Memory priming during light anaesthesia with desflurane and remifentanil anaesthesia.

BACKGROUND Previous studies of memory priming during anaesthesia with EEG monitoring have observed implicit memory effects for words presented during light and deep anaesthesia with and without surgical stimulation. We hypothesized that memory priming occurs under each of five different combinations of anaesthesia and surgery, and no significant differences occur in memory priming among the five conditions or between the two test points such as, 12 vs 24 h after surgery. METHODS Forty gynaecological patients (aged between 28 and 66 yr, median 44.5 yr) were included in the study. They received propofol and remifentanil induction followed by desflurane and remifentanil anaesthesia in conjunction with neuromuscular blocking agents. Each patient was exposed to 60 of 120 nouns in a double-blind randomized design. These 60 nouns were divided into 5 groups of 12 words, presented under one of the five different conditions, namely, intubation, skin incision, deep anaesthesia and moderate anaesthesia (both during surgery), and light anaesthesia during the emergence phase. The depth of anaesthesia was measured using the EEG monitor, Narcotrend. RESULTS No explicit memories were observed in a free recall or in a yes-no recognition test. A word-stem completion test revealed a significant implicit priming only for light anaesthesia (P < 0.01). No significant differences were detected among the five conditions. An overall implicit memory effect occurred for the second test point (P < 0.05). CONCLUSIONS Our hypotheses could not be verified. Implicit memory priming occurred only under light anaesthesia, when the patients were most probably conscious. Priming effects may be enhanced after night's sleep.