions per child was 28 (interquartile range: 10 to 33). There was no correlation between induction time and radiotherapy sessions. At the group level, the linear mixed-effect model showed, in a subgroup of patients, that alpha relative power and spectral edge frequency 95 were inversely correlated with the number of anesthesia sessions. Nonetheless, this subgroup did not differ from the other subjects in terms of age, sex, or the total number of radiotherapy sessions.

CONCLUSIONS

Our results suggest that children undergoing repeated anesthesia exposure for radiotherapy do not develop tolerance to sevoflurane. However, we found that a group of patients exhibited a reduction in the alpha relative power as a function of anesthetic exposure. These results may have implications that justify further studies.

Closed-loop anesthesia: foundations and applications in contemporary perioperative medicine

A closed-loop automatically controls a variable using the principle of feedback. Automation within anesthesia typically aims to improve the stability of a controlled variable and reduce workload associated with simple repetitive tasks. This approach attempts to limit errors due to distractions or fatigue while simultaneously increasing compliance to evidence based perioperative protocols. The ultimate goal is to use these advantages over manual care to improve patient outcome. For more than twenty years, clinical studies in anesthesia have demonstrated the superiority of closed-loop systems compared to manual control for stabilizing a single variable, reducing practitioner workload, and safely administering therapies. This research has focused on various closed-loops that coupled inputs and outputs such as the processed electroencephalogram with propofol, blood pressure with vasopressors, and dynamic predictors of fluid responsiveness with fluid therapy. Recently, multiple simultaneous independent closed-loop systems have been tested in practice and one study has demonstrated a clinical benefit on postoperative cognitive dysfunction. Despite their advantages, these tools still require that a well-trained practitioner maintains situation awareness, understands how closed-loop systems react to each variable, and is ready to retake control if the closed-loop systems fail. In the future, multiple input multiple output closed-loop systems will control anesthetic, fluid and vasopressor titration and may perhaps integrate other key systems, such as the anesthesia machine. Human supervision will nonetheless always be indispensable as situation awareness, communication, and prediction of events remain irreplaceable human factors.

Electroencephalographic density spectral array monitoring during propofol/sevoflurane coadministration in children, an exploratory observational study

INTRODUCTION

Propofol and sevoflurane have a long history in pediatric anesthesia. Combining both drugs at low dose levels offers new opportunities. However, monitoring the hypnotic effects of this drug combination in children is challenging, because the currently available processed EEG-based systems are insufficiently validated in young children and the co-administration of anesthetics. This study investigated electroencephalographic density spectral array monitoring during propofol/sevoflurane coadministration with fixed sevoflurane- and variable propofol dosages.

PATIENTS AND METHODS

We analyzed the density spectral array pattern recorded during propofol/sevoflurane anesthesia in pediatric patients from birth to 11 years of age. Data from 78 patients were suitable for analysis. The primary outcome parameter of this study was the correlation between variable propofol dosages and the expression of the four electroencephalogram frequency bands β, α, θ, and δ. The main secondary outcome parameters were the intra-operative total EEG power and the prevalence of burst suppression.

RESULTS

In patients above the age of 1 year, a dose-dependent correlation between the propofol dosage and the relative percentage of β (-12.2%, p < 0.001) and δ (5.1%, p < 0.001) was found. There was an age-dependent trend toward increasing mean EEG power, with the most significant increase in the first year of life. In 14.1% of our patients, at least one episode of burst suppression occurred.

CONCLUSION

DSA-guided augmentation of propofol anesthesia with sevoflurane provides sufficient depth of anesthesia at doses usually considered sub-anesthetic in children, leading to less anesthetic drug exposure for the individual child.

Combined depth and scalp electroencephalographic monitoring in acute brain injury: Yield and prognostic value

BACKGROUND AND PURPOSE

Depth electroencephalography (dEEG) is an emerging neuromonitoring technology in acute brain injury (ABI). We aimed to explore the concordances between electrophysiological activities on dEEG and on scalp EEG (scEEG) in ABI patients.

