Objective To investigate the
effect of different levels of sedation with
propofol given by TCI on learning and
memory and the relationship between memory and bispectral
index (BIS),
auditory evoked potential index (AEPI), effect-site concentration. Methods Thirty- six ASA Ⅰ - Ⅱ patients of either sex, aged 18-48 yr, undergoing operation on lower extremities were randomly assigned to one of three groups of 12 patients : group A = OOA / S score 3 ( only respond to loud or repeated request for eye-opening); group B = 00A / S score 2 ( only respond to light patting ) and group C = OOA / S score 1 ( only respond to squeezing the deltoid muscle ). The patients were subjected to the first auditory stimulus before sedation. The second stimulus was given when the target level of sedation was reached. BIS and AEP were monitored before and after the second auditory stimulation. Four hours after the experiment, the inclusion and exclusion test were performed on the surgical ward using process dissociation procedure and the explicit and
implicit memory
scores were determined. Results In group A, explicit and implicit memory scores were statistically greater than zero during sedation ( P < 0.05) . In group B only the implicit memory scores exceeded zero ( P < 0.05); whereas the explicit memory scores did not ( P > 0.05) . In group C both the explicit and implicit memory scores did not exceed zero ( P > 0.05). There was no significant difference in the implicit memory scores between group A and B during sedation. Implicit memory scores correlated well with BIS index and AEPI (P < 0.01). The BIS index, AEPI and effect-site concentration could predict the implicit memory (P<0.01). The area under ROC curve : BIS index > AEPI > effect-site concentration. The cutoff points of BIS index, AEPI and effect-site concentration for implicit memory were 47, 28 and 2.3 μg · ml-1 respectively.Conclusion Implicit memory exists in unconscious patients when there is no noxious stimulation. Implicit memory disappears at level 1 of OAA / S score. Implicit memory score correlates well with BIS index, AEPI. The BIS index, AEPI and effect-site concentration are good predictors of implicit memory during target-controlled infusion of propofol.