Accidental Awareness During General Anaesthesia (AAGA)

Two fears almost universally expressed by patients before surgery are first that they might die during the operation, and secondly that they may wake during the procedure unable to alert anyone to their plight. The latter is fear of ‘accidental awareness during general anaesthesia’ (AAGA), a very rare event arising from a variety of causes and in a number of ways.

Agents used to induce and maintain anaesthesia have individual effects on the brain (hypnosis, memory formation, blocking painful stimuli) and the spinal cord (impeding purposeful movement and blocking spinal reflexes) so that during very deep anaesthesia patients neither move nor have recall. However this depth has serious (potentially life-threatening) side effects (cardiac, respiratory and cognitive impairment) and a balance has to be struck. In consequence, consciousness is not uniformly absent and cognitive processing occurs in many patients but without recall or sequelae.

Recall after surgery has been reported and investigated for many years. It may be voluntary and spontaneous (very rare) or elicited by Brice questionnaire after surgery (about 1:600). The experience of AAGA is equally wide ranging; from detailed explicit recall, to implicit memory for ‘key words’ discoverable by psychological assessment. Outcomes vary from no harm at all to long-lasting psychological trauma, and doctor-patient communication, stoicism and patients’ knowledge of anaesthesia have effects on outcome.

General anaesthesia for adults in the UK is mainly induced intravenously and maintained with volatile agents (‘gases’). In young children induction is often by volatile agents alone. Sometimes (e.g. transfers) intravenous drugs are used both for induction and maintenance: total intravenous anaesthesia (TIVA). Once asleep, patients may be permitted to breathe spontaneously or are given a paralysing agent (muscle relaxant/neuromuscular blocker (NMB)) and their lungs ventilated mechanically. To maintain a clear airway patients have a device placed in their mouth (laryngeal mask) or their trachea (intubation). The former usually occurs without paralysis; the latter almost always requires it. Muscle relaxation permits surgery which would otherwise be impossible (cardiac, thoracic, abdominal, obstetric, and laryngeal) and is monitored by electrical stimulation of peripheral nerves and palpation (or objective measurement) of the resultant twitch in a muscle; confusingly, not all muscle groups are equally sensitive.

Depth of anaesthesia is assessed by surrogate means: absence of movement, changes in heart rate and blood pressure, absence of lacrimation or sweating. However, these are unreliable so expired concentration of the volatile agent (etAG) is compared to a dose-response curve of minimum anaesthetic concentration (MAC); the concentration which prevents movement in 50% of subjects (often animal) and due more to effects on the spinal cord than on the brain. The concentration which prevents recall to Brice questionnaire (v.s.) is about 0.7MAC.

For TIVA another surrogate monitor is used: usually processed EEG. This has significant processing time, artefactual error and is less reliable than etAG at preventing recall. One final monitor exists: the isolated forearm technique (IFT). The forearm is isolated from the circulation by a tourniquet preventing NMB effect. The anaesthetised patient is then asked (usually via headphones) to move their hand. Further commands establish if the patient is comfortable, knows what is happening, or has pain or concern.

The IFT demonstrates connected consciousness, but presence of IFT response in studies was not followed by explicit recall or adverse outcome. Drawbacks of IFT are that it is possible only in some operations and the tourniquet may not be without complications.

AAGA is extremely unlikely if paralysis is avoided. A large national audit in 2014 (NAP5) reported a rate of 1:135,900 for this subset: with paralysis the incidence rises (1:8,200). There is also variation between specialties. In cardiothoracic surgery the rate is 1:8600 whereas in obstetrics it is 1:670. To complicate matters, not all reports of awareness are from patients receiving general anaesthesia at all. NAP5 estimated that 1:15,000 patients receiving sedation reported ‘awareness’ from miscommunication and suboptimal expectation management.

Half of all UK reports arise around the point of intubation or soon after (transfer into theatre/start of surgery) and half these (25% of the total) were emergencies. A third of reports came from the period of surgery itself and a fifth from emergence and extubation (tube removal).

Contributory factors for AAGA are: failure to maintain anaesthesia during prolonged or difficult intubation (particularly ‘rapid sequence induction’ used for emergency surgery); obesity (rapid offset of drugs and relative underdosing); and the ‘gap’ during transfer from anaesthetic room to theatre, exacerbated by failure to ‘switch on’ the volatile in theatre. During emergence, failure to monitor (and reverse) intraoperative paralysis led to patients being awakened who were unable to move, breathe or communicate. Others, not paralysed, disliked the experience of extubation which had not been explained to them before surgery. The final group (10% of NAP5 reports) were drug error: administration of a neuromuscular blocker to an awake patient.

Main findings from reports were that paralysis and pain (however caused) led to greatest distress and long term effects, including post-traumatic stress disorder (PTSD) and that some patients have increased risk: young adults, women, the obese, and those with a past history of AAGA (or difficult intubation). In contrast, there are no apparent links with race or health status. When assessing a report of AAGA it is important to recognise that memory is not a tape recording and that patient experience contains misunderstandings. Events may be misplaced in time or place, overheard speech and actions misinterpreted, well intended reassurance from staff produce erroneous assumptions. Even with good communication, good patient information systems and the best care, the experience of surgery and anaesthesia may itself lead to unavoidable distress. Finally, about 7% of patient reports of AAGA occur even when all the evidence points to impeccable care. These patients may represent a subgroup ‘resistant’ to anaesthesia where no fault can be ascribed.

References

Pandit J. J. 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: 549– 559 http://www.nationalauditprojects.org.uk/NAP5report

Sanders J. et al Incidence of Connected Consciousness after Tracheal Intubation. Anesthesiology 2017; 126: 214-22

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