Nabilone produces marked impairments to cognitive function and changes in subjective state in healthy volunteers.

This was a double-blind, randomised, placebo-controlled, crossover study of the acute cognitive and subjective effects of nabilone 1-3 mg in healthy male volunteers. The Cognitive Drug Research computerised system (CDR system) was used to assess changes in attention, working and episodic memory. In addition, a number of self-ratings were conducted including those of mood, alertness and perceived drug effects. Impairments to attention, working and episodic memory and self-ratings of alertness were evident. Volunteers also experienced a number of subjective drug effects. These data demonstrate that acute doses of nabilone in the range 1-3 mg produce clear cognitive and subjective effects in healthy volunteers, and therefore they may be used as reference data in the future study of peripherally acting cannabinoids believed to be free from such effects.

Awareness and memory function during paediatric anaesthesia.

BACKGROUND: Previous research indicates a much higher incidence of awareness during anaesthesia in children than in adults. The present study is the first large-scale, intraoperative assessment of awareness during paediatric anaesthesia using the isolated forearm technique, and the first large-scale study of memory function during paediatric anaesthesia. METHODS: One hundred and eighty-four children, 5-18 yr, underwent the isolated forearm technique during the first 17 min of surgery while receiving volatile anaesthesia. The isolated forearm technique was modified to accommodate brief or no paralysis. Bispectral index was monitored in a subset of 54 patients. Sixteen neutral words were played 20 times during surgery and, on recovery, implicit memory for these words was tested with a word identification task. Explicit memory for the surgical period was tested with a structured interview. Behavioural changes were assessed with age-appropriate questionnaires. RESULTS: No child had explicit recall of intraoperative events on recovery, and there was no evidence of implicit memory for words presented during anaesthesia. Two of 184 children made unambiguous and verified responses on the modified isolated forearm technique, an incidence of intraoperative awareness of 1.1%. One of these children reported that he was uncomfortable and not completely unconscious during surgery. Neither child had implicit memory for the neutral words, or adverse behaviour change. CONCLUSIONS: The incidence of awareness during surgery in children is approximately eight times that measured in adults by postoperative recall. In contrast to adults, there is no evidence for preserved memory priming during anaesthesia.

Unconscious auditory priming during surgery with propofol and nitrous oxide anaesthesia: a replication.

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 microg 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> or =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.

Unconscious learning during surgery with propofol anaesthesia.

BACKGROUND: Learning during anaesthesia has been demonstrated, but little is known about the circumstances under which it may occur. This study investigated the hypothesis that learning during anaesthesia occurs during, but not before, surgical stimulation. METHODS: Words were played through headphones to 64 day-surgery patients during propofol anaesthesia. Fourteen words were played repeatedly (15 times) for 1 min each either before (n=32) or during (n=32) surgical stimulation. The depth of anaesthesia was estimated using the bispectral index (BIS). Heart rate, ventilatory frequency, mean arterial pressure, end-tidal carbon dioxide concentration, and infusion rate of propofol were recorded at 1 min intervals during word presentation. On recovery, memory was assessed using an auditory word stem completion test and word recognition test. RESULTS: The mean BIS, arterial pressure, end-tidal carbon dioxide and heart rate during word presentation did not differ between the groups. The infusion rate of propofol and the ventilatory frequency were significantly greater in the during-surgical stimulation group. There was no evidence for explicit recall or recognition, nor of awareness during anaesthesia (median mean-BIS=38 in the before-surgical stimulation group and 42 in the during-surgical stimulation group). Only patients who were played words during surgical stimulation showed significant implicit memory on recovery (mean score=0.08, P<0.02) However, their scores were not significantly higher than those of the before-surgical stimulation group (mean score=0.01). CONCLUSIONS: Learning during anaesthesia seems more likely to occur during rather than before surgical stimulation at comparable anaesthetic depth. We hypothesize that surgical stimulation facilitates learning during anaesthesia, independently of its effects on anaesthetic depth.