The relationship of bispectral index values to conscious state: an analysis of two volunteer cohort studies

BACKGROUND

The ability of current depth-of-anaesthesia monitors to differentiate subtle changes in the conscious state has not been well characterised. We examine the variability in bispectral index (BIS) scores associated with disconnected conscious and unconscious states as confirmed by a novel serial awakening paradigm.

METHODS

Seventy adult participants, given propofol or dexmedetomidine, had a cumulative 1381 electroencephalographic (EEG) recordings across two centres. Participants were awakened periodically, and their recent conscious experience interrogated by structured questioning. BIS were reconstructed from EEG using openibis, and the distribution of BIS scores were compared using linear mixed effects modelling. The predictive capacity of BIS across states of consciousness was also examined.

RESULTS

Reconstructed BIS scores correlated significantly with blood concentrations of propofol and dexmedetomidine (all P<0.001). However, while the average BIS was different between baseline wakefulness (mean BIS=95.1 [standard deviation=3.5]); connected consciousness with drug present (84.0 [10.9]); disconnected consciousness (70.0 [16.9]); and unconsciousness (68.1 [16.1]), the interquartile range of these states (3.6, 15.1, 23.3 and 26.8, respectively) indicated high degrees of overlap and individual variability. Connected consciousness could be differentiated from either disconnected consciousness or unconsciousness with 86% accuracy (i.e. 14% error rate), and disconnected consciousness differentiated from unconsciousness with 74% accuracy.

CONCLUSIONS

These results agree with previous studies that BIS scores fail to reliably differentiate between states of consciousness, exacerbated by segregating connected, disconnected, and unconscious states. To develop a method that reliably identifies the conscious state of an individual (not an average), work is needed to establish the causal mechanisms of disconnection and unconsciousness.

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.

Relationships between the qNOX, qCON, burst suppression ratio, and muscle activity index of the CONOX monitor during total intravenous anesthesia: a pilot study

BACKGROUND

Processed electroencephalographic (EEG) indices can help to navigate general anesthesia. The CONOX (Fresenius Kabi) calculates two indices, the qCON (hypnotic level) and the qNOX (nociception). The CONOX also calculates indices for electromyographic (EMG) activity and EEG burst suppression (BSR). Because all EEG parameters seem to influence each other, our goal was a detailed description of parameter relationships.

METHODS

We used qCON, qNOX, EMG, and BSR information from 14 patients receiving propofol anesthesia. We described index relationships with linear models, heat maps, and box plot representations. We also evaluated associations between qCON/qNOX and propofol/remifentanil effect site concentrations (ceP/ceR).

RESULTS

qNOX and qCON (qCON = 0.79*qNOX + 5.8; p < 0.001; R2 = 0.84) had a strong linear association. We further confirmed the strong relationship between qCON/qNOX and BSR for qCON/qNOX < 25: qCON=-0.19*BSR + 25.6 (p < 0.001; R2 = 0.72); qNOX=-0.20*BSR + 26.2 (p < 0.001; R2 = 0.72). The relationship between qCON and EMG was strong at higher indices: qCON = 0.55*EMG + 33.0 (p < 0.001; R2 = 0.68). There was no qCON > 80 without EMG > 0. The relationship between ceP and qCON was qCON=-3.8*ceP + 70.6 (p < 0.001; R2 = 0.11). The heat maps also suggest that the qCON and qNOX can at least partially separate the hypnotic and analgetic components of anesthesia.

CONCLUSION

We could describe relationships between qCON, qNOX, EMG, BSR, ceP, and ceR, which may help the anaesthesiologist better interpret the information provided. One major finding is the dependence of qCON > 80 on EMG activity. This may limit the possibility of detecting wakefulness in the absence of EMG. Further, qNOX seems generally higher than qCON, but high opioid doses may lead to higher qCON than qNOX indices.

Overcoming age: Slow anesthesia induction may prevent geriatric patients from developing burst suppression and help developing intraoperative EEG signatures of a younger brain

Elderly patients are prone to develop postoperative neurocognitive deficits potentially precipitated by inadequate anesthetic management. To investigate the potential of EEG-guided individualized anesthetic titration we evaluated the effect of the patient's age on the spectral composition of the EEG during slow propofol induction. Twenty-six young (<65 years) and 25 old (≥65 years) patients received propofol until loss of responsiveness (LOR). After LOR, we switched from a flow rate-based to a target-controlled infusion mode keeping the calculated effect-site concentration at LOR stable. We recorded a frontal EEG and calculated the power spectral density (PSD) and the band powers. For the comparison of the spectral composition of old and young patients, we used an effect size, the area under the receiver operating characteristic curve. The older patients received significantly less propofol (p < 0.001). No patient showed a burst suppression pattern. Whereas the absolute power in all frequency bands decreased significantly with the patient's age, the spectral composition did not change throughout the extended induction period. Slow anesthesia induction may be a suitable approach for geriatric patients to preserve spectral composition patterns typically found in younger brains and to individually identify anesthetic requirements reducing the risk of excessive anesthetic effects.

Depth of anesthesia monitoring: an argument for its use for patient safety

PURPOSE OF REVIEW

There have been significant advancements in depth of anesthesia (DoA) technology. The Anesthesia Patient Safety Foundation recently published recommendations to use a DoA monitor in specific patient populations receiving general anesthesia. However, the universal use of DoA monitoring is not yet accepted. This review explores the current state of DoA monitors and their potential impact on patient safety.

RECENT FINDINGS

We reviewed the current evidence for using a DoA monitor and its potential role in preventing awareness and preserving brain health by decreasing the incidence of postoperative delirium and postoperative cognitive dysfunction or decline (POCD). We also explored the evidence for use of DoA monitors in improving postoperative clinical indicators such as organ dysfunction, mortality and length of stay. We discuss the use of DoA monitoring in the pediatric population, as well as highlight the current limitations of DoA monitoring and the path forward.

SUMMARY

There is evidence that DoA monitoring may decrease the incidence of awareness, postoperative delirium, POCD and improve several postoperative outcomes. In children, DoA monitoring may decrease the incidence of awareness and emergence delirium, but long-term effects are unknown. While there are key limitations to DoA monitoring technology, we argue that DoA monitoring shows great promise in improving patient safety in most, if not all anesthetic populations.

Aperiodic component of the electroencephalogram power spectrum reflects the hypnotic level of anaesthesia

BACKGROUND

Aperiodic (nonoscillatory) electroencephalogram (EEG) activity can be characterised by its power spectral density, which decays according to an inverse power law. Previous studies reported a shift in the spectral exponent α from consciousness to unconsciousness. We investigated the impact of aperiodic EEG activity on parameters used for anaesthesia monitoring to test the hypothesis that aperiodic EEG activity carries information about the hypnotic component of general anaesthesia.

METHODS

We used simulated noise with varying inverse power law exponents α and the aperiodic component of EEGs recorded during wakefulness (n=62) and maintenance of general anaesthesia (n=125) in a diverse sample of surgical patients receiving sevoflurane, desflurane, or propofol, extracted using the Fitting Oscillations and One-Over-F algorithm. Four spectral EEG parameters (beta ratio, spectral edge frequency 95, spectral entropy, and alpha-to-delta ratio) and two time-series parameters (approximate [ApEn] and permutation entropy [PeEn]) were calculated from the simulated signals and human EEG data. Performance in distinguishing between consciousness and unconsciousness was evaluated with AUC values.

