Marko Jelicic

Implicit memory for words presented during anaesthesia

Abstract Tests for implicit memory seem to be rather insensitive to the amount of attention given to stimuli during study. In the experiment reported here, the effect of a complete absence of attention during presentation of stimulus material on implicit memory performance was studied. Surgical patients were auditorily presented with exemplars of word categories during general anaesthesia. At the earliest convenient time after surgery, they were requested to generate category exemplars. Although none of the patients expressed any conscious recollection of events during the surgical episode, experimental patients generated significantly more critical exemplars than a control group. Apparently, information presented during anaesthesia can influence post-operative performance in an implicit memory task. Repetition priming seems possible even in the absence of attentional processing at the time of encoding. It is argued that the nature of the unattended encoding process can best be described as the automatic ...

Unconscious learning during anaesthesia

Forty‐three surgical patients were, during general anaesthesia, presented (via headphones) with either statements about common facts of some years ago (group A), or new verbal associations, i.e. the names of fictitious, nonfamous people (group B). None had any recall of intra‐operative events. In a postoperative test of indirect memory, patients in group A answered more questions about the ‘common facts’ correctly than those in group B (p < 0.005), which reflects the activation of pre‐existing knowledge. Furthermore, patients in group B designated more ‘nonfamous names’ as famous (thus falsely attributing fame) than patients in group A (p < 0.001), which demonstrates that information‐processing during anaesthesia can also take place as unconscious learning.

The effect of midazolam premedication on implicit memory activation during alfentanil‐nitrous oxide anaesthesia

Eighty‐three patients were given midazolam 0.1 mg.kg‐1 by intramuscular injection as premedication before general anaesthesia with alfentanil‐nitrous oxide. During anaesthesia patients were presented (through headphones) with either statements about common facts of some years ago (group A) (n = 43) or new verbal associations, e.g. names of fictitious, nonfamous people (group B) (n = 40). In a previous study with the same anaesthetic technique, but without premedication there was significant activation of implicit memory (p < 0.001). In this study we found no explicit or implicit memory for the auditory information presented during anaesthesia. Midazolam premedication can prevent implicit memory activation during alfentanil‐nitrous oxide anaesthesia.

Implicit learning during enflurane anaesthesia in spontaneously breathing patients

Forty‐one patients breathing spontaneously during enflurane anaesthesia were presented (via headphones) either with statements about common facts of some years ago, or new verbal associations, i.e. names of fictitious people. Postoperatively, there were no differences between the two groups in the responses to questions about the common facts or attribution of fame to the fictitious people. This finding suggests that unconscious learning and activation may not occur during enflurane anaesthesia without neuromuscular block.

LEVEL OF PROCESSING AFFECTS PERFORMANCE ON EXPLICIT AND IMPLICIT MEMORY TASKS

We examined the effect of level of processing on explicit and implicit memory performance. 58 high school students were shown a word list and were given either semantic or nonsemantic instructions. Subsequently, they were administered a free-recall test to assess explicit memory retention and a word-completion test to assess implicit memory retention. Level of processing affected both explicit and implicit performance. Depth of processing had a larger effect on the expression of explicit memory than on implicit memory.

Information processing under anaesthesia

We read with interest the paper by Marshall et al. (Anaesthesia 1992; 47: 461-6) comparing recovery from anaesthesia after dental and gynaecological surgery. We perform around 800 dental procedures per annum under general anaesthesia at this hospital, the majority as day cases. We were interested to note that no significant advantage could be demonstrated for maintenance of anaesthesia with either propofol or isoflurane in terms of recovery characteristics. It would therefore seem logical to base the choice of technique and agent on other factors, which might include the cost of anaesthesia and the time taken to administer it. We repeated Marshall’s protocol. Two groups of patients received alfentanil 10 pg.kg-’ at induction and anaesthesia was induced with propofol 2.5 mg.kg-’. Neuromuscular blockade was achieved with atracurium 0.3 mg.kg-’. In the first group, anaesthesia was maintained with a propofol infusion at 9 mg.kg-’.h-’ for I5 min then 6 mg.kg-’.h-’ for the remainder of the procedure. In the second group isoflurane was used at a measured end-tidal concentration of 1%. A semiclosed system with absorber was used with flows as low as practicable. Anaesthesia in a third group of patients was induced with propofol and intubation was achieved after suxamethonium 1 mg.kg-’. Anaesthesia was subsequently maintained with spontaneous respiration of isoflurane. Fentanyl in 25 pg increments was used for analgesia in this group. The latter was our preferred technique. We calculated the cost per hour of anaesthesia with each of these three techniques by accurately measuring the quantities of isoflurane or propofol used and the time spent with the vaporizer or infusion pump on. Costing is based on the price of agents as supplied to the hospital pharmacy. Propofol infusion cost E15.90 per hour, isoflurane (IPPV) cost E9.20 per hour and isoflurane (SV) cost €11.60 per hour. Table 1. Mean anaesthetic times (s).

Information processing during general anaesthesia

the anaesthetist in addition to customary monitoring. A questionnaire was completed by the staff when the patient arrived in the PAR. The patients studied were aged between 4 months and 15 years. The monitor was well-accepted by the medical and nursing staff and was found to be useful and reliable in 23 out of 25 cases. The ,small size, portability and simplicity of the monitor were the features most frequently favoured by the users. The monitor was deemed to be unreliable in two patients in whom visual but no audio signals were displayed. The audio failure may be attributed in part to an inadequate gain setting in these patients. Negative comments concerned the relatively short duration (5 hours) of battery power available when the bar-graph is used. This problem can be overcome by disabling the bar-graph, and relying only on the audible indication of respiration. The monitor can be used for approximately 50 hours when only audio indicator is in use. We would like to acknowledge the help of the anaesthetists who participated in the evaluation of the breath monitor, especially Dr D. Shulman.