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Awareness during anesthesia
Anesthesiology Clin N Am 20 (2002) 555 – 570
Awareness during anesthesia Pete H. Spitellie, MD, Megan A. Holmes, MS, Karen B. Domino, MD, MPH* Department of Anesthesiology, University of Washington School of Medicine, Box 356540, Health Sciences Building, Room BB 1457, 1959 NE Pacific Street, Seattle, WA 98195-6540, USA
The number of patients who have preoperative anxiety over possibly ‘‘waking up’’ in the middle of surgery has increased dramatically over the last decade. McCleane and Cooper [1] found that more than 50% of 247 patients were concerned that they would not be asleep during their surgery. Even after having an adequate anesthetic, 25% were still worried about being asleep with future anesthetics [1]. With increased media coverage, these anxieties are not likely to go away anytime soon. For the patient, awareness or recall while under general anesthesia is a frightening experience that can lead to debilitating emotional injury and even post-traumatic stress disorder. For anesthesiologists, awareness under anesthesia ranks second only to death as a ‘‘dreaded’’ complication [2]. This chapter reviews the incidence, etiology, psychological sequelae, medicolegal consequences, and prevention of awareness during anesthesia.
Incidence and etiology of awareness The history of awareness during anesthesia is as old as the specialty itself. During the first successful administration of ether, William Morton’s patient reported being aware during the surgical procedure, but without pain. Oliver Wendell Holmes soon suggested the term anaesthesia to describe this state of temporary insensibility [3]. Performing surgery with little or no pain was such an advancement that awareness was not an issue. It was not until the advent and widespread use of neuromuscular blockade that awareness became a concern. Neuromuscular blockade could prevent patient movement, the most common sign of light anesthesia. Because the anesthetic concentrations needed to prevent awareness are lower than those necessary to prevent movement, [4,5] the patient is usually amnestic at the time of movement. Deepening the anesthetic at this
* Corresponding author. E-mail address: [email protected] (K.B. Domino). 0889-8537/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S 0 8 8 9 - 8 5 3 7 ( 0 2 ) 0 0 0 0 5 - 6
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point usually prevents awareness. After more than a century since the first anesthetic and almost 60 years since the introduction of neuromuscular blockers, the situation has changed little and there is still no guaranteed method for determining anesthetic depth in a paralyzed patient. Much of the research on incidence awareness has been conflicting and remains controversial. Ghoniem [6,7] suggests there are basically two camps in the modern anesthesia world. In the conservative camp are those who feel that consciousness and recall occur rarely and that when it does, it is generally explainable (ie, light anesthesia) and does not represent a widespread phenomenon. In the liberal camp are those who feel that the documented clinical reports of consciousness and explicit recall under general anesthesia are just the tip of the iceberg. The true incidence of awareness and recall, at least in the United States, is unknown. The incidence of awareness in noncardiac, nonobstetric surgery in Europe is 0.1% to 0.2% [8,9]. Of 18,785 patients, Sandin et al [9] found the incidence of awareness was 0.18% in those in whom neuromuscular blocking drugs were used and 0.10% in the absence of such drugs. Approximately half the episodes of awareness were reported in the recovery room, and the rest were reported 7 to 14 days after surgery [9]. Higher incidences of awareness has been reported in patients undergoing Cesarean section (0.4% incidence) [10,11], cardiac surgery (1.5% incidence) [12,13], or treatment for trauma (as high as 11%-43% incidence) [14]. The increased incidence is generally the result of intentionally light anesthesia because of the patient’s limited cardiac reserve, hypovolemia, or hypotension or for fear of decreasing uterine tone and increasing blood loss during obstetric procedures. Lyons and Macdonald [11] showed a decrease in the incidence of awareness during Cesarean section from 1.3% to 0.4% after a change in anesthetic technique to include isoflurane throughout the operation rather than nitrous oxide alone after delivery. In addition, the incidence of awareness in trauma surgery patients may have decreased to that for noncardiac, nonobstetric patients [15] perhaps because of improved resuscitation of the trauma patient, which in turn has allowed more appropriate use of amnestic/anesthetic agents. The anesthetic technique is important in the pathogenesis of awareness during anesthesia. Several case reports and small clinical studies have suggested that intraoperative awareness is more likely to occur during anesthesia based on nitrous oxide and intravenous agents (eg, opioids, propofol, benzodiazepines, and barbiturates) and is less likely to occur when potent volatile anesthetics are used [16 –22]. Ranta et al [23] found that the doses of propofol and isoflurane were smaller in patients with awareness than in those who did not have recall during general anesthesia. When nitrous oxide 70% is used alone, there is a 2% incidence of recall [24]. Volatile anesthetics are markedly more effective than nitrous oxide in reducing recall. Responsiveness to commands was impaired in volunteers at 0.2 minimum alveolar concentration (MAC) and lost at 0.4 MAC [5,25]. Recall of ‘‘shock’’ words also disappeared at 0.4 MAC. Because surgical stimulation may increase arousal, volatile anesthetic levels greater than 0.8 MAC are recommended to prevent recall [6]. Explicit recall is also abolished at lower doses of intravenous anesthetics than is responsiveness to verbal commands [4,26].