RESULTS

We observed an increase in the spectral exponent from consciousness to unconsciousness (AUC=0.98 (0.94-1)). The spectral parameters exhibited linear or nonlinear responses to changes in α. Using aperiodic EEG activity instead of the entire spectrum for spectral parameter calculation improved the separation between consciousness and unconsciousness for all parameters (AUCaperiodic=0.98 (0.94-1.00) vs AUCoriginal=0.71 (0.62-0.79) to AUCoriginal=0.95 (0.92-0.98)) up to the level of ApEn (AUC=0.96 (0.93-0.98)) and PeEn (AUC=0.94 (0.90-0.97)).

CONCLUSIONS

Aperiodic EEG activity could improve discrimination between consciousness and unconsciousness using spectral analyses.

Continuity with caveats in anesthesia: state and response entropy of the EEG

The growing use of neuromonitoring in general anesthesia provides detailed insights into the effects of anesthetics on the brain. Our study focuses on the processed EEG indices State Entropy (SE), Response Entropy (RE), and Burst Suppression Ratio (BSR) of the GE EntropyTM Module, which serve as surrogate measures for estimating the level of anesthesia. While retrospectively analyzing SE and RE index values from patient records, we encountered a technical anomaly with a conspicuous distribution of index values. In this single-center, retrospective study, we analyzed processed intraoperative electroencephalographic (EEG) data from 15,608 patients who underwent general anesthesia. We employed various data visualization techniques, including histograms and heat maps, and fitted custom non-Gaussian curves. Individual patients' anesthetic periods were evaluated in detail. To compare distributions, we utilized the Kolmogorov-Smirnov test and Kullback-Leibler divergence. The analysis also included the influence of the BSR on the distribution of SE and RE values. We identified distinct pillar indices for both SE and RE, i.e., index values with a higher probability of occurrence than others. These pillar index values were not age-dependent and followed a non-equidistant distribution pattern. This phenomenon occurs independently of the BSR distribution. SE and RE index values do not adhere to a continuous distribution, instead displaying prominent pillar indices with a consistent pattern of occurrence across all age groups. The specific features of the underlying algorithm responsible for this pattern remain elusive.

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.

Does Cognitive Load Affect Measures of Consciousness?

BACKGROUND

Developing and testing methods for reliably measuring the state of consciousness of individuals is important for both basic research and clinical purposes. In recent years, several promising measures of consciousness, grounded in theoretical developments, have been proposed. However, the degrees to which these measures are affected by changes in brain activity that are not related to changes in the degree of consciousness has not been well tested. In this study, we examined whether several of these measures are modulated by the loading of cognitive resources.

METHODS

We recorded electroencephalography (EEG) from 12 participants in two conditions: (1) while passively attending to sensory stimuli related to the measures and (2) during increased cognitive load consisting of a demanding working memory task. We investigated whether a set of proposed objective EEG-based measures of consciousness differed between the passive and the cognitively demanding conditions.

RESULTS

The P300b event-related potential (sensitive to conscious awareness of deviance from an expected pattern in auditory stimuli) was significantly affected by concurrent performance on a working memory task, whereas various measures based on signal diversity of spontaneous and perturbed EEG were not.

CONCLUSION

Because signal diversity-based measures of spontaneous or perturbed EEG are not sensitive to the degree of cognitive load, we suggest that these measures may be used in clinical situations where attention, sensory processing, or command following might be impaired.

Assessing pain in paralyzed critically ill patients receiving neuromuscular blocking agents: A monocenter prospective cohort

INTRODUCTION

Given the absence of established recommendations for pain assessment in pharmacologically paralyzed Intensive-Care-Units (ICU) patients under Neuro-Muscular-Blocking Agents (NMBA), this study assessed the validity of various parameters for evaluating pain in this specific population.

PATIENTS AND METHODS

Four electrophysiological parameters (instant-Analgesia-Nociception-Index (ANI), Bispectral index (BIS), Heart Rate (HR) and Mean Arterial Blood Pressure (ABP)) and one clinical parameter (Behavioural-Pain-Scale (BPS)) were recorded during tracheal-suctioning in all consecutive ICU patients who required a continuous infusion of cisatracurium, before and just after paralysis recovery measured by Train-of-Four ratio. The validity of the five pain-related parameters was assessed by comparing the values recorded during different situations (before/during/after the nociceptive procedure) (discriminant-validity, primary outcome), and the effect of paralysis was assessed by comparing values obtained during and after paralysis (reliability, secondary outcome).

RESULTS

Twenty patients were analyzed. ANI, BIS, and HR significantly changed during the nociceptive procedure in both paralysis and recovery, while BPS changed only post-recovery. ANI and HR were unaffected by paralysis, unlike BIS and BPS (mixed-effect model). ANI exhibited the highest discriminant-validity, with values (min 0/max 100) decreasing from 71 [48-89] at rest to 41 [25-72] during tracheal suctioning in paralyzed patients, and from 71 [53-85] at rest to 40 [31-52] in non-paralyzed patients.

CONCLUSIONS

ANI proves the most discriminant parameter for pain detection in both paralyzed and non-paralyzed sedated ICU patients. Its significant and clinically relevant decrease during tracheal suctioning remains unaltered by NMBA use. Pending further studies on analgesia protocols based on ANI, it could be used to assess pain during nociceptive procedures in ICU patients receiving NMBA.

Alternative sensor montage for Index based EEG monitoring. A systematic review

The main objective of this systematic review is to assess the reliability of alternative positions of processed electroencephalogram sensors for depth of anesthesia monitoring and its applicability in clinical practice. A systematic search was conducted in PubMed, Embase, Cochrane Library, Clinical trial.gov in accordance with reporting guidelines of PRISMA statement together with the following sources: Google and Google Scholar. We considered eligible prospective studies, written in the English language. The last search was run on the August 2023. Risk of bias and quality assessment were performed. Data extraction was performed by two authors and results were synthesized narratively owing to the heterogeneity of the included studies. Thirteen prospective observational studies (438 patients) were included in the systematic review after the final assessment, with significant diversity in study design. Most studies had a low risk of bias but due to lack of information in one key domain of bias (Bias due to missing data) the overall judgement would be No Information. However, there is no clear indication that the studies are at serious or critical risk of bias. Bearing in mind, the heterogeneity and small sample size of the included studies, current evidence suggests that the alternative infraorbital sensor position is the most comparable for clinical use when the standard sensor position in the forehead is not possible.

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.

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.

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.

