Investigation of implicit memory during isoflurane anesthesia for elective surgery using the process dissociation procedure.
BACKGROUND
This prospective study evaluated memory function during general anesthesia for elective surgery and its relation to depth of hypnotic state. The authors also compared memory function in anesthetized and nonanesthetized subjects.


METHODS
Words were played for 70 min via headphones to 48 patients (aged 18-70 yr) after induction of general anesthesia for elective surgery. Patients were unpremedicated, and the anesthetic regimen was free. The Bispectral Index (BIS) was recorded throughout the study. Within 36 h after the word presentation, memory was assessed using an auditory word stem completion test with inclusion and exclusion instructions. Memory performance and the contribution of explicit and implicit memory were calculated using the process dissociation procedure. The authors applied the same memory task to a control group of nonanesthetized subjects.


RESULTS
Forty-seven patients received isoflurane, and one patient received propofol for anesthesia. The mean (+/- SD) BIS was 49 +/- 9. There was evidence of memory for words presented during light (BIS 61-80) and adequate anesthesia (BIS 41-60) but not during deep anesthesia (BIS 21-40). The process dissociation procedure showed a significant implicit memory contribution but not reliable explicit memory contribution (mean explicit memory scores 0.05 +/- 0.14, 0.04 +/- 0.09, and 0.05 +/- 0.14; mean automatic influence scores 0.14 +/- 0.12, 0.17 +/- 0.17, and 0.18 +/- 0.21 at BIS 21-40, 41-60, and 61-80, respectively). Compared with anesthetized patients, the memory performance of nonanesthetized subjects was better, with a higher contribution by explicit memory and a comparable contribution by implicit memory.


CONCLUSIONS
During general anesthesia for elective surgery, implicit memory persists even in adequate hypnotic states, to a comparable degree as in nonanesthetized subjects.
Iselin-Chaves
Irène A
IA
Department of Anesthesiology, University Hospital of Geneva, Switzerland. irene.iselin-chaves@hcuge.ch
Willems
Sylvie J
SJ
Jermann
Françoise C
FC
Forster
Alain
A
Adam
Stéphane R
SR
Van der Linden
Martial
M
D000293:Adolescent; D000328:Adult; D000368:Aged; D000768:Anesthesia, General / Q000009:adverse effects*; D018685:Anesthetics, Inhalation / Q000009:adverse effects*; D003071:Cognition / Q000187:drug effects; D003463:Cues; D017558:Elective Surgical Procedures; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000009:adverse effects*; D008297:Male; D008568:Memory / Q000187:drug effects*; D011939:Mental Recall / Q000502:physiology; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D009483:Neuropsychological Tests; D012107:Research Design
D018685:Anesthetics, Inhalation; D007530:Isoflurane