The benefits of anaesthesia are enormous. Being prepped for surgery two hundred years ago, you might be offered a few numbing swigs from a brandy bottle. Occasionally, the surgeon would attempt to spare your agony by punching you unconscious. Most operations were amputations, so we can be very thankful for the medical advances of the intervening years.
As a patient under general anaesthetic today, your awareness of an operation usually ends with counting down from ten and falling asleep around “seven”. The next thing you know, you are waking up in a hospital bed in a pleasantly vague state of drowsiness. For most patients, the duration of the surgical procedure itself is merely benign unconsciousness.
In rare cases, however, a degree of consciousness can arise during the operation itself. According to a National Audit Project report into accidental awareness during general anaesthesia (AAGA), such experiences vary widely. Some patients reported hearing the voices of the surgical team or feeling the touch of their hands. About half of patients who experienced an episode of awareness found it neutral or even reassuring: for example, the overheard discussion of surgical procedures reinforced a sense of being cared for by competent professionals.
At the other end of the scale, patients experienced full awareness of their predicament, with sensations of paralysis and being trapped, unable to alert anyone, and even feelings of imminent death. Sometimes, but not always, there was pain as well. “These sensations can be terrifying, and potentially induce a trauma that remains with the patient long after the operation,” says Jackie Andrade of Plymouth University, one of the authors of the report. Indeed, in the worst cases, there is evidence of post-traumatic stress disorder, such as anxiety and flashbacks, together with an unsurprising aversion to future anaesthesia.
Overall, the National Audit Project survey found self-reported incidents of accidental awareness in only one per 20,000 operations. Other surveys, where patients are explicitly asked about awareness after operations, have found the incidence of AAGA as high as one in 600.
The reasons for the differences in reported rate are not clear: “Routine active questioning about accidental awareness could help to identify cases earlier and allow more effective psychological support,” says Jackie Andrade, “but there is a risk – of unknown size – that such questioning could serve to induce false but still distressing memories of AAGA.”
Most AAGA incidents identified by the National Audit Project survey were judged to have been preventable, with errors by members of the surgical team contributing to the episode of awareness. About 20% of cases were either not preventable or were otherwise unexplained. Patient predisposition may be a factor in a small number of these events, but predicting if someone will experience accidental awareness is confounded by the still relatively poor understanding of the basic biological mechanisms behind successful anaesthesia. Anaesthetic substances are highly diverse, from the element xenon and very simple molecules like nitrous oxide to complex steroids. Unlike for many well-understood pharmaceutical effects, there is no single biochemical lock that fits all those keys.
Whatever the causes, for that small minority of surgical patients affected, feeling that their experience is believed and taken seriously can be an important part of minimising subsequent distress. Whether pre-emptive action could also be effective is less clear. Warning all patients before surgery of the possibility of accidental awareness may induce unnecessary fear or even provoke an experience of trauma, real or imagined. Just as the safety warnings we hear before every flight implicitly raise the possibility that our plane might crash into the sea, it could be that some risks are better not contemplated in advance.
Jackie Andrade writes: NAP5 is the largest study of accidental awareness during general anaesthesia ever conducted. It involved monthly reporting from every NHS hospital in the UK, and every hospital in Ireland, for a whole year. NAP5 has provided a huge amount of information about the situations that pose the biggest risks of awareness, from effects of different anaesthetic techniques to human factors to individual patient characteristics. The project has generated recommendations for changes in practice and a wealth of suggestions for new research. For me as a psychologist, the most fascinating findings are that patients do not always find the experience distressing (a finding that offers hope for effective intervention to reduce distress), that being distressed during anaesthesia is strongly associated with long-term psychological harm, and that communication is critical. Reassurance and explanation went a long way to ameliorating the psychological effects of accidental awareness.
Pandit, J.J., Andrade, J., Bogod, D.G., Hitchman, J.M., Jonker, W.R., Lucas, N., … & Cook, T.M. (2014). The 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: protocol, methods and analysis of data. Anaesthesia, 69, 1078-1088.
Cook, T.M., Andrade, J., Bogod, D.G., Hitchman, J.M., Jonker, W.R., Lucas, N., … & Pandit, J.J. (2014). The 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: patient experiences, human factors, sedation, consent and medicolegal issues. Anaesthesia, 69, 1102-1116.
Photo credit: Lloyd Russell, Plymouth University.