I read with interest the recent editorial by Wang et al.  and found it greatly informative. However, I question the authors’ equating of the state of unconsciousness with hypnosis and also draw attention to the use of medical hypnosis in uncovering episodes of intra-operative awareness.
The word hypnosis is derived from the Greek word ‘hypnos’, meaning sleep, but there is widespread agreement that subjects in the state of hypnosis are neither asleep nor unconscious . The Encyclopaedia Britannica defines hypnosis as “a special psychological state with certain physiological attributes, resembling sleep only superficially and marked by a functioning of the individual at a level of awareness other than the ordinary conscious state…” . There is no single agreed definition of hypnosis among learned medical authorities, but common descriptions include ‘a state of focused attention’, a ‘hypersuggestible’ or ‘dissociated’ state . This state is often found in normal everyday activities, such as becoming engrossed in watching a film or when undertaking a sporting activity, activities where a subject temporarily minimises external influences to concentrate fully on another task. The American Psychological Association describes hypnosis as ‘a procedure during which a health professional or researcher suggests that a client, patient or subject experience changes in sensations, perceptions, thoughts or behavior’ . Anyone who has undergone hypnosis or observed hypnosis in a therapeutic setting will recognise that both control and awareness of surroundings are commonly maintained.
It is interesting to note that hypnosis has long been recognised as a means for uncovering patients’ memories of intra-operative events whilst under anaesthesia [4, 5]. In 1965, Levinson  exposed 10 patients under deep anaesthesia to verbal suggestions indicative of an anaesthetic crisis. One month later, none of the patients could remember any of the intra-operative events explicitly but, under hypnosis, four of them accurately recalled the verbal communication used whilst they were anaesthetised. A further four patients recalled some of the communication and developed symptoms of anxiety. It seems that under hypnosis, certain patients are able to recover memories of events that happened under anaesthesia, that they are unable to recall in their normal waking state . As Wang et al. point out, it is well recognised that, although patients may have no explicit recall of events under anaesthesia, emotional symptoms may persist from the experience. The therapeutic importance of using hypnosis in this way is clear – once the cause of the psychological symptoms is known, treatment strategies can be more clearly directed.
The 5th National Audit Project (NAP5)  will, one hopes, give us a much clearer idea of the current incidence of explicit awareness but the incidence of implicit awareness will remain unknown. Hypnosis may be one of the few tools capable of discovering the presence of implicit awareness and may prove very useful in future investigations into the true incidence of anaesthetic awareness.