M-Entropy guidance vs standard practice during propofol-remifentanil anaesthesia: a randomised controlled trial

Current perioperative nociception monitoring and potential directions

Perioperative nociception-antinociception balance is essential for the prevention of adverse postoperative events. Estimating the nociception level helps optimize intraoperative management. In the past two decades, various nociception monitoring devices have been developed for the identification of intraoperative nociception. However, each type of nociception monitoring device has advantages and disadvantages, limiting their clinical application in particular patients and settings. Therefore, this review aimed to summarize the information on nociceptor monitoring in current clinical settings, explore each technique's particularities, and possible future directions to provide a reference for clinicians and researchers.

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.

Evaluation and correlation of nociceptive response index and spectral entropy indices as monitors of nociception in anesthetized patients

Objectives

During anesthesia, the response to these stimuli depends on the balance between nociception and antinociception. Recently, various monitoring systems based on the variables derived from electroencephalography, plethysmography, autonomic tone, reflex pathways, and composite algorithms have been introduced for monitoring nociception. The main aim of our study was to evaluate and correlate the physiological variables which reflect the autonomic nervous system response to nociception, such as heart rate (HR), systolic blood pressure (SBP), perfusion index (PI), and nociceptive response index (NRI), with the spectral entropy indices response entropy (RE) and RE-state entropy (SE), which reflects electromyographic (EMG) activation as a response to pain.

Materials and Methods

This is a retrospective analysis of the data from a prospective study on the hypnotic and analgesic effects and the recovery profile of sevoflurane-based general anesthesia. Eighty-six patients undergoing single-agent sevoflurane anesthesia were recruited in the study. The study parameters, HR, SBP, SE, RE, RE-SE, PI, and NRI, were recorded at predefined time points before and after a standardized noxious stimulus. Correlation between the variables was carried out by applying the Pearson correlation equation for normal and the Spearman correlation equation for non-normally distributed data. Receiver operating characteristic (ROC) graphs were plotted, and the area under the curve was calculated to assess the diagnostic accuracy of post-stimulus NRI in detecting pain which was defined as RE-SE >10.

Results

There was a significant increase in the SBP, HR, NRI, RE, SE, and RE-SE and a considerable decrease in PI values during the post-noxious period compared to the pre-noxious period. There was no correlation between the absolute values of NRI and entropy indices at T2. However, among the reaction values, there was a weak correlation between the reaction values of NRI and RE (r = 0.30; P = 0.05). The area under the ROC curve for NRI to detect pain as defined by RE-SE >10 was 0.56.

Conclusion

During sevoflurane anesthesia, the application of noxious stimulus causes significant changes in variables reflecting sympathetic response and EMG activity. However, NRI failed to detect nociception, and there was only a weak correlation between the reaction values of NRI and RE-SE.

Time-trend analysis of the center frequency of the intrinsic mode function from the Hilbert-Huang transform of electroencephalography during general anesthesia: a retrospective observational study

BACKGROUND

Anesthesiologists are required to maintain an optimal depth of anesthesia during general anesthesia, and several electroencephalogram (EEG) processing methods have been developed and approved for clinical use to evaluate anesthesia depth. Recently, the Hilbert-Huang transform (HHT) was introduced to analyze nonlinear and nonstationary data. In this study, we assessed whether the changes in EEG characteristics during general anesthesia that are analyzed by the HHT are useful for monitoring the depth of anesthesia.

METHODS

This retrospective observational study enrolled patients who underwent propofol anesthesia. Raw EEG signals were obtained from a monitor through a previously developed software application. We developed an HHT analyzer to decompose the EEG signal into six intrinsic mode functions (IMFs) and estimated the instantaneous frequencies (HHT_IF) for each IMF. Changes over time in the raw EEG waves and parameters such as HHT_IF, BIS, spectral edge frequency 95 (SEF95), and electromyogram parameter (EMGlow) were assessed, and a Gaussian process regression model was created to assess the association between BIS and HHT_IF.

RESULTS

We analyzed EEG signals from 30 patients. The beta oscillation frequency range (13-25 Hz) was detected in IMF1 and IMF2 during the awake state, then after loss of consciousness, the frequency decreased and alpha oscillation (8-12 Hz) was detected in IMF2. At the emergence phase, the frequency increased and beta oscillations were detected in IMF1, IMF2, and IMF3. BIS and EMGlow changed significantly during the induction and emergence phases, whereas SEF95 showed a wide variability and no significant changes during the induction phase. The root mean square error between the observed BIS values and the values predicted by a Gaussian process regression model ranged from 4.69 to 9.68.

