A comparison of spectral edge, delta power, and bispectral index as EEG measures of alfentanil, propofol, and midazolam drug effect.

BACKGROUND: The effects of anesthetic drugs on electroencephalograms (EEG) have been studied to develop the EEG as a measure of anesthetic depth. Bispectral analysis is a new quantitative technique that measures the consistency of the phase and power relationships and returns a single measure, the bispectral index. The purpose of this study was to compare the performance of the bispectral index, version 1.1, with other spectral analysis EEG measures of drug effect for three commonly used anesthetic drugs. METHODS: The EEG waveforms from 31 adults receiving infusions of alfentanil, propofol, or midazolam were analyzed. The time course of spectral edge (SE95), relative power in delta band, and bispectral index were related to the estimated effect-site concentration with use of a sigmoidal Emax model to estimate the potency (IC50) and the plasma effect-site equilibration rate constant (Ke0) for each measure. The performance of the fitting was assessed by the coefficient of correlation between predicted and observed effect. RESULTS: Alfentanil induced a high-amplitude low-frequency EEG response. Propofol induced a biphasic response. At low concentrations, both frequency and amplitude increased. When the concentration increased, the EEG slowed and the amplitude decreased. High concentration produced burst suppression. Midazolam increased EEG frequency and amplitude. Bispectral index, SE95, and delta power yield similar estimates of IC50 and ke0. Except for alfentanil, the performance of the modeling with the bispectral index was as good that with SE95 or delta power. CONCLUSION: Bispectral analysis can be used as a measure of the EEG effects of anesthetic drugs.

EEG bispectrum predicts movement during thiopental/isoflurane anesthesia.

OBJECTIVE: The objective of our study was to test the efficacy of the bispectral index (BIS) compared with spectral edge frequency (SEF), relative delta power, median frequency, and a combined univariate power spectral derivative in predicting movement to incision during isoflurane/oxygen anesthesia. METHODS: A total of 42 consenting patients were assigned to 3 groups, isoflurane 0.75, 1.0, and 1.25 minimal alveolar concentration (MAC). Anesthesia was induced with thiopental and maintained with the appropriate end-tidal concentration of isoflurane. The electroencephalogram (EEG) was recorded using a microcomputer system, and data were analyzed off-line. The EEG during the 2 min before incision was analyzed. Following skin incision, each patient was carefully observed for 60 sec to detect occurrence of purposeful movement. RESULTS: For all groups combined, there was a statistically significant difference for BIS (p < 0.0001) and also for relative delta power (p < 0.016) between movers and nonmovers. There was a statistically significant difference between movers and nonmovers at 1.25 MAC isoflurane for BIS (p < 0.01). There were no other significant differences for any other EEG variable at any concentration of isoflurane. No EEG variable showed a relationship to isoflurane concentration. CONCLUSIONS: When bispectral analysis of the EEG was used to develop a retrospectively determined index, there was an association of the index with movement. Thus, it may be a useful predictor of whether patients will move in response to skin incision during anesthesia with isoflurane/oxygen.

Bispectral analysis of the electroencephalogram correlates with patient movement to skin incision during propofol/nitrous oxide anesthesia.

BACKGROUND: Bispectral analysis is a signal-processing technique that determines the harmonic and phase relations among the various frequencies in the electroencephalogram. Our purpose was to compare the accuracy of a bispectral descriptor, the bispectral index, with that of three power spectral variables (95% spectral edge, median frequency, and relative delta power) in predicting patient movement in response to skin incision during propofol-nitrous oxide anesthesia. METHODS: Forty-four adult patients scheduled for elective noncranial surgery were studied. Gold cup electroencephalographic electrodes were placed on each patient in a frontoparietal montage (Fp1, Fp2, P3, and P4) referred to Cz, and the electroencephalogram was recorded continuously and processed off-line. Conventional frequency bands were used to describe power spectrum variables. Anesthesia was induced with propofol (1.5-3.0 mg-1.kg-1) and maintained with 60% nitrous oxide in oxygen and with propofol at one of three randomized infusion rates (100, 200, or 300 micrograms.kg-1.min-1). Inadequate anesthetic depth was defined as patient movement in response to a 2-cm skin incision at the planned site of surgery. Plasma propofol concentrations were measured within 2 min after skin incision. RESULTS: Complete data were available for 38 patients, of whom 17 moved in response to skin incision. Analysis of the area under the receiver operating characteristic curves showed that only for bispectral index and drug dose group was there a significant predictive relation (area > 0.5). Furthermore, the bispectrum was significantly predictive even after stratification by dose group. CONCLUSIONS: The bispectral index of the electroencephalogram is a more accurate predictor of patient movement in response to skin incision during propofol-nitrous oxide anesthesia than are standard power spectrum parameters or plasma propofol concentrations.

An introduction to bispectral analysis for the electroencephalogram.

The goal of much effort in recent years has been to provide a simplified interpretation of the electroencephalogram (EEG) for a variety of applications, including the diagnosis of neurological disorders and the intraoperative monitoring of anesthetic efficacy and cerebral ischemia. Although processed EEG variables have enjoyed limited success for specific applications, few acceptable standards have emerged. In part, this may be attributed to the fact that commonly used signal processing tools do not quantify all of the information available in the EEG. Power spectral analysis, for example, quantifies only power distribution as a function of frequency, ignoring phase information. It also makes the assumption that the signal arises from a linear process, thereby ignoring potential interaction between components of the signal that are manifested as phase coupling, a common phenomenon in signals generated from nonlinear sources such as the central nervous system (CNS). This tutorial describes bispectral analysis, a method of signal processing that quantifies the degree of phase coupling between the components of a signal such as the EEG. The basic theory underlying bispectral analysis is explained in detail, and information obtained from bispectral analysis is compared with that available from the power spectrum. The concept of a bispectral index is introduced. Finally, several model signals, as well as a representative clinical case, are analyzed using bispectral analysis, and the results are interpreted.

Bispectral analysis of the electroencephalogram during induction of anesthesia may predict hemodynamic responses to laryngoscopy and intubation.

The use of electroencephalography as a measure of adequacy of anesthesia has achieved limited success. Our purpose was to determine whether the non-linear properties of the electroencephalogram (EEG) as defined by the bispectral index was a better predictor of autonomic responses to endotracheal intubation during opioid-based anesthesia than the linear statistical properties of the EEG formulated by power spectral analysis. Thirty-nine adults scheduled for elective non-cranial surgery had a continuous EEG recorded during induction of anesthesia and endotracheal intubation. Anesthesia consisted of thiopental and nitrous oxide in oxygen, followed by 1 of 5 randomized opioid dose regimens. The EEG was continuously recorded and blood pressure was measured every minute. All electroencephalographic parameters were derived for the 3 min before and after intubation and were compared to the blood pressure and heart rate responses. Responders were defined by 2 analyses: patients who had a 20% or greater increase (1) in blood pressure or (2) in heart rate to laryngoscopy. Responders and non-responders were compared using Student's unpaired t test, and differences due to dose regimens were examined with logistic regression. Based on the criterion for blood pressure change, there were 27 responders and 12 non-responders. Heart rate changes did not differentiate between the two groups. There was a significant difference between response groups as measured by the bispectral index which distinguished responders from non-responders independently of the amount of drug given. None of the variables of power spectral analysis accurately distinguished responder from non-responder.(ABSTRACT TRUNCATED AT 250 WORDS)