Analysis of Memory Formation during General Anesthesia (Propofol/Remifentanil) for Elective Surgery Using the Process-dissociation Procedure

Anesthesiology. 2009 Aug;111(2):293-301. doi: 10.1097/ALN.0b013e3181ac4a4b.

Abstract

Background: There have been reports of memory formation during general anesthesia. The process-dissociation procedure has been used to determine if these are controlled (explicit/conscious) or automatic (implicit/unconscious) memories. This study used the process-dissociation procedure with the original measurement model and one which corrected for guessing to determine if more accurate results were obtained in this setting.

Methods: A total of 160 patients scheduled for elective surgery were enrolled. Memory for words presented during propofol and remifentanil general anesthesia was tested postoperatively by using a word-stem completion task in a process-dissociation procedure. To assign possible memory effects to different levels of anesthetic depth, the authors measured depth of anesthesia using the BIS XP monitor (Aspect Medical Systems, Norwood, MA).

Results: Word-stem completion performance showed no evidence of memory for intraoperatively presented words. Nevertheless, an evaluation of these data using the original measurement model for process-dissociation data suggested an evidence of controlled (C = 0.05; 95% confidence interval [CI] 0.02-0.08) and automatic (A = 0.11; 95% CI 0.09-0.12) memory processes (P < 0.01). However, when the data were evaluated with an extended measurement model taking base rates into account adequately, no evidence for controlled (C = 0.00; 95% CI -0.04 to 0.04) or automatic (A = 0.00; 95% CI -0.02 to 0.02) memory processes was obtained. The authors report and discuss parallel findings for published data sets that were generated by using the process-dissociation procedure.

Conclusion: Patients had no memories for auditory information presented during propofol/remifentanil anesthesia after midazolam premedication. The use of the process-dissociation procedure with the original measurement model erroneously detected memories, whereas the extended model, corrected for guessing, correctly revealed no memory.

MeSH terms

  • Adult
  • Aged
  • Algorithms
  • Anesthesia, General*
  • Anesthetics, Intravenous*
  • Dissociative Disorders / psychology*
  • Elective Surgical Procedures
  • Electroencephalography
  • Female
  • Humans
  • Hypnotics and Sedatives
  • Male
  • Memory / drug effects*
  • Mental Recall
  • Midazolam
  • Middle Aged
  • Monitoring, Intraoperative
  • Piperidines*
  • Postoperative Period
  • Preanesthetic Medication
  • Propofol*
  • Psychomotor Performance / drug effects
  • Remifentanil

Substances

  • Anesthetics, Intravenous
  • Hypnotics and Sedatives
  • Piperidines
  • Remifentanil
  • Midazolam
  • Propofol