Bispectral index and A-line AAI index as guidance for desflurane-remifentanil anaesthesia compared with a standard practice group: a multicentre study

Effectiveness Assessment of Bispectral Index Monitoring Compared with Conventional Monitoring in General Anesthesia: A Systematic Review and Meta-Analysis

Background and Objective. The Bispectral Index (BIS) is utilized to guide the depth of anesthesia monitoring during surgical procedures. However, conflicting results regarding the benefits of BIS for depth of anesthesia monitoring have been reported in numerous studies. The purpose of this meta-analysis and systematic review was to assess the effectiveness of BIS for depth of anesthesia monitoring. Search Methods. A systematic search of Ovid-MEDLINE, Cochrane, and PubMed was conducted from inception to April 20, 2023. Clinical trial registers and grey literature were also searched, and reference lists of included studies, as well as related review articles, were manually reviewed. Selection Criteria. The inclusion criteria were randomized controlled trials without gender or age restrictions. The control groups used conventional monitoring, while the intervention groups utilized BIS monitoring. The exclusion criteria included duplicates, reviews, animal studies, unclear outcomes, and incomplete data. Data Collection and Analysis. Two independent reviewers screened the literature, extracted data, and assessed methodological quality, with analyses conducted using R 4.0 software. Main Results. Forty studies were included. In comparison to the conventional depth of anesthesia monitoring, BIS monitoring reduced the postoperative cognitive dysfunction risk (RR = 0.85, 95% CI: 0.73∼0.99, P = 0.04), shortened the eye-opening time (MD = -1.34, 95% CI: -2.06∼-0.61, P < 0.01), orientation recovery time (MD = -1.99, 95% CI: -3.62∼-0.36, P = 0.02), extubation time (MD = -2.54, 95% CI: -3.50∼-1.58, P < 0.01), and postanesthesia care unit stay time (MD = -7.11, 95% CI: -12.67∼-1.55, P = 0.01) and lowered the anesthesia drug dosage (SMD = -0.39, 95% CI: -0.63∼-0.15, P < 0.01). Conclusion. BIS can be used to effectively monitor the depth of anesthesia. Its use in general anesthesia enhances the effectiveness of both patient care and surgical procedures.

Effect of bispectral index on intra-operative awareness: A meta-analysis of randomized controlled studies

Background

Randomized controlled trials (RCTs) investigating the efficacy of bispectral index (BIS) to reduce intra-operative awareness (IOA) have reported conflicting results. The purpose of this meta-analysis is to consolidate results from RCTs to assess the efficacy of BIS in reducing IOA when compared to controls. Secondary outcomes included time to extubation, time to spontaneous and/or verbal eye opening, PACU discharge time, and utilization of inhaled anesthetics.

Methods

RCTs which reported on one of the primary and/or secondary outcomes were included. Literature search utilized keywords "randomized control trial" and "intraoperative awareness." Meta-analysis was performed using RevMan 5.

Results

Twenty-seven RCTs were included in the study with a total of 35,585 patients, with 18,146 patients in the BIS and 17,439 in the control group. Eighteen of 14,062 patients (0.12%) and 42 of 16,765 (0.25%) reported definite IOA in the BIS and control group, respectively, with no statistically significant difference. BIS was effective in reducing the time to spontaneous eye opening by an average of 1.3 minutes and the time to extubation by an average of 1.97 minutes. There was no difference in PACU discharge times among the groups. There was a significant decrease in consumption of sevoflurane but no difference in desflurane and propofol compared to the control group.

Conclusion

While BIS monitoring results in decreased incidence of intra-operative awareness by half, it was not statistically significant. BIS provides modest benefits with regard to reducing the time to extubation, the time to spontaneous eye opening, and consumption of sevoflurane.Level of evidence: I.

Guidelines for reducing the environmental impact of general anaesthesia

OBJECTIVE

To provide guidelines for reducing the environmental impact of general anaesthesia.

DESIGN

A committee of ten experts from SFAR and SF2H and SFPC learned societies was set up. A policy of declaration of competing interests was applied and observed throughout the guideline-writing process. Likewise, it did not benefit from any funding from a company marketing a health product (drug or medical device). The committee followed the GRADE® method (Grading of Recommendations Assessment, Development and Evaluation) to assess the quality of the evidence on which the recommendations were based.

METHODS

We aimed to formulate recommendations according to the GRADE® methodology for three different fields: anaesthesia vapours and gases; intravenous drugs; medical devices and the working environment. Each question was formulated according to the PICO format (Population, Intervention, Comparator, Outcome). The literature review and recommendations were formulated according to the GRADE® methodology.

RESULTS

The experts' work on the synthesis and application of the GRADE® method led to the formulation of 17 recommendations. Since the GRADE® method could not be entirely applied to all of the questions, some of the recommendations were formulated as expert opinions.

CONCLUSION

Based on strong agreement between experts, we produced 17 recommendations designed to guide reducing the environmental impact of general anaesthesia.

Electroencephalography and Brain Oxygenation Monitoring in the Perioperative Period

Maintaining brain function and integrity is a pivotal part of anesthesiological practice. The present overview aims to describe the current role of the 2 most frequently used monitoring methods for evaluation brain function in the perioperative period, ie, electroencephalography (EEG) and brain oxygenation monitoring. Available evidence suggests that EEG-derived parameters give additional information about depth of anesthesia for optimizing anesthetic titration. The effects on reduction of drug consumption or recovery time are heterogeneous, but most studies show a reduction of recovery times if anesthesia is titrated along processed EEG. It has been hypothesized that future EEG-derived indices will allow a better understanding of the neurophysiological principles of anesthetic-induced alteration of consciousness instead of the probabilistic approach most often used nowadays.Brain oxygenation can be either measured directly in brain parenchyma via a surgical burr hole, estimated from the venous outflow of the brain via a catheter in the jugular bulb, or assessed noninvasively by near-infrared spectroscopy. The latter method has increasingly been accepted clinically due to its ease of use and increasing evidence that near-infrared spectroscopy-derived cerebral oxygen saturation levels are associated with neurological and/or general perioperative complications and increased mortality. Furthermore, a goal-directed strategy aiming to avoid cerebral desaturations might help to reduce these complications. Recent evidence points out that this technology may additionally be used to assess autoregulation of cerebral blood flow and thereby help to titrate arterial blood pressure to the individual needs and for bedside diagnosis of disturbed autoregulation.

Bispectral index for improving intraoperative awareness and early postoperative recovery in adults

BACKGROUND

The use of clinical signs, or end-tidal anaesthetic gas (ETAG), may not be reliable in measuring the hypnotic component of anaesthesia and may lead to either overdosage or underdosage resulting in adverse effects because of too deep or too light anaesthesia. Intraoperative awareness, whilst uncommon, may lead to serious psychological disturbance, and alternative methods to monitor the depth of anaesthesia may reduce the incidence of serious events. Bispectral index (BIS) is a numerical scale based on electrical activity in the brain. Using a BIS monitor to guide the dose of anaesthetic may have advantages over clinical signs or ETAG. This is an update of a review last published in 2014.

