Bilateral bispectral index monitoring during suppression of unilateral hemispheric function

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.

Cerebral oxygenation and processed EEG response to clamping and shunting during carotid endarterectomy under general anesthesia

Clamping and shunting during carotid endarterectomy (CEA) surgery causes changes in cerebral blood flow. The purpose of this study was to assess and compare, side by side, the cerebral oxygenation (rSO2) and processed electroencephalogram (EEG) response bilaterally to carotid artery clamping and shunting in patients undergoing CEA under general anesthesia. With institutional approval and written informed consent, patients undergoing CEA under general anesthesia and routine carotid artery shunting were recorded bilaterally, simultaneously and continuously with an rSO2 and processed EEG monitor. The response of the monitors during carotid artery clamping and shunting were assessed and compared between monitors and bilaterally within each monitor. Sixty-nine patients were included in the study. At clamping the surgical-side and contralateral-side rSO2 dropped significantly below the baseline incision value (-17.6 and -9.4% respectively). After shunting, the contralateral-side rSO2 returned to baseline while the surgical-side rSO2 remained significantly below baseline (-9.0%) until the shunt was removed following surgery. At clamping the surgical-side and contralateral-side processed EEG also dropped below baseline (-19.9 and -20.6% respectively). However, following shunt activation, the processed EEG returned bilaterally to baseline. During the course of this research, we found the rSO2 monitor to be clinically more robust (4.4% failure rate) than the processed EEG monitor (20.0% failure rate). There was no correlation between the rSO2 or processed EEG changes that occurred immediately after clamping and the degree of surgical side stenosis measured pre-operatively. Both rSO2 and processed EEG respond to clamping and shunting during CEA. Cerebral oximetry discriminates between the surgical and contralateral side during surgery. The rSO2 monitor is more reliable in the real-world clinical setting. Future studies should focus on developing algorithms based on these monitors that can predict clamping-induced cerebral ischemia during CEA in order to decide whether carotid artery shunting is worth the associated risks. From the practical point of view, the rSO2 monitor may be the better monitor for this purpose.

Changes in bilateral bispectral index VISTA monitoring system during Wada test

The Wada test is a procedure used in the preoperative assessment before epilepsy surgery in order to determine language lateralization, to assess the post-operative risk of an amnesia syndrome, and to evaluate the risk of material-specific memory deficits, in particular verbal memory deficits. This test involves inserting a cannula into the internal carotid artery via the femoral artery, and then to inject amobarbital to shut down brain function, usually in one of the brain hemispheres. The bilateral bispectral index (BIS) VISTA™ monitoring system (BVMS) was used to detect changes in EEG, and in the power spectrum distribution using the density spectral array (DSA) of both hemispheres. We describe a patient with an agenesis of the A1 segment of the right anterior cerebral artery, scheduled for a Wada test, in whom the BVMS demonstrated its potential value.

[Usefulness of Bispectral Index (BIS) monitoring for early detection of cerebral hypoperfusions]

OBJECTIVES

The goal of the study was to assess whether clinically significant cerebral hypoperfusion in awake patients would be associated with some alterations in the values of the bispectral index (BIS) monitoring.

STUDY DESIGN

Observational study.

POPULATION AND METHODS

We monitored the BIS during endovascular carotid artery occlusion testing in awake patients.

RESULTS

Twenty-eight patients were included. Twenty-one adequately tolerated the procedure. Their BIS value remained stable throughout the procedure. Four patients had poor angiographic tolerance, but no clinical symptoms. Their BIS value slightly decreased during the test (minimal BIS: 83 [79-87]). Three patients had poor clinical and angiographic tolerance of the occlusion. They all experienced an immediate and dramatic decrease in their BIS value (minimal BIS: ipsilateral to clamping: 50 [45-60]; contralateral to clamping: 48 [45-52]). In all patients, the clinical symptoms and the BIS normalized after deflating the occlusion balloon.

CONCLUSION

In awake patients, the observed values of the BIS monitoring seem to be associated with clinically relevant cerebral hypoperfusion.

