The Comparability of Bispectral Index and State Entropy Index During Maintenance of Sufentanil-Sevoflurane-Nitrous Oxide Anesthesia

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.

PRISMA: accuracy of response entropy and bispectral index to predict the transition of consciousness during sevoflurane anesthesia: A systematic review and meta-analysis

Background:

Bispectral index (BIS) and response entropy (RE) are used to monitor the depth of anesthesia.

Objectives:

To collect published data and compare the accuracy of BIS and RE in detecting the transition of consciousness during sevoflurane anesthesia.

Data sources:

Studies indexed in the PubMed, Embase, or Cochrane databases.

Study eligibility criteria:

Participants:

Patients who need to use BIS and RE to monitor sevoflurane anesthesia depth simultaneously.

Interventions:

A random-effects model was fitted using RevMan 5.3. Subgroup analyses were performed on patient age. The Cochrane I 2 methodology was used to determine the heterogeneity of the statistical results, while GRADE Pro served to assess the quality of evidence.

Results:

Overall, 195 articles were identified, of which 7 were finally included. The meta-analysis results showed that BIS is more accurate than RE in predicting loss of consciousness (LOC) during sevoflurane anesthesia (MD, .06; 95% confidence interval [CI], .02–.09; P  = .009; I 2  = 92%). In contrast, there was no significant difference between BIS and RE for recovery of consciousness (ROC; MD, .01; 95% CI, .00–.02; P  = .79; I 2  = 83%). Subgroup analyses revealed no significant differences in LOC (MD, .02; 95% CI, .01–.05; P  = .13; I 2  = 60%) and ROC (MD, −.01; 95% CI, −.06–.04; P  = .58; I 2  = 95%) in children. However, the results in adults demonstrated that BIS is more accurate than RE in predicting LOC (MD, −.07; 95% CI, .05–.10; P  = .002; I 2  = 76%).

Limitations:

First, this meta-analysis was affected by a large study heterogeneity. Second, this analysis only included publications in English, therefore, some studies may have been omitted.

Conclusion:

BIS is more accurate than RE in predicting LOC during sevoflurane anesthesia in adults. However, no significant differences were identified in children.

Registration number (PROSPERO):

CRD42020163119

Effect of Laryngeal Mask Airway Insertion on Parameters Derived From Catacrotic Phase of Photoplethysmography Under Different Concentrations of Remifentanil

BACKGROUND

Some parameters have been extracted from photoplethysmography (PPG) with a good relativity with nociception, but without encouraging results in qualifying the balance of nociception-anti-nociception (NAN). The features of PPG have not been thoroughly depicted and more prospective univariate parameters deserve to be explored. The aim of this study was to investigate the ability of parameters derived from catacrotic phase of PPG to grade the level of analgesia.

METHODS

45 patients with ASA I or II were randomized to receive a remifentanil effect-compartment target controlled infusion (Ceremi) of 0, 1, or 3 ng/ml, and a propofol effect-compartment target controlled infusion to maintain an acceptable level of hypnosis with state entropy (SE) at 40~60. Laryngeal mask airway (LMA) insertion was applied as a noxious stimulus. Five diastole-related parameters, namely diastolic interval (DI), diastolic slope (DS), the minimum slope during catacrotic phase (DSmin), the interval between DSmin and its nearest trough (DTI), and area difference ratio (ADR), were extracted. Pulse beat interval (PBI) was calculated as a reference parameter.

RESULTS

LMA insertion elicited a significant variation in all parameters except ADR during Ceremi of 0 and 1 ng/ml. Compared to PBI (prediction probability ([Formula: see text]) = 0.796), the parameters of DI, DS, and DTI presented a better consistence with the level of anti-nociceptive medication, with [Formula: see text] of 0.825, 0.822, and 0.822 respectively.

CONCLUSION

The features extracted from catacrotic phase of PPG, including DI, DS, and DTI, could provide a promising potential to qualify the balance of NAN.

Comparison of bispectral index and spectral entropy during isoflurane and medetomidine general anaesthesia in horses

BACKGROUND

The bispectral index (BIS) has been evaluated as an indicator of central nervous system (CNS) depression in horses during general anaesthesia. The spectral entropy is another electroencephalographic device and it has not been evaluated yet in horses.

OBJECTIVES

To determine if spectral entropy can assess anaesthetic depth during the different phases of anaesthesia, define the value of state and response entropy during surgical plane of anaesthesia and compare them with BIS.

