In a blog for non-medical readers, anaesthetist Jennifer Kielty discusses a common fear about an uncommon problem – awareness during surgery, and looks at the latest Cochrane evidenceCochrane Reviews are systematic reviews. In systematic reviews we search for and summarize studies that answer a specific research question (e.g. is paracetamol effective and safe for treating back pain?). The studies are identified, assessed, and summarized by using a systematic and predefined approach. They inform recommendations for healthcare and research. on ways to reduce the riskA way of expressing the chance of an event taking place, expressed as the number of events divided by the total number of observations or people. It can be stated as ‘the chance of falling were one in four’ (1/4 = 25%). This measure is good no matter the incidence of events i.e. common or infrequent. of that happening.
“Keep me well asleep Doctor” and “I just want to be completely knocked out” are a few of the most common things I hear on meeting patients before an operation. The release of the film ‘Awake’ in 2007 did nothing to ease the fact that awareness while under anaesthetic (intraoperative awareness) is one the most common fears patients have before surgery. Unfortunately, in the rare scenario when it occurs, it can be highly distressing for the patient, and can lead to recurrent dreams, anxiety and depression.
We have only a few ways of monitoring for awareness under anaesthesia: clinical signs (such as the patient’s blood pressure and heart rateThe speed or frequency of occurrence of an event, usually expressed with respect to time. For instance, a mortality rate might be the number of deaths per year, per 100,000 people.); end tidal volatile anaesthetic gas (ETAG) which is the amount of anaesthetic gas the patient exhales; and via processed electroencephalogram (EEG) (for example, Bispectral index or BIS) which involves placing electrodes on a patient’s head to monitor brain waves.
An evidence gap
Current guidelines from the AssociationA relationship between two characteristics, such that as one changes, the other changes in a predictable way. For example, statistics demonstrate that there is an association between smoking and lung cancer. In a positive association, one quantity increases as the other one increases (as with smoking and lung cancer). In a negative association, an increase in one quantity corresponds to a decrease in the other. Association does not necessarily mean that one thing causes the other. of Anaesthetists consider measuring the amount of exhaled anaesthetic part of the minimum monitoring required when someone has an anaesthetic. Brain wave monitoring, as mentioned above, is another method of monitoring depth of anaesthesia. However there is a lack of evidence comparing the efficacyThe extent to which an intervention (for example a drug, surgery, or exercise), produces a beneficial result under ideal conditions. of brain wave monitoring with the use of clinical signs or with monitoring of amount of exhaled anaesthetic gases.
New evidence from Cochrane
An important Cochrane reviewCochrane Reviews are systematic reviews. In systematic reviews we search for and summarize studies that answer a specific research question (e.g. is paracetamol effective and safe for treating back pain?). The studies are identified, assessed, and summarized by using a systematic and predefined approach. They inform recommendations for healthcare and research. (published in 2019) summarises the evidence on the effectiveness of brain wave monitoring to reduce the risk of the patient being aware while under general anaesthetic, and its effect on the time until a patient wakes up after the operation. It includes 52 research studies and over 41,000 adults having surgery under general anaesthetic. Brain wave monitoring (BIS) was compared with clinical signs as a guide to depth of the anaesthetic or with monitoring of amount of exhaled anaesthetic (ETAG).
Overall the findings of the review were:
- BIS may improve the time it takes for a patient to wake up from an anaesthetic compared to use of clinical signs.
- There may be little or no difference in the risk of intraoperative awareness between use of BIS or use of measurement of amount of exhaled anaesthetic gas.
- Overall the incidenceThe number of new occurrences of something in a population over a particular period of time, e.g. the number of cases of a disease in a country over one year. of intraoperative awareness was very small.
Limitations of the studies meant that the evidence was all assessed as being low-certaintyThe certainty (or quality) of evidence is the extent to which we can be confident that what the research tells us about a particular treatment effect is likely to be accurate. Concerns about factors such as bias can reduce the certainty of the evidence. Evidence may be of high certainty; moderate certainty; low certainty or very-low certainty. Cochrane has adopted the GRADE approach (Grading of Recommendations Assessment, Development and Evaluation) for assessing certainty (or quality) of evidence. Find out more here: https://training.cochrane.org/grade-approach, so the review authors can’t be confident about their results. They also note that most of the studies reported that none of the people taking part woke up during surgery as it’s a rare event!
Finally there were three studies which looked at people who were thought to be high risk of being aware while under anaesthetic and two studies that did not grade a patient’s risk. They found that brain wave monitoring in these two groups may reduce the risk of intraoperative awareness compared to monitoring clinical signs.
Only one studyAn investigation of a healthcare problem. There are different types of studies used to answer research questions, for example randomised controlled trials or observational studies. comparing monitoring brain waves (BIS) with exhaled anaesthetic gases (ETAG) looked at recovery times, and this low-certainty evidence showed that discharge from the post anaesthetic care unit may be earlier in patients who had BIS guided anaesthesia compared to ETAG guided anaesthesia.
What does this mean?
This review supports what we know from the findings of the 5th National Audit Project (NAP5), that accidental awareness under anaesthetic is rare. This review also supports the recommendations in the 2015 guideline from the Association of Anaesthetists on the Standards of monitoring during anaesthesia and recovery, which advise: the continued presence of an anaesthetist; always using minimum monitoring devices, from before the patient receives an anaesthetic until after the patient completely wakes up; that these monitoring devices are checked and maintained appropriately; and the importance of audible alarms.
Talking to your anaesthetist
We can be reassured by knowing that awareness during anaesthesia is very rare. However if you are worried I would encourage you to meet with your anaesthetist before your operation. It is important to tell them about your past medical history, your regular medications and about any previous problems you may have had with anaesthesia. Ask about what kind of anaesthetic you will get and about possible risks and side effects. You should tell them about your concerns so that any specific worries can be addressed. By having this conversation and learning more we can help alleviate stress, and help you to have a more comfortable time while in hospital.
Take-home points
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Here you can read a Cochrane Clinical Answer: ‘How does the bispectral index (BIS) compare with clinical signs or end‐tidal anesthetic gas (ETAG) for guiding anesthesia?’