OBJECTIVES

To assess the effectiveness of BIS to reduce the risk of intraoperative awareness and early recovery times from general anaesthesia in adults undergoing surgery.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, and Web of Science on 26 March 2019. We searched clinical trial registers and grey literature, and handsearched reference lists of included studies and related reviews.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) and quasi-RCTs in which BIS was used to guide anaesthesia compared with standard practice which was either clinical signs or end-tidal anaesthetic gas (ETAG) to guide the anaesthetic dose. We included adult participants undergoing any type of surgery under general anaesthesia regardless of whether included participants had a high risk of intraoperative awareness. We included only studies in which investigators aimed to evaluate the effectiveness of BIS for its role in monitoring intraoperative depth of anaesthesia or potential improvements in early recovery times from anaesthesia.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for inclusion, extracted data, and assessed risk of bias. We assessed the certainty of evidence with GRADE.

MAIN RESULTS

We included 52 studies with 41,331 participants; two studies were quasi-randomized and the remaining studies were RCTs. All studies included participants undergoing surgery under general anaesthesia. Three studies recruited only participants who were at high risk of intraoperative awareness, whilst two studies specifically recruited an unselected participant group. We analysed the data according to two comparison groups: BIS versus clinical signs; and BIS versus ETAG. Forty-eight studies used clinical signs as a comparison method, which included titration of anaesthesia according to criteria such as blood pressure or heart rate and, six studies used ETAG to guide anaesthesia. Whilst BIS target values differed between studies, all were within a range of values between 40 to 60.BIS versus clinical signsWe found low-certainty evidence that BIS-guided anaesthesia may reduce the risk of intraoperative awareness in a surgical population that were unselected or at high risk of awareness (Peto odds ratio (OR) 0.36, 95% CI 0.21 to 0.60; I2 = 61%; 27 studies; 9765 participants). However, events were rare with only five of 27 studies with reported incidences; we found that incidences of intraoperative awareness when BIS was used were three per 1000 (95% CI 2 to 6 per 1000) compared to nine per 1000 when anaesthesia was guided by clinical signs. Of the five studies with event data, one included participants at high risk of awareness and one included unselected participants, four used a structured questionnaire for assessment, and two used an adjudication process to identify confirmed or definite awareness.Early recovery times were also improved when BIS was used. We found low-certainty evidence that BIS may reduce the time to eye opening by mean difference (MD) 1.78 minutes (95% CI -2.53 to -1.03 minutes; 22 studies; 1494 participants), the time to orientation by MD 3.18 minutes (95% CI -4.03 to -2.33 minutes; 6 studies; 273 participants), and the time to discharge from the postanaesthesia care unit (PACU) by MD 6.86 minutes (95% CI -11.72 to -2 minutes; 13 studies; 930 participants).BIS versus ETAGAgain, events of intraoperative awareness were extremely rare, and we found no evidence of a difference in incidences of intraoperative awareness according to whether anaesthesia was guided by BIS or by ETAG in a surgical population at unselected or at high risk of awareness (Peto OR 1.13, 95% CI 0.56 to 2.26; I2 = 37%; 5 studies; 26,572 participants; low-certainty evidence). Incidences of intraoperative awareness were one per 1000 in both groups. Only three of five studies reported events, two included participants at high risk of awareness and one included unselected participants, all used a structured questionnaire for assessment and an adjudication process to identify confirmed or definite awareness.One large study (9376 participants) reported a reduced time to discharge from the PACU by a median of three minutes less, and we judged the certainty of this evidence to be low. No studies measured or reported the time to eye opening and the time to orientation.Certainty of the evidenceWe used GRADE to downgrade the evidence for all outcomes to low certainty. The incidence of intraoperative awareness is so infrequent such that, despite the inclusion of some large multi-centre studies in analyses, we believed that the effect estimates were imprecise. In addition, analyses included studies that we judged to have limitations owing to some assessments of high or unclear bias and in all studies, it was not possible to blind anaesthetists to the different methods of monitoring depth of anaesthesia.Studies often did not report a clear definition of intraoperative awareness. Time points of measurement differed, and methods used to identify intraoperative awareness also differed and we expected that some assessment tools were more comprehensive than others.

AUTHORS' CONCLUSIONS

Intraoperative awareness is infrequent and, despite identifying a large number of eligible studies, evidence for the effectiveness of using BIS to guide anaesthetic depth is imprecise. We found that BIS-guided anaesthesia compared to clinical signs may reduce the risk of intraoperative awareness and improve early recovery times in people undergoing surgery under general anaesthesia but we found no evidence of a difference between BIS-guided anaesthesia and ETAG-guided anaesthesia. We found six studies awaiting classification and two ongoing studies; inclusion of these studies in future updates may increase the certainty of the evidence.

Effect of entropy-guided low-flow desflurane anaesthesia on laryngeal mask airway removal time in children undergoing elective ophthalmic surgery - A prospective, randomised, comparative study

Background and Aims:

In children, entropy-guided titration of isoflurane and sevoflurane leads to faster recovery after anaesthesia. However, role of entropy in recovery following desflurane anaesthesia is not known. Hence, we compared laryngeal mask airway (LMA) removal time and desflurane consumption with entropy and minimal alveolar concentration–guided titration in children given low-flow desflurane anaesthesia.

Methods:

After ethics committee approval and parental consent, 80 American Society of Anesthesiologists grade I–II children, age 2–14 years, undergoing elective ophthalmic surgery were randomised into entropy and minimal alveolar concentration–guided groups. After LMA insertion, anaesthesia was maintained using oxygen, air (FiO₂ 0.5) and desflurane using low fresh gas flow of 0.75 L/min. In the entropy-guided group, desflurane was titrated to maintain state entropy between 40 and 60. In the minimal alveolar concentration–guided group, desflurane was titrated to maintain a minimal alveolar concentration between 1 and 1.3. We recorded LMA removal time (from switching off desflurane at the end of surgery till removal of LMA), haemodynamic parameters, uptake and consumption of desflurane between the groups.

Results:

LMA removal time was significantly decreased in the entropy-guided group in comparison to the minimal alveolar concentration–guided group (4.34 ± 2.03 vs 8.8 ± 2.33 min) (P < 0.0001). Consumption of desflurane was significantly less in the entropy-guided group compared with the minimal alveolar concentration–guided group (18.7 ± 5.07 vs 25.3 ± 8.11 mL) (P < 0.0001).

Conclusion:

Entropy-guided low-flow desflurane anaesthesia is associated with faster LMA removal and reduced consumption of desflurane in children undergoing ophthalmic surgery.

