Case History

A 40-year-old female patient became severely emotionally distressed following an anaesthetic for myomectomy surgery. She reported to recovery room staff that she had unpleasant memories that she attributed to the period that she was expecting to be under general anaesthesia during her surgery. She had a history of fibroids, a body mass index of 38 kg/m², but was otherwise medically healthy. This was the first time that she had undergone general anaesthesia.

She recalled hearing voices asking for numbered objects, feeling her neck being extended further back then a plugging sensation in her mouth and a sense of suffocating. The patient tried to cry and shout out to indicate that she was still awake, but was unable to move or communicate. The patient recalled being positioned on the operating table and feeling a sharp pain in her lower abdomen at the start of surgery. The patient did not think she would survive.

The patient later developed post-traumatic stress disorder with flashbacks, panic attacks, fear of the dark (including seeing the anaesthetist’s face when asleep) and an inability to lie flat, and was subsequently referred to a psychologist.

What Is the Question?

What is accidental awareness under general anaesthesia, its incidence, its mechanism and methods by which it might be avoided?

Discussion

What Is Accidental Awareness during General Anaesthesia?

Patients expect general anaesthesia to be associated with unconsciousness, alongside an absence of pain, sensation and memory for the duration that anaesthesia is provided. Failure of these processes is termed accidental awareness during general anaesthesia (AAGA), which describes an unintended experience of consciousness and explicit recall of sensory perception between the planned induction and emergence periods of general anaesthesia.

Accidental awareness during general anaesthesia remains a fundamental complication of anaesthetic practice and the only complication of surgical patients for which anaesthetists have sole, undivided responsibility. Even though AAGA is rare, the vast numbers of surgical procedures carried out each day mean that the odds are high that someone, somewhere in the world, is unintentionally aware during surgery right now, as you read this chapter.

Understanding AAGA relies upon an appreciation of the underlying complexity of the apparently simple goal of anaesthesia – to safely take a patient from a conscious to an unconscious state, then back again. Both consciousness and general anaesthesia are extremely complex, with multiple theories and levels of understanding regarding mechanisms of action. A key feature from neuroimaging and electroencephalography studies, however, is that hypnotic doses of general anaesthetic drugs preferentially reduce brain activation in higher-order regions rather than in the primary sensory areas.

This conceptual model has implications for understanding how awareness is perceived and how other higher-order cortical processing, such as memory, is affected during general anaesthesia. The easiest to detect (and arguably most important) form of AAGA is with declarative memory or explicit recall – the patient can remember and report, in detail, the events that occurred during the awareness episode. But return of consciousness may also occur without a clear memory of the experience being encoded or able to be retrieved later. This form of awareness is known as implicit recall, and may manifest as behavioural changes, depression or sometimes not at all.

The process of dimming, then loss of consciousness is experienced by most patients with the same clear pattern: one moment they remember being in the operating or anaesthetic room, lying on their back, with a mask delivering oxygen over their mouth and an anaesthetist beside them. The next moment they wake in the recovery room with a total ‘black out’ in between; feeling like no time has passed and with no memory of intraoperative events. This experience is exactly our intention as anaesthetists: to generate hypnosis, analgesia and amnesia, and therefore make the intolerable process of surgery tolerable and less harmful.

As a frightening iatrogenic complication, AAGA has a high public profile, increases patients’ apprehension of surgery and affects the medical–legal risks associated with anaesthesia. The root cause is always inadequate delivery of anaesthetic drug to the brain, which can occur for a variety of reasons (be they situational, human error, patient factors or equipment failure). But because the mechanism and spectrum of consciousness is graduated rather than a binary on–off conversion (and because total failure of anaesthetic delivery is extremely rare), individual perceptions of awareness vary greatly.