STUDY DESIGN

Clinical, prospective, non-blinded observational study.

METHODS

Thirty-five horses ASA I or II undergoing scheduled surgical procedure were used. BIS and electromyography (EMG) with a BIS monitor and state and response entropy with a spectral entropy monitor were recorded at baseline after receiving 5 µg/kg bwt i.v. of medetomidine (sedation period), during the anaesthetic maintenance with isoflurane and medetomidine (intraoperative period) and once the trachea was extubated (recovery period). A general linear model for repeated measurements was employed. Correlation and agreement between methods were also assessed. Data are presented as mean ± SD.

RESULTS

State entropy, response entropy and EMG showed significant differences according to the anaesthetic period (P < .001). There was no significant difference in BIS between baseline and sedation period, but there were differences between the remainder of the periods (P < .001). BIS (53.4 ± 11.2) was significantly higher (P < .001) than response entropy (35.1 ± 7.1) and state entropy (27.4 ± 4.8) during surgical plane of anaesthesia. The ICC between BIS and response entropy was 0.56 and between BIS and state entropy was 0.43, without agreement between them.

MAIN LIMITATIONS

The need to shave the skin in contact with the sensors and the difficulty in taking measurements during recovery period.

CONCLUSIONS

Spectral entropy can be used to detect the different periods of an anaesthetic protocol, with the lowest values during the intraoperative period. A low correlation and no concordance were observed between both methods.

Comparing Nasal End-Tidal Carbon Dioxide Measurement Variation and Agreement While Delivering Pulsed and Continuous Flow Oxygen in Volunteers and Patients

BACKGROUND

Supplemental oxygen is administered during procedural sedation to prevent hypoxemia. Continuous flow oxygen, the most widespread method, is generally adequate but distorts capnography. Pulsed flow oxygen is novel and ideally will not distort capnography. We have developed a prototype oxygen administration system designed to try to facilitate end-tidal carbon dioxide (ETCO2) measurement. We conducted a volunteer study (ClinicalTrials.gov, NCT02886312) to determine how much nasal ETCO2 measurements vary with oxygen flow rate. We also conducted a clinical study (NCT02962570) to determine the median difference and limits of agreement between ETCO2 measurements made with and without administering oxygen.

METHODS

Both studies were conducted at the University of Utah and participants acted as their own control. Inclusion criteria were age 18 years and older with an American Society of Anesthesiologists physical status of I-III. Exclusion criteria included acute respiratory distress syndrome, pneumonia, lung or cardiovascular disease, nasal/bronchial congestion, pregnancy, oxygen saturation measured by pulse oximetry <93%, and a procedure scheduled for <20 minutes. For the volunteer study, pulsed and continuous flow was administered at rates from 2 to 10 L/min using a single sequence of technique and flow. The median absolute deviation from the median value was analyzed for the primary outcome of ETCO2. For the clinical study, ETCO2 measurements (the primary outcome) were collected while administering pulsed and continuous flow at rates between 1 and 5 L/min and were compared to measurements without oxygen flow. Due to institutional review board requirements for patient safety, this study was not randomized. After completing the study, measurements with and without administering oxygen were analyzed to determine median differences and 95% limits of agreement for each administration technique.

RESULTS

Thirty volunteers and 60 patients participated in these studies which ended after enrolling the predetermined number of participants. In volunteers, the median absolute deviation for ETCO2 measurements made while administering pulsed flow oxygen (0.89; 25%-75% quantiles: 0.3-1.2) was smaller than while administering continuous flow oxygen (3.93; 25%-75% quantiles: 2.2-6.2). In sedated patients, the median difference was larger during continuous flow oxygen (-6.8 mm Hg; 25%-75% quantiles: -12.5 to -2.1) than during pulsed flow oxygen (0.1 mm Hg; 25%-75% quantiles: -0.5 to 1.5). The 95% limits of agreement were also narrower during pulsed flow oxygen (-2.4 to 4.5 vs -30.5 to 2.4 mm Hg).

CONCLUSIONS

We have shown that nasal ETCO2 measurements while administering pulsed flow have little deviation and agree well with measurements made without administering oxygen. We have also demonstrated that ETCO2 measurements during continuous flow oxygen have large deviation and wide limits of agreement when compared with measurements made without administering oxygen.

