Spectral entropy monitoring allowed lower sevoflurane concentration and faster recovery in children

Quantifying influence of epidural analgesia on entropy guided general anaesthesia using sevoflurane - A randomised controlled trial

Background and Aims

Minimum alveolar concentration (MAC) of inhalational agent denotes the requirement of it to maintain adequate plane of general anaesthesia. The precision to the maintenance of anaesthesia can be further guided by use of entropy to titrate the depth of anaesthesia. Regional anaesthesia and the concomitant deafferentation will decrease the need of general anaesthetics. We conducted a randomised double-blind trial to quantify the effect of addition of regional anaesthesia to sevoflurane based general anaesthesia technique guided by entropy to achieve satisfactory depth of anaesthesia.

Methods

Forty patients posted for elective laparotomies were randomised to two groups. All patients received a bolus followed by an epidural infusion. Group GE (general anaesthesia + epidural bupivacaine) received 0.25% epidural bupivacaine and Group GS received epidural saline. Both groups received narcotic, relaxant and sevoflurane anaesthesia guided by entropy monitoring. The state entropy (SE) was maintained at 40-60 by titrating end tidal sevoflurane concentration (ET_sevo). Heart rate, blood pressure, SpO₂, end tidal carbon dioxide (ETCO₂) and sevoflurane were recorded.

Results

Both groups were similar in heart rate and mean blood pressure during anaesthesia maintenance. The minimum ET_Sevo required to maintain entropy between 40 and 60 in group GE was 0.53% compared to 0.95% in group GS the epidural saline group (P < 0.001). The end-tidal sevoflurane requirement to maintain adequate depth of anaesthesia dropped by 44.2% in group GE.

Conclusion

Lower concentrations of volatile anaesthetic are required when entropy-guided general anaesthesia is combined with regional blockade.

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.

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.

Evolution of electroencephalogram signal analysis techniques during anesthesia

Biosignal analysis is one of the most important topics that researchers have tried to develop during the last century to understand numerous human diseases. Electroencephalograms (EEGs) are one of the techniques which provides an electrical representation of biosignals that reflect changes in the activity of the human brain. Monitoring the levels of anesthesia is a very important subject, which has been proposed to avoid both patient awareness caused by inadequate dosage of anesthetic drugs and excessive use of anesthesia during surgery. This article reviews the bases of these techniques and their development within the last decades and provides a synopsis of the relevant methodologies and algorithms that are used to analyze EEG signals. In addition, it aims to present some of the physiological background of the EEG signal, developments in EEG signal processing, and the effective methods used to remove various types of noise. This review will hopefully increase efforts to develop methods that use EEG signals for determining and classifying the depth of anesthesia with a high data rate to produce a flexible and reliable detection device.

Impact of Entropy Monitoring on Volatile Anesthetic Uptake

Background:

Electroencephalogram-derived monitoring to assess anesthetic depth may allow more accurate hypnotic drug administration, resulting in decreased anesthetic drug consumption. The authors hypothesized that the use of M-Entropy monitoring (Datex-Ohmeda, Helsinki, Finland) is associated with reduced sevoflurane uptake (primary outcome) in patients undergoing major abdominal surgery.

Methods:

A total of 50 patients with an American Society of Anesthesiology score of II–III, scheduled for elective laparoscopic rectosigmoidectomy were randomized into two groups in this randomized controlled trial. In the control group, the target expiratory fraction of sevoflurane was adapted according to standard clinical practice. In the study group, the target expiratory fraction of sevoflurane was adapted to maintain state entropy values between 40 and 60. State entropy values were continuously recorded in both groups but were not available to the anesthesiologist in the control group. In both groups, patients were ventilated using the auto-control mode of the Zeus® (Dräger, Lübeck, Germany) respirator, which allows precise measurements of sevoflurane uptake. Sufentanil was administered using a target-controlled infusion system.

Results:

Demographics did not differ between groups. During the anesthesia maintenance phase, state entropy values were lower in the control group than the study group (P &lt; 0.0001). Sevoflurane uptake was higher in the control group than the study group (5.2 ± 1.4 ml/h vs. 3.8 ± 1.5 ml/h; P = 0.0012). Three patients in the control group developed intraoperative hypotension compared with none in the study group (P = 0.03).

Conclusions:

Monitoring the depth of anesthesia using M-Entropy was associated with a significant reduction in sevoflurane uptake.

Ambulatory anesthesia aspects for tonsillectomy and abrasion in children

PURPOSE OF REVIEW

Tonsillectomy is a very common procedure, but with risks or challenges, both for the surgeon and anesthesiologist. Many places have considerable experience and expertise with this procedure, and a lot of clinical studies are continuously being presented.

RECENT FINDINGS

Most preoperative aspects are covered, including indications, preoperative risk assessment, premedication, anesthetic induction and maintenance, as well as recovery function and side-effects; such as bleeding, agitation, pain, nausea and sleep apnea. Controversies exist as to ambulatory versus in-patient care, laryngeal mask airway versus endotracheal intubation, use of local anesthetic infiltration and use of glucocorticoids.

SUMMARY

Preoperative evaluation should identify increased bleeding risk, potential airway problems, ongoing infection and symptoms of obstructive sleep apnea.Intravenous propofol is most often used for anesthetic induction, although inhalational sevoflurane is a valid alternative. Laryngeal mask airway or endotracheal tube may both be used safely and effectively; the choice will depend upon the routine and experience of the team. Paracetamol and NSAIDs are useful baseline medication for nonopioid multimodal postoperative pain treatment and prophylaxis. Similar with local anesthesia infiltration and dexamethasone medication, although somewhat more disputed. Dexamethasone is also useful for nausea/vomiting prophylaxis, together with ondansetron and also propofol for anesthesia maintenance.

Monitoring the depth of anaesthesia

One of the current challenges in medicine is monitoring the patients’ depth of general anaesthesia (DGA). Accurate assessment of the depth of anaesthesia contributes to tailoring drug administration to the individual patient, thus preventing awareness or excessive anaesthetic depth and improving patients’ outcomes. In the past decade, there has been a significant increase in the number of studies on the development, comparison and validation of commercial devices that estimate the DGA by analyzing electrical activity of the brain (i.e., evoked potentials or brain waves). In this paper we review the most frequently used sensors and mathematical methods for monitoring the DGA, their validation in clinical practice and discuss the central question of whether these approaches can, compared to other conventional methods, reduce the risk of patient awareness during surgical procedures.

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.