There are a wide range of patient experiences of AAGA. Most reports are short in duration, described with neutral emotional interpretation by patients and consist of brief, incomplete recollections. Less commonly, patients recall more specific details of sensory input from their surroundings during surgery. This may be a feeling of something in a patient’s mouth, hearing noises or feeling touch. Most patients reporting awareness during surgery do not feel pain, but may describe experiences such as: hearing voices or noise of equipment, trying to move to alert staff and being unable to, feeling anxious that something has gone wrong with the operation and powerless to do anything, or feeling frightened that things are going to get worse. Half of patients reporting memories of awareness find the experience distressing; the inclusion of pain and paralysis in reports is predictably associated with distress and may be implicated in longer-term psychological sequelae.

One theoretical explanation is that, like consciousness, our unconscious state under general anaesthesia may also be graduated. As mentioned, sensory stimuli can still reach cortical brain centres despite general anaesthesia. Play a piece of music to a patient under general anaesthesia and the auditory cortex is still activated. Another vivid example comes from an infrequently used anaesthetic monitoring approach called the isolated forearm technique. This technique consists of the inflation of a blood pressure cuff on a patient’s arm to above systolic blood pressure during induction of general anaesthesia. Neuromuscular blocking drugs are injected intravenously, but because the arm is vascularly isolated from the rest of the circulation, the distal hand remains unparalysed. Surgery can proceed (with the cuff deflated after 20 min) and if awake, the patient could use this unparalysed arm to communicate. It is also possible to issue verbal instruction to the anaesthetised patient to test for appropriate motor reactions.

Incidence of Accidental Awareness during General Anaesthesia

Although studies of response during the isolated forearm technique are small in sample size and few in number, remarkably up to 30 per cent of tested patients are able to respond to verbal commands by contraction of their hands; almost all with no memory of doing so afterwards. This is in spite of no otherwise apparent clinical signs of awareness and provision of general anaesthesia sufficient to obtund a response to surgical stimulation, and no spontaneous movement in the absence of command.

The state of wakefulness without recall that is detected by the isolated forearm technique may be very similar to that of intended sedation with amnesia (e.g. by use of drugs like midazolam). In contrast, the responses may also be explained by a distinct brain state in which conscious perceptions are uncoupled from surgical stimulation, but responses are not uncoupled from verbal stimulation. This state has been termed dysanaesthesia.

Understanding how the neurobiology of memory is modulated by both the pharmacology and process of anaesthesia is important when interpreting AAGA reporting. Not only do most anaesthetic drugs have amnesic properties at sub-anaesthetic threshold, but all memories are vulnerable to bias or being overwritten by later similar events, which can impair their subsequent retrieval. When patients regain consciousness during emergence at the end of surgery, the memory of this episode of waking may be more easily understood and recalled, suppressing any intraoperative memory of wakefulness.

Awareness can therefore be thought of as a ‘doughnut’ model. The majority of patients undergoing surgery experience no awareness whatsoever (the outermost ring of the doughnut). However, a smaller proportion might experience a period of return of consciousness during surgery, but are left with no memory of that process (these patients might be those represented by a positive response to verbal command during isolated forearm technique). An even smaller proportion will remember being awake, but variation in the encoding of memories means that they may require prompting or direct questioning to retrieve the memory. A tiny minority experience awareness and are able to immediately and spontaneously describe their experience after surgery (the innermost part of the doughnut).

The largest ever study of AAGA was the 5th National Audit Project (NAP5) of the Royal College of Anaesthetists and the Association of Anaesthetists of Great Britain and Ireland, Accidental Awareness during General Anaesthesia in the United Kingdom and Ireland, undertaken in the UK and published in 2014. In contrast to previous research involving direct questioning, NAP5 collected only spontaneous reports from patients. Although reports were only admissible if they were collected during a hospital admission in the UK and Ireland between June 2012 and May 2013, the awareness event could occur at any time in the past.

Of the 300 reported cases of awareness, a committee judged 141 to be certain or probable cases of awareness. Based on the results of a previous activity survey, the incidence of spontaneously reported awareness was estimated as 1:19 600. This proportion is so markedly low compared with outcomes reported by studies in which patients are directly questioned about their memories of anaesthesia (e.g. 1:600 in the Sandin et al. study from 2000) that its value cannot be interpreted without critical discussion of the discrepancy. In this context, given relatively similar patient cohorts and anaesthetic techniques with other UK and USA studies, there must be a difference in outcomes detected. The explanation returns to the ‘doughnut’ model for awareness; that some awareness occurs, but is not remembered by patients without prompting and a smaller proportion of cases are always recalled.

