Bispectral index-guided comparison of dexmedetomidine and fentanyl as an adjuvant with propofol to achieve an adequate depth for endotracheal intubation - A double-blind randomised controlled trial

Background and Aims

Laryngoscopy and tracheal intubation require an adequate depth of anaesthesia. The study's primary objective was to compare the time needed to achieve the bispectral index (BIS)-guided adequate depth of anaesthesia for endotracheal intubation using fentanyl and dexmedetomidine.

Methods

After institutional ethics committee clearance and written informed consent, this randomised study was conducted on 140 patients of either gender between 18 and 60 years who were scheduled for elective surgeries under general anaesthesia. Patients were randomised to intravenous dexmedetomidine 1 μg/kg (Group D) or fentanyl 2 μg/kg (Group F). The drugs were given as an intravenous infusion over 10 min before induction of anaesthesia. The primary outcome was the time required to achieve BIS 50. Normally distributed variables were compared using Student's t-test, and non-normally distributed variables were compared using the Mann-Whitney U test. Qualitative data were analysed using Chi-square/Fisher's exact test. A P value <0.05 was considered significant.

Results

The time to achieve BIS 50 was lesser in Group F, 1546 (27) as compared to Group D, 1558 (11) s [mean difference (95% confidence interval (CI) 12[5.11, 18.89]), P < 0.001]. Haemodynamic parameters were comparable at all time points between both the groups, except heart rate, which was significantly lower. Propofol consumption was significantly less in group D than in group F [125.9 (25.36) versus 157.3 (42.80) mg, respectively, mean difference (95% CI) 31.4 (-44.16 to -20.63) P < 0.001)].

Conclusion

Dexmedetomidine achieves BIS 50 faster and has a propofol-sparing effect as compared to fentanyl.

Intraoperative monitoring of the central and peripheral nervous systems: a narrative review

The central and peripheral nervous systems are the primary target organs during anaesthesia. At the time of the inception of the British Journal of Anaesthesia, monitoring of the central nervous system comprised clinical observation, which provided only limited information. During the 100 yr since then, and particularly in the past few decades, significant progress has been made, providing anaesthetists with tools to obtain real-time assessments of cerebral neurophysiology during surgical procedures. In this narrative review article, we discuss the rationale and uses of electroencephalography, evoked potentials, near-infrared spectroscopy, and transcranial Doppler ultrasonography for intraoperative monitoring of the central and peripheral nervous systems.

The Use of Isoflurane and Adjunctive Magnesium Chloride Provides Fast, Effective Anaesthetization of Octopus vulgaris

A wide variety of substances have been used to anaesthetise invertebrates, but many are not anaesthetics and merely incapacitate animals rather than preventing pain. In essence, the role of an ideal general anaesthetic is to act as a muscle relaxant, an analgesic, an anaesthetic, and an amnesic. To achieve all these properties with a single substance is difficult, and various adjuvants usually need to be administered, resulting in a cocktail of drugs. In a clinical setting, the vast majority of patients are unaware of surgery being carried out and have no memory of it, so they can claim to have felt no pain, but this is much more difficult to demonstrate in invertebrates. Here, we show that 1% MgCl2, a muscle relaxant, is a useful adjuvant for the clinical anaesthetic isoflurane on Octopus vulgaris when applied alone in seawater for 10 min before the clinical anaesthetic. After this, full anaesthesia can be achieved in 5 min using 1% isoflurane insufflated into the saline still containing MgCl2. Full recovery takes place rapidly in about 10 to 15 min. The depth of anaesthesia was monitored using changes in respiratory rate, chromatophore pattern, and withdrawal movements of the arms and siphon. This methodology reduces stress on the animal and minimises the quantity of anaesthetic used.

Effect of Preoperative Anxiety on Depth of Anaesthesia and In Vitro Fertilization Success

Objective

Infertility anxiety may have a harmful effect on embryo quality and fertilization during in vitro fertilization (IVF). Monitoring brain function gives real-time information about the depth of anaesthesia of a patient. This study examined the effect of preoperative anxiety on the depth of anaesthesia and IVF success.

Methods

One hundred thirty-one patients who had undergone oocyte retrieval were divided into two groups according to the Beck Anxiety Inventory (BAI): the low-anxious Group L (n = 71) and high-anxious Group H (n = 60). Hemodynamic stability, intraoperative total propofol and fentanyl consumption, good quality embryo (GQE) rate, and fertilization rate were recorded.

Results

Fertilization and GQE rates were not significant between groups L and H. Total propofol consumption was significantly higher in group H than in group L. Heart rate (HR) preoperatively and postoperatively and systolic arterial pressure (SAP) preoperatively and diastolic arterial pressure (DAP) postoperatively were significantly increased in group H than in group L. The time for the modified Aldrete score to reach 9 (MAS 9) in group H was significantly higher than that in group L. The effect of variables that were found significantly in the univariate analysis (Propofol, HRpreop, HRpostop, SAPpreop, DAPpostop, and MAS 9) on BAI score.

