Cognitive states and the isolated forearm technique – time to be objective and dispassionate


In their editorial [1], Wang et al. offer a view on consciousness during anaesthesia and propose a ‘classification’. However, the work contains statements and assumptions that I question.

The authors state: “In the past it was assumed that there were only two cognitive stages to anaesthesia: consciousness with memory; and unconsciousness”. Published work (including their own) suggests otherwise [2-4]. Most anaesthetists recognise that patients may move under anaesthesia and even respond without having postoperative recall. They also understand something about implicit memory. Brice et al. [5] described recall and dreaming in patients who received only nitrous oxide plus muscle paralysis, and considered “It is at least theoretically possible that in some patients there was awareness of the surgical procedure, but that this awareness was suppressed”, although they made it clear that they considered this unlikely. Therefore, the intellectual starting point of our profession wasn't necessarily from a binary viewpoint.

The authors are well-known advocates of the isolated forearm technique (IFT). However, the consciousness/awareness research community and the wider clinical anaesthesia community have not adopted IFT as either a research or a clinical technique, because in many circumstances IFT is impractical, there being no commercially available, CE-designated equipment, and there has been no meaningful dialogue about balancing the risk of forearm ischaemia against any benefit of IFT.

The isolated forearm technique was a timely and helpful reminder that consciousness is a continuum, and that during ‘general anaesthesia’ at least some patients (especially those submitted to now obsolete anaesthetic techniques) will respond to command even if they are subsequently amnesic. However, more contemporary discussion should concern the extent to which intra-operative responses without recall is harmful to patients or associated with poorer outcomes or psychological damage.

The authors state that “it is ethically unacceptable for a patient to be in pain and/or emotional distress intra-operatively without consent, even with postoperative amnesia”, with which many anaesthetists would agree, but which does not necessarily translate into promoting IFT as the only meaningful, applicable form of anaesthetic depth monitoring. Multiple large studies have now suggested that virtually all cases of awareness with recall can be abolished by application of 0.7 MAC of an inhalational anaesthetic agent [6, 7], and this appears to be an equilibrium that practising anaesthetists and their patients accept.

Finally, I suggest that rather than offering a ‘classification of intra-operative cognitive states’, as Table 1's caption states, the patients are partly classified according their immediate and late postoperative recall of distress (with or without pain). Furthermore, it may be that after a similar intra-operative stimulus, different patients may exhibit different or multiple responses or outcomes, and there may be no genuine intra-operative difference between two patients of whom one develops emotional sequelae whilst the other does not.