Processed electroencephalogram and evoked potential techniques for amelioration of postoperative delirium and cognitive dysfunction following non-cardiac and non-neurosurgical procedures in adults

BACKGROUND

Postoperative delirium (POD) and postoperative cognitive dysfunction (POCD) may complicate a patient's postoperative recovery in several ways. Monitoring of processed electroencephalogram (EEG) or evoked potential (EP) indices may prevent or minimize POD and POCD, probably through optimization of anaesthetic doses.

OBJECTIVES

To assess whether the use of processed EEG or auditory evoked potential (AEP) indices (bispectral index (BIS), narcotrend index, cerebral state index, state entropy and response entropy, patient state index, index of consciousness, A-line autoregressive index, and auditory evoked potentials (AEP index)) as guides to anaesthetic delivery can reduce the risk of POD and POCD in non-cardiac surgical or non-neurosurgical adult patients undergoing general anaesthesia compared with standard practice where only clinical signs are used.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase and clinical trial registry databases up to 28 March 2017. We updated this search in February 2018, but these results have not been incorporated in the review.

SELECTION CRITERIA

We included randomized or quasi-randomized controlled trials comparing any method of processed EEG or evoked potential techniques (entropy, BIS, AEP etc.) against a control group where clinical signs were used to guide doses of anaesthetics in adults aged 18 years or over undergoing general anaesthesia for non-cardiac or non-neurosurgical elective operations.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by Cochrane. Our primary outcomes were: occurrence of POD; and occurrence of POCD. Secondary outcomes included: all-cause mortality; any postoperative complications; and postoperative length of stay. We used GRADE to assess the quality of evidence for each outcome.

MAIN RESULTS

We included six randomized controlled trials (RCTs) with 2929 participants comparing processed EEG or EP indices-guided anaesthesia with clinical signs-guided anaesthesia. There are five ongoing studies and one study awaiting classification.Anaesthesia administration guided by the indices from a processed EEG (bispectral index) probably reduces the risk of POD within seven days after surgery with risk ratio (RR) of 0.71 (95% CI 0.59 to 0.85; number needed to treat for an additional beneficial outcome (NNTB) of 17, 95% CI 11 to 34; 2197 participants; 3 RCTs; moderate quality of evidence). Three trials also showed the lower rate of POCD at 12 weeks after surgery (RR 0.71, 95% CI 0.53 to 0.96; NNTB 38, 95% CI 21 to 289; 2051 participants; moderate-quality evidence), but it is uncertain whether processed EEG indices reduce POCD at one week (RR 0.84, 95% CI 0.69 to 1.02; 3 trials; 1989 participants; moderate-quality evidence), and at 52 weeks (RR 0.30, 95% CI 0.05 to 1.80; 1 trial; 59 participants; very low quality of evidence). There may be little or no effect on all-cause mortality (RR 1.01, 95% CI 0.62 to 1.64; 1 trial; 1155 participants; low-quality evidence). One trial suggested a lower risk of any postoperative complications with processed EEG (RR 0.51, 95% CI 0.37 to 0.71; 902 participants, moderate-quality evidence). There may be little or no effect on reduced postoperative length of stay (mean difference -0.2 days, 95% CI -2.02 to 1.62; 1155 participants; low-quality evidence).

AUTHORS' CONCLUSIONS

There is moderate-quality evidence that optimized anaesthesia guided by processed EEG indices could reduce the risk of postoperative delirium in patients aged 60 years or over undergoing non-cardiac surgical and non-neurosurgical procedures. We found moderate-quality evidence that postoperative cognitive dysfunction at three months could be reduced in these patients. The effect on POCD at one week and over one year after surgery is uncertain. There are no data available for patients under 60 years. Further blinded randomized controlled trials are needed to elucidate strategies for the amelioration of postoperative delirium and postoperative cognitive dysfunction, and their consequences such as dementia (including Alzheimer's disease (AD)) in both non-elderly (below 60 years) and elderly (60 years or over) adult patients. The one study awaiting classification and five ongoing studies may alter the conclusions of the review once assessed.

Comparison of bispectral index and end-tidal anaesthetic concentration monitoring on recovery profile of desflurane in patients undergoing lumbar spine surgery

Background and Aims:

Several techniques have evolved over time to monitor depth of anesthesia and ensure enhanced recovery. This randomized double-blinded trial was designed to compare bispectral index (BIS) or end-tidal anaesthetic concentration (ETAC) monitoring on the recovery characteristics of patients undergoing thoracolumbar spine surgeries.

Methods:

Seventy American Society of Anesthesiologist I–II patients of either sex were randomized to Group B – BIS-guided protocol, Group E – ETAC-guided protocol, or Group S – Standard protocol. After intravenous induction, anaesthesia was maintained with desflurane in O₂/N₂O (50:50) mixture. In BIS, ETAC and Standard groups, inspired end-tidal desflurane concentration was varied to achieve BIS of 45–55, 0.8–1.0 age-corrected minimum alveolar concentration, and haemodynamic parameters within 20% of the baseline, respectively. Time to eye opening (emergence time, the primary outcome), time to extubation, and time to name recall from the discontinuation of the anaesthetic agent were recorded. Incidence of nausea, vomiting, and total analgesic consumption was noted for 24 h.

Results:

Emergence time (mean ± SD) in ETAC (5.1 ± 1.53 min) and BIS (5.0 ± 2.12 min)-guided groups was significantly lower than Standard group (7.5 ± 2.90 min). Extubation time in ETAC (6.3 ± 2.22 min) and BIS-guided group (6.5 ± 1.78 min) was significantly lower than Standard group (9.0 ± 3.20 min) (P < 0.001). Time to achieve fast track score of more than 12 was significantly less in BIS-guided group (13.12 ± 2.59 min).

Conclusion:

ETAC-guided anaesthesia is comparable to BIS-guided anaesthesia in achieving early recovery.

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.

Benefit of general anesthesia monitored by bispectral index compared with monitoring guided only by clinical parameters. Systematic review and meta-analysis

BACKGROUND

The bispectral index parameter is used to guide the titration of general anesthesia; however, many studies have shown conflicting results regarding the benefits of bispectral index monitoring. The objective of this systematic review with meta-analysis is to evaluate the clinical impact of monitoring with the bispectral index parameter.

METHODS

The search for evidence in scientific information sources was conducted during December 2013 to January 2015, the following primary databases: Medline/PubMed, LILACS, Cochrane, CINAHL, Ovid, SCOPUS and TESES. The criteria for inclusion in the study were randomized controlled trials, comparing general anesthesia monitored, with bispectral index parameter with anesthesia guided solely by clinical parameters, and patients aged over 18 years. The criteria for exclusion were studies involving anesthesia or sedation for diagnostic procedures, and intraoperative wake-up test for surgery of the spine.

