Absence of explicit and implicit memory in unconscious patients using a TCI of propofol.

Abstract

Episodes of implicit memory have been described during propofol anaesthesia. It remains unclear whether implicit memory is caused by short periods of awareness or occurs in an unconscious subject. Sixty patients were randomized in an experimental group (EG), a control group (CG) and a reference group (RG). Loss of consciousness (LOC) was obtained by progressive stepwise increases of propofol using a target-controlled infusion device (Diprifusor, Alaris Medical Systems, San Diego, CA). A tape containing 20 words was played to the patients in the CG before the start of anaesthesia and to the patients in the EG at a constant calculated concentration of propofol associated with LOC. The tape was not played to the patients in the RG. Three memory tests were performed postoperatively. Explicit and implicit memories were evidenced in the CG but not in the EG. In our group of young ASA I/II patients, in the absence of any noxious stimulus, no implicit or explicit memory was found when the calculated concentration of propofol using a Diprifusor was maintained at the level associated with LOC.