CONCLUSIONS

We applied the HHT to EEG analyses during propofol anesthesia. The instantaneous frequency in IMF1 and IMF2 identified changes in EEG characteristics during induction and emergence from general anesthesia. Moreover, the HHT_IF in IMF2 showed strong associations with BIS and was suitable for depicting the alpha oscillation. Our study suggests that the HHT is useful for monitoring the depth of anesthesia.

High peak inspiratory pressure may be associated with intraoperative coughing during neurosurgery under general anesthesia without neuromuscular blockade: a retrospective study

BACKGROUND

The endotracheal cuff pressure depends on the airway pressure during positive-pressure ventilation. A high endotracheal cuff pressure may be related to intraoperative coughing, which can be detrimental during neurosurgery. We investigated the incidence of intraoperative coughing and its association with peak inspiratory pressure (PIP) during neurosurgery under general anesthesia without neuromuscular blockade.

METHODS

This retrospective study divided 1656 neurosurgical patients who underwent total intravenous anesthesia without additional neuromuscular blockade after tracheal intubation into high (PIP > 21.6 cmH₂O, n = 318) and low (PIP ≤ 21.6 cmH₂O, n = 1338) PIP groups. After propensity score matching, 206 patients were selected in each group. Demographic, preoperative, surgical, and anesthetic data were collected retrospectively from electronic medical records and continuous ventilator, infusion pump, and bispectral index data from a data registry.

RESULTS

Intraoperative coughing occurred in 30 (1.8%) patients, including 9 (0.5%) during the main surgical procedure. Intraoperative coughing was more frequent in the high PIP group than in the low PIP group before (14/318 [4.4%] vs. 16/1338 [1.2%], P < 0.001) and after (13/206 [6.3%] vs. 1/206 [0.5%], P = 0.003) propensity score matching. In multivariable logistic regression analysis after propensity score matching, a high PIP (odds ratio [95% confidence interval] 14.22 [1.81-111.73], P = 0.012), tidal volume divided by predicted body weight (mL/kg, 1.36 [1.09-1.69], P = 0.006), and surgical duration (min, 1.01 [1.00-1.01], P = 0.025) predicted intraoperative coughing.

CONCLUSION

The incidence of intraoperative coughing was 1.8% in neurosurgical patients undergoing general anesthesia without neuromuscular blockade and might be associated with a high PIP.

An Entropy-Based Prospective Randomized Controlled Trial to Evaluate the Analgesic and Hypnotic Effects of Equipotent Doses of Sevoflurane and Isoflurane in Patients Presenting for Spine Surgeries

Objectives  Minimal alveolar concentration (MAC) of anesthetic agents has been considered a suitable measure of the potency of inhalational anesthetics. Furthermore, it is assumed that equi-MAC concentrations of different anesthetic agents have a similar potency in suppressing responses to painful stimuli. Isoflurane and sevoflurane are two commonly used volatile anesthetic agents in spine surgeries. Therefore, these agents' hypnotic and analgesic potencies should be distinguished and comprehended for the optimal administration of anesthesia. Consequently, we undertook this study to compare the analgesic and hypnotic potencies between these agents at equi-MAC concentrations, using the entropy monitor.

Materials and Methods  Forty patients undergoing lumbar spine surgery were randomly assigned to two groups receiving either isoflurane ( n  = 20) or sevoflurane ( n  = 20). After induction, maintenance of anesthesia was done with age-corrected 1.0 MAC of either isoflurane or sevoflurane. A standardized noxious stimulus was provided to all the patients after achieving a steady state of 1.0 MAC. The state entropy (SE), response entropy (RE), and RE–SE were recorded at baseline, prestimulus, and poststimulus time points in both groups.

Statistical Analyses  Data are presented as frequency and percentages for categorical variables and mean ± standard deviation for continuous variables. The comparison of categorical variables between the two groups was made using the Fisher's exact test, and the Student's t -test was used for continuous variables. A p -value of < 0.05 was considered to be statistically significant.

Results  At age-corrected 1.0 MAC, there was no significant difference in the SE, RE, and RE–SE in both the groups at any time point.

