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The American Association of Nurse Anesthetists (AANA) supports practices considered beneficial in minimizing the incidence of unintended awareness under general anesthesia. Further, the AANA recommends that every anesthetizing location have a well-defined written policy for the prevention and management of this potentially devastating outcome and has developed Considerations for Policy Development: Unintended Intraoperative Awareness to provide guidance for policy development. The AANA believes that the written policy should include the following essential practices:
- During preanesthesia assessment, the risk of awareness should be assessed, and those risks discussed during informed consent.
- Proper function of all anesthesia equipment should be verified in order to ensure delivery of anesthetic agents to the patient.
- If appropriate, the anesthesia care plan should include pharmacologic agents, anesthesia techniques and patient monitoring techniques considered beneficial in reducing the incidence of unintended awareness.
- Brain function monitoring, if available, should be considered particularly in situations where the risk of intraoperative awareness is increased.
- Patients should be appropriately assessed to identify possible occurrence of unintended awareness. Any such cases should be promptly managed to minimize the potential for psychological injury.
Background: Unintended intraoperative awareness occurs during general anesthesia when a patient regains consciousness and becomes cognizant of certain events occurring during surgery or a procedure and has recall of some or all of those events. Serious, and potentially disabling, psychological injury may result in some patients who experience intraoperative awareness.
For the purposes of this statement, key terms are defined as follows:
- General anesthesia: a drug-induced loss of consciousness during which patients do not respond in a purposeful manner to any stimulus. A patient under general anesthesia may exhibit impaired ventilatory and/or cardiovascular function, thereby requiring techniques and devices to support these systems.
- Consciousness: a state in which a patient is cognizant of his or her surroundings. Normally a conscious patient is able to respond in a purposeful manner to various stimuli unless paralysis is present as a consequence of neurological disease or the administration of a neuromuscular blocking drug. The state of being conscious does not necessarily mean the individual will form memory of some or all events.
- Arousal: the phenomenon of becoming conscious from a previously unconscious state.
- Recall: the ability to demonstrate memory of specific events that took place in the past.
- Amnesia: the absence of memory or recall.
- Anesthesia awareness (or simply, "Awareness): the postoperative recall of events experienced under general anesthesia. This state does not include the phenomenon of dreaming. Unintended awareness refers to any a situation in which intraoperative arousal of the patient was not part of the anesthesia care plan.
Incidence
The frequency of anesthesia awareness has been found in multiple studies to range between 0.1% - 0.2% of adult patients undergoing general anesthesia.1,2 While few studies related to awareness have been conducted in the pediatric population, it appears that the rate may be similar to or higher than that of adults.3
The incidence of awareness is increased in certain clinical situations, including specific types of surgery, patients, and anesthesia techniques (Table I). In these clinical situations, the incidence of unintended awareness may be closer to 1% - a risk of 1 patient in 100.
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- Acute trauma with hypovolemia
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- ASA Physical Status 3, 4 and 5 Patients
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- Cardiac surgery, including off-pump
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- Impaired cardiovascular status
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- Caesarean section under general anesthesia
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- Severe end-stage lung disease
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- Bronchoscopy, laryngoscopy or both
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- History of awareness
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- Expected intraoperative hypotension requiring
treatment
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- Chronic use of benzodiazepine, opioids
requiring treatment or both
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- Anticipated difficult intubation
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- Heavy alcohol intake
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Causes
A variety of etiologies have been reported to cause episodes of anesthesia awareness. Generally, insufficient anesthetic effect (thus allowing a state of consciousness that permits memory formation) results from inadequate dosing or delivery of the primary anesthetic agent.4 Inadequate dosing presumably would include situations where low concentrations are selected in response to the patient’s conditions (e.g., hypotension), inadvertent paralysis of an awake patient, as well as in situations where a patient may have a larger-than-expected anesthetic requirement. Inadequate delivery of anesthetic agents may result from any failure or misuse of anesthesia equipment that is vital to agent administration. Such equipment includes the anesthesia machine, vaporizer, airway management device, breathing circuit, infusion pump, intravenous line and catheter.