Behavioral measures and EEG monitoring using the Brain Symmetry Index during the Wada test in children

EEG monitoring is used routinely during the Wada test in children. We quantified EEG asymmetry using the Brain Symmetry Index (BSI) to reduce subjectivity of EEG interpretation. Clinical and procedural variables were obtained and EEG data were retrieved from 46 patients with a total of 89 injections. The BSI, the absolute value of the relative difference of the average spectral density of the right and left hemisphere, was calculated over time for all EEGs. Lateralized slowing was correctly identified in all procedures. Asymmetry was minimal at baseline (BSI 0.16) and increased with injection of amobarbital (BSI 0.49). Various patterns of the BSI were seen in distinct clinical and procedural scenarios. In this retrospective analysis, the BSI could not predict an unsuccessful Wada procedure. Our results suggest application of the BSI during the Wada test in children is feasible. Real-time calculation of the BSI during EEG monitoring in the angiography suite is warranted for further validation.

Comparison of SNAP™ II and BIS Vista indices during normothermic cardiopulmonary bypass under isoflurane anesthesia

OBJECTIVE

Processed EEG monitoring during cardiopulmonary bypass (CPB) may help determine loss of consciousness and depth of anesthesia. This study compared the SNAP(™) II and BIS Vista monitors in patients undergoing isoflurane anesthesia with normothermic CPB.

METHODS

40 subjects undergoing CPB with isoflurane anesthesia were enrolled. Subjects were premedicated with 1-2 mg midazolam approximately 5 min prior to acquisition of baseline index values and anesthesia induced with midazolam and fentanyl. Anesthesia was maintained with isoflurane, midazolam, and fentanyl and a cis-atracurium infusion. SNAP(™) II (version 1.2.9 algorithm 1.88) and BIS Vista (application version 3.00 platform version 2.03) indices were recorded at baseline, pre-induction, post-intubation, incision, start of CPB, every 15 min during CPB, end of CPB, and end of case. Agreement between methods was determined using Pearson correlation and the Bland-Altman method with repeated observa- tions.

RESULTS

Twenty-four male and 12 female subjects completed the analysis. The correlation between SNAP(™) II and BIS Vista index values was 0.61 (P < 0.005). A linear relationship between the difference in the indices and the average index values was observed following the induction of anesthesia. In awake subjects, the bias between the SNAP(™) II and BIS Vista was 5 (95% CI 3-7). The limits of agreement were 23 (95% CI 19-26) and -13 (95% CI -9--16). During anesthesia, the mean difference on a log scale was 0.11 (95% CI 0.09-0.12). The limits of agreement were 0.43 (95% CI 0.40-0.45) and -0.21 (95% CI -0.18--0.24). The antilog of the mean difference demonstrated that the SNAP(™) II value was 28% (95% CI 24-33%) higher than the BIS Vista value following induction of anesthesia.

CONCLUSIONS

The SNAP(™) II monitor demonstrates a consistently positive bias during cardiopulmonary bypass under isoflurane anesthesia compared with the BIS Vista.

The utility of using the bispectral index-Vista for detecting cross-clamping decline in cerebral blood flow velocity

BACKGROUND

Patients undergoing carotid endarterectomy for extracranial internal carotid artery stenosis are at risk of cerebral ischemia/hypoperfusion. Criterion recommended by European and American committees to determine whether to place a shunt consisted of a decline in transcranial Doppler ultrasonography-measured middle cerebral artery blood flow velocity (MCBFV) to < 30% to 40% of intraoperative preclamp value.

OBJECTIVE

To assess the discriminative power of the bispectral index (BIS)-Vista monitor for detecting a 40% decline in MCBFV with cross-clamping.

METHODS

In 20 patients undergoing carotid endarterectomy under remifentanil/propofol anesthesia, BIS-Vista data, MCBFV, and pulsatility index from bilaterally mounted BIS-Vista and transcranial Doppler monitors were continuously recorded.