RESULTS

The use of monitoring with the bispectral index has shown benefits reducing time to extubation, orientation in time and place, and discharge from both the operating room and post anesthetic care unit. The risk of nausea and vomiting after surgery was reduced by 12% in patients monitored with bispectral index. Occurred a reduction of 3% in the risk of cognitive impairment postoperatively at 3 months postoperatively and 6% reduction in the risk of postoperative delirium in patients monitored with bispectral index. Furthermore, the risk of intraoperative memory has been reduced by 1%.

CONCLUSION

Clinically, anesthesia monitoring with the BIS can be justified because it allows advantages from reducing the recovery time after waking, mainly by reducing the administration of general anesthetics as well as the risk of adverse events.

Intraoperative brain activity monitoring and postanesthesia care unit length of stay: results of a systematic review

A systematic review represents the highest level of evidence to inform clinical practice and research. The results of this systematic review report on the impact of intraoperative brain activity monitoring on postanesthesia care unit length of stay. If used to guide anesthesia practice, the intraoperative brain activity monitor will have a statistically insignificant impact on reducing postanesthesia care unit length of stay. Clinicians should be aware, however, that there is a clinically useful reduction in postanesthesia care unit length of stay resulting in potential cost savings.

Bispectral index for improving anaesthetic delivery and postoperative recovery

BACKGROUND

The use of clinical signs may not be reliable in measuring the hypnotic component of anaesthesia. The use of bispectral index (BIS) to guide the dose of anaesthetic may have certain advantages over clinical signs. This is the second update of a review originally published in 2007.

OBJECTIVES

The primary objective of this review focused on whether the incorporation of BIS into the standard practice for management of anaesthesia can reduce the risk of intraoperative awareness, consumption of anaesthetic agents, recovery time and total cost of anaesthesia in surgical patients undergoing general anaesthesia.

SEARCH METHODS

In this updated version, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 1), MEDLINE (1990 to 31 January 2013), EMBASE (1990 to 31 January 2013) and reference lists of articles. Previously, we searched to May 2009.

SELECTION CRITERIA

We included randomized controlled trials comparing BIS with standard practice criteria for titration of anaesthetic agents.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality, extracted data and analysed the data. We contacted study authors for further details.

MAIN RESULTS

We included 36 trials. In studies using clinical signs as standard practice, the results demonstrated a significant effect of the BIS-guided anaesthesia in reducing the risk of intraoperative awareness among surgical patients at high risk for awareness (7761 participants; odds ratio (OR) 0.24, 95% confidence interval (CI) 0.12 to 0.48). This effect was not demonstrated in studies using end tidal anaesthetic gas (ETAG) monitoring as standard practice (26,530 participants; OR 1.13, 95% CI 0.56 to 2.26). BIS-guided anaesthesia reduced the requirement for propofol by 1.32 mg/kg/hr (672 participants; 95% CI -1.91 to -0.73) and for volatile anaesthetics (desflurane, sevoflurane, isoflurane) by 0.65 minimal alveolar concentration equivalents (MAC) (95% CI -1.01 to -0.28) in 985 participants. Irrespective of the anaesthetics used, BIS reduced the following recovery times: time for eye opening (2557 participants; by 1.93 min, 95% CI -2.70 to -1.16), response to verbal command (777 participants; by 2.73 min, 95% CI -3.92 to -1.54), time to extubation (1501 participants; by 2.62 min, 95% CI -3.46 to -1.78), and time to orientation (373 participants; by 3.06 min, 95% CI -3.63 to -2.50). BIS shortened the duration of postanaesthesia care unit stay by 6.75 min (1953 participants; 95% CI -11.20 to -2.31) but did not significantly reduce the time to home readiness (329 participants; -7.01 min, 95% CI -30.11 to 16.09).

AUTHORS' CONCLUSIONS

BIS-guided anaesthesia can reduce the risk of intraoperative awareness in surgical patients at high risk for awareness in comparison to using clinical signs as a guide for anaesthetic depth. BIS-guided anaesthesia and ETAG-guided anaesthesia may be equivalent in protection against intraoperative awareness but the evidence for this is inconclusive. In addition, anaesthesia guided by BIS kept within the recommended range improves anaesthetic delivery and postoperative recovery from relatively deep anaesthesia.

The Effect of BIS Usage on Anaesthetic Agent Consumption, Haemodynamics and Recovery Time in Supratentorial Mass Surgery

OBJECTIVE

In this study, we aimed to compare Bispectral Index (BIS) monitoring with the conventional anaesthesia approach based on haemodynamic changes in terms of anaesthetic agent consumption, haemodynamic recordings, recovery time and cost.

METHODS

This study was performed in 82 patients, aged 20 to 60 years, who were operated for supratentorial mass and were graded ASA I or II. Cases were randomly divided into two equal groups. In the standard control group haemodynamic parameters were used to determine depth of anaesthesia and in the BIS group, BIS monitoring was applied. In the BIS group the BIS values were kept between 40 and 60; in the control group haemodynamic changes within the range of +/-20% of initial values were controlled using appropriate anaesthetic practice. Haemodynamic parameters, awakening conditions and drug usage were recorded.

RESULTS

The difference between the two groups in terms of timing of eye opening and initial spontaneous breath was not statistically significant. The 'Aldrete' score at the 20(th) postoperative minute for the BIS group was significantly higher than the score calculated for the control group (p<0.05). Rocuronium consumption (mg kg(-1) hr(-1)) was significantly lower in the BIS group than the control group (p<0.05). Although a statistically significant difference (p<0.05) was found between the two groups in terms of initial heart rate and SpO2 values, there was no clinically significant difference in other haemodynamic parameters.

CONCLUSION

Although using BIS monitoring to evaluate depth of anaesthesia does not bring much benefit versus the use of haemodynamic parameters, it may be beneficial for selected surgeries such as awake craniotomy, for patients with a history of awareness and in haemodynamically unstable patients.

The Effects of Bispectral Index and Neuromuscular Blockade Monitoring on the Depth of Anaesthesia and Recovery in Cardiac Patients Under Desflurane Anaesthesia

OBJECTIVE

In this study, we aimed to investigate the effects of bispectral index (BIS) and neuromuscular blockade monitoring on the depth of anaesthesia and recovery in cardiac patients, scheduled to undergo open cholecystectomy operation with desflurane anaesthesia.

