Absence of explicit or implicit memory in patients anesthetized with sufentanil/nitrous oxide

Verbal paired associates were presented to 25 surgical patients from initial incision to closure of the incision during general anesthesia. Sufentanil with nitrous oxide and oxygen was administered; intravenous morphine (0.05 mg/kg) was administered when the skin suturing was completed; no volatile anesthetic agents or benzodiazepines were administered. When ready for discharge from the postanesthesia care unit, and again 2 weeks later by telephone, patients were tested for free recall, cued recall, recognition, and free association. No evidence of explicit memory for the word list was demonstrated by patients on tests of free recall, cued recall, or recognition, nor did a free-association test of implicit memory demonstrate a significant priming effect, in contrast to previous results obtained with isoflurane. The precise conditions under which surgical events can be processed, and retained in the form of implicit memory outside of conscious awareness, remain to be determined.