Conclusion

Total propofol consumption was higher in patients with high anxiety levels, but it did not have a negative effect on IVF success.

Impact of female sex on anaesthetic awareness, depth, and emergence: a systematic review and meta-analysis

BACKGROUND

Suggested anaesthetic dose ranges do not differ by sex, likely because of limited studies comparing sexes. Our objective was to systematically synthesise studies with outcomes of unintended anaesthesia awareness under anaesthesia, intraoperative connected consciousness, time to emergence from anaesthesia, and dosing to achieve adequate depth of anaesthesia, and to compare between females and males.

METHODS

Studies were identified from MEDLINE, Embase, and the Cochrane library databases until August 2, 2022. Controlled clinical trials (randomised/non-randomised) and prospective cohort studies that reported outcomes by sex were included. Results were synthesised by random effects meta-analysis where possible, or narrative form.

RESULTS

Of the 19 749 studies identified, 64 (98 243 participants; 53 143 females and 45 100 males) were eligible for inclusion, and 44 citations contributed to meta-analysis. Females had a higher incidence of awareness with postoperative recall (33 studies, odds ratio 1.38, 95% confidence interval [CI] 1.09-1.75) and connected consciousness during anaesthesia (three studies, OR 2.09, 95% CI 1.04-4.23) than males. Time to emergence was faster in females, including time to eye-opening (10 studies, mean difference -2.28 min, 95% CI -3.58 to -0.98), and time to response to command (six studies, mean difference -2.84 min, 95% CI -4.07 to -1.62). Data on depth of anaesthesia were heterogenous, limiting synthesis to a qualitative review which did not identify sex differences.

CONCLUSIONS

Female sex was associated with a greater incidence of awareness under general anaesthesia, and faster emergence from anaesthesia. These data suggest reappraisal of anaesthetic care, including whether similar drug dosing for females and males represents best care.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42022336087.

Sedline® Miscalculation of Depth of Anaesthesia Variables in Two Pigs Due to Electrocardiographic Signal Contamination

Two young (11-week-old) pigs underwent sole propofol anaesthesia as part of an experimental study. The depth of anaesthesia was evaluated both clinically and using the electroencephalography(EEG)-based monitor Sedline; in particular, the patient state index, suppression ratio, raw EEG traces, and its spectrogram were assessed. Physiological parameters and electrocardiographic activity were continuously monitored. In one pig (Case 1), during the administration of high doses of propofol, the Sedline-generated variables suddenly indicated an increased EEG activity while this was not confirmed by observation of either the raw EEG or its spectrogram. In the second pig (Case 2), a similar event was recorded during euthanasia with systemic pentobarbital. Both events happened while the EEG activity was isoelectric except for signal interferences and synchronous in rhythm and shape with the electrocardiographic activity. The suggestion of increased brain activity based on the interpretation of the Sedline variables was suspected wrong; most probably due to electrocardiographic interferences. In pigs, the patient state index and suppression ratio, as calculated by the Sedline monitor, could be influenced by the electrocardiographic activity contaminating the EEG trace, especially during otherwise isoelectric periods (strong EEG depression). Visual interpretation of the raw EEG and of the spectrogram remains necessary to identify such artefacts.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLINICAL TRIAL REGISTRATION

CRD42022285195 (PROSPERO).

Rapid-Onset Obesity, Hypothalamic Dysregulation, Hypoventilation, Autonomic Dysregulation, and Neuroendocrine Tumour: Rare Syndrome with Myriad Anaesthesia Implications

Anaesthesia management of a child with rapid-onset obesity, hyperphagia, and hypothalamic dysfunction syndrome is complex due to the multisystem involvement, the most important features being morbid obesity, autonomic dysfunction, and dyselectrolytemia due to hypothalamic dysfunction. The acronym of the disease was amended in 2008 to rapid-onset obesity, hyperphagia, hypothalamic dysfunction neural crest tumour to include the risk of ganglioneuroma or ganglioneuroblastoma. Patients usually require removal of tumour in the prone position. Obstructive sleep apnea, difficult airway and intravenous access, and haemodynamic lability all add to the trials faced by the paediatric anaesthesiologist. Invasive haemodynamic monitoring, ultrasonography, bispectral index monitoring, and meticulous calculation of drug dosages help in smoothening the course of anaesthesia in the presence of constant vigilance.