Conclusion  Our study shows that during a steady state of age-corrected 1.0 MAC single-agent anesthesia, sevoflurane and isoflurane have comparable analgesic and hypnotic potencies as measured by entropy indices when a standardized nociceptive stimulus is provided.

Spectral Entropy Monitoring Accelerates the Emergence from Sevoflurane Anesthesia in Thoracic Surgery: A Randomized Controlled Trial

The clinical efficacy of spectral entropy monitoring in improving postoperative recovery remains unclear. This trial aimed to investigate the impact of M-Entropy (GE Healthcare, Helsinki, Finland) guidance on emergence from anesthesia and postoperative delirium in thoracic surgery. Adult patients undergoing video-assisted thoracoscopic surgery for lung resection at a medical center were randomly allocated into the M-Entropy guidance group (n = 39) and the control group (n = 37). In the M-Entropy guidance group, sevoflurane anesthesia was titrated to maintain response and state entropy values between 40 and 60 intraoperatively. In the control group, the dosing of sevoflurane was adjusted based on clinical judgment and vital signs. The primary outcome was time to spontaneous eye opening. M-Entropy guidance significantly reduced the time proportion of deep anesthesia (entropy value <40) during surgery, mean difference: −21.5% (95% confidence interval (CI): −32.7 to −10.3) for response entropy and −24.2% (−36.3 to −12.2) for state entropy. M-Entropy guidance significantly shortened time to spontaneous eye opening compared to clinical signs, mean difference: −154 s (95% CI: −259 to −49). In addition, patients of the M-Entropy group had a lower rate of emergence agitation (absolute risk reduction: 0.166, 95% CI: 0.005−0.328) and delirium (0.245, 0.093−0.396) at the postanesthesia care unit. M-Entropy-guided anesthesia hastened awakening and potentially prevented emergence agitation and delirium after thoracic surgery. These results may provide an implication for facilitating postoperative recovery and reducing the complications associated with delayed emergence and delirium.

Different perspectives for monitoring nociception during general anesthesia

Safe anesthesia is achieved using objective methods that estimate the patient’s state during different phases of surgery. A patient’s state under anesthesia is characterized by three major aspects, which are linked to the main effects produced by each of the families of anesthetic agents administered: hypnosis, analgesia, and muscular relaxation.

While quantification techniques designed to assess muscular relaxation under neuromuscular blocking agents have a relatively long history with a high degree of standardization and understanding (e.g., the train-of-four), the knowledge and techniques used to the depth of hypnosis assessment suffer from a lesser degree in both standardization and interpretation due to brain complexity.

The problem of standardization and interpretation in the analgesia and nociception assessment increases since it involves more systems, the central nervous system, and the autonomic nervous system.

This helps to explain why there are multiple a priori valid approaches to develop nociception monitoring from different interpretations and physiological bases of noxious stimuli processing. Thus, in this review, the current monitoring technologies clinically available for estimating a patient’s nociception under general anesthesia are described.

Adequacy of Anesthesia Guidance for Colonoscopy Procedures

In patients undergoing colonoscopy procedures (CPs), inadequate dosing of hypnotic drugs (HD) and opioid analgesics (OA) during intravenous sedoanalgesia (ISA) may lead to intraprocedural awareness with recall (IAwR), intraprocedural (IPP) and postprocedural pain (PPP), as well as postoperative nausea and vomiting (PONV). The aim of this study was to evaluate whether the titration of HD and OA based on the observance of changing values of state entropy (SE) and surgical pleth index (SPI) (adequacy of anesthesia-AoA), state entropy alone, or standard practice may reduce the number of adverse events. One hundred and fifty-eight patients were included in the final analysis. The rate of IAwR and IPP was statistically more frequent in patients from the C group in comparison with the AoA and SE groups (p < 0.01 and p < 0.05, respectively). In turn, the rate of PPP, PONV, and patients' and operators' satisfaction with ISA between groups was not statistically significant (p > 0.05). Changes in hemodynamic parameters, demand for HD, and OA were statistically significant, but of no clinical value. In patients undergoing CPs under ISA using propofol and FNT, as compared to standard practice, intraprocedural SE monitoring reduced the rate of IAwR and IPP, with no influence on the rate of PPP, PONV, or patients' and endoscopists' satisfaction. AoA guidance on propofol and FNT titration, as compared to SE monitoring only, did not reduce the occurrence of the aforementioned studied parameters, imposing an unnecessary extra cost.

