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 E(max) model to estimate the potency (IC₅₀) and the plasma effect-site equilibration rate constant (k(e0)) 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 concentraton produced burst suppression. Midazolam increased EEG frequency and amplitude. Bispectral index, SE₉₅, and delta power yield similar estimates of IC₅₀ and k(e0). 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.