Learning During General Anaesthesia: Implicit Recall After Methohexitone or Propofol Infusion

Abstract

Forty-four patients undergoing coronary artery surgery were allocated randomly to receive an infusion of propofol or methohexitone as a hypnotic supplement to a fentanyl-based anaesthetic technique. A taped message was played to the patients, consisting of 10 words associated with prompt sentences and a suggestion for a specific postoperative behavioural response. Twenty patients (10 propofol and 10 methohexitone) (perioperative group) were exposed to the taped message during surgery and in the immediate postoperative period and the other 24 patients (postoperative group) were exposed to the tape only in the postoperative period, after return to the intensive care unit (ICU). No patient had explicit recall of any events during the period when the tape was played. The patients in the propofol group who heard the tape during surgery had significant implicit recall of the word associations compared with the equivalent 10 methohexitone patients (P = 0.004), when tested 48 h after surgery. The patients who were played the tape whilst receiving identical infusion regimens for sedation in the ICU did not demonstrate implicit recall of the word associations in either the propofol or the methohexitone groups. There was no evidence of a response to the specific behavioural suggestion during the postoperative interview. The results confirm that auditory perception can occur during clinically adequate anaesthesia, and that suppression of auditory awareness or learning is a function of both the pharmacological degree of sedation and the degree of surgical stimulation.

An Investigation of Learning during Propofol Sedation and Anesthesia Using the Process Dissociation Procedure

“…A possible explanation of the different outcomes in the study of Lubke et al 32 and our study is that propofol impairs learning more effectively than isoflurane, but evidence is mixed in this regard. Learning has been demonstrated during anesthesia with propofol 33 and with isoflurane, 34,35 but other authors have found that no learning occurs with these drugs. 19,36 Our speculative hypothesis that surgery contributes to learning by raising catecholamine levels offers another potential explanation.…”

Absence of explicit and implicit memory in unconscious patients using a TCI of propofol

“…Several studies have shown that this type of memory may occur frequently during general anaesthesia (3)(4)(5)(6)(7) while other studies have failed to demonstrate such a phenomenon (8)(9)(10)(11). Several studies have shown that this type of memory may occur frequently during general anaesthesia (3)(4)(5)(6)(7) while other studies have failed to demonstrate such a phenomenon (8)(9)(10)(11).…”

Memory for Unconsciously Perceived Events: Evidence from Anesthetized Patients

“…We did not include studies involving nonsurgical volunteers (for reviews see Andrade, 1995;Ghoneim & Block, 1992) or children (Bonke, van Dam, van Kleef, & Slijper, 1992: Standen, Hain, & Hosker, 1987 because we felt that these two groups may represent considerably different populations than the adult surgical patients used in the majority of studies. In addition, we did not include four studies involving cardiac surgery (Bethune et al, 1992(Bethune et al, , 1993De Houwer, Demeyere, Verhamme, & Eelen, 1995;Schwender, Madler, Klasing, Peter, & Poppel, 1994) because it is generally agreed that the anesthesia used for cardiac surgery is not as deep as the anesthesia used for many other types of surgery (cf. Hug, 1993).…”