Awareness during general anaesthesia

Abstract

THE I'nOBLeM Or awareness during anaesthesia has existed since the introduction of the muscle relaxant technique. Any study of the problem must necessarily involve a study of the unconscious mind where such memories are recorded. It must also involve an understanding of some basic psychological mechanisms. The writer has attempted to correlate the published evidence, both clinical reports and research results, and evaluate this from his own experience in anaesthetics and clinical hypnotherapy. It is emphasized that this is a personal evaluation of a difficult subiect, in which "scientific proof", in its normally accepted sense, is virtually impossible. Historical The first account of "awareness" was a letter by Winterbottom, x published in 1950. A brisk correspondence followed, but there was a gap of nearly nine years before further reports appeared, as though anaesthetists were reluctant, or embarrassed, to make such events public. Then, in 1959, Cratt and Phillips ~ published a case and an editorial s appeared in which it was mentioned that "doubtless there have been others." Two more editorials appeared in the Lancet 4 and in Anesthesiology, ~ and reports of single or several cases were described by the following authors:

Wakefulness during Cesarean Section after Anesthetic Induction with Ketamine, Thiopental, or Ketamine and Thiopental Combined

“…Yet awareness and recall are only partly related because awareness may occur without remembrance (10). Also, studies reveal that a patient can recall an experience but can be unable to verbalize it (11,12). If we had measured awareness by evaluating recall, we would have reported an 8% incidence (3 of 36), which is similar to that reported in other studies (13)(14)(15).…”

The Assessment of Postoperative Mental Function

“…They found that this was relatively constant at about 0.6 of the actual MAC for that agent. Scott (1972), in a review of reports of consciousness during anaesthesia, has described initial return of hearing, before discomfort or vision. Evidence of selective attention or awareness of "threatening" auditory input, as reported by Levinson (1965) on the basis of e.e.g.…”

Awareness during anaesthesia: A comparison of anaesthesia with nitrous oxide-oxygen and nitrous oxide-oxygen with Innovar®

“…When using light anaesthesia in combination with muscle paralysis, it is possible for the patient to temporarily "surface" into a zone of partial or complete awareness (Scott 1972).11 Hearing appears to be the last sensation retained before loss of consciousness and is probably the first to return when consciousness is regained; hence this method of testing appeared justified to us. 94.6 per cent patients in Group I and 91.1 per cent in Group II could recall up to the moment of induction of anaesthesia, so that there was no significant retrograde amnesia in this series.…”

“…The addition of Innovar appears to be one way of achieving this. Another method is the intermittent addition of inhalational adjuncts (Scott 1972). 11 Brice, Hetherington, and Utting ~~ found that the addition of 0.3 to 0.5 per cent halothane completely eliminated dreaming.…”