Comparison of adequacy of anaesthesia monitoring with standard clinical practice monitoring during routine general anaesthesia: An international, multicentre, single-blinded randomised controlled trial

BACKGROUND

Previous studies have suggested that monitoring the levels of both hypnosis and antinociception could reduce periods of inadequate anaesthesia. However, the evidence regarding associated benefits of this monitoring is still limited.

OBJECTIVE

The primary objective of this study was to confirm that guidance of anaesthesia by depth of hypnosis and antinociception monitoring decreases the number of inadequate anaesthesia events in comparison with standard clinical practice.

DESIGN

A multicentre, single-blinded, randomised controlled trial.

SETTING

The study was conducted in four European University hospitals in four different countries between December 2013 and November 2016.

PATIENTS

The study population consisted of a total of 494 adult patients undergoing elective surgery requiring tracheal intubation.

INTERVENTIONS

The patients were allocated to one of two groups. The first group was treated using Entropy for depth of hypnosis and surgical pleth index to determine depth of antinociception (adequacy of anaesthesia group; AoA group). The second group was monitored using standard monitoring alone (control group). Anaesthesia was conducted with target-controlled infusions of propofol and remifentanil.

MAIN OUTCOME MEASURES

The primary outcome of the study was the number of total unwanted events for example signs of inadequately light or unintentionally deep anaesthesia.

RESULTS

Evidence of inadequate anaesthesia had an incidence of around 0.7 events per patient in both groups with no difference between groups (P = 0.519). In the AoA group, the overall consumption of propofol was significantly reduced (6.9 vs. 7.5 mg kg h, P = 0.008) in comparison with the control group. The consumption of remifentanil was equal in both groups. The times to emergence [8.0 vs. 9.6 min (P = 0.005)] and full recovery in the postanaesthesia care unit (P = 0.043) were significantly shorter in the AoA group. No differences were seen in postoperative pain scores or in the use of analgesics.

CONCLUSION

In the current study, the guidance of total intravenous anaesthesia by Entropy and surgical pleth index in comparison with standard monitoring alone was not able to validate reduction of unwanted anaesthesia events. However, there was a reduction in the use of propofol, and shorter times for emergence and time spent in the postanaesthesia care unit.

TRIAL REGISTRATION

at ClinicalTrials.gov NCT01928875.

The Impact of Monitoring Depth of Anesthesia and Nociception on Postoperative Cognitive Function in Adult Multiple Trauma Patients

Background and Objectives: Patients with traumatic injuries have often been excluded from studies that have attempted to pinpoint modifiable factors to predict the transient disturbance of the cognitive function in the postoperative settings. Anesthetists must be aware of the high risk of developing postoperative delirium and cognitive dysfunction (POCD) in patients undergoing emergency surgery. Monitoring the depth of anesthesia in order to tailor anesthetic delivery may reduce this risk. The primary aim of this study was to improve the prevention strategies for the immediate POCD by assessing anesthetic depth and nociception during emergency surgery. Material and Methods: Of 107 trauma ASA physical status II-IV patients aged over 18 years undergoing emergency noncardiac surgery, 95 patients were included in a prospective randomized study. Exclusion criteria were neurotrauma, chronic use of psychoactive substances or alcohol, impaired preoperative cognitive function, pre-existing psychopathological symptoms, or expected surgery time less than 2 h. Entropy and Surgical Pleth Index (SPI) values were constantly recorded for one group during anesthesia. POCD was assessed 24 h, 48 h, and 72 h after surgery using the Neelon and Champagne (NEECHAM) Confusion Scale. Results: Although in the intervention group, fewer patients experienced POCD episodes in comparison to the control group, the results were not statistically significant (p < 0.08). The study showed a statistically significant inverse correlation between fentanyl and the NEECHAM Confusion Scale at 24 h (r = -0.32, p = 0.0005) and 48 h (r = -0.46, p = 0.0002), sevoflurane and the NEECHAM Confusion Scale at 24 h (r = -0.38, p = 0.0014) and 48 h (r = -0.52, p = 0.0002), and noradrenaline and POCD events in the first 48 h (r = -0.46, p = 0.0013 for the first 24 h, respectively, and r = -0.46, p = 0.0002 for the next 24 h). Conclusions: Entropy and SPI monitoring during anesthesia may play an important role in diminishing the risk of developing immediate POCD after emergency surgery.