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When a patient has been found to be aware during general anesthesia, the cause is usually traceable to one of three factors: light anesthesia, machine malfunction or misuse of a technique, or increased anesthetic requirement (Box 1) [6]. At times the anesthesiologist may be purposefully trying to administer light anesthesia, or it can happen accidentally. Occasionally, certain patient characteristics (limited cardiac reserve, hypovolemia/hypotension, emergency Cesarean section) and intraoperative factors make it difficult to use anesthetic agents without deleterious consequences for the patient. Failure to repeat the induction dose during a difficult intubation is a relatively common cause of awareness [27]. At other times the anesthesiologist may try to awaken the patient more quickly by decreasing recovery from general anesthesia, thereby improving discharge times. This may dangerously approach the point of overly light anesthesia and possible awareness. Box 1. Causes of Awareness Light anesthesia Nitrous/opioid/relaxant anesthesia Myocardial depression– hypovolemia Cesarean section Difficult intubation Premature discontinuation of anesthetic Machine malfunction or misuse of technique Failure to check equipment Vaporizer and circuit leaks Intravenous infusion errors Accidental administration of muscle relaxant to awake patient Increased anesthetic requirements Variability in anesthetic requirements for intravenous agents Increased anesthetic requirement because of chronic alcohol, opioid, and cocaine abuse Awareness may also be the result of machine malfunction or misuse/ misinterpretation of a technique (Box 1). Machine malfunction and equipment failure are less common now than they used to be. With improved technology (ie, end-tidal gas analysis), unknowingly giving an unintentional diminished dose as a result of an empty vaporizer or tubing leak should never happen. However, even with modern sophisticated equipment, misuse and failure still occur. Sandin and Nordstrom [21] report five cases of awareness with total intravenous anesthesia (TIVA). In that report, examples of a misused technique, misused equipment, and increased drug requirements for the patient were given. TIVA presents a different and difficult problem in this area. There are no end-tidal equivalents such as measuring plasma levels in real time. Even with computerized target-controlled delivery devices, plasma concentrations can vary considerably
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from the set point [28]. In addition, there is significantly more inter-individual pharmacokinetic variability between patients than with volatile agents. However, to date no difference has been shown in awareness incidence between TIVA and inhalational agents. The third cause of awareness is that some patients may have increased anesthetic requirements (Box 1). Many drugs have altered kinetics and potency in patients on different medications. It is entirely possible that some patient populations may have altered responses to general anesthetic and amnestic agents. Chronic use of alcohol, opiates, and cocaine may increase the dose requirements of anesthetic agents [29 –31]. Chronic cocaine exposure increased MAC of isoflurane in sheep by approximately 25% [29]. Chronic ethanol administration also increased MAC in mice by a similar amount [30].