Anaesthetic interventions for prevention of awareness during surgery

BACKGROUND

General anaesthesia is usually associated with unconsciousness. 'Awareness' is when patients have postoperative recall of events or experiences during surgery. 'Wakefulness' is when patients become conscious during surgery, but have no postoperative recollection of the period of consciousness.

OBJECTIVES

To evaluate the efficacy of two types of anaesthetic interventions in reducing clinically significant awareness:- anaesthetic drug regimens; and- intraoperative anaesthetic depth monitors.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, ISSUE 4 2016); PubMed from 1950 to April 2016; MEDLINE from 1950 to April 2016; and Embase from 1980 to April 2016. We contacted experts to identify additional studies. We performed a handsearch of the citations in the review. We did not search trial registries.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of either anaesthetic regimens or anaesthetic depth monitors. We excluded volunteer studies, studies of patients prior to skin incision, intensive care unit studies, and studies that only randomized different word presentations for memory tests (not anaesthetic interventions).Anaesthetic drug regimens included studies of induction or maintenance, or both. Anaesthetic depth monitors included the Bispectral Index monitor, M-Entropy, Narcotrend monitor, cerebral function monitor, cerebral state monitor, patient state index, and lower oesophageal contractility monitor. The use of anaesthetic depth monitors allows the titration of anaesthetic drugs to maintain unconsciousness.

DATA COLLECTION AND ANALYSIS

At least two authors independently scanned abstracts, extracted data from the studies, and evaluated studies for risk of bias. We made attempts to contact all authors for additional clarification. We performed meta-analysis statistics in packages of the R language.

MAIN RESULTS

We included 160 studies with 54,109 enrolled participants; 53,713 participants started the studies and 50,034 completed the studies or data analysis (or both). We could not use 115 RCTs in meta-analytic comparisons because they had zero awareness events. We did not merge 27 of the remaining 45 studies because they had excessive clinical and methodological heterogeneity. We pooled the remaining 18 eligible RCTs in meta-analysis. There are 10 studies awaiting classification which we will process when we update the review.The meta-analyses included 18 trials with 36,034 participants. In the analysis of anaesthetic depth monitoring (either Bispectral Index or M-entropy) versus standard clinical and electronic monitoring, there were nine trials with 34,744 participants. The overall event rate was 0.5%. The effect favoured neither anaesthetic depth monitoring nor standard clinical and electronic monitoring, with little precision in the odds ratio (OR) estimate (OR 0.98, 95% confidence interval (CI) 0.59 to 1.62).In a five-study subset of Bispectral Index monitoring versus standard clinical and electronic monitoring, with 34,181 participants, 503 participants gave awareness reports to a blinded, expert panel who adjudicated or judged the outcome for each patient after reviewing the questionnaires: no awareness, possible awareness, or definite awareness. Experts judged 351 patient awareness reports to have no awareness, 87 to have possible awareness, and 65 to have definite awareness. The effect size favoured neither Bispectral Index monitoring nor standard clinical and electronic monitoring, with little precision in the OR estimate for the combination of definite and possible awareness (OR 0.96, 95% CI 0.35 to 2.65). The effect size favoured Bispectral Index monitoring for definite awareness, but with little precision in the OR estimate (OR 0.60, 95% CI 0.13 to 2.75).We performed three smaller meta-analyses of anaesthetic drugs. There were nine studies with 1290 participants. Wakefulness was reduced by ketamine and etomidate compared to thiopental. Wakefulness was more frequent than awareness. Benzodiazepines reduces awareness compared to thiopental, ketamine, and placebo., Also, higher doses of inhaled anaesthetics versus lower doses reduced the risk of awareness.We graded the quality of the evidence as low or very low in the 'Summary of findings' tables for the five comparisons.Most of the secondary outcomes in this review were not reported in the included RCTs.

AUTHORS' CONCLUSIONS

Anaesthetic depth monitors may have similar effects to standard clinical and electrical monitoring on the risk of awareness during surgery. In older studies comparing anaesthetics in a smaller portion of the patient sample, wakefulness occurred more frequently than awareness. Use of etomidate and ketamine lowered the risk of wakefulness compared to thiopental. Benzodiazepines compared to thiopental and ketamine, or higher doses of inhaled anaesthetics versus lower doses, reduced the risk of awareness.

Differences between state entropy and bispectral index during analysis of identical electroencephalogram signals: a comparison with two randomised anaesthetic techniques

BACKGROUND

It is claimed that bispectral index (BIS) and state entropy reflect an identical clinical spectrum, the hypnotic component of anaesthesia. So far, it is not known to what extent different devices display similar index values while processing identical electroencephalogram (EEG) signals.

