Does a BIS-guided Maintenance of Anesthetic Depth Prevent Implicit Memory?


Recent studies investigating the relationship between depth of anesthesia and implicit memory have conflicting results. Limitations of these studies include lack of standardization in surgical procedures and failure to control depth of anesthesia prospectively. We assessed implicit memory function at two different (BIS-guided and pro-spectively controlled) anesthetic depths during surgical stimulus. A list of words was played via headphones to 37 patients during orthopedic surgery under general anesthesia. The Bispectral (BIS) Index was monitored and patients were randomized to remain in a deeper (BIS 40-45) or lighter (BIS 55-60) plane of surgical anesthesia during word presentation. Postoperatively, implicit memory performance was tested using a simple auditory word-stem completion test for presented as well as non-presented words. Absence of explicit memory was evaluated by asking four standard questions regarding intraoperative awareness. All patients received sevoflu-rane and fentanyl for general anesthesia. There was no evidence of implicit memory in either study group. Hit rates for presented and non-presented words were 0.23 ± 0.14 and 0.25 ± 0.09, respectively. No explicit memory was reported by any patient. Depth of anesthesia did not affect implicit memory formation in anesthetized pa-tients undergoing surgery. General anesthesia, even at a higher BIS range, appears to abolish implicit memory as assessed by a simple word-stem completion test.

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Ozcan, M. , Gronlund, S. , Trojan, R. , Khan, Q. , Cure, J. & Wong, C. (2011). Does a BIS-guided Maintenance of Anesthetic Depth Prevent Implicit Memory?. Psychology, 2, 143-149. doi: 10.4236/psych.2011.23023.

Conflicts of Interest

The authors declare no conflicts of interest.


[1] Andrade, J., & Deeprose, C. (2007). Unconscious memory formation during anesthesia. Best Practices and Research Cliicaln Anesthesiology, 21, 385-401.
[2] Bowdle, T. A. (2006). Depth of anesthesia monitoring. Anesthesiology Clinics of North America, 24, 793-822.
[3] Deeprose, C., Andrade, J., Varma, S., & Edwards, N. (2004). Unconscious learning during surgery with propofol anesthesia. British Journal of Anesthesia, 92, 171-177.
[4] Dobrunz, U. E., Jaeger, K., & Vetter, G. (2007). Memory priming during light anesthesia with desflurane and remifentanil anesthesia. British Journal of Anesthesia, 98, 491-496.
[5] Gold, P. E., Weinberger, N. M., & Sternberg, D. B. (1985). Epinephrine-induced learning under anesthesia: Retention performance at several training-testing intervals. Behavioral Neuroscience, 99, 1019-1022.
[6] Hadzidiakos, D. A., Horn, N., Degener, R., Buchner, A., & Rehberg, B. (2009). Analysis of memory formation under general anesthesia (propofol/remifentanil) for elective surgery using the process-dissociation procedure. Anesthesiology, 111, 293-301.
[7] Iselin-Chaves, I. A., Willems, S. J., Jermann, F. C., Forster, A., Adam, S. R., & Van der Linden, M. (2005). Investigation of implicit memory during isoflurane anesthesia for elective surgery using the process dissociation procedure. Anesthesiology, 103, 925-933.
[8] Jacoby, L. L. (1991). A process dissociation framework: Separating automatic from intentional uses of memory. Journal of Memory and Language, 30, 513-541.
[9] John, C. H. (1988). Emotionality ratings and free association norms of 240 emotional and non-emotional words. Cognition and Emotion, 2, 49-70.
[10] Kerssens, C., Ouchi, T., & Sebel, P. S. (2005). No evidence of memory function during anesthesia with propofol or isoflurane with close control of hypnotic state. Anesthesiology, 102, 57-62.
[11] Lequeux, P. Y., Cantraine, F., Levarlet, M., & Barvais, L. (2003). Absence of explicit and implicit memory in unconscious patients using a TCI of propofol. Acta Anaesthesiologica Scandinavica, 47, 833-837.
[12] Lequeux, P. Y., Velghe-Lenelle, C. E., Cantraine, F., Sosnowski, M., & Barvais, L. (2005). Absence of implicit and explicit memory during propofol/remifentanil anesthesia. European Journal of Anaesthesiology, 22, 333-336.
[13] Lubke, G. H., Kerssens, C., Phaf, H., & Sebel, P. S. (1999). Dependence of explicit and implicit memory on hypnotic state in trauma patients. Anesthesiology, 90, 670-680.
[14] Munte, S., Munte, T. F., Mitzlaff, B., Walz, R., Leuwer, M., & Piepenbrock, S. (2001). Postoperative reading speed does not indicate implicit memory in elderly cardiac patients after propofol and remifentanyl anesthesia. Acta Anaesthesiologica Scandinavica, 45, 750-755.
[15] Phelps, E. A. (2004). Human emotion and memory: Interactions of the amygdala and hippocampal complex. Current Opinion in Neurobiology, 14, 198-202.
[16] Rouder, J. N., Speckman, P. L., Sun, D., Morey, R. D., & Iverson, G. (2009). Bayesian t-tests for accepting and rejecting the null hypothesis. Psychonomic Bulletin and Review, 16, 225-237.
[17] Russell, I. F., & Wang, M. (1997). Absence of memory for intraoperative information during surgery under adequate general anesthesia. British Journal of Anesthesia, 78, 3-9.
[18] Russell, I. F., & Wang, M. (2001). Absence of memory for intra-operative information during surgery with total intravenous anesthesia. British Journal of Anesthesia, 86, 196-202.
[19] Sandin, R. (2006). Outcome after awareness with explicit recall. Acta Anaesthesiologica Belgica, 57, 429-432.
[20] Schacter, D. L. (1987). Implicit memory: History and current status. Journal of Experimental Psychology: Learning, Memory, and Cognition, 13, 501-518.
[21] Stoelting: APSF survey results identify safety issue priorities. APSF Newsletter 1999; 14: 2
[22] Stoelting, R. K. (1999). APSF survey results identify safety issue priorities. APSF Newsletter, Spring, 5-6.
[23] Stonell, C. A., Leslie, K., He, C., & Lee, L. (2006). No sex differences in memory formation during general anesthesia. Anesthesiology, 105, 920-926.
[24] Wright, A. J., & Aldrete, A. (1987). Patient memories of anesthesia--historical perspective. Middle East Journal of Anesthesiology, 9, 233-254.

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