EEG AND MEMORY EFFECTS OF LOW-DOSE INFUSIONS OF PROPOFOL

The purpose of this study was to identify EEG changes associated with low-dose propofol infusion producing only sedative effects, and to describe the memory effects of low-dose propofol infusion. Ten healthy volunteers underwent EEG monitoring (at F(z), C(z), P(z) and O(z) electrode sites) before, during and after propofol 0.5 mg kg-1 i.v. bolus and 75-mu-g kg-1 min-1 as an infusion. Mean serum concentration of propofol during infusion was 0.86 (SD 0.14)mu-g ml-1. The EEG changed significantly during infusion, with increased power in the beta1 (15-20 Hz), beta2 (20.5-30 Hz) and delta (1-3.5 Hz) frequencies. Beta1 and beta2 power changes were most marked at the F(z) and C(z) electrodes. Subjects were sedated, but able to complete cognitive tasks. Visual analogue scales of attention and sleepiness were obtained throughout the study and demonstrated a sedative effect during propofol infusion, but were not a significant factor in memory performance or EEG changes. A verbal learning task (Rey Auditory-Verbal Learning Task) administered before, during and after infusion showed a marked reduction in short-term memory capacity and dramatically impaired free recall and recognition during infusion. Nine of 10 subjects had partial amnesia for complex visual scenes presented during infusion, recalling less than 50% of the material. Stronger cueing was required to retrieve information presented during propofol infusion, with an increase in mean retrieval time from 95.4 (41.2) s to 426.8 (83. 1) s. EEG and memory effects resolved quickly after the end of infusion. We conclude that anterior, high frequency EEG activity increases significantly during low-dose propofol infusion and that propofol produces significant memory impairment which has characteristics of true amnesia, concurrent with changes in beta-1 power in the EEG. The fact that low-dose propofol produces significant changes in both cognitive and EEG measures warrants further investigation into the utility of the EEG power spectrum as a useful monitor of amnesia during conscious sedation with propofol.