In a root-cause analysis of 81 cases of intraoperative awareness, three primary categories were identified. In 44% of the events, awareness was felt to be due to low inspired volatile agent concentration or inadequate hypnosis. In 40% of cases, a drug error led to inadvertent paralysis of an awake patient. Finally, in 16% of patients, the awareness incident had no obvious cause.5
Consequences
Patients who experience awareness may recall hearing operative sounds and voices or may experience the sensation of not being able to move or breathe, pain, or panic. While not every episode of intraoperative awareness is associated with negative recollections, it appears that over 50% of these patients experience some degree of mental distress during or following an awareness episode. Prolonged psychological effects may include intrusive thoughts, nightmares, and in some patients, development of post-traumatic stress disorder. The need for prolonged psychological or psychiatric care may be in the range of 40-60% following traumatic awareness episodes.6 In some situations, patients who claim to have no after-effects of an awareness episode in the early postoperative period may still be at risk for developing subsequent psychological disability. Prompt identification and appropriate psychological management of patients who experience awareness is felt to minimize these complications.
Prevention of Awareness
Table II summarizes possible clinical strategies that have been advocated as effective best practices to reduce the occurrence of intraoperative awareness. It is recognized that the anesthesia provider must balance the psychological risks of anesthesia awareness against the physiological risks of excessive anesthesia, particularly in situations where cardiovascular status is compromised. Essential considerations in developing strategies include:
Preanesthesia Assessment
While the incidence of awareness is seemingly infrequent, many patients are concerned about the potential for awareness to occur. Yet, few openly bring their concerns to the attention of the anesthesia provider or other perioperative staff. The preoperative interview and informed consent process can be used to solicit discussion about such concerns and set reasonable expectations. This is particularly important for those patients who may be at increased risk for awareness. While anesthesia providers may have a concern that such discussions may set the stage, or "prime" the patient, for increased reports of intraoperative recall, there is no evidence that the incidence of actual awareness events increases following such discussions.
Intraoperative Anesthesia Care Plan
Regarding the choice of anesthetic technique, it is important to note that there is no available evidence that a certain anesthetic regimen will unequivocally prevent unintended awareness. The use of agents with amnestic properties, such as benzodiazepines, has not been shown to reduce the incidence of awareness. Similarly, benzodiazepines show no ability to provide retrograde amnesia if administered following an apparent awareness event.7 The use of neuromuscular blocking agents is associated with an increased risk of awareness; however, avoidance of muscle relaxants does not eliminate the risk.
Concerns have also been raised about other portions of the anesthesia care plan that may contribute to the risk of unintended awareness. The use of total intravenous anesthesia (TIVA), preoperative administration or intraoperative use of drugs that mask hemodynamic signs of light anesthesia (e.g., beta adrenergic blockade), and the premature lightening of anesthesia at the end of procedures to facilitate operating room turnover could potentially increase the occurrence of unintended awareness. However, there is no evidence regarding the relative risk of these care plan decisions.
Routine intraoperative assessment, including both traditional clinical signs and hemodynamic monitoring, frequently misses the occurrence of awareness.8 Hemodynamic values are particularly poor indicators of the return to consciousness.9 While end-tidal anesthetic agent monitoring offers the ability to verify the concentration of inhaled anesthetic delivered to the patient, to date there is no clearly defined MAC-equivalent value deemed sufficient to uniformly prevent recall.
Brain Function Monitoring
As a class, brain function monitors (also known as 'consciousness monitors") enable the anesthesia provider to measure the level of consciousness by presenting a numerical index based upon advanced signal processing algorithms of the patient's electroencephalogram (EEG). A variety of brain function monitors are available to the anesthesia provider and their healthcare facilities and it is critical that anesthesia providers be cognizant that the recommended values for managing the hypnotic state vary among the manufacturers of different devices. Because these devices are based upon the cortical EEG, they measure the relative hypnotic effect of the anesthetic rather than a comprehensive measure of "anesthetic depth." Consequently, brain function monitors should be adjuncts to other patient monitoring modalities. Adjunctive use of bran functioning monitors during anesthesia has been found to reduce awareness. Not all brain function monitors have been studied for their effectiveness in reducing the incidence of anesthesia awareness. Individual health care facilities and anesthesia departments should consider the evidence-based measures of clinical efficacy and regulatory indications for use for the monitors they select.
Postoperative Care
Postoperative identification of patients who have experienced awareness facilitates appropriate access to psychological counseling and therapy. The occurrence of awareness is under reported since many patients do not seek out their providers postoperatively to discuss their experiences.12 This may be due to a delayed return of memory function or a manifestation of avoidance behavior that frequently accompanies traumatic experiences.