Psychological sequelae of awareness Awareness during anesthesia is a frightening experience. Patients who experience awareness and recall during anesthesia describe auditory perceptions (eg, sounds and conversations in the operating room), the sensation of paralysis, anxiety, panic, helplessness, and powerlessness (Box 2) [32 – 35]. Pain has been reported in up to 40% of patients with awareness during anesthesia [34]. Visual perceptions and feeling the endotracheal tube being placed or feeling the operation without pain are less commonly reported [34]. Patient testimonials describing the sensation of suffocation, being buried alive, overwhelming pain, and inability to escape or signal their distress are particularly chilling. One account from a patient is described below [36]: ‘‘I remember feeling the cold plastic tube being inserted down the back of my throat. I remember trying to cough, talk, open my eyes, and do anything to signal that I was awake. At that point, I began to panic and I could feel my heart racing. I was crying inside, but no one noticed my tears. The sensation and memory were similar to what I have read about people being buried alive.’’
Box 2. Patient perceptions of awareness Most common Sounds and conversation Sensation of paralysis Anxiety and panic Helplessness and powerlessness Pain Least common Visual perceptions Intubation or tube Feeling the operation without pain
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Awareness that one is awake and paralyzed creates an overwhelming sense of anxiety and panic, and the inability to alert the surgical team that he or she is awake leaves the patient feeling helpless. The inability to take action to escape the experience leads to a failure of the normal fight or flight response, preventing active coping and increasing the likelihood of passive coping or dissociation [37]. Nonparalyzed patients are less likely to experience anxiety during an episode of awareness. As many as 70% of patients with intraoperative awareness experience unpleasant aftereffects including sleep disturbances, dreams and nightmares, and flashbacks and anxiety during the day [34,35,37]. Nonparalyzed patients may be less likely to develop aftereffects than paralyzed patients. Sometimes these effects are so severe and persistent that post-traumatic stress disorder (PTSD) develops (Box 3). The primary features of PTSD are defined by three clusters of symptoms: intrusive and distressing thoughts and images recalling the traumatic event, avoidance of stimuli that may prompt memory of the trauma, and increased autonomic arousal and generalized anxiety [38]. In the months and years after the awareness episode, PTSD manifests itself in the form of panic attacks, distressing flashbacks of the event during the day, exaggerated startle response, difficulty concentrating, recurrent nightmares, and insomnia. Patients often feel betrayed by their doctors and nurses, which results in general distrust of medical personnel. This leads to avoidance of physicians and hospitals and of other places and situations that may remind them of the surgery [35].
Box 3. Psychological sequelae of awareness Sleep disturbances Nightmares Anxiety and panic attacks Flashbacks Avoidance of medical care Post-traumatic stress disorder
The predisposing factors for the development of PTSD are unknown, though a number of factors have been associated with the disorder. In the patient with awareness during anesthesia, full recall of the awareness episode, the sensation of pain during awareness, the experience of paralysis, and an underlying psychiatric disorder may increase the risk for PTSD [39]. An abnormal biologic response to trauma and female gender may also play a role. Many people recover from PTSD, with symptoms decreasing over an average period of a few months to a few years. However, 10% to 25% of patients experience chronic PTSD [40]. Early diagnosis and treatment are important in those with PTSD. Untreated, it can lead to comorbid depression, agoraphobia, or
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substance abuse [35,39,40]. It has also been associated with higher rates of hypertension, peptic ulcer, and infectious disease [41]. Consultation or debriefing by the anesthesiologist after an awareness episode has been shown to be effective in preventing prolonged traumatic reaction. The anesthesiologist should listen carefully to the patient’s account and show concern about what the patient has experienced (Box 4). It is essential to provide a reasonable explanation of why the awareness occurred and reassurance that the probability of a re-occurrence in future procedures is slight [39]. Sandin et al [9] found that with repeated discussion and information, nightmares, anxiety, and flashbacks resolved within 3 weeks in 18 patients with intraoperative awareness. Therefore, frequent contact with the patient should be made to monitor psychological sequelae and to provide interpersonal support during the first few weeks after awareness.