RESULTS

Coefficient of determination revealed good correlation (r = 0.763) between ipsilateral BIS-Vista and MCBFV after cross-clamping. BIS-Vista exhibited a high discriminative power of 0.850 (95% confidence interval, 0.455-0.966) area under the receiver-operating characteristic curve in detecting an ipsilateral 40% MCBFV decline. Two-way analysis of variance (location by time) suggests that BIS-Vista exhibited a global decline; ie, both BIS-Vistas declined when 1 carotid on either side was clamped because there was no significant interhemispheric difference (P = .112) in mean BIS-Vista values over time.

CONCLUSION

Although we demonstrated good correlation and high discriminative power of the BIS-Vista monitor in depicting a MCBFV decline that could serve as indicator of decline in cerebral activity, BIS-Vista cannot be considered a reliable indicator of cerebral ischemia/hypoperfusion that could replace transcranial Doppler monitoring to determine whether a shunt is to be placed.

Cross-frequency coupling in mesiotemporal EEG recordings of epileptic patients

Semi-invasive foramen ovale (Fov) electrodes were used to record electrical activity in the vicinity of the inferior mesial temporal region of epileptic patients, in addition to standard scalp EEG. Third order cumulant analysis was used to measure the phase-coupled frequencies corresponding to non-linear coupling of spectral frequency components, somewhat analogous to frequencies of resonance. On the basis of the distribution of these frequencies, an index of resonance (IR) is defined as the ratio between the number of peaks in the gamma-band (40-55Hz) vs. the number of peaks in the beta-band (15-30Hz). The epileptogenic focus was located in the hemisphere with lower resonant frequencies because these frequencies were characteristic of a spread of the seizure over a broader area. In the case of Fov electrodes IR could differentiate a group of patients affected by a tumor compared to patients with mesial temporal sclerosis. The novel index IR appears as an interesting parameter to evaluate the level of interareal functional connectivity in Fov recordings in epileptic patients, but its usage is likely to be extended in electrophysiological studies.

Different bispectral index values from both sides of the forehead in unilateral carotid artery stenosis

Bispectral index (BIS) values derived from the left and right forehead are usually the same. We report on two patients with unilateral carotid artery stenosis in whom we observed differences between the BIS values obtained from sensors placed on each side of the forehead. During surgery, the BIS values of the diseased side decreased more than those of the opposite side when the mean arterial pressure decreased below 70 mmHg. BIS monitors should be used with caution in patients with unilateral carotid artery and cerebrovascular disease.

Monitoring consciousness: the current status of EEG-based depth of anaesthesia monitors

Direct and indirect inhibitory effects of anaesthetic agents on cortical activity are reflected in the electroencephalogram (EEG) as: (i) a shift from low-amplitude, high-frequency EEG, to high-amplitude, low-frequency activity (indicative of cortical depowering) and; (ii) the appearance of spindles and K-complexes (indicative of thalamocortical hyperpolarisation and sensory blockade). Existing EEG monitors use cortical activity as a proxy measure for consciousness. However the state of the cortex at any given moment does not accurately predict the state that it will enter in response to a noxious stimulus, and EEG monitors do not differentiate well between different levels of rousability. Also the literature reveals many instances where the EEG pattern is dissociated from conscious state (e.g. an awake-looking EEG, but an unresponsive patient; or a slow-wave EEG in an awake patient). Fortunately, a slow-wave EEG (even in the presence of a responsive patient) usually indicates profound amnesia for explicit memory.

Bispectral Index Monitoring of Unihemispheric Effects in Dolphins

When dolphins sleep, their electroencephalographic activity may change in only one cerebral hemisphere; i.e., the left and right brain hemispheres can take turns sleeping. We demonstrate that the bispectral index (BIS) monitor can detect interhemispheric asymmetry in the dolphin species Tursiops truncatus. Using two BIS sensors placed simultaneously over each side of the dolphin's head, we often, but not always, found significant differences between the two BIS values (e.g., left side 60 and right side 90) in non-medicated animals and in animals given propofol, atropine, and/or diazepam. Observations were each made over a period of approximately 3 h on dolphins resting out of the water. Unihemispheric effects may be inducible pharmacologically in dolphins. The dolphin, with its human-sized brain, may provide an animal model for study of unihemispheric effects in humans.