IS THERE IMPLICIT MEMORY AFTER PROPOFOL SEDATION

Recent evidence indicates that implicit memory may be preserved during general anaesthesia. We tested for the presence of explicit and impli cit memory in patients undergoing surgical procedures with local or re gional anaesthesia and sedation with propofol. Initial i.v, boluses of propofol 0.5 mg kg(-1) and fentanyl 1 mu g kg(-1) were administered, followed by an infusion of propofol 50 mu kg(-1) min(-1) Administratio n of one or more doses of propofol 30 mg i.v, during operation was con trolled either by the patient or the anaesthetist. At the start of the last skin stitch, patients were presented with a list of 15 stimulus words and the most frequently associated response. The infusion was th en discontinued. After 1 h in the recovery area, all patients were tes ted for free recall, free association, cued recall and recognition on the list presented during surgery (critical list) and a matched list n ot presented (neutral list). Data of all patients without free recall (explicit memory) were analysed with repeated-measures analysis of var iance. Of 36 patients, five demonstrated free recall. For the remainin g 31 patients, cued recall and recognition showed no evidence of expli cit memory. However, the free association tests demonstrated significa nt priming. The mean number of critical free associations was 6.6 (SEM 0.4) compared with 5.5 (0.4) neutral free association (P < 0.05). In the absence of explicit memory, implicit memory persists after intraop erative sedation with propofol.