Indirect Memory during Anesthesia

Abstract

The preservation of implicit memory function during anesthesia is controversial, with conflicting results appearing in the literature. This study was designed to elucidate the effect of midazolam as part of an anesthetic technique on implicit memory function during anesthesia. Using a prospective randomized, double-blind study design, performance in three tasks (category generation, free association, and homophone spelling) was assessed. Forty-eight consenting patients were assigned to two equal groups, to receive 2 mg intravenous midazolam or normal saline before induction of anesthesia. Anesthesia was induced with fentanyl and propofol and maintained with isoflurane 1.3 MAC until incision and isoflurane 1.0 MAC in 70% nitrous oxide thereafter. Fentanyl was used for supplementation of anesthesia. During anesthesia, one of two 50-min tapes containing the test material was played to each patient on a portable cassette player. In the postanesthesia care unit and 48 h after surgery, patients were engaged in three tasks by an observer unaware of the treatment group or tape. No significant main effect of priming or midazolam was observed in any of the tasks. In the word-association task, an interaction was observed between priming and treatment group (F = 9.62, P < .01) due to negative priming in the placebo group. The lack of a main effect of priming in any of the three tasks is consistent with the conclusion that indirect memory was not demonstrated for events occurring during the standard anesthetic conditions of this study. Further, midazolam appeared to have no effect.