Real-Time Depth of Anaesthesia Assessment Based on Hybrid Statistical Features of EEG

This paper proposed a new depth of anaesthesia (DoA) index for the real-time assessment of DoA using electroencephalography (EEG). In the proposed new DoA index, a wavelet transform threshold was applied to denoise raw EEG signals, and five features were extracted to construct classification models. Then, the Gaussian process regression model was employed for real-time assessment of anaesthesia states. The proposed real-time DoA index was implemented using a sliding window technique and validated using clinical EEG data recorded with the most popular commercial DoA product Bispectral Index monitor (BIS). The results are evaluated using the correlation coefficients and Bland-Altman methods. The outcomes show that the highest and the average correlation coefficients are 0.840 and 0.814, respectively, in the testing dataset. Meanwhile, the scatter plot of Bland-Altman shows that the agreement between BIS and the proposed index is 94.91%. In contrast, the proposed index is free from the electromyography (EMG) effect and surpasses the BIS performance when the signal quality indicator (SQI) is lower than 15, as the proposed index can display high correlation and reliable assessment results compared with clinic observations.

Spectral edge frequency during general anaesthesia: A narrative literature review

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

Anaesthetic depth and delirium: a challenging balancing act

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

Effect of electroencephalogram-guided anaesthesia administration on 1 yr mortality: 1 yr follow-up of a randomised clinical trial

BACKGROUND

Intraoperative EEG suppression duration has been associated with postoperative delirium and mortality. In a clinical trial testing anaesthesia titration to avoid EEG suppression, the intervention did not decrease the incidence of postoperative delirium, but was associated with reduced 30 day mortality. The present study evaluated whether the EEG-guided anaesthesia intervention continued to be associated with reduced 1 yr mortality.

METHODS

This manuscript reports 1 yr follow-up of patients from a single-centre RCT, including a post-hoc secondary outcome (1 yr mortality) in addition to pre-specified secondary outcomes. The trial included patients aged 60 yr or older undergoing surgery with general anaesthesia between January 2015 and May 2018. Patients were randomised to receive EEG-guided anaesthesia or usual care. The previously reported primary outcome was postoperative delirium. The outcome of the current study was all-cause 1 yr mortality.

RESULTS

Of the 1232 patients enrolled, 614 patients were randomised to EEG-guided anaesthesia and 618 patients to usual care. One year mortality was 57/591 (9.6%) in the guided group and 62/601 (10.3%) in the usual-care group. No significant difference in mortality was observed (adjusted absolute risk difference, -0.7%; 99.5% confidence interval, -5.8% to 4.3%; P=0.68).

CONCLUSIONS

An EEG-guided anaesthesia intervention aiming to decrease duration of EEG suppression during surgery did not significantly decrease 1 yr mortality. These findings, in the context of other studies, do not provide supportive evidence for EEG-guided anaesthesia to prevent intermediate term postoperative death.

CLINICAL TRIAL REGISTRATION

NCT02241655.

Applications and Limitations of Neuro-Monitoring in Paediatric Anaesthesia and Intravenous Anaesthesia: A Narrative Review

Safe management of anaesthesia in children has been one of the top areas of research over the last decade. After the large volume of articles which focused on the putative neurotoxic effect of anaesthetic agents on the developing brain, the attention and research efforts shifted toward prevention and treatment of critical events and the importance of peri-anaesthetic haemodynamic stability to prevent negative neurological outcomes. Safetots.org is an international initiative aiming at raising the attention on the relevance of a high-quality anaesthesia in children undergoing surgical and non-surgical procedures to guarantee a favourable outcome. Children might experience hemodynamic instability for many reasons, and how the range of normality within brain autoregulation is maintained is still unknown. Neuro-monitoring can guide anaesthesia providers in delivering optimal anaesthetic drugs dosages and also correcting underling conditions that can negatively affect the neurological outcome. In particular, it is referred to EEG-based monitoring and monitoring for brain oxygenation.

Recommendations for standards of monitoring during anaesthesia and recovery 2021: Guideline from the Association of Anaesthetists

This guideline updates and replaces the 5th edition of the Standards of Monitoring published in 2015. The aim of this document is to provide guidance on the minimum standards for monitoring of any patient undergoing anaesthesia or sedation under the care of an anaesthetist. The recommendations are primarily aimed at anaesthetists practising in the UK and Ireland, but it is recognised that these guidelines may also be of use in other areas of the world. Minimum standards for monitoring patients during anaesthesia and in the recovery phase are included. There is also guidance on monitoring patients undergoing sedation and during transfer. There are new sections specifically discussing capnography, sedation and regional anaesthesia. In addition, the indications for processed electroencephalogram and neuromuscular monitoring have been updated.

Burst-suppression ratio underestimates absolute duration of electroencephalogram suppression compared with visual analysis of intraoperative electroencephalogram

Background

Machine-generated indices based on quantitative electroencephalography (EEG), such as the patient state index (PSI™) and burst-suppression ratio (BSR), are increasingly being used to monitor intraoperative depth of anaesthesia in the endeavour to improve postoperative neurological outcomes, such as postoperative delirium (POD). However, the accuracy of the BSR compared with direct visualization of the EEG trace with regard to the prediction of POD has not been evaluated previously.

