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Investigation into memory formation according to the level of hypnotic depth using process dissociation
Anesth Pain Med 2018;13(4):388-93
Published online October 31, 2018
© 2018 Korean Society of Neuroscience in Anesthesiology and Critical Care.

Yu-Ri Jung1, Byung-Moon Choi1 , and Gyu-Jeong Noh1,2
Departments of 1Anesthesiology and Pain Medicine, 2Clinical Pharmacology and Therapeutics, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
Correspondence to: Byung-Moon Choi, M.D., Ph.D.
Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea
Tel: 82-2-3010-1704
Fax: 82-2-3010-6790
Received April 3, 2018; Revised May 30, 2018; Accepted May 30, 2018.
cc This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: Process dissociation procedure has been used to evaluate explicit and implicit memories. Two process-dissociation measurement models are described.
Methods: This prospective study evaluated intraoperative memory formation in Korean patients undergoing elective surgery under general anesthesia and its relation to the depth of hypnotic state. A total of 270 patients enrolled were randomly assigned to three groups based on Bispectral Index (BIS) values in the following ranges: 30 to 40, BIS 40 to 50, and BIS 50 to 60 according to the level of hypnotic depth induced by propofol or sevoflurane during the presentation of wordlists. When the level of hypnotic depth was maintained at the target BIS range, words were played for 15 minutes via headphones to patients. Within 24 hours after the word presentation, memory was assessed using an auditory word stem completion test. The probability of explicit and implicit memory was calculated using original and extended measurement models. Brice interviews were performed within 1 and 24 hours after surgery.
Results: A total of 119 patients who did not deviate from the target BIS range were included in the analysis. The 95% confidence interval (CI) of the probability of occurrence of implicit memory evaluated by the original model did not include zero. However, when the extension model was used, 0 was included in the 95% CI. Explicit memory evaluated via Brice interviews did not occur in any group.
Conclusions: When BIS was maintained in the range of 30 to 60 during surgery, no explicit or implicit memory was observed.
Key Words : Anesthesia; Intraoperative awareness; Memory.

October 2018, 13 (4)
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