Waking under anaesthetic may be rarer than thought


'Surgery shock' announces the Daily Mirror, warning that, '150 patients woke up during operations last year and many couldn't alert the doctor.' It's unsurprising that a tabloid headline plays on our nightmares...

'Surgery shock' announces the Daily Mirror, warning that, '150 patients woke up during operations last year and many couldn't alert the doctor.'

It's unsurprising that a tabloid headline plays on our nightmares – being awake but unable to move during surgery sounds like something out of a horror film. In fact, the news is based on a study looking at the number of patients who experience 'accidental awareness' after being given a general anaesthetic.

Researchers found that the incidence of accidental awareness was actually far lower than expected. Contrary to the impression given by the Mirror, only 46 incidents happened during operations in a one-year period.

Previous research calculated the incidence of accidental awareness as between one and two per 1,000 general anaesthetics given.

This study, based on a survey of senior UK anaesthetists, found a far lower rate of only around one in 15,000. More reassuringly still, two-thirds of patients who woke up "reported feeling no pain or distress".

The findings of this study need to be viewed with some caution, however. Survey data has limitations: as the authors note, it is possible that cases of accidental awareness may have been either under- or over-reported.

It is worth investigating why there seems to be a gap between the incidence of accidental awareness found in this study and the much higher incidence found by previous research. This useful research will be followed up with a similar survey of anaesthetists during 2012-13.

Where did the story come from?

The study was carried out by researchers from Oxford University Hospitals, Royal United Hospital in Bath and St James's Hospital, Dublin. It was part of the 5th National Audit Project (NAP5) of the Royal College of Anaesthetists and the Association of Anaesthetists of Great Britain and Ireland, and was funded by these two organisations. 

The study was published in the peer-reviewed journals Anaesthesia and the British Journal of Anaesthesia, and can be read free in full online (open access).

The Mirror's headline seemed calculated to inspire fear, as does the harrowing account of an unfortunate woman who was accidentally aware during stomach surgery. The fact that researchers found far fewer instances of awareness than expected – a risk of about one in 15,000 – is only grudgingly acknowledged towards the end of the Mirror's story.

BBC News' coverage of the article was much more balanced.

What kind of research was this?

This was a survey of all anaesthetists in the UK, to find out the number of patients known to them to have accidentally gained consciousness during general anaesthesia in the UK during 2011. The current survey represents the first (baseline) stage of the planned work in this area. It will be followed by a study that will prospectively collect data about accidental awareness during general anaesthesia (AAGA) in the UK for 2012/2013.

AAGA refers to the phenomenon of a patient being awake or conscious despite having been given a general anaesthetic in preparation for surgery, and which the patient can remember after surgery.

Some patients who experience AAGA report only having vague, dream-like recollections. The study's authors explain that, "they might feel some awareness of tugging or hear some noises". But others who experience AAGA have reported being in pain or being awake but unable to move.

The researchers, and authors of an accompanying editorial, point out that this can be an understandably traumatic experience, with a high proportion of people who experience it going on to develop post-traumatic stress disorder.

The authors point out that in previous studies based on patient questionnaires, AAGA is reported to occur in between one and two per 1,000 procedures under general anaesthetic. They aimed to find out how many cases of AAGA had come to the knowledge of anaesthetists.

What did the research involve?

The researchers recruited a team of consultant anaesthetists in 329 NHS hospitals throughout the UK. They asked the consultants to act as local co-ordinators and distribute data collection forms to all consultant and senior anaesthetists in their hospitals. The co-ordinators collated the responses and summarised the results, which were returned to the researchers.

Questions asked on the form included:

  • the number of new AAGA cases which they were notified of during 2011, under their direct or supervised care
  • the availability and use of anaesthesia monitors – these are devices that measure a range of body functions, such as heart beat and brain activity, to see how the patient is responding to the effects of the anaesthesia
  • whether their hospital had policies for preventing and managing AAGA

The frequency of AAGA cases was calculated based on the number of general anaesthetics performed in the UK, taking into account that some anaesthetists did not respond to the survey.

What were the basic results?

Data was collected from 7,125 anaesthetists (82%) in all 329 hospitals. A total of 153 new cases of AAGA were notified to these anaesthetists in 2011. This was estimated to equate to one case of AAGA for every 15,414 general anaesthetics administered.

The survey showed that:

  • 72 of the cases (47%) occurred as a general anaesthetic was given or soon after, but before surgery started
  • 46 of the cases (30%) occurred during surgery
  • 35 of the cases (23%) occurred after surgery, but before full recovery

Just over a third of people (38%) reporting AAGA reported experiencing pain or distress as a result of the experience. Almost two-thirds (62%) of people who reported awareness during surgery reported experiencing pain, but this was less common among people with AAGA before surgery (28%) or after surgery (23%).

Monitors to assess the depth of anaesthesia were reported to be available in 164 centres (62%), but only 1.8% of anaesthetists reported using these monitors routinely. Only 12 hospitals (4.5%) had policies for the prevention and management of AAGA.

How did the researchers interpret the results?

The researchers say the most striking finding is that the incidence of new cases of AAGA notified to anaesthetists in the UK during 2011 is about one in 15,000 – much lower than findings from previous studies based on asking surgical patients directly about their experiences.

They say that if both sets of data are valid, then for every case of AAGA notified to the anaesthetist per 15,000 general anaesthetics administered, up to a further 30 patients will experience AAGA but not report it.

Further investigation into the disparity between AAGA notified to anaesthetists and that reported in previous studies is needed, the researchers argue. They also point out that the apparent adverse consequences of AAGA seem to be very low, with two-thirds of patients who 'woke up' feeling no pain or distress.


This comprehensive national survey of anaesthetists has found that reports made to them of accidental awareness during general anaesthesia (AAGA) were rare, at about one case per 15,000 general anaesthetics, which seems reassuring news. Previous studies using different methods have suggested higher incidence of between one and two cases per 1,000 general anaesthetics.

This was a retrospective survey that relied on patients reporting AAGA to their anaesthetist, and these anaesthetists recording or recalling accurately all notifications of AAGA over a year. This may mean that the results underestimate the true frequency of this phenomenon.

The researchers list several other reasons why this might be an underestimate, including that anaesthetists may not routinely see patients after surgery.

On the other hand, as the researchers also point out, the use of anaesthesia techniques associated with a lower risk of AAGA, as well as an increasingly consultant-delivered service in the UK, may mean AAGA is less common here than in other countries where the phenomenon has been studied.

This important research is the first phase of the planned audit with a second prospective phase of this study planned, which will further address some of these concerns. Ideally, this study would include direct patient interviews to further increase understanding of how common AAGA is in the UK.

While AAGA seems to be much rarer in the UK than previously thought, it could be argued that a single case is one too many. The researchers conclude by saying that while AAGA is a rare complication of anaesthesia, it remains an important complication that should always be avoided.

Article Metadata Date Published: Di, 15 Aug 2017
Author: Zana Technologies GmbH
NHS Choices