Bispectral EEG Analysis Research Articles

Monitoring of Anesthesia by Bispectral Analysis of EEG Signals.

Background In intensive care, monitoring the depth of anesthesia during surgical procedures is a key element in the success of the medical operation and postoperative recovery. However, despite the development of anesthesia thanks to technological and pharmacological advances, its side effects such as underdose or overdose of hypnotics remain a major problem. Observation and monitoring must combine clinical observations (loss of consciousness and reactivity) with tools for real-time measurement of changes in the depth of anesthesia. Methodology. In this work, we will develop a noninvasive method for calculating, monitoring, and controlling the depth of general anesthesia during surgery. The objective is to reduce the effects of pharmacological usage of hypnotics and to ensure better quality recovery. Thanks to the overall activity of sets of neurons in the brain, we have developed a BIS technique based on bispectral analysis of the electroencephalographic signal EEG. Discussion. By collecting the electrical voltages from the brain, we distinguish light sleep from deep sleep according to the values of the BIS indicator (ranging from 0 : sleep to 100 : wake) and also control it by acting on the dosage of propofol and sevoflurane. We showed that the BIS value must be maintained during the operation and the anesthesia at a value greater than 60. Conclusion This study showed that the BIS technology led to an optimization of the anesthetic management, the adequacy of the hypnotic dosage, and a better postoperative recovery.

Non-linear Analysis of Scalp EEG by Using Bispectra: The Effect of the Reference Choice.

Bispectral analysis is a signal processing technique that makes it possible to capture the non-linear and non-Gaussian properties of the EEG signals. It has found various applications in EEG research and clinical practice, including the assessment of anesthetic depth, the identification of epileptic seizures, and more recently, the evaluation of non-linear cross-frequency brain functional connectivity. However, the validity and reliability of the indices drawn from bispectral analysis of EEG signals are potentially biased by the use of a non-neutral EEG reference. The present study aims at investigating the effects of the reference choice on the analysis of the non-linear features of EEG signals through bicoherence, as well as on the estimation of cross-frequency EEG connectivity through two different non-linear measures, i.e., the cross-bicoherence and the antisymmetric cross-bicoherence. To this end, four commonly used reference schemes were considered: the vertex electrode (Cz), the digitally linked mastoids, the average reference, and the Reference Electrode Standardization Technique (REST). The reference effects were assessed both in simulations and in a real EEG experiment. The simulations allowed to investigated: (i) the effects of the electrode density on the performance of the above references in the estimation of bispectral measures; and (ii) the effects of the head model accuracy in the performance of the REST. For real data, the EEG signals recorded from 10 subjects during eyes open resting state were examined, and the distortions induced by the reference choice in the patterns of alpha-beta bicoherence, cross-bicoherence, and antisymmetric cross-bicoherence were assessed. The results showed significant differences in the findings depending on the chosen reference, with the REST providing superior performance than all the other references in approximating the ideal neutral reference. In conclusion, this study highlights the importance of considering the effects of the reference choice in the interpretation and comparison of the results of bispectral analysis of scalp EEG.

Bispectral EEG analysis for knowledge scaffolding in music perception: A mirror neurons-based approach

'Motion' and intention that are involved in the perception of musical structure combined with mirror neuron (MN) system activation are studied in this article. The mechanism of MN involved in the p...

Bispectral EEG analysis for knowledge scaffolding in music perception: A mirror neurons-based approach

'Motion' and intention that are involved in the perception of musical structure combined with mirror neuron (MN) system activation are studied in this article. The mechanism of MN involved in the perception of musical structures is seen as a means for cueing the learner on `known' factors that can be used for his/her knowledge scaffolding. To explore such relationships, EEG recordings, and especially the Mu-rhythm in the premotor cortex that relates to the activation of MN, were acquired and explored. Three experiments were designed to provide the auditory and visual stimuli to a group of subjects, including both musicians and non-musicians. The acquired signals, after appropriate averaging in the time domain, were analyzed in frequency and bifrequency domains, using spectral and bispectral analysis, respectively. Experimental results have shown that an intention - related activity shown in musicians could be associated with Mu - rhythm suppression. Moreover, an underlying ongoing function appearing in the transition from heard sound to imagined sound could be revealed in the bispectrum domain. A Mu-rhythm modulation provoked by the MNs could cause bispectral fluctuations, especially when visual stimulation is combined with an auditory one for the case of musicians. These results pave the way for further exploitation of the role of MNs in music and, in general, knowledge perception.