METHODS

After the approval of the Ethics Committee and consent from the patients, patients were randomly divided into two groups. All patients received standard induction drugs, and 4-6% desflurane was used for maintenance of anaesthesia. In Group I, the anaesthesiologist was blind to BIS, and end-tidal volatile agent concentration (ETVAC) of desflurane was titrated according to the patients' hemodynamic changes. In Group II, ETVAC of desflurane was titrated to maintain BIS at 50-60. The hemodynamic data, BIS values, end-tidal volatile agent concentration (ETVAC) and train of four (TOF) values were recorded at pre-induction, post-induction, post-intubation, 1st and 5th minutes after surgical incision and then every 15 min. At the end of the operation, extubation time and the time to reach an Aldrete recovery score ≥9 were recorded in each group. Additionally, neuromuscular agent and narcotic agent doses were recorded.

RESULTS

The BIS values were lower for Group I in all times, except pre- and post-induction times (p<0.05). ETVAC values of all times were lower for Group II (p<0.05).

CONCLUSION

The requirement of volatile agent, which was given according to BIS monitoring, was lower than in the standard technique, but it is considered not to affect the early extubation, recovery and neuromuscular agent requirement dependent on TOF monitoring.

Randomized clinical trial on the influence of anaesthesia protocol on intestinal motility during laparoscopic surgery requiring small bowel anastomosis

Background

Hyperperistalsis of the small bowel during laparoscopic surgery may cause mucosal prolapse and reduce exposure, making laparoscopic suturing or stapling more demanding for the surgeon. Although it is commonly accepted that both opioids and volatile anaesthetics induce intestinal paralysis, intestinal hyperactivity during anaesthesia is not uncommon. This randomized trial investigated the effect of different volatile anaesthetics on intestinal motility and the impact on surgeon satisfaction.

Methods

Patients scheduled for laparoscopic gastric bypass surgery were randomized to receive sevoflurane or desflurane in a balanced anaesthetic regimen. After surgical exposure peristaltic waves were counted over 1 min in a segment of the jejunum. Following evaluation of intestinal motility, N-butylhyoscine, an antimuscarinic anticholinergic agent that relaxes bowel smooth muscle cells, could be administered if the surgeon judged the intestinal motility as disturbing. The endpoints were number of peristaltic waves and incidence of N-butylhyoscine administration, a surrogate for surgeon satisfaction.

Results

Twenty-two patients were randomized to each group. The groups were similar in age, sex and body mass index. There was a statistically significant difference in intestinal motility between the desflurane and sevoflurane groups: median (range) 7 (0–12) versus 1 (0–10) waves counted over 1 min respectively (P &lt; 0·001). A higher proportion of patients in the desflurane group received N-butylhyoscine (10 of 22 versus 1 of 22 in the sevoflurane group; P = 0·004).

Conclusion

Desflurane increased intestinal motility and decreased surgeon satisfaction compared with sevoflurane during laparoscopic gastric bypass surgery. A sevoflurane-based anaesthetic protocol can help to avoid disturbing hyperperistalsis. Registration number: B39620097060 (http://www.clinicaltrials.be).

Intraoperative brain activity monitoring and post-anesthesia care length of stay: A systematic review

BACKGROUND

The use of intraoperative brain activity monitoring helps to guide the administration of general anesthesia. Additional benefits of brain activity monitoring in the face of general anesthesia include increased patient satisfaction, decreased nausea and vomiting, decreased pain, and decreased risk of intraoperative recall. Conflicting reports in the literature exist concerning the efficacy of brain activity monitoring at reducing the post-anesthesia care unit length of stay.

OBJECTIVES

The objective of this systematic review was to determine the effect of intraoperative brain activity monitoring on post-anesthesia care unit length of stay.

INCLUSION CRITERIA

The review considered studies that included all patients over eight years of age receiving general anesthesia for any medical procedure.The review included studies that compared the use of intraoperative brain activity monitoring to standard clinical practice and reported post-anesthesia care unit length of stay data.This review included randomized controlled trials which met all inclusion criteria.The review considered studies that included as outcome the length of stay in the post-anesthesia care unit following general anesthesia.

SEARCH STRATEGY

A three-step search strategy was utilized to find both published and unpublished studies in English language only. The search time frame was January 1990 through December 2010. An initial limited MEDLINE search was completed followed by analysis of the text words contained in the title and abstract, and the index terms used to describe the article. A second search using all identified terms was then undertaken across all included databases. Finally, the reference list for all identified studies was searched for additional studies.

METHODOLOGICAL QUALITY

The reviewers utilized the Joanna Briggs Institute Critical Appraisal Checklist for Randomized Controlled Trials to assess methodological quality.

DATA COLLECTION

Data was extracted using the Joanna Briggs Institute Data Extraction Form for Observational/Experimental Studies.

DATA SYNTHESIS

Results were analyzed using SUMARI software from the Joanna Briggs Institute. Nine randomized control trials were included in the final analysis. Results indicated a statistically insignificant 3.47 minute (p=0.14) reduction in post-anesthesia care unit length of stay when intraoperative brain activity monitoring was utilized.

RESULTS

Pooling of data indicated a statistically nonsignificant 3.47 minute (p=0.14) reduction in post-anesthesia care unit length of stay when general anesthesia administration was guided by intraoperative brain activity monitoring.

CONCLUSIONS

Based on the results of this review, the use of intraoperative brain activity monitoring can be recommended to help decrease the post-anesthesia care unit length of stay in patients receiving general anesthesia. Although statistically insignificant, any reduction in post-anesthesia care unit length of stay will decrease cost to the patient, decrease burden to the post-anesthesia care unit, and expedite patient throughput thereby reducing cost and impact on the healthcare system as a whole.

IMPLICATIONS FOR PRACTICE

Anesthesia providers utilizing intraoperative brain activity monitoring will realize a clinically relevant reduction in post-anesthesia care unit length of stay for their patients receiving general anesthesia. Impact on practice includes increased efficiency and decreased patient and health care system cost. Although not necessarily realized in small surgical settings, the cumulative reduction in post-anesthesia care unit length of stay in larger facilities will be significant.

IMPLICATIONS FOR RESEARCH

Additional work to quantify the range of depth of general anesthesia to produce the best reduction in post-anesthesia care unit length of stay is needed. This review simply looked at the use of the technology and did not stratify the range or level of general anesthesia, as determined by intraoperative brain activity monitoring, that would result in the greatest reduction in post-anesthesia care unit length of stay.

Processed electroencephalogram in depth of anesthesia monitoring

PURPOSE OF REVIEW

We critically review the principles underlying processed electroencephalogram (EEG) monitors and recent studies validating their use in monitoring anesthetic depth.

RECENT FINDINGS

Depth of anesthesia is a theoretical construct to conceptualize anesthetic effects on the central nervous system as discrete or continuous phases or states. Clinical signs for assessing anesthetic depth are currently being supplemented by brain monitors. Their use may help to prevent insufficient anesthesia, which can lead to intraoperative awareness with recall, as well as anesthetic overdose, which may be associated with adverse events. Commercial and open-source brain monitoring indices are computed from frequency, entropy, or information theoretic analysis of the spontaneous or evoked EEG. These techniques are undergoing refinement to determine the best method for titrating anesthetics. Future depth-of-anesthesia monitors will benefit from current work aimed at correlating anesthetic effects to alterations in specific neural circuits.