An in-depth analysis of parameter settings and probability distributions of specific ordinal patterns in the Shannon permutation entropy during different states of consciousness in humans

As electrical activity in the brain has complex and dynamic properties, the complexity measure permutation entropy (PeEn) has proven itself to reliably distinguish consciousness states recorded by the EEG. However, it has been shown that the focus on specific ordinal patterns instead of all of them produced similar results. Moreover, parameter settings influence the resulting PeEn value. We evaluated the impact of the embedding dimension m and the length of the EEG segment on the resulting PeEn. Moreover, we analysed the probability distributions of monotonous and non-occurring ordinal patterns in different parameter settings. We based our analyses on simulated data as well as on EEG recordings from volunteers, obtained during stable anaesthesia levels at defined, individualised concentrations. The results of the analysis on the simulated data show a dependence of PeEn on different influencing factors such as window length and embedding dimension. With the EEG data, we demonstrated that the probability P of monotonous patterns performs like PeEn in lower embedding dimension (m = 3, AUC = 0.88, [0.7, 1] in both), whereas the probability P of non-occurring patterns outperforms both methods in higher embedding dimensions (m = 5, PeEn: AUC = 0.91, [0.77, 1]; P(non-occurring patterns): AUC = 1, [1, 1]). We showed that the accuracy of PeEn in distinguishing consciousness states changes with different parameter settings. Furthermore, we demonstrated that for the purpose of separating wake from anaesthesia EEG solely pieces of information used for PeEn calculation, i.e., the probability of monotonous patterns or the number of non-occurring patterns may be equally functional.

Bispectral Index Changes Following Boluses of Commonly Used Intravenous Medications During Volatile Anesthesia Identified From Retrospective Data

BACKGROUND

Although patients are commonly monitored for depth of anesthesia, it is unclear to what extent administration of intravenous anesthetic medications may affect calculated bispectral (BIS) index values under general anesthesia.

METHODS

In a retrospective analysis of electronic anesthesia records from an academic medical center, we examined BIS index changes associated with 14 different intravenous medications, as administered in routine practice, during volatile-based anesthesia using a novel screening approach. Discrete-time windows were identified in which only a single drug bolus was administered, and subsequent changes in the BIS index, concentration of volatile anesthetic, and arterial pressure were analyzed. Our primary outcome was change in BIS index, following drug administration. Adjusted 95% confidence intervals were compared to predetermined thresholds for clinical significance. Secondary sensitivity analyses examined the same outcomes, with available data separated according to differences in baseline volatile anesthetic concentrations, doses of the administered medications, and length of time window.

RESULTS

The study cohort was comprised of data from 20,170 distinct cases, 54.7% of patients were men, with a median age of 55. In the primary analysis, ketamine at a median dose of 20 mg was associated with a median (confidence limits) increase in BIS index of 3.8 (2.5-5.0). Midazolam (median dose 2 mg) was associated with a median decrease in BIS index of 3.0 (1.5-4.5). Neither of these drug administrations occurred during time periods associated with changes in volatile anesthetic concentration. Analysis for dexmedetomidine was confounded by concomitant decreases in volatile anesthetic concentration. No other medication analyzed, including propofol and common opioids, was associated with a significant change in BIS index. Secondary analyses revealed that similar BIS index changes occurred when midazolam and ketamine were administered at different volatile anesthetic concentrations and different doses, and these changes persisted 11 to 20 minutes postadministration.

CONCLUSIONS

Modest, but persistent changes in BIS index occurred following doses of ketamine (increase) and midazolam (decrease) during periods of stable volatile anesthetic administration.

Sedation for Patients with Sepsis: Towards a Personalised Approach

This article looks at the challenges of sedoanalgesia for sepsis patients, and argues for a personalised approach. Sedation is a necessary part of treatment for patients in intensive care to reduce stress and anxiety and improve long-term prognoses. Sepsis patients present particular difficulties as they are at increased risk of a wide range of complications, such as multiple organ failure, neurological dysfunction, septic shock, ARDS, abdominal compartment syndrome, vasoplegic syndrome, and myocardial dysfunction. The development of any one of these complications can cause the patient's rapid deterioration, and each has distinct implications in terms of appropriate and safe forms of sedation. In this way, the present article reviews the sedative and analgesic drugs commonly used in the ICU and, placing special emphasis on their strategic administration in sepsis patients, develops a set of proposals for sedoanalgesia aimed at improving outcomes for this group of patients. These proposals represent a move away from simplistic approaches like avoiding benzodiazepines to more "objective-guided sedation" that accounts for a patient's principal pathology, as well as any comorbidities, and takes full advantage of the therapeutic arsenal currently available to achieve personalised, patient-centred treatment goals.

Pro-Con Debate: Electroencephalography-Guided Anesthesia for Reducing Postoperative Delirium

Postoperative delirium (POD) has significant implications on morbidity, mortality, and health care expenditures. Monitoring electroencephalography (EEG) to adjust anesthetic management has gained interest as a strategy to mitigate POD. In this Pro-Con commentary article, the pro side supports the use of EEG to reduce POD, citing an empiric reduction in POD with processed EEG (pEEG)-guided general anesthesia found in several studies and recent meta-analysis. The Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) trial is the exception to this, and issues with methods and achieved depths are discussed. Meanwhile, the Con side advocates that the use of EEG to reduce POD is not yet certain, citing that there is a lack of evidence that associations between anesthetic depth and POD represent causal relationships. The Con side also contends that the ideal EEG signatures to guide anesthetic titration are currently unknown, and the potential benefits of reduced anesthesia levels may be outweighed by the risks of potentially insufficient anesthetic administration. As the public health burden of POD increases, anesthesia clinicians will be tasked to consider interventions to mitigate risk such as EEG. This Pro-Con debate will provide 2 perspectives on the evidence and rationales for using EEG to mitigate POD.

Response of the GE Entropy™ monitor to neuromuscular block in awake volunteers

BACKGROUND

The GE Entropy™ monitor analyses the frontal electroencephalogram (EEG) and generates two indices intended to represent the degree of anaesthetic drug effect on the brain. It is frequently used in the context of neuromuscular block. We have shown that a similar device, the Bispectral Index monitor (BIS), does not generate correct values in awake volunteers when neuromuscular blocking drugs are administered.

METHODS

We replayed the EEGs recorded during awake paralysis from the original study to an Entropy monitor via a calibrated electronic playback system. Each EEG was replayed 30 times to evaluate the consistency of the Entropy output.

RESULTS

Both State Entropy and Response Entropy decreased during periods of neuromuscular block to values consistent with anaesthesia, despite there being no change in conscious state (State Entropy <60 in eight of nine rocuronium trials and nine of 10 suxamethonium trials). Entropy values did not return to pre-test levels until after the return of movement. Entropy did not generate exactly the same results when the same EEG was replayed multiple times, which is primarily because of a cyclical state within the Entropy system itself.

CONCLUSIONS

The GE Entropy™ monitor requires muscle activity to generate correct values in an awake subject. It could therefore be unreliable at detecting awareness in patients who have been given neuromuscular blocking drugs. In addition, Entropy does not generate the same result each time it is presented with the same EEG.

Performance of the SEDLine Monitor: Age Dependency and Time Delay

BACKGROUND

Devices monitoring the hypnotic component of general anesthesia can help to guide anesthetic management. The main purposes of these devices are the titration of anesthesia dose. While anesthesia at low doses can result in awareness with intraoperative memory formation, excessive administration of anesthetics may be associated with an increased risk of postoperative neurocognitive disorder. We have previously shown for various indices that they are significantly influenced by the patient's age and that the monitors have a significant time delay. Here, we evaluated the influence of patient's age and time delay on the patient state index (PSI) of the SEDLine monitor.