Influence of perioperative stress on central and peripheral oxytocin and arginine-vasopressin concentrations

Perioperative stress provides not only physical, but also psychic and emotional aspects, which may influence the hypothalamic neuropeptide system. Studies investigating the perioperative course of central neuropeptide activity are missing. Therefore, the present study aimed to determine perioperative fluctuations in central and concomitant peripheral concentrations of the hypothalamic neuropeptides oxytocin (OXT) and arginine-vasopressin (AVP), as well as their impact on perioperative anxiety and depression. Cerebrospinal fluid (CSF), blood and saliva were collected from 12 patients who underwent elective endovascular aortic repair with a routinely inserted spinal catheter. AVP and OXT concentrations were analysed at four timepoints: (i) the evening before the operation; (ii) the operation day immediately before anaesthesia induction; (iii) intraoperatively after the stent was placed; and (iv) on day 1 after the operation. Patients completed the Hospital Anxiety and Depression Scale (HADS) at timepoints 1 and 4. For CSF OXT, the present study showed a significant intraoperative decline, accompanied by a decrease in saliva. OXT blood concentrations before anaesthesia induction were higher than at the evening before the operation. OXT concentrations in CSF and saliva correlated well at timepoints 2-4. AVP concentrations in CSF, blood and saliva did not show any significant changes perioperatively. However, postoperative AVP blood concentrations showed a significant negative correlation with anxiety and depression scores according to the HADS. This pilot study demonstrates perioperative fluctuations in central OXT concentrations, which are better reflected by saliva than by blood. Further studies are required to determine whether OXT and AVP can predict postoperative post-traumatic stress disorder.

Monitoring of nociception, reality or fiction?

There are currently various projects underway that attempt to monitor the nociceptive responses caused by surgical stress and ensure patients the best analgesic conditions. The systemic response to surgical stress has repercussions in the postoperative period, such as worse pain control, delayed recovery, greater complications, longer stay in resuscitation and hospital units, and increased healthcare costs. However, treatment with higher doses of opioids than necessary may lead to slower awakening, increased drowsiness and adverse effects, as well as situations of postoperative opioid-induced hyperalgesia. There are 2 large groups of nociceptive monitoring according to the origin of the theoretical objective of monitoring response to the stimulus, that may derive from changes in the electroencephalogram or the response of the autonomic nervous system.

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.

Spectral entropy in monitoring anesthetic depth

Monitoring the brain response to hypnotics in general anesthesia, with the nociceptive and hemodynamic stimulus interaction, has been a subject of intense investigation for many years. Nowadays, monitors of depth of anesthesia are based in processed electroencephalogram by different algorithms, some of them unknown, to obtain a simplified numeric parameter approximate to brain activity state in each moment. In this review we evaluate if spectral entropy suitably reflects the brain electric behavior in response to hypnotics and the different intensity nociceptive stimulus effect during a surgical procedure.

Spectral entropy monitoring for adults and children undergoing general anaesthesia

BACKGROUND

Anaesthetic drugs during general anaesthesia are titrated according to sympathetic or somatic responses to surgical stimuli. It is now possible to measure depth of anaesthesia using electroencephalography (EEG). Entropy, an EEG-based monitor can be used to assess the depth of anaesthesia using a strip of electrodes applied to the forehead, and this can guide intraoperative anaesthetic drug administration.