SUMMARY

Current processed EEG monitors are limited by their calibration range and the interpatient variability in their dose-response curves. The next generation of depth-of-anesthesia monitors will require a greater understanding of the transformations of cortical and subcortical activity into EEG signals, the effects of anesthetics at a systems level, and the neural correlates of consciousness.

The Entropy Module® and Bispectral Index® as Guidance for Propofol-Remifentanil Anaesthesia in Combination with Regional Anaesthesia Compared with a Standard Clinical Practice Group

This study was designed to investigate the impact of the Entropy Module® and Bispectral Index® (BIS) monitoring on drug consumption and recovery times compared with standard anaesthetic practice in patients undergoing orthopaedic surgery using a combination of regional and general anaesthesia as performed by an experienced anaesthesiologist. We hypothesised that electroencephalogram monitoring would lead to a lower drug consumption as well as shorter recovery times.

With institutional review board approval and written informed consent, 90 adult patients undergoing surgery to the upper or lower extremity received regional anaesthesia for post- and intraoperative pain control and were randomised to receive general anaesthesia by propofol/remifentanil infusion controlled either solely by clinical parameters or by targeting Entropy or BIS values of 50. Recovery times and drug consumption were recorded.

Data from 79 patients were analysed. Compared with standard practice, patients with Entropy or BIS monitoring showed a similar propofol consumption (standard practice 101±22 μg/kg/minute, Entropy 106±24 μg/kg/minute, BIS 104±20 μg/kg/minute) and showed similar Aldrete scores (10/10) one minute after extubation: 9.1∓0.3, 9.2±0.6 and 9.3±0.5, respectively. Time points of extubation were 7.3±2.9 minutes, 9.2∓3.9 minutes and 6.8±2.9 minutes, respectively, demonstrating a significant difference between Entropy and BIS (P=0.023).

Compared with standard practice, targeting an Entropy or BIS value of 50 did not result in a reduction of propofol consumption during general anaesthesia combined with regional anaesthesia as performed by an experienced anaesthesiologist in orthopaedic patients.

[Measurement of the depth of anaesthesia]

One of the most important mandates of the anaesthesiologist is to control the depth of anaesthesia. An unsolved problem is that a straight definition of the depth of anaesthesia does not exist. Concerning this it is rational to separate hypnosis from analgesia, from muscle relaxation and from block of cardiovascular reactions. Clinical surrogate parameters such as blood pressure and heart rate are not well-suited for a valid statement about the depth of hypnosis. To answer this question the brain has become the focus of interest as the target of anaesthesia. It is possible to visualize the brain's electrical activity from anelectroencephalogram (EEG). The validity of the spontaneous EEG as an anesthetic depth monitor is limited by the multiphasic activity, especially when anaesthesia is induced (excitation) and in deep anaesthesia (burst suppression). Recently, various commercial monitoring systems have been introduced to solve this problem. These monitoring systems use different interpretations of the EEG or auditory-evoked potentials (AEP). These derived and calculated variables have no pure physiological basis. For that reason a profound knowledge of the algorithms and a validation of the monitoring systems is an indispensable prerequisite prior to their routine clinical use. For the currently available monitoring systems various studies have been reported. At this time it is important to know that the actual available monitors can only value the sedation and not the other components of anaesthesia. For example, they cannot predict if a patient will react to a painful stimulus or not. In the future it would be desirable to develop parameters which allow an estimate of the other components of anaesthesia in addition to the presently available monitoring systems to estimate sedation and muscle relaxation. These could be sensoric-evoked potentials to estimate analgesia and AEPs for the detection of awareness.

Prevention of awareness during anaesthesia

Inadequate anaesthesia may lead to awareness. A properly trained anaesthetist, administering anaesthesia according to their knowledge of pharmacology and patient and surgical characteristics, assisted by clinical signs and monitoring, can minimize this risk. Relying upon volatile-based anaesthesia delivered at a concentration of at least 0.5 MAC may be effective, but this precludes the use of total intravenous anaesthesia techniques and in any case may lead to unwanted hypotension. Equipment failure may occur. Benzodiazepines do not protect the patient from awareness. The development of electroencephalographic monitors of anaesthetic depth provides an opportunity to prevent awareness. Two large scale studies, one of which was a randomized trial, have identified a 5-fold reduction in risk of awareness when depth of anaesthesia using bispectral index monitoring was used. The incidence of awareness can be further reduced with currently available techniques used more widely.

Narcotrend-assisted propofol/remifentanil anaesthesia vs clinical practice: does it make a difference?

BACKGROUND

The Narcotrend is a computer-based EEG monitor designed to measure the depth of anaesthesia. The aim of the present study is to test the hypothesis that the intraoperative level of anaesthetic depth differs if decision-making is guided by Narcotrend monitoring or not.

METHODS

Forty-eight patients undergoing elective surgery were randomized to receive a Narcotrend-controlled propofol/remifentanil anaesthetic regimen or standard clinical practice. In the EEG group, anaesthesia was adjusted to achieve a Narcotrend level of D2-E0, which is recommended for moderate to deep anaesthetic depth for surgery. EEG values were recorded continuously every 20 s in both groups. Depending on data distribution, group comparisons of the EEG parameters, propofol plasma concentration, and recovery characteristics were performed by analysis of variance for repeated measurements or non-parametric statistics.

RESULTS

About 62 (sd 29)% of the Narcotrend values were within the target level in the EEG group during maintenance of anaesthesia; this was true for 64 (26)% of the data in the non-EEG group. The variance of the Narcotrend data was significantly lower in the EEG group compared with the non-EEG group [median: 0.4 (range: 3.5) vs 0.6 (2.5); P = 0.048]. There was no difference in propofol or remifentanil dosage, propofol plasma concentrations, and time for extubation. Ten minutes after extubation, visual analogue scores for nausea indicated a lower incidence in the Narcotrend group [7 (15) vs 24 (34); P = 0.005].

CONCLUSIONS

Guidance of anaesthesia with the Narcotrend-monitor leads to fewer deviations from a defined target than clinical assessment of anaesthetic depth only. This results in lower scores of nausea in the immediate period after anaesthesia.

Bispectral index for improving anaesthetic delivery and postoperative recovery

BACKGROUND

The use of clinical signs may not be reliable to measure the hypnotic component of anaesthesia. The use of bispectral index to guide the dose of anaesthetics may have certain advantages over clinical signs.

OBJECTIVES

The objective of this review was to assess whether bispectral index (BIS) reduced anaesthetic use, recovery times, recall awareness and cost.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, Issue 2), MEDLINE (1990 to May 2007), EMBASE (1990 to May 2007) and reference lists of articles.

