Effects of propofol on nociceptive response and power spectra of electroencephalographic and systemic arterial pressure signals in the rat: correlation with plasma concentration.

We applied simultaneous spectral analysis of electroencephalographic (EEG) and systemic arterial pressure signals in Sprague-Dawley rats to monitor the status of consciousness and cardiovascular functions during intravenous anesthesia with propofol and to assess their correlations with plasma propofol concentration. Our results support the hypothesis that a 'threshold' plasma concentration (1.7-1.8 micrograms/ml) exists for propofol anesthesia. This threshold level, we further showed, may be attained by both i.v. bolus injection and continuous infusion, although the pharmacokinetic profiles, as well as EEG and hemodynamic correlates, may be different. Continuous, on-line power spectral analysis of EEG signals revealed that the degree of reduction in the power density of the theta and delta bands and root mean square value paralleled the level of anesthesia. Significant suppression of both alpha and beta components occurred only concomitant with EEG burst suppression. At the subanesthetic dose, i.v. infusion of propofol increased preferentially the power density of the theta and delta bands, suggesting the validity of including sedation as a nonhypnotic therapeutic application of propofol. We also found that appreciable cardiovascular suppression took place only upon anesthetic doses of propofol. Power spectral analysis of systemic arterial pressure signals indicated that this was accompanied by a progressive depression of spectral parameters that signify peripheral vascular resistance and baroreceptor reflex response.