Electroencephalogram approximate entropy correctly classifies the occurrence of burst suppression pattern as increasing anesthetic drug effect

Background Approximate entropy a measure of signal complexity and regularit y, quantifies electroencephalogram changes during anesthesia. With increasi ng doses of anesthetics, burst-suppression patterns occur. Because of the h igh-frequency bursts, spectrally based parameters such as median electroenc ephalogram frequency and spectral edge frequency 95 do not decrease, incorr ectly suggesting lightening of anesthesia. The authors investigated whether the approximate entropy algorithm correctly classifies the occurrence of b urst suppression as deepening of anesthesia. Methods: Eleven female patients scheduled for elective major surgery were s tudied. After propofol induction, anesthesia was maintained with isoflurane only. Before surgery, the end-tidal isoflurane concentration was varied be tween 0.6 and 1.3 minimum alveolar concentration. The raw electroencephalog ram was continuously recorded and sampled at 128 Hz. Approximate entropy, e lectroencephalogram median frequency, spectral edge frequency 95, burst-sup pression ratio, and burst-compensated spectral edge frequency 95 were calcu lated offline from 8-s epochs. The relation between burst-suppression ratio and approximate entropy, electroencephalogram median frequency, spectral e dge frequency 95, and hurst-compensated spectral edge frequency 95 was anal yzed using Pearson correlation coefficient. Results: Higher isoflurane concentrations were associated with higher burst -suppression ratios. Electroencephalogram median frequency (r = 0.34) and s pectral edge frequency 95 (r = 0.29) increased, approximate entropy (r = -0 .94) and burst-compensated spectral edge frequency 95 (r = -0.88) decreased with increasing burst-suppression ratio. Conclusion: Electroencephalogram approximate entropy, but not electroenceph alogram median frequency or spectral edge frequency 95 without burst compen sation, correctly classifies the occurrence of burst-suppression pattern as increasing anesthetic drug effect.