OBJECTIVES

The primary objective of this review was to assess the effectiveness of entropy monitoring in facilitating faster recovery from general anaesthesia. We also wanted to assess mortality at 24 hours, 30 days, and one year following general anaesthesia with entropy monitoring.The secondary objectives were to assess the effectiveness of the entropy monitor in: preventing postoperative recall of intraoperative events (awareness) following general anaesthesia; reducing the amount of anaesthetic drugs used; reducing cost of the anaesthetic as well as in reducing time to readiness to leave the postanaesthesia care unit (PACU).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 10), MEDLINE via Ovid SP (1990 to September 2014) and EMBASE via Ovid SP (1990 to September 2014). We reran the search in CENTRAL, MEDLINE via Ovid SP and EMBASE via Ovid SP in January 2016. We added one potential new study of interest to the list of 'Studies awaiting Classification' and we will incorporate this study into the formal review findings during the review update.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) conducted in adults and children (aged greater than two years of age), where in one arm entropy monitoring was used for titrating anaesthesia, and in the other standard practice (increase in heart rate, mean arterial pressure, lacrimation, movement in response to noxious surgical stimuli) was used for titrating anaesthetic drug administration. We also included trials with an additional third arm, wherein another EEG monitor, the Bispectral index (BIS) monitor was used to assess anaesthetic depth.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. Two review authors independently extracted details of trial methodology and outcome data from trials considered eligible for inclusion. All analyses were made on an intention-to-treat basis. We used a random-effect model where there was heterogeneity. For assessments of the overall quality of evidence for each outcome that included pooled data from RCTs, we downgraded evidence from 'high quality' by one level for serious (or by two for very serious) study limitations (risk of bias, indirectness of evidence, serious inconsistency, imprecision of effect or potential publication bias).

MAIN RESULTS

We included 11 RCTs (962 participants). Eight RCTs (762 participants) were carried out on adults (18 to 80 years of age), two (128 participants) involved children (two to 16 years) and one RCT (72 participants) included patients aged 60 to 75 years. Of the 11 included studies, we judged three to be at low risk of bias, and the remaining eight RCTs at unclear or high risk of bias.Six RCTs (383 participants) estimated the primary outcome, time to awakening after stopping general anaesthesia, which was reduced in the entropy as compared to the standard practice group (mean difference (MD) -5.42 minutes, 95% confidence interval (CI) -8.77 to -2.08; moderate quality of evidence). We noted heterogeneity for this outcome; on performing subgroup analysis this was found to be due to studies that included participants undergoing major, long duration surgeries (off-pump coronary artery bypass grafting, major urological surgery). The MD for time to awakening with four studies on ambulatory procedures was -3.20 minutes (95% CI -3.94 to -2.45). No trial reported the second primary outcome, mortality at 24 hours, 30 days, and one year with the use of entropy monitoring.Eight trials (797 participants) compared the secondary outcome, postoperative recall of intraoperative events (awareness) in the entropy and standard practice groups. Awareness was reported by only one patient in the standard practice group, making meaningful estimation of benefit of entropy monitoring difficult; moderate quality of evidence.All 11 RCTs compared the amount of anaesthetic agent used between the entropy and standard practice groups. Six RCTs compared the amount of propofol, four compared the amount of sevoflurane and one the amount of isoflurane used between the groups. Analysis of three studies (166 participants) revealed that the MD of propofol consumption between the entropy group and control group was -11.56 mcg/kg/min (95% CI -24.05 to 0.92); low quality of evidence. Analysis of another two studies (156 participants) showed that the MD in sevoflurane consumption in the entropy group compared to the control group was -3.42 mL (95% CI -6.49 to -0.35); moderate quality of evidence.No trial reported on the secondary outcome of the cost of general anaesthesia.Three trials (170 participants) estimated MD in time to readiness to leave the PACU of the entropy group as compared to the control group (MD -5.94 minutes, 95% CI -16.08 to 4.20; low quality of evidence). Heterogeneity was noted, which was due to the difference in anaesthetic technique (propofol-based general anaesthesia) in one study. The remaining two studies had used volatile-based general anaesthesia. The MD in time to readiness to leave the PACU was -4.17 minutes (95% CI -6.84 to -1.51) with these two studies.

AUTHORS' CONCLUSIONS

The evidence as regards time to awakening, recall of intraoperative awareness and reduction in inhalational anaesthetic agent use was of moderate quality. The quality of evidence of as regards reduction in intravenous anaesthetic agent (propofol) use, as well as time to readiness to leave the PACU was found to be of low quality. As the data are limited, further studies consisting of more participants will be required for ascertaining benefits of entropy monitoring.Further studies are needed to assess the effect of entropy monitoring on focal issues such as short-term and long-term mortality, as well as cost of general anaesthesia.

Comparison of electroencephalogram entropy versus loss of verbal response to determine the requirement of propofol for induction of general anaesthesia

Background and Aims:

Propofol causes dose-dependent reduction in blood pressure (BP). This study was done to evaluate the use of spectral entropy on the dose of propofol required and the haemodynamic stability during induction of general anaesthesia (GA).

