The assessment of memory under total intavenous anesthesia

SUMMARY The Assessment of Memory Under Total Intravenous Anesthesia Gülüstan AKTAŞ, MD; Dokuz Eylül University, Faculty of Medicine, Department of Anesthesiology and Reanimation, Izmir/Turkey. Aim: We planned to assess implicit and explicit memory of the patients having abdominal surgery under total intravenous anesthesia with propofol and remifentanil in which anesthesia level is controlled by bispectral index (BIS) monitorization. Methods: The study was approved by the Ethics Committee of DEUTF, and an informed consent was obtained from the patients. Sixty healthy adult patients, ASA class l-ll, aged between 18 and 50 years, finished 8 years of elementary education, undergoing abdominal surgery were enrolled in the study. Their stress levels and cognitive functions were assessed by Strait Trait Anxiety (STA) l-ll and Mini Mental State Examination (MMSE) tests. Anesthesia was induced with 0.5 Hg/kg/min IV infusion of remifentanil and 2 mg/kg IV propofol and 20 mg IV additional propofol if necessary, to obtain BIS levels between 40 and 60, followed by 0.1 mg/kg of vecuronium to facilitate intubation. Anesthesia was maintained 4 - 6 mg/kg/h propofol and 0.1-2 u.g/kg/min remifentanil infusions and %50 air/02 in order to keep the BIS levels between 40 and 60. Immediately after intubation; a tape of natural seaside sounds was played to all patients through headphones. Five minutes after skin incision, it was replaced with a 7.5-minute study tape. Patients were randomly allocated to 3 groups according to the tapes they listened. Patients in the category group (Group KT, n:20) listened 5 animal names with intermediate spontaneous generation frequency which were chosen after the pilot study at our hospital. Patients in the word recognition group (Group KÖ, n:20) listened 5 words with intermediate frequency from the Turkish version of Rey's Auditory Verbal Learning Test list. Then, the study tape was changed with the tape including seaside sounds and it played till the end of the surgery.Patients in the control group (Group KG, n:20) only listened the sea sounds till the end of the surgery. BIS values of the patients were recorded at intubation, skin incision, each 5 minutes peroperatively, extubation and 5 minutes after extubation. Two hours after surgery, tests for assessing memory were performed to each patient in the recovery room. The statistics of the tests were done with p<0.05 significance. Results: The demographic data and STA l-ll scores were similar between the groups. Although there was a difference between Group KT and Group KG for the MMSE scores, all values were >20. There was no statistical difference for the surgery types between the groups. Category and word recognition test's results used for assessing implicit memory were not statistically different between the groups. There was no evidence of implicit memory in any patients. One patient remembered hearing of "the sound of water" as a proof of explicit memory. 11 patients told that they had dreamed. Four of these patients were in Group KÖ, 3 of them were in Group KT, and the other 4 of them were in Group KG. There was no difference among the groups in terms of dreaming. Conclusion: Although no evidence of implicit memory under adequate anesthesia with TlVA was found, one patient showed explicit memory, which assumed to be occurred under light anesthesia. These findings support the hypothesis of implicit and explicit memory uses different pathways. Achieving adequate anesthesia by means of BIS monitorization did not prevent explicit memory formation and did not decrease the incidence of dreaming. On the other hand, our results do not seem to be sufficient to assess memory the patients under anesthesia. There is no definite evidence for the time of the implicit memory tests. With that reason, we think further studies should be done with different methodologies. Key words: Memory, implicit memory, explicit memory, total intravenous anesthesia, BIS, remifehtanil, propofol.