METHODS

To analyze the influence of the patient's age, we replayed 2 minutes of electroencephalography (EEG) of 141 patients (19-88 years, ASA I-IV) undergoing general anesthesia maintained with desflurane, sevoflurane, or propofol to the SEDLine monitor. We extracted the PSI as well as the spectral edge frequency (SEF) and performed a linear regression analysis. For evaluation of the time delay, we replayed 5 minutes of EEG of stable episodes of adequate anesthesia (PSI between 25 and 50) or light sedation/wake (PSI >70) in different orders to the SEDLine to simulate sudden changes between the states. Time delays were defined as the required time span of the monitor to reach the stable target index.

RESULTS

PSI and SEF increased significantly with the patient's age. These findings did not depend on the administered anesthetic. The evaluation of the correlation between SEF and PSI showed a strong correlation with Spearman's correlation coefficient of ρ = 0.86 (0.82; 0.89). The time delays depended on the type of transition. We found a median time delay of 54 (Min: 46; Max: 61) seconds for the important transition between adequate anesthesia and awake and 55 (Min: 50; Max: 67) seconds in the other direction.

CONCLUSIONS

With our analyses, we show that the indices presented on the SEDLine display, the PSI and the SEF, increase with age for patients under general anesthesia. Additionally, a delay of the PSI to react to sudden neurophysiologic changes due to dose of the maintenance anesthetic is of a time course that is clinically significant. These factors should be considered when navigating anesthesia relying on only the proprietary index for the SEDLine monitor.

Effect of sugammadex on processed EEG parameters in patients undergoing robot-assisted radical prostatectomy

BACKGROUND

Sugammadex has been associated with increases in the bispectral index (BIS). We evaluated the effects of sugammadex administration on quantitative electroencephalographic (EEG) and electromyographic (EMG) measures.

METHODS

We performed a prospective observational study of adult male patients undergoing robot-assisted radical prostatectomy. All patients received a sevoflurane-based general anaesthetic and a continuous infusion of rocuronium, which was reversed with 2 mg kg-1 of sugammadex i.v. BIS, EEG, and EMG measures were captured with the BIS Vista™ monitor.

RESULTS

Twenty-five patients were included in this study. Compared with baseline, BIS increased at 4-6 min (β coefficient: 3.63; 95% confidence interval [CI]: 2.22-5.04; P<0.001), spectral edge frequency 95 (SEF95) increased at 2-4 min (β coefficient: 0.29; 95% CI: 0.05-0.52; P=0.016) and 4-6 min (β coefficient: 0.71; 95% CI: 0.47-0.94; P<0.001), and EMG increased at 4-6 min (β coefficient: 1.91; 95% CI: 1.00-2.81; P<0.001) after sugammadex administration. Compared with baseline, increased beta power was observed at 2-4 min (β coefficient: 93; 95% CI: 1-185; P=0.046) and 4-6 min (β coefficient: 208; 95% CI: 116-300; P<0.001), and decreased delta power was observed at 4-6 min (β coefficient: -526.72; 95% CI: -778 to -276; P<0.001) after sugammadex administration. Neither SEF95 nor frequency band data analysis adjusted for EMG showed substantial differences. None of the patients showed clinical signs of awakening.

CONCLUSIONS

After neuromuscular block reversal with 2 mg kg-1 sugammadex, BIS, SEF95, EMG, and beta power showed small but statistically significant increases over time, while delta power decreased.

[Processed EEG for personalized dosing of anesthetics during general anesthesia]

Electroencephalogram (EEG)-guided anesthesia is indispensable in modern operating rooms and has become established as the standard form of monitoring. Many anesthesiologists rely on processed EEG indices in the hope of averting anesthesia-related complications, such as intraoperative awareness, postoperative delirium and other cognitive complications in their patients. This educational review aims to provide information on the five most prevalent monitors used to guide depth of sedation during general anesthesia. This article elucidates the principles underpinning the application of these monitors where known, which are generally based on power in various EEG frequency bands and on the burst suppression pattern. Convinced that EEG-guided anesthesia has the potential of benefitting many surgical patients, it is felt that many basic principles and shortcomings of processed EEG indices need to be better understood in the clinical practice. After discussing the different monitors and clinically relevant data from the literature, the article gives a short practical guidance on how to critically interpret processed EEG information and troubleshooting of confounded indices in the context of clinical situations.

A Pilot Investigation Evaluating Relative Changes in Fronto-Occipital Alpha and Beta Spectral Power as Measurement of Anesthesia Hypnotic Depth

BACKGROUND

Other than clinical observation of a patient's vegetative response to nociception, monitoring the hypnotic component of general anesthesia (GA) and unconsciousness relies on electroencephalography (EEG)-based indices. These indices exclusively based on frontal EEG activity neglect an important observation. One of the main hallmarks of transitions from wakefulness to GA is a shift in alpha oscillations (7.5-12.5 Hz activity) from occipital brain regions toward anterior brain regions ("alpha anteriorization"). Monitoring the degree of this alpha anteriorization may help to guide induction and maintenance of hypnotic depth and prevent intraoperative awareness. However, the occipital region of the brain is completely disregarded and occipital alpha as characteristic of wakefulness and its posterior-to-anterior shift during induction are missed. Here, we propose an application of Narcotrend's reduced power alpha beta (RPAB) index, originally developed to monitor differences in hemispheric perfusion, for determining the ratio of alpha and beta activity in the anterior-posterior axis.

METHODS

Perioperative EEG data of 32 patients undergoing GA in the ophthalmic surgery department of Bern University Hospital were retrospectively analyzed. EEG was recorded with the Narcotrend® monitor using a frontal (Fp1-Fp2) and a posterior (T9-Oz) bipolar derivation with reference electrode over A2. The RPAB index was computed between both bipolar signals, defining the fronto-occipital RPAB (FO-RPAB). FO-RPAB was analyzed during wakefulness, GA maintenance, and emergence, as well as before and after the intraoperative administration of a ketamine bolus. FO-RPAB was compared with a classical quantitative EEG measure-the spectral edge frequency 95% (SEF-95).

RESULTS

A significant shift of the FO-RPAB was observed during both induction of and emergence from GA ( P < .001). Interestingly, the additional administration of ketamine during GA did not lead to a significant change in FO-RPAB ( P = 0.81). In contrast, a significant increase in the SEF-95 in the frontal channel was observed during the 10-minute period after ketamine administration ( P < .001).

CONCLUSIONS

FO-RPAB appears to qualify as a marker of unconsciousness, reflecting physiological fronto-occipital activity differences during GA. In contrast to frontal SEF-95, it is not disturbed by additional administration of ketamine for analgesia.

Depth of anaesthesia monitoring: time to reject the index?

Depth of anaesthesia monitors can fail to detect consciousness under anaesthesia, primarily because they rely on the frontal EEG, which does not arise from a neural correlate of consciousness. A study published in a previous issue of the British Journal of Anaesthesia showed that indices produced by the different commercial monitors can give highly discordant results when analysing changes in the frontal EEG. Anaesthetists could benefit from routinely assessing the raw EEG and its spectrogram, rather than relying solely on an index produced by a depth of anaesthesia monitor.

