One in 15,000 patients who undergo general anesthesia report experiencing "anesthesia awareness," according to a recent survey of British and Irish providers. But when they're questioned directly about the condition, 1 in 500 patients report awareness.

Interestingly, though, only one-third of the patients who spontaneously reported awareness said they suffered distress, notes a researcher who proposes that the condition may not be what we think it is.

"The difference between the incidence of 1:500 and 1:15,000 suggests that even in the rare instances where patients are experiencing awareness, in most cases the sensation is a 'neutral' one," says Jaideep Pandit, MA, BM, DPHIL, FRCA, a consultant anesthetist and fellow in physiological sciences at St. John's College, Oxford, in England. "What we are possibly seeing is a third state of consciousness — dysanaesthesia — in which the patient is certainly aware of events, but not concerned by this knowledge, especially as they are not in pain."

Dr. Pandit and his colleagues reached that speculation after surveying members of the Royal College of Anaesthetists and the Association of Anaesthetists of Great Britain and Ireland earlier this year on annual incidence rates of what they call "accidental awareness," reviewing existing evidence and conducting their own clinical trials. Their findings were published in the British Journal of Anaesthesia earlier this year.

"The disparity between the incidence of awareness as notified to anaesthetists and that reported in trials warrants further examination and explanation," they write. More research could also determine if dysanaesthesia is detectable by way of brain signal monitoring, which could produce data — and a warning — on the incidence of patient consciousness under anesthesia.

David Bernard