SELECTION CRITERIA

We included randomized controlled trials comparing BIS with clinical signs (CS) in titrating anaesthetic agents.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality, extracted data and analysed the data. We contacted study authors for further details.

MAIN RESULTS

We included 20 studies with 4056 participants. Seven recent trials are still awaiting assessment. BIS-guided anaesthesia reduced the requirement for propofol by 1.30 mg/kg/hr (578 participants; 95% confidence interval (CI) -1.97 to -0.62) and for volatile anaesthetics (desflurane, sevoflurane, isoflurane) by 0.17 minimal alveolar concentration equivalents (MAC) (689 participants; 95% CI -0.27 to -0.07). Irrespective of the anaesthetic, BIS reduced the recovery times: time for eye opening by 2.43 min (996 participants; 95% CI -3.60 to -1.27), response to verbal command by 2.28 min (717 participants; 95% CI -3.47 to -1.09), time to extubation by 3.05 min (1057 participants; 95% CI -3.98 to -2.11) and orientation by 2.46 min (316 participants; 95% CI -3.21 to -1.71). BIS shortened the duration of postanaesthesia care unit stay by 6.83 min (584 participants; 95% CI -12.08 to -1.58) but did not reduce time to home readiness (329 participants; 95% CI -30.11 to 16.09). The BIS-guided anaesthesia significantly reduced the incidence of intraoperative recall awareness in surgical patients with high risk of awareness (OR 0.20, 95% CI 0.05 to 0.79).

AUTHORS' CONCLUSIONS

Anaesthesia guided by BIS within the recommended range (40 to 60) could improve anaesthetic delivery and postoperative recovery from relatively deep anaesthesia. In addition, BIS-guided anaesthesia has a significant impact on reduction of the incidence of intraoperative recall in surgical patients with high risk of awareness.

Bispectral index-guided general anesthesia in combination with thoracic epidural analgesia reduces recovery time in fast-track colon surgery

BACKGROUND

The impact of bispectral index (BIS)-guided general anesthesia on recovery from general anesthesia has been evaluated in different patient populations. The benefit of using BIS has been inconsistent. We designed this study to examine the value of BIS-guided anesthesia in a fast-track setting where the goal is rapid recovery.

METHODS

Forty-four patients undergoing open colon resection were randomly assigned to receive either BIS-guided (BIS group, n = 22) or clinically guided (standard care group, n = 22) total IV anesthesia with propofol after placing a thoracic epidural catheter. Duration of postanesthesia care unit stay, time to tracheal extubation, direct drug cost, the incidence of hemodynamic abnormalities, ability of ambulation on the day of surgery, and patient satisfaction with anesthetic management were assessed.

RESULTS

In the BIS-guided group, tracheal extubation was achieved significantly earlier (7.6 vs. 15.4 min, P < 0.01) and the postanesthesia care unit stay was significantly shorter (51 vs. 85 min, P < 0.01). Total anesthetic drug cost was reduced by 23% and the incidence of hypotension requiring treatment was significantly lower in the BIS group. Early ambulation, patient satisfaction, and incidence of adverse events were not significantly different between the groups.

CONCLUSIONS

BIS-guided IV anesthesia in combination with thoracic epidural analgesia facilitates rapid recovery and reduces the overall cost of care in patients undergoing fast-track colon surgery.

Dexmedetomidine infusion as a supplement to isoflurane anaesthesia for vitreoretinal surgery

BACKGROUND

We explored the sympatholytic property of dexmedetomidine, especially its role in intraocular pressure (IOP) reduction, haemodynamic stability, and attenuation of extubation response.

METHOD

In this double-blind, randomized, controlled trial approved by the Hospital Ethics Committee, 60 patients undergoing elective vitreoretinal surgery were allocated to two groups, receiving either placebo or dexmedetomidine. A loading dose of dexmedetomidine 2.5 microg kg(-1) h(-1) (or placebo in same volume) was infused for 10 min immediately before induction of anaesthesia with propofol, followed by a maintenance dexmedetomidine or placebo infusion at 0.4 microg kg(-1) h(-1) till 30 min before the end of the operation. Anaesthesia was maintained with isoflurane, oxygen, and air mixture. IOP was measured before the loading dose and 1 min after tracheal intubation. The mean arterial pressure (MAP) and heart rate (HR) during loading, induction, maintenance, extubation, and recovery period were measured. The degree of strain on extubation was graded from 0 to 5.

RESULTS

The use of vasopressor/labetalol/atropine and the reduction in IOP were comparable between the two groups. There was a significant variation in MAP and HR over time within group, but not between groups. The median degree of strain was significantly lower (P = 0.049), and the time to reach Aldrete score of 10 shorter (P = 0.031) in the dexmedetomidine group.

CONCLUSION

Dexmedetomidine can be used without undue haemodynamic fluctuation and can decrease the excitatory response during extubation. The reduction in IOP with dexmedetomidine was comparable with placebo.

Spectral entropy assessment with auditory evoked potential in neuroanesthesia

OBJECTIVE

The assessment of the level of anesthesia is a very hard task, since no gold standard has stood out in the past three decades. Middle Latency Auditory Evoked Potential (MLAEP) is one of the most popular neurophysiological tools for anesthesia monitoring. Recently, Spectral Entropy (SpEn) has been introduced: it provides two different parameters, State Entropy (SE) and Response Entropy (RE). The aim of this prospective study is to check SpEn end-point, comparing it to MLAEPs in neurosurgical anesthesia.

METHODS

Twenty patients submitted to elective supratentorial neurosurgery for removal of a temporal-parietal meningioma were included in the study. SpEn and MLAEPs were simultaneously monitored using the M-entropy module S/5 (GE Health Care, Helsinki, Finland) and Alaris Medical System AEP-ARX index monitor (AAI) (Kidemosevej, Denmark), respectively.

RESULTS

Four thousand and sixty four data points of SE, RE and AAI were recorded and ROC curves comparing AAI to RE and SE showed a highly significant (p<0.0001) area under the curve. The RE and SE cut-off values (showing maximal sensitivity with maximal specificity) to discriminate anesthesia from awake or consciousness sedation were 61 and 58, respectively. However, in a group of data points, low AAI was associated to high SpEn (577 data points for RE and 770 for SE) and vice versa (31 data points for RE and 43 for SE). The prediction probability for SE was 0.977 and for RE was 0.968.

CONCLUSIONS

Our results suggest that SpEn is as effective as AAI.

SIGNIFICANCE

Our results show that SpEn is able to discriminate between the levels of wakefulness and surgical anesthesia. However, the meaning of data showing a discrepancy between AAI and SpEn is not yet clear and calls for further study.

Does Monitoring Bispectral Index or Spectral Entropy Reduce Sevoflurane Use?