It is not surprising that anesthesia providers believe that the incidence of awareness in their own practices - typically based on patient self-reporting - to be significantly lower than the recent large-scale prospective investigations.1,2 These results were obtained using structured interviews two or three times following surgery.
Because of the potential and frequency of adverse psychological symptoms following an awareness episode, additional evaluation and treatment for these patients should be considered.6 Recognizing the anesthesia provider may lack sufficient competencies in this area, it is appropriate that a referral to qualified mental health care professionals be provided to the patient.13
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1 During preanesthesia evaluation, assess the risk of awareness. Incorporate the possibility of awareness as part of the informed consent for all high-risk scenarios.
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2 Check all anesthesia equipment (anesthesia machine, vaporizer, infusion pumps) to ensure ability to deliver adequate amounts of anesthetic agents.
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3 Consider the use of brain function monitoring, particularly for high-risk scenarios, if available.
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4 Consider premedication with amnestic agents.
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5 Clearly label all drug syringes immediately when they are drawn up. Do not rely on recognition of syringe size to confirm its contents. Consider other methods of ensuring correct drug given to avoid inadvertent paralysis of awake patient.
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6 Provide additional doses of hypnotic or initiate volatile agent administration for repeated intubation attempts.
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7 Use an end-tidal agent monitor, with the low alarm set for a sufficient volatile concentration to prevent awareness.
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8 When using total intravenous anesthesia, ensure a patent intravenous line and periodically check the function of the syringe pump.
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9 Avoid excessive muscle paralysis unless required for surgical indications. Routinely use a peripheral nerve stimulator to measure degree of paralysis.
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10 Conduct postoperative assessment to determine if unintended awareness occurred. If appropriate, refer patient to healthcare professional for support and therapy.
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Adapted from:
Ghoneim, MM. Awareness During Anesthesia. Anesthesiology 2000; 92: 597-602 4 Bergman et al. Awareness during general anesthesia: a review of 81 cases from the Anaesthetic Incident Monitoring Study. Anaesthesia 2002;57:549-56 5.
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References
1 Sandin RH, Enlund G, Samuelsson P, Lennrnarken C. Awareness during anaesthesia: a prospective case study. Lancet. 2000;355:707-11.
2 Sebel PS, Bowdle TA, Ghoneim MM, Rainpil IJ, Padilla RE, Gan TJ, Domino KB. The incidence of awareness during anesthesia: a multicenter United States study. Anesth Analg 2004;99:833-9.
3. Davidson AJ, I-luang GH, Czarnecki C, Gibson NIA, Stewart SA, Jamsen K, Stargatt R. Awareness during anesthesia in children: a prospective cohort study. Anesth Analg 2005;100:653-61.
4 Ghoneim MM. Awareness during anesthesia. Anesthesiology. 2000;92:597-602.
5 Bergman IJ, Kluger MT, Short TG. Awareness during general atiaesthesia: a review of 81 cases from the Anaesthetic Incident Monitoring Study. Anaesthesia 2002;57:549-56.
6 Lennmarken C, Bildfors K, Enlund G, Samuelsson P, Sandin R. Victims of Awareness. Acta Anaesthesiol Scand 2002;46:229-31.
7 Bulach R, Myles PS, Russnak M. Double-blind randomized controlled trial to determine extent of amnesia with midazolam given immediately before general anaesthesia. Br J Anaesth. 2005;94:300-5.
8. Domino KB, Posner KL, Caplan RA, Cheney FW. Awareness during anesthesia: a closed claims analysis. Anesthesiology. 1999;90:1053-61.
9. Flaishon R, Windsor A, Sigl J, Sebel PS. Recovery of consciousness after thiopental or propofol. Bispectral index and isolated forearm technique. Anesthesiology. 1997;86:613-9.
12. Moerman N, Bonke B, Oosting J. Awareness and recall during general anesthesia. Facts and feelings. Anesthesiology. 1993;79:454-64.
13. Osterman JE, Hopper J, Heran WJ, Keane TM, Van der Kolk B. Awareness under anesthesia and the development of posttraumatic stress disorder. Gen Hosp Psychiatry. 2001;23:198-204.
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