One conclusion of these findings is that direct questioning detection is weighted towards sensitivity; whereas cases of awareness in NAP5 may be more specific and reliable. However, sensitivity in NAP5 detection may be compromised by unknown circumstances that interfere with decisions or the capacity of patients to file a report. For these reasons it is reasonable to consider NAP5 as the most powerful study for describing relative risks of AAGA between different patient populations, but the absolute risk values are subject to variable interpretation.

There is no simple answer for exactly how rare AAGA is – it depends upon how you detect and measure the outcome. However, most estimates using direct questioning put the risk of recalling some memories attributable to the intraoperative period at about 1 or 2:1000.

Several major findings on relative risk were clear from NAP5. Especially that obstetric, emergency and cardiac surgery patients, obese patients or those with difficult airway management were all at elevated risk of experiencing AAGA. Obstetric patients were markedly over-represented in reported cases of AAGA in NAP5 – accounting for 0.8 per cent of all general anaesthetics in the NAP5 activity survey but almost 10 per cent of AAGA reports. This translated into an estimated incidence of awareness of approximately 1:670 general anaesthetics (versus ~1:8000 in non-pregnant individuals receiving neuromuscular blockade drugs during anaesthesia). Overall, the reports of AAGA in NAP5 occurred overwhelmingly in patients receiving neuromuscular blockade drugs (~1:8000 versus ~1:136 000 in patients with no paralysis).

How to Minimise the Risk of Accidental Awareness during General Anaesthesia?

The skill and experience of a trained anaesthetist is vital in carefully selecting and adjusting the dose of hypnotic agent that is likely to be sufficient to prevent awareness in the majority of patients. One adjunctive technique is to apply depth of anaesthesia monitors. These monitors are readily available, recommended (albeit with a guarded wording – as an ‘option’ – and even then, only in an undefined ‘higher-risk’ population) by the National Institute for Health and Care Excellence, are relatively affordable, but not routinely used in many countries. Depth of anaesthesia monitors use a form of processed electroencephalogram to estimate the degree to which electrical activity in the brain is suppressed by hypnotic drugs. Depth of anaesthesia monitors are necessarily impaired by the fact that they aim to measure something that we have no reliable means of measuring: a graduated degree of unconsciousness. Although we can objectively describe sedation, the responses that we rely upon to chart depth of sedation are clearly absent in the unconscious patient. Instead, depth of anaesthesia monitors use extrapolations of data from sedated volunteers. At best, depth of anaesthesia monitors are probably only useful as a crude measure that the anaesthetic is having some effect, rather than it is having a sufficient effect. The evidence from several randomised controlled trials is that depth of anaesthesia monitors are no better at preventing AAGA then measurement of end tidal volatile anaesthetic agent, a commonly used and understood measure of anaesthetic agent delivery to the patient.

Most cases of AAGA are potentially avoidable. Therefore, improving anaesthetist education, understanding drug pharmacokinetics and dynamics, drawing attention to the issue of AAGA and establishing best organisational practice for vigilance of drug errors and preoperative assessment of risk factors are all vital steps in preventing awareness. These solutions affect not just individuals, but systematic approaches to problems such as the risk of drug error posed by similar packaging and presentation of different drugs. Guidance for most appropriate anaesthetic technique to prevent awareness is weighted with expert opinion rather than empirical evidence. Ultimately, the recommendations are centred on providing a vigilant and safe environment for delivery of anaesthetic care, with particular focus on continuous and adequate hypnotic drug delivery – especially when risk factors for AAGA are present.

Should AAGA occur, then early identification and supportive intervention may reduce the risk of developing psychological harm. Aftercare focuses on providing prompt, sympathetic communication alongside an investigation of the root cause of the event and shared learning. In some cases, a duty of candour response may be mandated. The presence of signs of anxiety state or depression is an indicator for formal psychological assessment and ongoing support (e.g. cognitive behaviour therapy).

