BJA Advance Access originally published online on October 14, 2004
British Journal of Anaesthesia 2005 94(1):57-62; doi:10.1093/bja/aeh289
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2004
Unconscious auditory priming during surgery with propofol and nitrous oxide anaesthesia: a replication
1 Department of Psychology, University of Sheffield, Western Bank, Sheffield, S10 2TP, UK. 2 Northern General Hospital, Sheffield, UK
* Corresponding author: E-mail c.deeprose{at}shef.ac.uk
Background. Priming during anaesthesia has been hard to replicate and the conditions under which it occurs remain poorly understood. We replicated and extended a recent study to determine whether intraoperative priming during propofol and nitrous oxide anaesthesia is a reliable phenomenon, whether it occurs due to awareness during word presentation and whether it is suppressed by a dose of fentanyl at induction.
Methods. Words were played through headphones during surgery to 62 patients receiving propofol and nitrous oxide anaesthesia. Thirty-two patients received fentanyl 1.5 µg kg–1 at induction and 30 received no fentanyl. Neuromuscular blocking drugs were not used. Depth of anaesthesia was measured using the bispectral index (BIS). Anaesthetic variables were recorded at 1 min intervals during word presentation. On recovery, implicit and explicit memory were assessed using an auditory word-stem completion test and a yes–no word-recognition test, respectively.
Results. BIS, blood pressure, end-tidal carbon dioxide and heart rate during word presentation did not differ between the study groups. The infusion rate of propofol and the patients' ventilatory frequency were significantly higher in the group not receiving fentanyl. No patient had unprompted explicit recall of surgery, although there was above-zero performance in six patients on the yes–no recognition task (P<0.05). There was no physiological evidence of awareness during anaesthesia (median mean-BIS=38 in the no-fentanyl group and 42 in the fentanyl group). There was evidence for priming (mean priming score=0.09, P<0.05 in the no-fentanyl study group; mean priming score=0.07, P<0.05 in the fentanyl group) even when patients with momentary light anaesthesia (maximum recorded BIS
60) and/or positive recognition scores were excluded from the analysis.
Conclusions. Existing knowledge can be primed by information presented during propofol and nitrous oxide anaesthesia. This priming is evidence of unconscious information processing and not the result of moments of awareness.
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