The Effect of the Assignment of a Pre-Sedation Target Level on Procedural Sedation Using Propofol

The goal of this study was to determine if there is a difference in the achieved depth of sedation, the rate of respiratory depression, procedural difficulty, or patient perceived pain or recall between patients randomized to a pre-procedural target sedation level of moderate or deep procedural sedation using propofol during the reduction of fractures and dislocations in the Emergency Department (ED). This was a randomized, prospective study of adults undergoing procedural sedation (PS) with propofol for fracture or dislocation reduction in the ED between July 2003 and March 2004. Patients were randomized to a target sedation level of moderate or deep, using American Society of Anesthesiologists’ definitions. Doses, vital signs, nasal end tidal CO 2 (ETCO 2), pulse oximetry, and bispectral EEG analysis (BIS) scores were recorded. Respiratory depression was defined as a change in ETCO 2 >10, an oxygen saturation of <90% at any time, or an absent ETCO 2 waveform at any time. After the procedure, patients were asked if they perceived any pain or had any recall of the procedure. Physicians were asked to rate the difficulty of completing the reduction using a 100-mm visual analog scale (VAS). Respiratory depression rates were compared with chi-square tests, BIS and VAS scores were compared with t tests. Seventy-five patients were enrolled, 39 randomized to the target of moderate PS and 36 to the target of deep PS. No significant complications were noted. There were 25/36 (69%) of the patients assigned to the deep sedation target group who actually achieved a deep level of sedation and 21/39 (54%) of the patients assigned to the moderate sedation target group who actually achieved a moderate level of sedation ( p = 0.40). Respiratory depression was seen in 19/39 (49%) patients with the moderate PS target and 18/36 (50%) with the deep PS target ( p = 0.91). The mean minimum recorded BIS score was 67.7 (95% confidence interval [CI] 62.2–73.3) for the moderate PS target group and 59.2 (95% CI 55.1–64.2) for the deep PS target group ( p = 0.03). There were 12/39 (31%) in the moderate PS target group and 4/36 (11%) in the deep PS target group who reported pain with or recall of the procedure ( p = 0.04). The mean physician VAS for procedural difficulty was 34.0 (95% CI 23.7–44.3) for the moderate PS group and 28.8 (95% CI 18.4–39.2) for the deep PS group ( p = 0.46). In this study, the assignment of a pre-procedural target sedation level of moderate or deep PS did not influence the level of sedation achieved, the rate of respiratory depression, the occurrence of complications, the time to return of baseline mental status, or the success of the procedure. It does not seem that the assignment of a pre-procedural target sedation level is an effective means of changing the outcome of ED PS.

What we can know from bispectral analysis of EEG?

Bispectral analysis is an advanced signal processing technique that quantifies quadratic nonlinearities (phase-coupling) among the components of a signal. As bicoherence is the direct indicator of the degree of phase coupling, it is the most important element of bispectral analysis. Here we investigated the changes of EEG bicoherence induced by anesthesia or noxious stimuli. First, we investigated the changes of EEG bicoherence during isoflurane anesthesia. We found EEG bicoherence showed two peaks in fairly restricted regions of bi-frequency space and their heights were well correlated with isoflurane concentration. It is well known that EEG is influenced by noxious stimuli as well as anesthetic concentration. Then we investigated the influence of noxious stimuli on EEG bicoherence during isoflurane or sevoflurane anesthesia. Two peaks of EEG bicoherence were both diminished after skin incision, which re-emerged after fentanyl administration. On the other hand, EEG bicoherence was not changed after incision, when fentanyl was administered before incision. Their data suggested that EEG bicoherence was sensitive to noxious stimuli, which suggested that EEG bicoherence would become an indicator for adequacy of analgesia during anesthesia. In conclusion, we would be able to manage both hypnosis and analgesia during anesthesia by EEG bicoherence monitoring.

Can Electroencephalographic Analysis Be Used to Determine Sedation Levels in Critically Ill Patients?