A decrease in volatile anesthetic consumption has been demonstrated using bispectral index (BIS), whereas data concerning spectral entropy are lacking. One hundred and forty adult patients scheduled for surgical procedures lasting more than 1 h were prospectively randomized to receive an anesthetic controlled either by BIS or by spectral entropy or solely by clinical variables. Anesthesia was induced with propofol and sufentanil. Sufentanil was infused continuously thereafter. Sevoflurane was administered in 1 L/min O2/N2O. The sevoflurane concentration was adjusted according to conventional clinical variables in the standard practice group, whereas the 40-60 interval was applied for the BIS and spectral entropy-guided groups. The sevoflurane vaporizer was weighed before and after anesthesia, and consumption was calculated. Groups were comparable for demographic data except for weight (heavier in the spectral entropy-guided group, P < 0.05). Compared with standard practice, patients with BIS or spectral entropy monitoring required 29% less sevoflurane (normalized sevoflurane consumption to the weights of the patients and to the durations of anesthesia; both P < 0.03) and a similar sufentanil dose. An unintended improvement in the standard practice group (positive bias) was observed. In conclusion, BIS and spectral entropy monitoring have the same sparing effect of sevoflurane.

Reduction in anaesthetic drug consumption is correlated with mean titrated intra-operative Bispectral Index values

BACKGROUND

Several studies have shown a reduction in anaesthetic drug consumption with Bispectral Index (BIS) titration compared with standard clinical practice. However, the amount of reduction varied widely between 1% and 40%. We investigated the correlation between reduction in anaesthetic drug consumption and mean titrated BIS values.

METHODS

An analysis upon randomized controlled trials cited until January 2006 in MEDLINE and other databases investigating the potential reduction in anaesthetic (hypnotic) drug consumption with BIS titration was performed. Investigations with a marked difference (> 15%) in opioid drug consumption between the BIS group and the standard practice group were excluded. Correlations between amount of reduction in hypnotic drug use and the mean titrated BIS value were analysed with linear regression.

RESULTS

Fourteen manuscripts covering 2582 patients were included into the analysis. The mean BIS value in the standard clinical practice group averaged over all studies was 43.6 +/- 3.2 and the mean BIS value in the BIS-titrated group was 49.9 +/- 5.4. The amount of reduction in hypnotic drug use correlated significantly with the mean BIS values in the BIS-titrated groups (r =0.68) and with the differences between the mean BIS value in the BIS-titrated group and the mean BIS value in the standard clinical practice group (r = 0.70). Every point of BIS difference between the two groups resulted in a reduced hypnotic drug use of approximately 2%.

CONCLUSION

Despite differences in the study designs and in the drugs used, a linear correlation between the mean titrated BIS value and the hypnotic drug saving potential was found.

Response entropy is more reactive than bispectral index during laparoscopic gastric banding

OBJECTIVE

There is a potential use for spectral entropy or bispectral index (BIS) for controlling level of anesthesia, but it is not known how these EEG monitors relate during steady state anesthesia. We compared Response Entropy (RE) and BIS during anesthesia for laparoscopic gastric banding with RE targeted to 45.

METHODS

Forty patients undergoing laparoscopic gastric banding were randomly assigned to receive either fentanyl or dexmedetomidine infusion, with desflurane concentration adjusted to maintain RE at 45. During anesthesia the average RE and BIS was determined in each patient and the RE-BIS difference plotted as a function of RE every 10 seconds. Fifteen of 40 patients showed activation of RE above 60 during surgery. In these patients RE, BIS and the electromyogram (EMG) were evaluated for the period 10 minutes before and including the peak change in RE.

RESULTS

In fentanyl and dexmedetomidine treated patients the average RE was 44-47 with no statistical difference between anesthesia groups or between RE and BIS. In each patient there was a linear relationship between the RE-BIS difference and RE during anesthesia. RE and BIS were similar at a level of 41-44 and RE showed a greater range at higher and lower values compared to BIS. When RE activation was identified during surgery in 15 patients, it was associated with an increase in BIS and EMG.

CONCLUSION

Within the range of 41-44, RE and BIS are equal but the gain of RE is 0.5 greater than BIS with deeper or lighter anesthesia. This is not likely due to increased smoothing with BIS. Identifying periods of RE activation show that BIS, EMG and RE increase together.

Use of cerebral monitoring during anaesthesia: effect on recovery profile

This review article examines the effect of cerebral monitoring using an EEG-based device [i.e. bispectral index (BIS), patient state analyzer (PSA), auditory evoked potential (AEP), cerebral state index (CSI), or entropy] on titration of anaesthetic, analgesic and cardiovascular drugs during surgery. In addition, articles discussing the effects of these cerebral monitoring devices on recovery profiles following general anaesthesia, postoperative side effects, and anaesthetic costs are reviewed.

Depth of anaesthesia monitoring: what's available, what's validated and what's next?

Depth of anaesthesia monitors might help to individualize anaesthesia by permitting accurate drug administration against the measured state of arousal of the patient. In addition, the avoidance of awareness or excessive anaesthetic depth might result in improved patient outcomes. Various depth of anaesthesia monitors based on processed analysis of the EEG or mid-latency auditory-evoked potentials are commercially available as surrogate measures of anaesthetic drug effect. However, not all of them are validated to the same extent.

A-Line, Bispectral Index, and Estimated Effect-Site Concentrations: A Prediction of Clinical End-Points of Anesthesia

Autoregressive modeling with exogenous input of middle-latency auditory evoked potentials (A-Line AEP index, AAI) has been developed for monitoring depth of anesthesia. We investigated the prediction of recovery and dose-response relationship of desflurane and AAI or bispectral index (BIS) values. Twenty adult men scheduled for radical prostatectomy were recruited. To minimize opioid effects, analgesia was provided by a concurrent epidural in addition to the general anesthetic. Electrodes for AAI and BIS monitoring and a headphone for auditory stimuli were applied. Propofol and remifentanil were used for anesthetic induction. Maintenance of anesthesia was with desflurane only. For comparison to AAI and BIS monitor parameters, pharmacokinetic models for desflurane and propofol distribution and effect-site concentrations were used to predict clinical end-points (Prediction probability P(K)). Patients opened their eyes at an AAI value of 47 +/- 20 and a BIS value of 77 +/- 14 (mean +/- sd), and the prediction probability for eye opening was P(K) = 0.81 for AAI, P(K) = 0.89 for BIS, and P(K) = 0.91 for desflurane effect-site concentration. The opening of eyes was best predicted by the calculated desflurane effect-site concentration. The relationship between predicted desflurane effect-site concentration versus AAI and BIS was calculated by nonlinear regression analysis (r = 0.75 for AAI and r = 0.80 for BIS). The correlation between BIS and clinical end-points of anesthesia or the desflurane effect-compartment concentration is better than for the AAI.