Neuromonitoring in Critically Ill Patients

OBJECTIVES

Critically ill patients are at high risk of acute brain injury. Bedside multimodality neuromonitoring techniques can provide a direct assessment of physiologic interactions between systemic derangements and intracranial processes and offer the potential for early detection of neurologic deterioration before clinically manifest signs occur. Neuromonitoring provides measurable parameters of new or evolving brain injury that can be used as a target for investigating various therapeutic interventions, monitoring treatment responses, and testing clinical paradigms that could reduce secondary brain injury and improve clinical outcomes. Further investigations may also reveal neuromonitoring markers that can assist in neuroprognostication. We provide an up-to-date summary of clinical applications, risks, benefits, and challenges of various invasive and noninvasive neuromonitoring modalities.

DATA SOURCES

English articles were retrieved using pertinent search terms related to invasive and noninvasive neuromonitoring techniques in PubMed and CINAHL.

STUDY SELECTION

Original research, review articles, commentaries, and guidelines.

DATA EXTRACTION

Syntheses of data retrieved from relevant publications are summarized into a narrative review.

DATA SYNTHESIS

A cascade of cerebral and systemic pathophysiological processes can compound neuronal damage in critically ill patients. Numerous neuromonitoring modalities and their clinical applications have been investigated in critically ill patients that monitor a range of neurologic physiologic processes, including clinical neurologic assessments, electrophysiology tests, cerebral blood flow, substrate delivery, substrate utilization, and cellular metabolism. Most studies in neuromonitoring have focused on traumatic brain injury, with a paucity of data on other clinical types of acute brain injury. We provide a concise summary of the most commonly used invasive and noninvasive neuromonitoring techniques, their associated risks, their bedside clinical application, and the implications of common findings to guide evaluation and management of critically ill patients.

CONCLUSIONS

Neuromonitoring techniques provide an essential tool to facilitate early detection and treatment of acute brain injury in critical care. Awareness of the nuances of their use and clinical applications can empower the intensive care team with tools to potentially reduce the burden of neurologic morbidity in critically ill patients.

Five commercial 'depth of anaesthesia' monitors provide discordant clinical recommendations in response to identical emergence-like EEG signals

BACKGROUND

'Depth of anaesthesia' monitors claim to measure hypnotic depth during general anaesthesia from the EEG, and clinicians could reasonably expect agreement between monitors if presented with the same EEG signal. We took 52 EEG signals showing intraoperative patterns of diminished anaesthesia, similar to those that occur during emergence (after surgery) and subjected them to analysis by five commercially available monitors.

METHODS

We compared five monitors (BIS, Entropy-SE, Narcotrend, qCON, and Sedline) to see if index values remained within, or moved out of, each monitors' recommended index range for general anaesthesia for at least 2 min during a period of supposed lighter anaesthesia, as observed by changes in the EEG spectrogram obtained in a previous study.

RESULTS

Of the 52 cases, 27 (52%) had at least one monitor warning of potentially inadequate hypnosis (index above range) and 16 of the 52 cases (31%) had at least one monitor signifying excessive hypnotic depth (index below clinical range). Of the 52 cases, only 16 (31%) showed concordance between all five monitors. Nineteen cases (36%) had one monitor discordant compared with the remaining four, and 17 cases (33%) had two monitors in disagreement with the remaining three.

CONCLUSIONS

Many clinical providers still rely on index values and manufacturer's recommended ranges for titration decision making. That two-thirds of cases showed discordant recommendations given identical EEG data, and that one-third signified excessive hypnotic depth where the EEG would suggest a lighter hypnotic state, emphasizes the importance of personalised EEG interpretation as an essential clinical skill.

The use of processed electroencephalography (pEEG) in obstetric anaesthesia: a narrative review

Accidental awareness under general anaesthesia (AAGA) remains a major complication of anaesthesia. The incidence of AAGA during obstetric anaesthesia is high relative to other specialities. The use of processed electroencephalography (pEEG) in the form of "depth of anaesthesia" monitoring has been shown to reduce the incidence of AAGA in the non-obstetric population. The evidence for using pEEG to prevent AAGA in the obstetric population is poor and requires further exploration. Furthermore, pregnancy and disease states affecting the central nervous system, such as pre-eclampsia, may alter the interpretation of pEEG waveforms although this has not been fully characterised. National guidelines exist for pEEG monitoring with total intravenous anaesthesia and for "high-risk" cases regardless of technique, including the obstetric population. However, none of the currently available guidelines relates specifically to obstetric anaesthesia. Using pEEG monitoring for obstetric anaesthesia may also provide additional benefits beyond a reduction in risk of AAGA. These potential benefits include reduced postoperative nausea and vomiting, reduced anaesthetic agent use, a shorter post-anaesthetic recovery stay. In addition, pEEG acts as a surrogate marker of cerebral perfusion, and thus as an additional monitor for impending cardiovascular collapse, as seen in amniotic fluid embolism. The subtle physiological and pathological changes in EEG activity that may occur during pregnancy are an unexplored research area in the context of anaesthetic pEEG monitors. We believe that the direction of clinical practice is moving towards greater use of pEEG monitoring and individualisation of anaesthesia.

Performance of the bispectral index and electroencephalograph derived parameters of anesthetic depth during emergence from xenon and sevoflurane anesthesia

Many processed EEG monitors (pEEG) are unreliable when non-GABAergic anesthetic agents are used. The primary aim of the study was to compare the response of the Bispectral Index (BIS) during emergence from anesthesia maintained by xenon and sevoflurane. To better understand the variation in response of pEEG to these agents, we also compared several EEG derived parameters relevant to pEEG monitoring during emergence. Twenty-four participants scheduled for lithotripsy were randomized to receive xenon or sevoflurane anesthesia. Participants were monitored with the BIS and had simultaneous raw EEG collected. BIS index values were compared at three key emergence timepoints: first response, eyes open and removal of airway. Two sets of EEG derived parameters, three related to the BIS: relative beta ratio, SynchFastSlow and SynchFastSlow biocoherence, and two unrelated to the BIS: spectral edge frequency and the composite cortical state, were calculated for comparison. BIS index values were significantly lower in the xenon group than the sevoflurane group at each emergence timepoint. The relative beta ratio parameter increased significantly during emergence in the sevoflurane group but not in the xenon group. The spectral edge frequency and composite cortical state parameters increased significantly in both groups during emergence. The BIS index is lower at equivalent stages of behavioural response during emergence from xenon anesthesia when compared to sevoflurane anesthesia, most likely due to differences in how these two agents influence the relative beta ratio. The spectral edge frequency and composite cortical state might better reflect emergence from xenon anaesthesia.Clinical trial number and registry Australia New Zealand Clinical Trials Registry Number: ACTRN12618000916246.

Depth of anaesthesia and mortality after cardiac or noncardiac surgery: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Recent randomised controlled trials have failed to show a benefit in mortality by using processed electroencephalography (pEEG) to guide lighter anaesthesia. We performed a meta-analysis of mortality data from randomised trials of pEEG monitoring to assess the evidence of any protective effect of pEEG-guided light anaesthesia compared with deep anaesthesia in adults aged ≥18 yr.

