Awareness during anaesthesia

Abstract

The study by Pandit and colleagues 1 emphasises the discrepancy between the oft-quoted 1–2:1000 incidence of ‘awareness during anaesthesia’ and its extraordinary rarity in the clinical experience of most UK anaesthetists. Pandit et al. categorised awareness into that occurring: (i) after induction but before surgery; (ii) during surgery; and (iii) after surgery but before full recovery. Many regard awareness in stages 1 and 3 as the risky periods of anaesthesia because they are non-steady states, but arousal due to stimulation at these stages is ameliorated by attention to the basic rules of administering general anaesthesia, supplementation with local anaesthesia and powerful analgesia, not by using a monitoring device that in our hands had poor sensitivity to opioid effects. Arousal during stage 2 may occur during steady-state anaesthesia when there is an unrecognised and insufficient dose of anaesthetic and analgesic drugs administered. Is there a role for monitoring here? Gratifyingly, this distressing state seems to be rare, although the incidence of 1–2:1000 is often quoted. Pandit et al. recorded the prevalence of patients who complained of pain and were intent on a formal complaint or litigation as about 1:100 000. This observation is not new and is consistent with a similarly low incidence of awareness (1:80–90 000 anaesthetics) that we reported 2 from hospitals in the Cambridge region between 1993 and 1999. The incidence is very low; it means that almost 100 000 patients would need to be monitored to pick up one case of this type of awareness. This state seems to be the tip of the iceberg, but how far below the surface should we go to explore the large spectrum of explicit recall? Electroencephalography can be used to identify changes in consciousness during propofol anaesthesia 3, but is a research tool, not yet available for widespread clinical use. Instead, more research should be performed to explore consciousness and memory during anaesthesia, such as that performed in Cambridge 2 and Northwick Park 4, which emphasised the powerful inhibitory effects of sub-MAC doses of general anaesthesia on working memory – and therefore subsequent recall – as well as pain perception in seemingly fully conscious subjects. The veracity of what is recalled must also be questioned. If there is no immediate postoperative record of the awareness events, how can the later recall of this event be verified as exact? Anecdotally, during a depth of anaesthesia study, a patient recalled precisely the events that had occurred after accidental discontinuation of general anaesthesia mid-procedure, except that contemporaneous video records showed that none of the recalled events had actually occurred. The rarity of painful awareness during anaesthesia should re-assure patients and confirm the high level of clinical competence of UK anaesthetists, despite their historical rejection of monitoring every patient using electroencephalographic or isolated forearm monitoring techniques. Now is not the time, if ever, for the National Institute for Health and Clinical Excellence to consider mandating such monitoring.