Prolonged use of sedative drugs frequently leads to oversedation of intensive care patients. Clinical assessment scales are not reliable in deeply sedated patients. Parameters obtained from spectral and bispectral analysis of electroencephalogram (EEG) records have been combined to create an index (BIS) to monitor anesthesia depth. The role of such parameters in monitoring the depth of the sedation in intensive care unit (ICU) patients has yet to be determined. We designed the present prospective study to redefine and calculate available spectral and bispectral parameters from raw EEG records and estimate their clinical relevance for the diagnosis of under- or oversedation levels in ICU patients. Forty adult patients receiving continuous midazolam and morphine sedation were included. We obtained 167 clinical evaluations of sedation level using Ramsay and COMFORT scales along with an EEG record of 300 s. Six spectral parameters-relative power of 4 frequency bands (beta, alpha, Theta, and delta), 95th percentile of the power spectrum (SEF95), and 50th percentile of the power spectrum (SEF50) and four bispectral parameters, real triple product, bispectrum (Bispectrum), bicoherence, and ratio 10-were calculated. The relevance of each of these parameters and combinations in predicting too light (Ramsay 1 and 2) or deep (Ramsay 5 and 6) sedation levels was assessed. These calculations were performed before and after exclusion of the agitated patients, whose COMFORT 4 score was above 2. The most relevant parameters for predicting levels of deep sedation (Ramsay 5 and 6) were ratio 10 (area under the curve = 0.763; 95% confidence interval, 0.679-0.833) and SEF95 (area under the curve = 0.687; 95% confidence interval, 0.597-0.767). The most relevant parameters for predicting light levels of sedation (Ramsay 1 and 2) were also ratio 10 (area under the curve = 0.829; 95% confidence interval, 0.695-0.917) and SEF95 (area under the curve = 0.798; 95% confidence interval, 0.650-0.898). There is a modest improvement in relevance of their linear combination in predicting sedation level. Results were similar after exclusion of agitated patients. We conclude that various calculated EEG descriptive parameters exhibited large interindividual variability. There was a strong correlation between EEG spectral and bispectral parameters. Bispectral analysis slightly improves the predictive power of simple spectral analysis in distinguishing too light or deep sedation levels in ICU patients. Spectral edge frequency 95 and Ratio 10 are the most relevant electroencephalogram (EEG) indexes for monitoring the level of sedation in intensive care unit patients but calculated EEG values exhibited large interindividual variability. Bispectral analysis of EEG provides a slight improvement over simple spectral analysis.

Monitoring Level of Sedation With Bispectral EEG Analysis: Comparison Between Hypothermic and Normothermic Cardiopulmonary Bypass

Monitoring Level of Sedation With Bispectral EEG Analysis: Comparison Between Hypothermic and Normothermic Cardiopulmonary Bypass

Evaluation of Bispectral EEG Analysis and Recall in Paralyzed Intubated Patients

Evaluation of Bispectral EEG Analysis and Recall in Paralyzed Intubated Patients

Bispectral Index: A New Monitor In The Management of Acute Alprazolam Poisoning: Alprazolam Poisoning And BIS

Alprazolam is a triazolobenzodiazepine, which has antidepressant properties. Few overdoses were described with this agent. Major clinical symptoms of these overdoses are sedation. The bispectral index (BIS), a numeric value derived from bispectral analysis of EEG, has been introduced as a monitor of the hypnotic component of anaesthesia. In this case, our aim is to demonstrate the usefulness of BIS monitoring in the management of patients who were poisoned with benzodiazepines such as alprazolam.

Bispectral Index: A New Monitor In The Management of Acute Alprazolam Poisoning: Alprazolam Poisoning And BIS

Alprazolam is a triazolobenzodiazepine, which has antidepressant properties. Few overdoses were described with this agent. Major clinical symptoms of these overdoses are sedation. The bispectral index (BIS), a numeric value derived from bispectral analysis of EEG, has been introduced as a monitor of the hypnotic component of anaesthesia. In this case, our aim is to demonstrate the usefulness of BIS monitoring in the management of patients who were poisoned with benzodiazepines such as alprazolam.

Monitoring level of sedation with bispectral EEG analysis: comparison between hypothermic and normothermic cardiopulmonary bypass