Methods

Forty-one consecutive patients undergoing non-cardiac, non-intracranial surgery with general anaesthesia wore a SedLine ® monitor during surgery and were assessed after surgery for the presence of delirium with the Confusion Assessment Method. The intraoperative EEG was scanned for absolute minutes of EEG suppression and correlated with the incidence of POD. The BSR and PSI™ were compared between patients with and without POD.

Results

Visual analysis of the EEG by neurologists and the SedLine ® -generated BSR provided a significantly different distribution of estimated minutes of EEG suppression ( P =0.037). The Sedline ® system markedly underestimated the amount of EEG suppression. The number of minutes of suppression assessed by visual analysis of the EEG was significantly associated with POD ( P =0.039), whereas the minutes based on the BSR generated by SedLine ® were not associated with POD ( P =0.275).

Conclusions

Our findings suggest that SedLine ® (machine)-generated indices might underestimate the minutes of EEG suppression, thereby reducing the sensitivity for detecting patients at risk for POD. Thus, the monitoring of machine-generated BSR and PSI™ might benefit from the addition of a visual tracing of the EEG to achieve a more accurate and real-time guidance of anaesthesia depth monitoring and the ultimate goal, to reduce the risk of POD.

Sevoflurane-induced isoelectric EEG and burst suppression: differential and antagonistic effect of added nitrous oxide

The objective of this study was to investigate whether nitrous oxide influenced the ED50 of sevoflurane for induction of isoelectric electroencephalogram (ED50_isoelectric ) differently from its influence on the ED50 of sevoflurane for electroencephalogram burst suppression (ED50_burst ). In a prospective, randomised, double-blind, parallel group, up-down sequential allocation study, 77 ASA physical status 1 and 2 patients received sevoflurane induction and, after tracheal intubation, were randomly allocated to receive sevoflurane with either 40% oxygen in air (control group) or 60% nitrous oxide in oxygen mixture (nitrous group). The ED50_isoelectric in the two groups was determined using Dixon's up and down method, starting at 2.5% with 0.2% step size of end-tidal sevoflurane. The electroencephalogram was considered as isoelectric when a burst suppression ratio of 100% lasted > 1 min. The subsequent concentrations of sevoflurane administered were determined by the presence or absence of isoelectric electroencephalogram in the previous patient in the same group. The ED50_isoelectric in the nitrous group 4.08 (95%CI, 3.95-4.38)% was significantly higher than that in the control group 3.68 (95%CI, 3.50-3.78)% (p < 0.0001). The values for ED50_burst were 3.05 (95%CI, 2.66-3.90)% and 3.02 (95%CI, 3.00-3.05)% in nitrous group and control group, respectively (p = 0.52). The addition of 60% nitrous oxide increases ED50_isoelectric , but not the ED50_burst of sevoflurane. Neither result indicates an additive effect of anaesthetic agents, as might be expected, and possible reasons for this are discussed.

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.

Randomized controlled trial of the effect of depth of anaesthesia on postoperative pain

BACKGROUND

Our hypothesis was that deep anaesthesia, as estimated by a low target bispectral index (BIS) of 30-40, would result in less postoperative pain than that achieved at a conventional depth of anaesthesia.

METHODS

We undertook a randomized double-blind controlled study at two tertiary teaching hospitals in New Zealand (2010-1) recruiting 135 adult patients ASA I-II presenting for non-emergent surgery under general anaesthesia requiring tracheal intubation. Anaesthesia was maintained with desflurane and a multimodal analgesia regimen comprising fentanyl infusion, i.v. paracetamol, and parecoxib. Patients were randomly assigned to either a low BIS (30-40) group or a high BIS (45-60) group. Desflurane concentrations were titrated to achieve these targets. Postoperative pain was assessed by: the pain on awakening (0-10, verbal rating scale, VRS(awake)) in the post-anaesthetic care unit; pain on activity at 20-24 h after operation (VRS(d1A)); and the rate of morphine patient-controlled analgesia (PCA) usage over the first 24 h.

RESULTS

There was no statistically significant difference between the two groups for any of the pain scores. The median [inter-quartile range (IQR)] VRS(awake) was 4.0 (0-8) for the low and 4.0 (0-8) for the high BIS groups (P=0.56). The median (IQR) VRS(d1A) was 3.0 (1-5) for the low and 3.0 (1.5-4.5) for the high BIS groups (P=0.83). The median PCA morphine consumption in the low BIS group was 0.61 mg h(-1) (0.04-1.5) vs 0.43 mg h(-1) (0-1.59) in the high BIS group (P=0.98).

CONCLUSIONS

We conclude that there is no clinically useful analgesic effect of a deep anaesthesia regimen.