The aims of this study were to compare the stability, correlation with end-tidal sevoflurane, and area below the effect (AUC_effect) vs. time curves of temporal linear mode complexity (TLMC) and approximate entropy (ApEn) during sevoflurane anesthesia. Another study goal was to characterize the time course of the effects of sevoflurane.

Electroencephalogram (EEG) parame1ter stability was evaluated using the coefficients of variation (CV) of the median baseline ( E₀ ), maximal ( E_max ), and individual median E₀ - E_max values. Correlations between sevoflurane concentration and EEG parameters were tested. AUC_effect vs. time curves of TLMC and ApEn were calculated to quantitate any decrease in central nervous system activities. A sigmoid Emax model was used for pharmacodynamic modeling.

TLMC and ApEn demonstrated CVs of 8.36 and 7.35 (for E₀ ) and 19.61 and 13.45 ( E_max ), respectively. The CVs of the individual median E₀ - E_max values were 65.16 for TLMC and 59.97 for ApEn. The Spearman correlation coefficient was -0.3103 for TLMC and -0.3410 for ApEn (P < 0.001 for both parameters). The median AUC_effect value was 338.9 for TLMC and 246.5 for ApEn (P = 0.457). The final pharmacodynamic parameters estimated by sigmoid Emax models were described as follows; E₀ : 0.614, 0.617, E_max : 0.334, 0.287, Ce₅₀ : 5.48, 5.07 vol%, γ: 1.88, 2.01, k_e0 : 0.306, 0.236 min (TLMC, ApEn).

TLMC is comparable to ApEn according to the univariate EEG descriptors of the effects of sevoflurane. A sigmoid Emax model well described the pharmacodynamics of sevoflurane for TLMC and ApEn.