No implicit memory for stories played during isoflurane/alfentanil/nitrousoxide anesthesia: A reading speed measurement

Implicit memory of intraoperatively presented stories was recently detected by using the reading speed paradigm during propofol alfentanil-nitrous oxi de anesthesia. Our main goal was to evaluate the reading speed test procedu re under another anesthetic regimen, i.e., isoflurane combined with nitrous oxide and alfentanil-infusion. Ln both experiments, patients were premedic ated with oral midazolam. In a previous experiment, patients postoperativel y read "old" stories that had been presented during anesthesia quicker comp ared with "new," unpresented stories. The same study design and test materi al as in the previous experiment were used. One of two audio tapes with two short stories was played randomly to patients during lumbar disk surgery a nd to awake controls. Approximately 7 h later, a structured interview and t he reading speed test were used to determine whether the participants had a ny explicit or implicit memories of the presented stories. The results of 3 0 patients and 30 controls were calculated. Whereas the control participant s showed an intact explicit and implicit memory of the previously presented material, no such effect was found in the anesthetized patients. The prese nt experiment shows that changing the main anesthetic in otherwise equal st udy conditions, i.e., propofol to isoflurane (end-expiratory 0.7%), implici t memory is abolished in anesthetized patients. Implications: We showed tha t implicit memory during general anesthesia can be abolished by changing th e hypnotic anesthetic. Increased postoperative reading speed for stories pr esented during propofol-alfentanil-nitrous oxide anesthesia was shown in a previous experiment, but not in our study using isoflurane for balanced ane sthesia.