METHODS

Our study followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines. In February 2022, we searched three databases (Cochrane CENTRAL, OVID Medline, EMBASE) for RCTs of pEEG monitoring that provided mortality data at 30 days, 90 days, and/or 1 yr or longer.

RESULTS

We included 16 articles from 12 RCTs with 48 827 total participants. We observed no statistically significant mortality reduction with light anaesthesia compared with deep anaesthesia in patients aged ≥18 yr when all studies were pooled (odds ratio [OR]=0.99; 95% confidence interval (CI), 0.92-1.08). This result did not change significantly when analysing mortality at 30 days, 90 days, 1 yr or longer. We observed no mortality benefit for pEEG monitoring compared with usual care (OR=1.02; 95% CI, 0.89-1.18), targeting higher pEEG index values compared with lower values (OR=0.89; 95% CI, 0.60-1.32), or low pEEG index value alerts compared with no alerts (OR=1.02; 95% CI, 0.41-2.52).

CONCLUSIONS

pEEG-guided lighter anaesthesia does not appear to reduce the risk of postoperative mortality. The absence of a plausible rationale for why deeper anaesthesia should increase mortality has hampered appropriate design of definitive clinical trials.

CLINICAL TRIAL REGISTRATION

CRD42022285195 (PROSPERO).

Evaluation of patient state index, bispectral index, and entropy during drug induced sleep endoscopy with dexmedetomidine

Multiple electroencephalographic (EEG) monitors and their associated EEG markers have been developed to aid in assessing the level of sedation in the operating room. While many studies have assessed the response of these markers to propofol sedation and anesthetic gases, few studies have compared these markers when using dexmedetomidine, an alpha-2 agonist. Fifty-one patients underwent drug induced sleep endoscopy with dexmedetomidine sedation. Continuous EEG was captured using SedLine (Masimo, Inc), and a playback system was used to extract the bispectral index (BIS) (Medtronic Inc), the patient state index (PSI) (Masimo, Inc), the state and response Entropy (GE Healthcare), and calculate the spectral edge frequency 95% (SEF95). Richmond Agitation-Sedation Scale (RASS) scores were assessed continually throughout the procedure and in recovery. We assessed the correlation between EEG markers and constructed ordinal logistic regression models to predict the RASS score and compare EEG markers. All three commercial EEG metrics were significantly associated with the RASS score (p < 0.001 for all metrics) whereas SEF95 alone was insufficient at characterizing dexmedetomidine sedation. PSI and Entropy achieved higher accuracy at predicing deeper levels of sedation as compared to BIS (PSI: 58.3%, Entropy: 58.3%, BIS: 44.4%). Lightening secondary to RASS score assessment is significantly captured by all three commercial EEG metrics (p < 0.001). Commercial EEG monitors can capture changes in the brain state associated with the RASS score during dexmedetomidine sedation. PSI and Entropy were highly correlated and may be better suited for assessing deeper levels of sedation.

Comparison of bispectral index and phase lag entropy during general anesthesia: Sevoflurane or propofol anesthesia

BACKGROUND

Phase-lag entropy (PLE) based on functional connectivity between different regions of the brain may be superior to conventional depth of anesthesia (DoA) methods for monitoring changes in consciousness. However, few studies have compared the PLE and bispectral index (BIS) methods for monitoring consciousness during clinical anesthesia, such as total intravenous anesthesia (TIVA) or anesthesia via inhalation. Therefore, we evaluated differences between the PLE and BIS methods in clinical anesthesia, including TIVA using propofol and anesthesia with sevoflurane.

METHODS

The observational trial included 60 patients scheduled for elective surgery under general anesthesia. The BIS and PLE electrodes were placed together on the left temporal-frontal area of all patients. During anesthesia, anesthetic levels were adjusted using the BIS values, which are generally used to monitor the DoA; the level of anesthesia was maintained at between 40 and 60. BIS- and PLE-derived values were recorded continuously. Anesthetic events, the concentration of each anesthetic, and standard monitoring values were recorded. The patients included were divided into 2 groups, the TIVA and sevoflurane groups, with 30 patients in each. For the TIVA group, anesthesia was induced and maintained using propofol and remifentanil target-controlled infusion. For the sevoflurane group, anesthesia was induced using propofol and maintained using sevoflurane and remifentanil.

RESULTS

From loss of consciousness until the anesthetic maintenance period, PLE values were higher than BIS values at several time points. During the recovery period, BIS values were higher than PLE values (all P < .001). Spaghetti plots showed that there was more variation among the BIS values than among the PLE values.

CONCLUSIONS

For monitoring DoA during general anesthesia and surgery, PLE values vary less than BIS values; thus, PLE may be more reliable for monitoring changes in consciousness. However, further studies are needed to evaluate the clinical application of these methods in general anesthesia.

Electroencephalography spectral edge frequency and suppression rate-guided sedation in patients with COVID-19: A randomized controlled trial

Background

Sedation in coronavirus disease 2019 (COVID-19) patients has been identified as a major challenge. We aimed to investigate whether the use of a multiparameter electroencephalogram (EEG) protocol to guide sedation in COVID-19 patients would increase the 30-day mechanical ventilation-free days (VFD).

Methods

We conducted a double-blind randomized clinical trial. We included patients with severe pneumonia due to COVID-19 who required mechanical ventilation (MV) and deep sedation. We randomized to the control (n = 25) or multiparameter group (n = 25). Sedation in the intervention group was administered following the standard institutional protocols together with a flow chart designed to reduce the propofol administration dose if the EEG suppression rate was over 2% or the spectral edge frequency 95 (SEF95) was below 10 Hz. We performed an intention-to-treat analysis to evaluate our primary outcome (30-day VFD).

Results

There was no difference in VFD at day 30 (median: 11 [IQR 0–20] days in the control group vs. 0 [IQR 0–21] days in the BIS multiparameter group, p = 0.87). Among secondary outcomes, we documented a 17% reduction in the total adjusted propofol administered during the first 5 days of the protocol [median: 2.3 (IQR 1.9–2.8) mg/k/h in the control group vs. 1.9(IQR 1.5–2.2) mg/k/h in the MP group, p = 0.005]. This was accompanied by a higher average BIS value in the intervention group throughout the treatment period.

Conclusion

A sedation protocol guided by multivariate EEG-derived parameters did not increase the 30-day VFD. However, the intervention led to a reduction in total propofol administration.

Monitoring the Awake and Anesthetized Unconscious States Using Bispectral Index and Electroencephalographic Connectivity Measures

Objective. Our objective was to compare three electroencephalography (EEG)-based methods with anesthesiologist clinical judgment of the awake and anesthetized unconscious states. Methods. EEG recorded from 25 channels and from four channel bilateral Bispectral index (BIS) electrodes were collected from 20 patients undergoing surgery with general anesthesia. To measure connectivity we applied Directed Transfer Function (DTF) in eight channels of the EEG, and extracted data from BIS over the same time segments. Shannon's entropy was applied to assess the complexity of the EEG signal. Discriminant analysis was used to evaluate the data in relation to clinical judgment. Results. Assessing anesthetic state relative clinical judgment, the bilateral BIS gave the highest accuracy (ACC) (95.4%) and lowest false positive discovery rate (FDR) (0.5%) . Equivalent DTF gave 94.5% for ACC and 2.6% for FDR. Combining all methods gave ACC = 94.9% and FDR = 1%. Generally, entropy scored lower on ACC and higher on FDR than the other methods (ACC 90.87% and FDR 4.6%). BIS showed at least a one minute delay in 18 of the 20 patients. Conclusions. Our results show that BIS and DTF both have a high ACC and low FDR. Because of time delays in BIS values, we recommend combining the two methods.

