QUANTITATIVE ELECTROENCEPHALOGRAPHIC ANALYSIS OF THE BIPHASIC CONCENTRATION-EFFECT RELATIONSHIP OF PROPOFOL IN SURGICAL PATIENTS DURING EXTRADURAL ANALGESIA

We studied effects on the EEG of propofol infused at a rate of 0.5 mg kg(-1) min(-1) for 10 min in 10 healthy male surgical patients under e xtradural analgesia. The EEG amplitude in six frequency bands was rela ted to arterial blood propofol concentrations and responsiveness to ve rbal commands. The EEG amplitude showed a characteristic biphasic resp onse to increasing blood propofol concentrations in all frequency band s. During the infusion, patients lost responsiveness when EEG amplitud es in the high frequency bands were decreasing after having reached a maximum. EEG changes were different during infusion and emergence. Pha rmacodynamic modelling, using two effect compartments with dissimilar equilibration constants, resulted in satisfactory fits. We conclude th at propofol exerts a biphasic effect on the EEG amplitude in all frequ ency bands. The dissimilarity of EEG changes during infusion and durin g emergence suggests that two effect compartments with different equil ibration constants exert opposing effects on the EEG.