MEMORY DURING GENERAL ANAESTHESIA: VARIATIONS IN STIMULUS CHARACTERISTICS Annette Bonebakkel' CIP-GEGEYENS KONINKLIJKE BIBLIOTHEEK, DEN HAAG Bonebakker, Anne Elisabeth Memory during general anaesthesia: variations in stimulus characteristics I Anne Elisabeth Bonebakker. - Delft: Eburon P&L Proefschrift Erasmus Universiteit Rotterdam. - Met samenvatting in het Nederlands. ISBN 90-5651-004-5 NUGI 742 Trefw.: anesthesie Distributie: Ebllron P&L, Postblls 2867, 2601 CW Delft Dntkwerk: Ponsen & Looijen BY, Wageningen Copyright" 1995 by A.E. Bonebakker All rights reserved Omslagontwerp: Annelies Bernard MEMORY DURING GENERAL ANAESTIlESIA: VARIATIONS IN STIMULUS CHARACTERISTICS Geheugen tijdens algehele anesthesie: variaties in stimulus karakteristieken PROEFSCRRIFT TER VERKRlJGING VA N DE GRAAD VA N DOCTOR AAN DE ERASMUS UNIVERSITEIT ROTTERDAM OP GEZAG VA N DE RECTOR MAGNIFICUS PROF.DR. P.W.C. AKKERMANS, M.A. EN VOLGENS RET BESLUIT VA N RET COLLEGE VOOR PROMOTIES. DE OPENBARE VERDEDIGING ZAL PLAATSVINDEN OP WOENSDAG 7 JUNI 1995 OM 13.45 UUR Door Anne Elisabeth Bonebal<ker geboren te Goes PROMOTIECOMMISSIE: PROMOTOR: Prof. dr. J. Passchier CO-PROMOTOR: Dr. B. Bonke OVERIGE LEDEN: Prof.dr. J.G. Bovill Prof.dr. F.G.A. van der Meche Prof. P.M. Merikle Ph.D. "Your memory is like a monster; you forget - it doesn't. It simply files things away. It keeps things from you, or hides things from you -and summons them to your recall with a will of its own. You think you have a memory; but it has you!" John Trving, 1989 Voor Rlllld en voor mijll opo, Joseph Gosschalk MEMORY DURING GENERAL ANAESTHESIA: VARIATIONS IN SlThRJLUS CHARACTERISTICS Preface 3 Review of the literature: CHAPTER 1: Memory during general anaesthesia: practical and 4 methodological aspects CHAPTER 2: Outline of the thesis 38 Experimelllal studies CHAPTER 3: Implicit memory in balanced anaesthesia: 40 lack of evidence CHAPTER 4: Information-processing during balanced anaesthesia: 50 evidence for unconscious memory CHAPTER 5: Memory during anaesthesia and the effect of 68 number of stimulus presentations CHAPTER 6: General discussion 87 Summary 94 Samellvalfing 95 Dallkwoord 96 Curriculum vitae 98 3 Preface This thesis is the description of a research project into memory and perception during general anaesthesia. The question whether surgical patients can hear and process information without awareness (Le., during general anaesthesia) is adressed on the basis of psychological research into information processing during general anaesthesia (see Chapter 1). The general aim of this work is to determine if and when memory and perception takes place during general anaesthesia. Assessment of the experimental circumstances under which unconscious functioning is preserved in anaesthetized patients (Chapters 4 and 5) has important implications both for clinical practice and for psycholo gical theories of memory. The project is the result of the fruitful collaboration between the Department of Medical Psychology and Psychotherapy of Erasmus University Rotterdam, and the Departments of Anaesthesiology and General Surgery of St. Clara's Hospital Rotterdam. The work presented in this thesis was made possible by grant 900-559-027 from the Dutch Organisation for Scientific Research (NWO). NWO made it possible to present the findings of this project at different congresses. Financial support for the publication of this thesis was made possible by NWO and the Erasmus University Rotterdam. In the first chapter of this thesis, the literature on memory during anaesthesia is discussed. This chapter was written during the last months of the project. For this reason, the review includes two of the studies that were conducted within the context of the whole research project. At the moment this thesis was prepared, a shortened version of Chapter 1 was prepared for publication; the study described in Chapter 3 was published in Anaesthesia (1993, 48:657-660); and a manuscript of the studies described in Chapters 4 and 5 was submitted to Memory and Cognition. 4 CHAP1ER 1 Memory during general anaesthesia: practical and methodological aspects. A.E. BOllebakker, M. lelicic, l. Passchier, alld B. BOllke Abstract Evidence from studies of memory and awareness during general anaesthesia suggests that some form of cognitive functioning is preserved in surgical patients. This finding has important implications both for clinical practice and for psychological theories of memory. In order to give the methodological background of the present situation in this field of research, this article deals, on the basis of recent experiments, with important methodological aspects of studies into perception and memory during general anaesthesia. Introduction During the past decade, memory for information presented during general anaesthesia has been extensively investigated. Ever since the investigators Cheek' and Levinson' reported in 1959 and 1965 that patients, under hypnosis, could recall conversations and incidents that presumably had taken place during anaesthesia, researchers in the field have investigated the possibility that under some circumstances, anaesthetized patients may process information that was presented intraoperatively. Some studies yielded positive results, others did not. Nevertheless, memory for intraoperatively presented material could not be demonstrated convincingly. In 1992, at the Second International Symposium on Memory and Awareness in Anesthesia', about half of the relevant studies had yielded positive results, half nonsignificant findings'-', Although the experimental designs of the studies had become more and more sophisticated in comparison with the first congress on the topic three years earlier', the findings were still very inconsistent. Due to more advanced techniques to measure memory processes there now seems to be more reliable