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Further Learning

Learn about the ‘isolated forearm technique’.

Read this patient information leaflet about accidental awareness under general anaesthesia produced by the Royal College of Anaesthetists.

Read the NAP 5 Handbook which provides guidance on how to prevent and manage accidental awareness.

Use the NAP5 Awareness Support Pack as a template and pathway to follow in the event of accidental awareness during general anaesthesia.

Bibliography

Case Reports:

Winterbottom EH. Insufficient anaesthesia. British Medical Journal 1950;1(4647):247–8.

Liska J. Silenced Screams. Park Ridge, IL: AANA Publishing Inc., 2002,195.

Ghoneim MM, Block RI, Haffarnan M, Mathews MJ. Awareness during anesthesia: risk factors, causes and sequelae: a review of reported cases in the literature. Anesthesia and Analgesia 2009;108(2):527–35.

Selected Observational Studies:

Sandin RH, Enlund G, Samuelsson P, Lennmarken C. Awareness during anaesthesia: a prospective case study. Lancet (London, England) 2000;355(9205):707–11.

Sebel PS, Bowdle TA, Ghoneim MM, Rampil IJ, Padilla RE, Gan TJ, et al. The incidence of awareness during anesthesia: a multicenter United States study. Anesthesia and Analgesia 2004;99(3):833–9, table of contents.

Errando CL, Sigl JC, Robles M, Calabuig E, Garcia J, Arocas F, et al. Awareness with recall during general anaesthesia: a prospective observational evaluation of 4001 patients. British Journal of Anaesthesia 2008;101(2):178–85.

Selected Randomised Controlled Trials:

Myles PS, Leslie K, McNeil J, Forbes A, Chan MT. Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomised controlled trial. Lancet 2004;363(9423):1757–63.

Avidan MS, Zhang L, Burnside BA, Finkel KJ, Searleman AC, Selvidge JA, et al. Anesthesia awareness and the bispectral index. The New England Journal of Medicine 2008;358(11):1097–108.

Avidan MS, Jacobsohn E, Glick D, Burnside BA, Zhang L, Villafranca A, et al. Prevention of intraoperative awareness in a high-risk surgical population. The New England Journal of Medicine 2011;365(7):591–600.

Mashour GA, Shanks A, Tremper KK, Kheterpal S, Turner CR, Ramachandran SK, et al. Prevention of intraoperative awareness with explicit recall in an unselected surgical population: a randomized comparative effectiveness trial. Anesthesiology 2012;117(4):717–25.

NAP5:

Pandit JJ, Andrade J, Bogod DG, Hitchman JM, Jonker WR, Lucas N, et al. 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: protocol, methods, and analysis of data. British Journal of Anaesthesia. 2014;113(4):540–8.

Pandit JJ, Andrade J, Bogod DG, Hitchman JM, Jonker WR, Lucas N, et al. 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: summary of main findings and risk factors. British Journal of Anaesthesia 2014;113(4):549–59.

Isolated Forearm Technique and Dysanaesthesia:

Pandit JJ. Isolated forearm – or isolated brain? Interpreting responses during anaesthesia – or ‘dysanaesthesia’. Anaesthesia 2013;68(10):995–1000.

Pandit JJ. Acceptably aware during general anaesthesia: ‘dysanaesthesia’ – the uncoupling of perception from sensory inputs. Consciousness and Cognition 2014;27:194–212.

Pandit JJ, Russell IF, Wang M. Interpretations of responses using the isolated forearm technique in general anaesthesia: a debate. British Journal of Anaesthesia 2015;115 Suppl 1:i32–i45.

Article Information

Title: Accidental Awareness under General Anaesthesia
Author: Peter M Odor
Publisher: UCL Press
Publication date (Electronic): 31 January 2020
DOI: 10.14324/111.444.9781787356917.01
Copyright statement: © 2020 The Author.
License: This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY) 4.0 https://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

UCL Press

Case Studies in Perioperative Medicine

Edited by the Centre for Perioperative Medicine, UCL

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