The level of sedation of 28 patients undergoing elective coronary artery bypass grafting with fentanyl-propofol anaesthesia was monitored with bispectral analysis (BIS), spectral edge frequency, and band power of the electroencephalogram. Fourteen patients underwent hypothermic cardiopulmonary bypass (CPB) (32 degrees C, group H), and 14 normothermic CPB (group N). The level of sedation was measured with Observer's Assessment of Alertness/Sedation Score and with Ramsay Sedation Score. BIS was the only EEG measurement that paralleled the clinical course of the patients' sedation level. Values (median, 95% confidence intervals (CI)) changed significantly over time in both groups (P<0.0001). In group H, BIS decreased from 97 (95, 99) the day before surgery to 48 (44, 52) after tracheal intubation, to 46 (41, 52) before going off CPB, to 91 (85, 97) immediately before extubation. In group N, values were 93 (91, 97) the day before surgery, 53 (47, 59) after tracheal intubation, 48 (43, 53) before going off CPB, and 90 (84, 96) before extubation. During CPB, BIS values were significantly different between the two groups. Group H had a median of 41 (95% CI, 39, 42), and group N had a median of 49 (95% CI, 48, 51, P<0.0001). Peak values of all other processed EEG parameters during anaesthesia and surgery overlapped with values from the day before, when patients had no sedating medication, and these values did not correlate to the patients' course of sedation during the study. There was no explicit recall of the surgery in either group. During the phases of anaesthesia and surgery without CPB, the progression of BIS levels was comparable with previously published data for non-cardiac surgery. During normothermic CPB, the highest BIS values were close to values representing insufficient depth of sedation. It remains to be elucidated whether the much lower BIS values in the hypothermic group were solely a result of brain cooling or if increased serum propofol concentrations, because of slowed pharmacodynamics during hypothermia, also contributed.

Clonidine decreases propofol requirements during anaesthesia: effect on bispectral index

Assessment of the effect of clonidine on depth of anaesthesia is difficult because clonidine combines analgesic, sedative and direct haemodynamic effects. We thus evaluated the influence of clonidine on the bispectral index (BIS) and its potential dose-sparing effect on propofol. After induction of anaesthesia with target-controlled infusion of propofol and obtaining an unchanged bispectral index (pre-BIS), clonidine 4 microg kg(-1) or placebo was administered randomly to 50 patients in a double-blind manner. Subsequently, if there was a decrease in BIS we reduced the target concentration of propofol until pre-BIS was reached. The pre-BIS was maintained and a remifentanil infusion was added during surgery. The courses of the BIS, heart rate and blood pressure were recorded and the total amounts of intra-operative propofol and remifentanil were determined. Assessment of implicit memory during anaesthesia was performed with an auditory implicit memory test consisting of item sequences. Administration of clonidine resulted in a decrease in the BIS from 45 (SD 4) to 40 (6) (P<0.001), which allowed a reduction of propofol target concentration from 3.3 (0.6) to 2.7 (0.7) microg ml(-1) (P<0.001) and measured propofol concentration from 2.9 (0.6) to 2.5 (0.7) kg ml(-1) (P=0.009) in order to maintain the pre-BIS value. During subsequent surgery, propofol requirements were reduced by 20% (P=0.002) in the clonidine group and a similar amount of remifentanil was used in each group. The increase in anaesthetic depth given by clonidine can therefore be measured with bispectral EEG analysis and allows reduction of the propofol dose to achieve a specific depth of anaesthesia.

Comparison of Bispectral EEG Analysis and Auditory Evoked Potentials for Monitoring Depth Of Anaesthesia During Propofol Anaesthesia

Department of Anaesthesia, General Infirmary at Leeds, Leeds, United Kingdom; Department of Anaesthesia and Intensive Care, Hamamatsu University School of Medicine, Hamamatsu, Japan; Department of Anaesthetics, Law Hospital, Lanarkshire, United Kingdom; Glasgow University Department of Anaesthesia, Royal Infirmary, Glasgow, United Kingdom

Comparison of bispectral EEG analysis and auditory evoked potentials for monitoring depth of anaesthesia during propofol anaesthesia

We have compared the auditory evoked potential index (AEPIndex) and bispectral index (BIS) for monitoring depth of anaesthesia in spontaneously breathing surgical patients. Twenty patients (aged 17-49 yr) undergoing day surgery were anaesthetized with computer-controlled infusions of propofol. The mean (SD and range) of each measurement was determined during consciousness and unconsciousness and at specific times during the perioperative period. Mean values for AEPIndex during consciousness and unconsciousness were 74.5 (SD 14.7) 36.7 (7.1), respectively. BIS had mean values of 89.5 (SD 4.6) during consciousness and 48.8 (16.4) during unconsciousness. AEPIndex and BIS were greater during consciousness compared with during unconsciousness. The average awake values of AEPIndex were significantly higher than all average values during unconsciousness but this was not the case for BIS. BIS increased gradually during emergence from anaesthesia and may therefore be able to predict recovery of consciousness at the end of anaesthesia. AEPIndex was more able to detect the transition from unconsciousness to consciousness.

Target controlled infusion systems guided by bispectral EEG analysis

Euro-Neuro '98: First International Update on Neuro-Anaesthesia and Neuro-Intensive Care; Genk, Belgium, 5-7 February 1998