OBJECTIVE

To compare BIS and state entropy during analysis of identical EEG data. Inspection of raw EEG input to detect potential causes of erroneous index calculation.

DESIGN

Offline re-analysis of EEG data from a randomised, single-centre controlled trial using the Entropy Module and an Aspect A-2000 monitor.

SETTING

Klinikum rechts der Isar, Technische Universität München, Munich.

PATIENTS

Forty adult patients undergoing elective surgery under general anaesthesia.

INTERVENTIONS

Blocked randomisation of 20 patients per anaesthetic group (sevoflurane/remifentanil or propofol/remifentanil). Isolated forearm technique for differentiation between consciousness and unconsciousness.

MAIN OUTCOME MEASURES

Prediction probability (PK) of state entropy to discriminate consciousness from unconsciousness. Correlation and agreement between state entropy and BIS from deep to light hypnosis. Analysis of raw EEG compared with index values that are in conflict with clinical examination, with frequency measures (frequency bands/Spectral Edge Frequency 95) and visual inspection for physiological EEG patterns (e.g. beta or delta arousal), pathophysiological features such as high-frequency signals (electromyogram/high-frequency EEG or eye fluttering/saccades), different types of electro-oculogram or epileptiform EEG and technical artefacts.

RESULTS

PK of state entropy was 0.80 and of BIS 0.84; correlation coefficient of state entropy with BIS 0.78. Nine percent BIS and 14% state entropy values disagreed with clinical examination. Highest incidence of disagreement occurred after state transitions, in particular for state entropy after loss of consciousness during sevoflurane anaesthesia. EEG sequences which led to false 'conscious' index values often showed high-frequency signals and eye blinks. High-frequency EEG/electromyogram signals were pooled because a separation into EEG and fast electro-oculogram, for example eye fluttering or saccades, on the basis of a single EEG channel may not be very reliable. These signals led to higher Spectral Edge Frequency 95 and ratio of relative beta and gamma band power than EEG signals, indicating adequate unconscious classification. The frequency of other artefacts that were assignable, for example technical artefacts, movement artefacts, was negligible and they were excluded from analysis.

CONCLUSION

High-frequency signals and eye blinks may account for index values that falsely indicate consciousness. Compared with BIS, state entropy showed more false classifications of the clinical state at transition between consciousness and unconsciousness.

Rationale and Design of the Balanced Anesthesia Study: A Prospective Randomized Clinical Trial of Two Levels of Anesthetic Depth on Patient Outcome After Major Surgery

BACKGROUND

An association between relatively deep anesthesia, as guided by the bispectral index (BIS), and increased postoperative mortality has been demonstrated in 6 of 8 published observational studies, but association does not necessarily mean causality. Small clinical trials of anesthetic depth have demonstrated increased delirium and postoperative cognitive dysfunction in patients who were relatively deeply anesthetized, but have been inadequately powered to study mortality. A large-scale randomized study is required to determine whether causality exists.

METHODS

The primary hypothesis of our study is that "light" anesthesia, defined as a BIS target of 50, will reduce all-cause mortality within 1 year of surgery in comparison with "deep" anesthesia, defined as a BIS target of 35, in patients aged ≥60 years presenting for major surgery under general anesthesia. The trial is an international multicenter, randomized, parallel-group, double-blind (patients and investigators) prospective, intention-to-treat, safety and efficacy study. The relative reduction in mortality in the light anesthesia group is expected to be 20%, giving an absolute risk reduction from 10% to 8%. Power analysis using a = 0.049 and b = 0.2 indicates that 3250 patients are required in each group.

RESULTS

The study is underway, and 1325 patients have been recruited in 40 centers in 5 countries. It is anticipated that the study will be completed in 3 years.

CONCLUSIONS

This randomized controlled trial should definitively answer the question of whether titrating anesthetic depth makes a difference to patient outcome in a vulnerable patient group.

