Memory for auditory material presented during anaesthesia

We have assessed postoperative memory for lists of 10 neutralwords, presented by tape recording, in patients anaesthetizedby a standardized technique comprising thiopentone 5 mg kg^–1,midazolam 0.07 mg kg^–1, fentanyl 3 µg kg^–1and 70% nitrous oxide in oxygen, using both free recall anda test in which the subject was asked to indicate the presentedwords from a larger list. Twenty-four patients were exposedto one of four tape-recorded lists of words and 24 were presentedwith a blank tape. There was no instance of free recall of presentedwords. Analysis of the responses in the implicit memory testrevealed no difference between the performance of the patientswho had been exposed to a word list and those who had not.