Methods:

In this randomised controlled study, 72 American Society of Anesthesiologists’ physical status I and II patients undergoing general and orthopaedic surgeries were divided into Group S (n-36) and Group C (n-36). Patients in Group C were induced with propofol till loss of response to verbal commands and in Group S until the state entropy was <50 and state and response entropy difference was <10. The induction dose of propofol, haemodynamic parameters and the entropy values were recorded. Numerical data were expressed as a mean ± standard deviation and analysed using unpaired, two-tailed t-test. Categorical data were compared using Chi-square test. P < 0.05 value was considered significant.

Results:

The dose of propofol per kg was significantly more in the entropy group (1.80 ± 0.23 mg/kg in the Group C and 1.98 ± 0.217 mg/kg in the Group S [P < 0.05]). After induction, at intubation and 1 min after intubation, entropy values were lower in Group S than Group C (P < 0.05). The BP decreased significantly after induction compared with the baseline (P < 0.05), but there was no difference between the groups.

Conclusion:

Propofol required for induction of GA when guided by electroencephalogram entropy was significantly higher than the induction dose based on loss of verbal response. Both conventional induction and induction with entropy as the endpoint resulted in similar haemodynamic profile.

Correlation of surgical pleth index with stress hormones during propofol-remifentanil anaesthesia

Eighty patients undergoing elective ear-nose-throat surgery were enrolled in the present study to investigate the relationship between surgical pleth index (SPI) and stress hormones (ACTH, cortisol, epinephrine, norepinephrine) during general anaesthesia which was induced and maintained with propofol and remifentanil using a target-controlled infusion. The study concluded that the SPI had moderate correlation to the stress hormones during general anaesthesia, but no correlation during consciousness. Furthermore, SPI values were able to predict ACTH values with high sensitivity and specificity.

Entropy monitoring decreases isoflurane concentration and recovery time in pediatric day care surgery--a randomized controlled trial

AIM

To assess if titrating anesthesia with entropy would result in faster awakening in children undergoing day care surgery.

BACKGROUND

Entropy, an EEG-based anesthesia depth monitor, has been used in children; however, only one other study has evaluated the effectiveness of entropy monitoring in decreasing awakening time and for titrating anesthetic agents in children undergoing short procedures under anesthesia.

METHODS

In a randomized prospective single-blind parallel group trial, 50 ASA grade I-II children, aged 2-12 years, scheduled for lower abdominal or urological surgeries were studied after ethics committee approval and parental consent. The children were randomized to the entropy or control group. Following laryngeal mask airway insertion and caudal analgesia, anesthesia was maintained with nitrous oxide, oxygen, isoflurane. In the control group, anesthesia was titrated according to the hemodynamic parameters and the simultaneously monitored entropy values obscured from the anesthesiologist. In the entropy group, the entropy values (between 45 and 65) were used to titrate the anesthesia.

RESULTS

Time to awakening from anesthesia was 7 (3-18) min in the entropy group when compared to 10 (5-21) min in the control group. (P < 0.05) The difference in the mean time to awakening was 2.72 min 95% CI (0.34, 5.1). The end tidal isoflurane concentrations were lower in the entropy group when compared to the control group 15 s following airway insertion (0.78 ± 0.14 vs 1.24 ± 0.19), 15 s post caudal and skin incision (0.68 ± 0.40 vs 0.84 ± 0.05, 0.68 ± 0.03 vs 0.77 ± 0.32, respectively) as well as 5 min after skin incision 0.67 ± 0.04 vs 0.79 ± 0.02), (P ≤ 0.05).

CONCLUSION

In pediatric day care surgery, entropy monitoring resulted in statistically though not clinically significant faster awakening and significantly lower end – tidal isoflurane concentrations.

Comparison of spectral entropy and bispectral index electroencephalography in coronary artery bypass graft surgery

OBJECTIVE

The study's aim was to compare response entropy (RE) and state entropy (SE) with bispectral index (BIS) electroencephalography (EEG) as an alternative cerebral monitoring tool in patients scheduled for coronary artery bypass graft surgery.

DESIGN

Prospective, observational single-center study.

SETTING

University hospital.

PARTICIPANTS

Thirty patients undergoing coronary artery bypass graft surgery receiving remifentanil-propofol anesthesia.