METHODS

Consecutive ABI patients who received dEEG monitoring between 2018 and 2022 were included. Background, sporadic epileptiform discharges, rhythmic and periodic patterns (RPPs), electrographic seizures, brief potentially ictal rhythmic discharges, ictal-interictal continuum (IIC) patterns, and hourly RPP burden on dEEG and scEEG were compared.

RESULTS

Sixty-one ABI patients with a median dEEG monitoring duration of 114 h were included. dEEG significantly showed less continuous background (75% vs. 90%, p = 0.03), higher background amplitude (p < 0.001), more frequent rhythmic spike-and-waves (16% vs. 3%, p = 0.03), more IIC patterns (39% vs. 21%, p = 0.03), and greater hourly RPP burden (2430 vs. 1090 s/h, p = 0.01), when compared to scEEG. Among five patients with seizures on scEEG, one patient had concomitant seizures on dEEG, one had periodic discharges (not concomitant) on dEEG, and three had no RPPs on dEEG. Features and temporal occurrence of electrophysiological activities observed on dEEG and scEEG are not strongly associated. Patients with seizures and IIC patterns on dEEG seemed to have a higher rate of poor outcomes at discharge than patients without these patterns on dEEG (42% vs. 25%, p = 0.37).

CONCLUSIONS

dEEG can detect abnormal electrophysiological activities that may not be seen on scEEG and can be used as a complement in the neuromonitoring of ABI patients.

Alpha anteriorization and theta posteriorization during deep sleep

Brain states (wake, sleep, general anesthesia, etc.) are profoundly associated with the spatiotemporal dynamics of brain oscillations. Previous studies showed that the EEG alpha power shifted from the occipital cortex to the frontal cortex (alpha anteriorization) after being induced into a state of general anesthesia via propofol. The sleep research literature suggests that slow waves and sleep spindles are generated locally and propagated gradually to different brain regions. Since sleep and general anesthesia are conceptualized under the same framework of consciousness, the present study examines whether alpha anteriorization similarly occurs during sleep and how the EEG power in other frequency bands changes during different sleep stages. The results from the analysis of three polysomnography datasets of 234 participants show consistent alpha anteriorization during the sleep stages N2 and N3, beta anteriorization during stage REM, and theta posteriorization during stages N2 and N3. Although it is known that the neural circuits responsible for sleep are not exactly the same for general anesthesia, the findings of alpha anteriorization in this study suggest that, at macro level, the circuits for alpha oscillations are organized in the similar cortical areas. The spatial shifts of EEG power in different frequency bands during sleep may offer meaningful neurophysiological markers for the level of consciousness.

Support-vector classification of low-dose nitrous oxide administration with multi-channel EEG power spectra

Support-vector machines (SVMs) can potentially improve patient monitoring during nitrous oxide anaesthesia. By elucidating the effects of low-dose nitrous oxide on the power spectra of multi-channel EEG recordings, we quantified the degree to which these effects generalise across participants. In this single-blind, cross-over study, 32-channel EEG was recorded from 12 healthy participants exposed to 0, 20, 30 and 40% end-tidal nitrous oxide. Features of the delta-, theta-, alpha- and beta-band power were used within a 12-fold, participant-wise cross-validation framework to train and test two SVMs: (1) binary SVM classifying EEG during 0 or 40% exposure (chance = 50%); (2) multi-class SVM classifying EEG during 0, 20, 30 or 40% exposure (chance = 25%). Both the binary (accuracy 92%) and the multi-class (accuracy 52%) SVMs classified EEG recordings at rates significantly better than chance (p < 0.001 and p = 0.01, respectively). To determine the relative importance of frequency band features for classification accuracy, we systematically removed features before re-training and re-testing the SVMs. This showed the relative importance of decreased delta power and the frontal region. SVM classification identified that the most important effects of nitrous oxide were found in the delta band in the frontal electrodes that was consistent between participants. Furthermore, support-vector classification of nitrous oxide dosage is a promising method that might be used to improve patient monitoring during nitrous oxide anaesthesia.