Entropy correlates with Richmond Agitation Sedation Scale in mechanically ventilated critically ill patients

Sedation is routinely used in intensive care units. However due to absence of objective scoring systems like Bispectral Index and entropy our ability to regulate the degree of sedation is limited. This deficiency is further highlighted by the fact that agitation scores used in intensive care units (ICU) have no role in paralyzed patients. The present study compares entropy as a sedation scoring modality with Richmond Agitation Sedation Scale (RASS) in mechanically ventilated, critically ill patients in an ICU. Twenty-seven, mechanically ventilated, critically ill patients of either sex, 16-65 years of age, were studied over a period of 24 h. They received a standard sedation regimen consisting of a bolus dose of propofol 0.5 mg/kg and fentanyl 1 lg/kg followed by infusions of propofol and fentanyl ranging from 1.5 to 5 mg/kg/h and 0.5 to 2.0 lg/kg/h, respectively. Clinically relevant values of RASS for optimal ICU sedation (between 0 and -3) in non-paralyzed patients were compared to corresponding entropy values, to find if any significant correlation exists between the two. These entropy measurements were obtained using the Datex-Ohmeda-M-EntropyTM module. This module is presently not approved by Food and Drug Administration (FDA) for monitoring sedation in ICU. A total of 527 readings were obtained. There was a statistically significant correlation between the state entropy (SE) and RASS [Spearman's rho/rs = 0.334, p\0.0001]; response entropy (RE) and RASS [Spearman's rho/rs = 0.341, p\0.0001]). For adequate sedation as judged by a RASS value of 0 to -3, the mean SE was 57.86 ± 16.50 and RE was 67.75 ± 15.65. The present study illustrates that entropy correlates with RASS (between scores 0 and -3) when assessing the level of sedation in mechanically ventilated critically ill patients.

Comparison of spectral entropy and BIS VISTA™ monitor during general anesthesia for cardiac surgery

OBJECTIVES

We compared the primary metrics of the Spectral entropy M-ENTROPY™ module and BIS VISTA™ monitor-i.e., bispectral index (BIS), state entropy (SE), and response entropy (RE) in terms of agreement and correlation during general anesthesia for cardiac surgery. We also evaluated responsiveness of electroencephalogram (EEG)-based and hemodynamic parameters to surgical noxious stimulation, skin incision, and sternotomy, hypothesizing that RE would be a better responsiveness predictor.

METHODS

BIS and entropy sensors were applied before anesthesia induction in 32 patients having elective cardiac surgery. Total intravenous anesthesia was standardized and guided by the BIS index with neuromuscular blockade tested with train-of-four monitoring. Parameters included SE, RE, BIS, forehead electromyography (EMG), and hemodynamic variables. Time points for analyzing BIS, entropy, and hemodynamic values were 1 min before and after: anesthesia induction, intubation, skin incision, sternotomy, cannulation of the aorta, cardiopulmonary bypass (CPB), cross-clamping the aorta, de-clamping the aorta, and end of CPB; also after starting the re-warming phase and at 10, 20, 30, and 40 min following.

RESULTS

The mean difference between BIS and SE (Bland-Altman) was 2.14 (+16/- 11; 95% CI 1.59-2.67), and between BIS and RE it was 0.02 (+14/- 14; 95% CI 0.01-0.06). BIS and SE (r(2) = 0.66; P = 0.001) and BIS and RE (r(2) = 0.7; P = 0.001) were closely correlated (Pearson's). EEG parameters, EMG values, and systolic blood pressure significantly increased after skin incision, and sternotomy. The effect of surgical stimulation (Cohen's d) was highest for RE after skin incision (-0.71; P = 0.0001) and sternotomy (-0.94; P = 0.0001).

CONCLUSION

Agreement was poor between the BIS index measured by BIS VISTA™ and SE values at critical anesthesia time points in patients undergoing cardiac surgery. RE was a good predictor of arousal after surgical stimulation regardless of the surgical level of muscle relaxation. Index differences most likely resulted from different algorithms for calculating consciousness level.

Using a short-term parameter of heart rate variability to distinguish awake from isoflurane anesthetic states

The measurement of anesthetic depth is important in anesthesiology. Although heart rate variability (HRV) is profoundly affected by general anesthesia, it has not yet been commonly used in this field. One of the reasons is the lack of suitable parameters of HRV for short-term observations. In this study, we designed a time domain parameter of HRV named the similarity index. It was based on observing the trend of the distribution of instantaneous heart rates as time moved. Taking epochs of ECG data as short as 64 s can derive the index. We observed the values of this index of 30 patients when they were awake and under isoflurane anesthesia. The values had very little overlapping between the two states and the prediction probability to distinguish the two states was 0.91. We suggest that HRV, if suitably treated, can play more roles in the monitoring of anesthetic depth.