Are we really unconscious in "unconscious" states? Common assumptions revisited

In the field of consciousness science, there is a tradition to categorize certain states such as slow-wave non-REM sleep and deep general anesthesia as "unconscious". While this categorization seems reasonable at first glance, careful investigations have revealed that it is not so simple. Given that (1) behavioral signs of (un-)consciousness can be unreliable, (2) subjective reports of (un-)consciousness can be unreliable, and, (3) states presumed to be unconscious are not always devoid of reported experience, there are reasons to reexamine our traditional assumptions about "states of unconsciousness". While these issues are not novel, and may be partly semantic, they have implications both for scientific progress and clinical practice. We suggest that focusing on approaches that provide a more pragmatic and nuanced characterization of different experimental conditions may promote clarity in the field going forward, and help us build stronger foundations for future studies.

Early predictors of brain injury in patients with acute carbon monoxide poisoning and the neuroprotection of mild hypothermia

INTRODUCTION

Carbon monoxide (CO) poisoning can cause serious neurological sequelae. However, there is neither effective treatment strategy nor reliable indicators to determine the prognosis of patients with CO poisoning. The present study aimed to observe the changes of neurological function score, disease severity score, cerebral oxygen utilization (O₂UCc), bispectral (BIS) index and neuron-specific enolase (NSE) concentration, and to elucidate the clinical significance of these potential indicators and the neuroprotective effect of mild hypothermia on brain injury in patients with severe acute CO poisoning.

MATERIALS AND METHODS

A total of 277 patients with acute severe CO poisoning from 2013 to 2018 were enrolled in our hospital. Patients were divided into three groups according to their body temperature on the day of admission and their willingness to treat: a fever group (n = 78), a normal temperature group (NT group, n = 113), and a mild hypothermia group (MH group, n = 86). All patients were given hyperbaric oxygen therapy, while those in the MH group received additional mild hypothermia treatment. The severity of the disease, the neurobehavioral status, the incidence of delayed encephalopathy after acute carbon monoxide poisoning (DEACMP), and other indicators including BIS, O₂UCc, NSE were further evaluated in all patients at given time-points.

RESULTS

Mild hypothermia therapy improved the prognosis of patients with CO poisoning, significantly decreased the value of O₂UCc and NSE, and up-regulated BIS. The incidence of DEACMP at 6 months was 27% in the fever group, 23% in the NT group, and 8% in the MH group. The values of Glasgow-Pittsburgh coma scale (G-P score), BIS index and NSE were closely related to the occurrence of DEACMP, the cutoff values were 12.41, 52.17 and 35.20 ng/mL, and the sensitivity and specificity were 79.3%, 77.6%, 79.3% and 67.6%, 89.5%, 88.6% in the receiver operating characteristic curve (ROC), respectively.

CONCLUSIONS

Early mild hypothermia treatment could significantly reduce the severity of brain injury after CO poisoning, and might be further popularized in clinic. G-P scores, NSE and BIS index can be regarded as the prediction indicators in the occurrence and development of DEACMP.

CLINICAL TRIAL REGISTRATION

The study protocol was granted from Qingdao University Research Ethics Committee (Clinical trial registry and ethical approval number: QD81571283).

Spectral edge frequency during general anaesthesia: A narrative literature review

Previous studies have attempted to determine the depth of anaesthesia with different anaesthetic agents using electroencephalogram (EEG) measurements with variable success. Measuring depth of anaesthesia is confounded by the complexity of the EEG and the fact that different agents create different pattens. A narrative review was undertaken to examine the available research evidence on the effect and reliability of spectral edge frequency (SEF) for assessing the depth of anaesthesia in adult patients under general anaesthesia. A systematic search of the PubMed®, Scopus®, CINAHL and Cochrane databases identified six randomized controlled trials and five observational studies. The findings of these studies suggest that SEF varies according to the anaesthetic drugs used. Remifentanil and age are two factors that can affect SEF, while other opioids and benzodiazepine (administered separately) seem to have no effect. No patients experienced intraoperative awareness. However, this does not indicate that SEF can provide full protection against it and the number of articles in which intraoperative awareness was studied was too small to afford any certainty. None of the studies demonstrated a reliable SEF interval associated with adequate general anaesthesia. SEF must be adapted to the anaesthetic drug used, the patient’s age and state while under general anaesthesia.

Systematic review and meta‐analysis of the correlation between bispectral index ( BIS ) and clinical sedation scales: Toward defining the role of BIS in critically ill patients

INTRODUCTION

The bispectral index (BIS) is an attractive approach for monitoring level of consciousness in critically ill patients, particularly during paralysis, when commonly used sedation scales cannot be used.

OBJECTIVES

As a first step toward establishing the utility of BIS during paralysis, this review examines the strength of correlation between BIS and clinical sedation scales in a broad population of non-paralyzed, critically ill adults.

METHODS

We included studies evaluating the strength of correlation between concurrent assessments of BIS and Richmond Agitation Sedation Scale (RASS), Ramsay Sedation Scale (RSS), or Sedation Agitation Scale (SAS) in critically ill adult patients. Studies involving assessment of depth sedation periperative or procedural time periods, and those reporting BIS and sedation scale assessments conducted >5 min apart or while neuromuscular blocking agents (NMBA) were administered, were excluded. Data were abstracted on sedation scale, correlation coefficients, setting, patient characteristics, and BIS assessment characteristics that could impact the quality of the studies.

RESULTS

Twenty-four studies which enrolled 1235 patients met inclusion criteria. The correlation between BIS and RASS, RSS, and SAS overall was 0.68 (95% confidence interval, 0.61-0.74, Ƭ²  = 0.06 I²  = 71.26%). Subgroup analysis by sedation scale indicated that the correlation between BIS and RASS, RSS, and SAS were 0.66 (95% confidence interval 0.58-0.73, Ƭ²  = 0.01 I²  = 30.20%), 0.76 (95% confidence interval 0.69-0.82, Ƭ²  = 0.04 I²  = 67.15%), and 0.53 (95% confidence interval 0.42-0.63, Ƭ²  = 0.01 I²  = 26.59%), respectively. Factors associated with significant heterogeneity included comparator clinical sedation scale, neurologic injury, and the type of intensive care unit (ICU) population.

CONCLUSIONS

BIS demonstrated moderate to strong correlation with clinical sedation scales in adult ICU patients, providing preliminary evidence for the validity of BIS as a measure of sedation intensity when clinical scales cannot be used. Future studies should determine whether BIS monitoring is safe and effective in improving outcomes in patients receiving NMBA treatment.