INTERVENTIONS

Surgery was performed with cardiopulmonary bypass (CPB) and cardiac arrest in 15 patients, with CPB without cardiac arrest in 9 patients and without CPB in 6 patients.

MEASUREMENTS AND MAIN RESULTS

RE, SE, BIS, burst suppression ratio (BSR), and frontal electromyography (f-EMG) were detected simultaneously. RE and SE compared favorably with BIS and their correlations were strong (r(2) = 0.6, r(2) = 0.55, respectively). The mean bias of RE and BIS was -1.8, but limits of agreement were high (+20.5/-24.1). RE and SE tended to be lower than the BIS values in the CPB subgroups. The detection of BSR was similar with RE and SE and the BIS. A strong correlation existed between BIS and f-EMG (r(2) = 0.62) in contrast to RE (r(2) = 0.45) and SE (r(2) =0.39). BIS monitoring was significantly more disturbed than RE and SE with 9.1% +/-10.9% and 0.1% +/- 0.2% of the total anesthesia time, respectively. Neither implicit nor explicit memory was shown.

CONCLUSION

RE and SE are comparable with the BIS but showed significantly less interference from f-EMG and superior resistance against artifacts. Thus, spectral entropy is more suitable than the BIS during propofol-remifentanil anesthesia in cardiac surgery patients.

The three-way stopcock may be a weak component of total intravenous anaesthesia

BACKGROUND

An intravenous line is needed to administer anaesthesia, particularly when total intravenous anaesthesia (TIVA) is performed. A disadvantage of TIVA is that the intravenous concentration of anaesthetics cannot be easily measured compared with volatile anaesthetics. If a three-way stopcock is accidentally unscrewed, TIVA drugs cannot reach the patient's veins, thus resulting in inadequate anaesthesia levels, possibly resulting in awareness. We therefore measured the required torque to open five different brands of three-way stopcocks in an attempt to make an intravenous-line including all elements safer.

METHODS

The torque required to open one, two or three three-way stopcocks being connected in a perpendicular manner was measured with a biaxial servo hydraulic material testing machine.

RESULTS

The force required to open three-way stopcocks connected with an intravenous catheter ranged in five different stopcock models from 5.03+/-0.75 to 2.21+/-0.51 N respectively; with two three-way stopcocks from 2.68+/-0.42 to 1.31+/-0.59 N, respectively, and with three three-way stopcocks from 1.29+/-0.27 to 0.82+/-0.05 N, respectively.

CONCLUSION

Turning a three-way stopcock to become loose with possibly leaking drugs requires minimal amounts of force and decreases significantly if not connected in-line.

Influence of different remifentanil concentrations on the performance of the surgical stress index to detect a standardized painful stimulus during sevoflurane anaesthesia

BACKGROUND

Although measurement of cerebral hypnotic drug effect and muscle relaxation is common clinical routine during anaesthesia, a reliable measurement of the neurophysiological effects evoked by a painful stimulus is still missing. Recently, the surgical stress index (SSI) has been introduced as a surrogate measure of 'nociception'. The present study aimed to examine the influence of increasing remifentanil concentrations on the ability of SSI to detect a standardized painful stimulus during sevoflurane anaesthesia.

METHODS

Twenty-four patients received incremental or decremental doses of 0, 2, and 4 ng ml(-1) remifentanil effect-site concentration (Ce(remi)) during 0.7 MAC sevoflurane. Painful tetanic stimulation was applied at least 5 min after changing Ce(remi). SSI, heart rate (HR), response entropy (RE), state entropy (SE), RE-SE difference, and bispectral index (BIS) were obtained in each patient before and after stimulation. Further prediction of an author-defined response to painful stimulus was analysed.

RESULTS

SSI and BIS, but not HR, SE, RE, or RE-SE difference were significantly altered after stimulation. Change in SSI (Delta SSI) was significantly dependent on Ce(remi), as Delta SSI was [median (inter-quartile range)] 20 (15-31), 10 (1-19), and 3 (1-10) at 0, 2, and 4 ng ml(-1) Ce(remi). In 10 out of 63 cases, SSI detected response to stimulation, not detected by another variable. SSI was unable to predict movement after stimulation as P(K) value is 0.59 (0.09).

CONCLUSIONS

The SSI response to tetanic stimulation was dependent on the remifentanil concentration.