Approximate entropy as the measurement of the electroencephalographic effect during sevoflurane induction

Abstract

Background: The processed electroencephalograms are useful surrogate measures of quantification of volatile anesthetics effect. We hypothesized that there is a certain relationship between the end-tidal concentration of sevoflurane and approximate entropy (ApEn). The aim of this study was to investigate the effect of sevoflurane on ApEn during induction. Methods: Fourteen patients were enrolled. With recording of the electroencephalogram at the F3, F4, P3, and P4 montages, anesthesia was induced by increasing the vapor setting of sevoflurane by 1 vol% up to 8 vol% via a facemask. When the end-tidal concentration of sevoflurane did not show any further change, we increased vapor setting of sevoflurane by 1 vol%. When the end-tidal concentration of sevoflurane did not show any further change with 8 vol% of sevoflurane vapor setting, measurement of electroencephalogram was finished. The relation between end-tidal sevoflurane concentration and ApEn was tested by Spearman correlation. Results: ApEn showed a significant correlation (R = −0.7551, P < 0.0001) with end-tidal sevoflurane concentration. The final pharmacodynamic parameters estimated by a sigmoid Emax model were described as follows: E0 = 0.91, Emax = 0.28, Ce50 = 1.36 vol%, γ = 1.27, ke0 = 0.67 min -1 . Conclusions: Sevoflurane induction with gradual increase of end-tidal sevoflurane concentration increases the amount of regu- larity in approximate entropy. (Korean J Anesthesiol 2008; 55: 404∼11)