Mitigation of perioperative neurocognitive disorders: A holistic approach

William Morton introduced the world to ether anesthesia for use during surgery in the Bullfinch Building of the Massachusetts General Hospital on October 16, 1846. For nearly two centuries, the prevailing wisdom had been that the effects of general anesthetics were rapidly and fully reversible, with no apparent long-term adverse sequelae. Despite occasional concerns of a possible association between surgery and anesthesia with dementia since 1887 (Savage, 1887), our initial belief was robustly punctured following the publication in 1998 of the International Study of Post-Operative Cognitive Dysfunction [ISPOCD 1] study by Moller et al. (1998) in The Lancet, in which they demonstrated in a prospective fashion that there were in fact persistent adverse effects on neurocognitive function up to 3 months following surgery and that these effects were common. Since the publication of that landmark study, significant strides have been made in redefining the terminology describing cognitive dysfunction, identifying those patients most at risk, and establishing the underlying etiology of the condition, particularly with respect to the relative contributions of anesthesia and surgery. In 2018, the International Nomenclature Consensus Working Group proposed new nomenclature to standardize identification of and classify perioperative cognitive changes under the umbrella of perioperative neurocognitive disorders (PND) (Evered et al., 2018a). Since then, the new nomenclature has tried to describe post-surgical cognitive derangements within a unifying framework and has brought to light the need to standardize methodology in clinical studies and motivate such studies with hypotheses of PND pathogenesis. In this narrative review, we highlight the relevant literature regarding recent key developments in PND identification and management throughout the perioperative period. We provide an overview of the new nomenclature and its implications for interpreting risk factors identified by clinical association studies. We then describe current hypotheses for PND development, using data from clinical association studies and neurophysiologic data where appropriate. Finally, we offer broad clinical guidelines for mitigating PND in the perioperative period, highlighting the role of Brain Enhanced Recovery After Surgery (Brain-ERAS) protocols.

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.

Age, minimum alveolar concentration and choice of depth of sedation monitor: examining the paradox of age when using the Narcotrend monitor: A secondary analysis of an observational study

BACKGROUND

With an ageing global population, it is important to individualise titration of anaesthetics according to age and by measuring their effect on the brain. A recent study reported that during general surgery, the given concentration of volatile anaesthetics, expressed as a fraction of the minimum alveolar concentration (MAC fraction), decreases by around only 3% per age-decade, which is less than the 6% expected from age-adjusted MAC. Paradoxically, despite the excessive dosing, Bispectral index (BIS) values also increased.

OBJECTIVE

We planned to investigate the paradox of age when using the Narcotrend depth of anaesthesia monitor.

DESIGN

Secondary analyses of a prospective observational study.

SETTING

Tertiary hospital in Switzerland, recordings took place during 2016 and 2017.

PATIENTS

One thousand and seventy-two patients undergoing cardiac surgery entered the study, and 909 with noise-free recordings and isoflurane anaesthesia were included in this analysis.

INTERVENTION

We calculated mean end-tidal MAC fraction and mean index value of the Narcotrend depth of sedation monitor used in the study during the prebypass period. Statistical associations were modelled using linear regression, local weighted regression (LOESS) and a generalised additive model (GAM).

MAIN OUTCOME MEASURES

Primary endpoints in this study were the change in end-tidal MAC fraction and mean Narcotrend index values, both measured per age-decade.

RESULTS

We observed a linear decrease in end-tidal MAC fraction of 3.2% per age-decade [95% confidence interval (CI) -3.97% to -2.38%, P < 0.001], consistent with previous findings. In contrast to the BIS, mean Narcotrend index values decreased with age at 3.0 index points per age-decade (95% CI, -3.55 points to -2.36 points, P < 0.001), a direction of change commensurate with the increasing age-adjusted MAC fraction with patient age. These relationships were consistent regardless of whether age-adjusted MAC was displayed on the anaesthetic machine.

CONCLUSIONS

We caution that the 'paradox of age' may in part depend on the choice of depth of sedation monitor.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02976584.

A Processed Electroencephalogram-Based Brain Anesthetic Resistance Index Is Associated With Postoperative Delirium in Older Adults: A Dual Center Study

BACKGROUND

Some older adults show exaggerated responses to drugs that act on the brain. The brain's response to anesthetic drugs is often measured clinically by processed electroencephalogram (EEG) indices. Thus, we developed a processed EEG-based measure of the brain's resistance to volatile anesthetics and hypothesized that low scores on it would be associated with postoperative delirium risk.

METHODS

We defined the Duke Anesthesia Resistance Scale (DARS) as the average bispectral index (BIS) divided by the quantity (2.5 minus the average age-adjusted end-tidal minimum alveolar concentration [aaMAC] inhaled anesthetic fraction). The relationship between DARS and postoperative delirium was analyzed in 139 older surgical patients (age ≥65) from Duke University Medical Center (n = 69) and Mt Sinai Medical Center (n = 70). Delirium was assessed by geriatrician interview at Duke, and by research staff utilizing the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) instrument at Mt Sinai. We examined the relationship between DARS and delirium and used the Youden index to identify an optimal low DARS threshold (for delirium risk), and its associated 95% bootstrap confidence bounds. We used multivariable logistic regression to examine the relationship between low DARS and delirium risk.

RESULTS

The relationship between DARS and delirium risk was nonlinear, with higher delirium risk at low DARS scores. A DARS threshold of 28.755 maximized the Youden index for the association between low DARS and delirium, with bootstrap 95% confidence bounds of 26.18 and 29.80. A low DARS (<28.755) was associated with increased delirium risk in multivariable models adjusting for site (odds ratio [OR] [95% confidence interval {CI}] = 4.30 [1.89-10.01]; P = .001), or site-plus-patient risk factors (OR [95% CI] = 3.79 [1.63-9.10]; P = .003). These associations with postoperative delirium risk remained significant when using the 95% bootstrap confidence bounds for the low DARS threshold (P < .05 for all). Further, a low DARS (<28.755) was associated with delirium risk after accounting for opioid, midazolam, propofol, phenylephrine, and ketamine dosage as well as site (OR [95% CI] = 4.21 [1.80-10.16]; P = .002). This association between low DARS and postoperative delirium risk after controlling for these other medications remained significant (P < .05) when using either the lower or the upper 95% bootstrap confidence bounds for the low DARS threshold.

CONCLUSIONS

These results demonstrate that an intraoperative processed EEG-based measure of lower brain anesthetic resistance (ie, low DARS) is independently associated with increased postoperative delirium risk in older surgical patients.

Anaesthetic depth and delirium: a challenging balancing act

This editorial highlights the findings of the Balanced Anaesthesia Delirium study, a 515-patient substudy of the 6644 patient Balanced Anaesthesia trial, which found that targeting deep anaesthesia in patients undergoing major noncardiac surgery was not associated with significantly increased postoperative death or major morbidity. The substudy found that using bispectral index (BIS) guidance with the intention of deliberately achieving deep volatile agent-based anaesthesia (target BIS reading 35 vs 50) significantly increased delirium incidence (28% vs 19%), although not subsyndromal delirium incidence (45% vs 49%). We discuss the implications of these findings for anaesthetic practice, and address whether the BIS should be used as a guide to deliver precision anaesthesia for delirium prevention. We posit that subpopulation-based differences within this multicentre substudy could have affected delirium occurrence, since the findings appeared to rest on outcomes in patients from East Asia. We conclude that questions of whether and for whom deep anaesthesia is deliriogenic remain unanswered.