Box 4. Management of awareness during anesthesia Patient interview Validate the events Empathize Provide explanation Provide reassurance Maintain contact to monitor psychologic sequelae Refer to psychologist or psychiatrist if symptoms persist
Unfortunately, debriefing by the anesthesiologist does not resolve symptoms in all patients, and referral to a psychologist may be necessary. In addition, many patients do not report their awareness episodes, fearing disbelief on the part of physicians [34,42]. By the time these patients seek treatment, they have most likely been experiencing traumatic stress symptoms for an extended period of time. Many arrive seeking help for a comorbid somatization disorder, such as a gastrointestinal problem, or seeking relief from chronic anxiety, and underlying PTSD is discovered only after many tests and consultations [35]. Treatment for those with PTSD is often challenging and the PTSD may never be resolved completely, but a number of techniques have been shown to be effective in reducing symptoms. Psychotherapy can be beneficial for those who have experienced trauma. It has been suggested that for the greatest impact, cognitive-behavioral therapy should be combined with anxiety management techniques and direct confrontation of the event by the patient [40,41]. Another option is psychopharmacologic intervention. Antidepressants, especially selective serotonin reuptake inhibitors, have been shown to significantly reduce PTSD symptoms of intrusion and avoidance and of depression and anxiety [40]. Other agents, such as benzodiazepines and mood stabilizers, have produced mixed results. Eye movement desensitization and reprocessing allows reprocessing of the traumatic event while enabling the patient to develop a sense of mastery and
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control over the memories [35]. Each of these treatment modalities has been shown to have some effect when used alone, but the greatest improvement occurs when pharmacotherapy is used in conjunction with other types of treatment [41].
Medicolegal consequences of awareness during anesthesia Although awareness under general anesthesia may result in serious emotional injury and post-traumatic stress disorder, for most patients this awareness results in no litigation. However, a few patients file a medical malpractice claim as a result of their injury. Physician –patient communication, severity of the outcome, expected compensation for damages, and sociocultural factors all influence whether a malpractice claim is filed. Because of the implicit bias that emotional injuries are less severe and less documentable than physical injuries, the relatively low payment for an emotional rather than a physical injury may deter plaintiff attorneys from pursuing claims for intraoperative awareness [43].
Medicolegal implications in the United States The medicolegal ramifications of intraoperative awareness in the United States have been recently described by the American Society of Anesthesiologists (ASA) Closed Claims Project [27] and are summarized below. Awareness claims account for 100 of 5480 (1.8%) claims in the ASA Closed Claims Project database, a proportion similar to that for burns, aspiration pneumonia, myocardial infarction, hepatic dysfunction, and renal failure. Compared with all other claims, awareness claims involved more women (78% of awareness claims vs 59% of all other claims), patients younger than 60 (82% for awareness claims vs 74% for all other claims), and patients undergoing elective surgery (82% of awareness claims vs 75% for all other claims). Claims for awareness in the Closed Claims database fall into two categories: awake paralysis, that is, the inadvertent paralysis of an awake patient (22 claims), and recall under general anesthesia, that is, patient recall of events during general anesthesia (78 claims). Claims for recall during anesthesia represent typical cases of awareness during anesthesia. The proportion of claims for awareness in the Closed Claims database has increased since the 1970s, mostly because of an increase in claims for recall under general anesthesia (Fig. 1). The proportion of claims for awake paralysis has remained relatively constant. Most claims for awake paralysis were related to intravenous infusion errors or syringe swaps. The periods of highest risk were in the pre-induction and induction periods, when a muscle relaxant was administered instead of a sedative or hypnotic agent. Reviewers considered most cases of awake paralysis to be examples of substandard anesthesia care, though the paralysis was promptly recognized and appropriately managed. Ninety-six percent of awake paralysis closed claims were judged to represent substandard care by the anesthesiologist,
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Fig. 1. Proportion of claims for awareness in the Closed Claims database in each decade. The proportion of claims for awareness increased in the 1980s and 1990s compared with the 1970s because of an increase in claims for recall under general anesthesia ( P < 0.05).
in contrast to 37% of all other closed claims. One case for which the care by the anesthesiologist was judged to be appropriate involved mislabeling of a syringe in the pharmacy. Payments were made in a greater proportion of awake paralysis claims (76%) than in all other claims (59%), consistent with the judgment of substandard care. However, payments for awake paralysis claims were lower than those for all other claims, with a median payment of only $10,250 (range, $1,000 to $215,000), reflecting the low severity of injury. Claims for recall during general anesthesia were more diverse. Most of the cases of recall originated during the maintenance phase of anesthesia. In contrast to awake paralysis, the anesthesia care in claims for recall during anesthesia was judged to be substandard in 44%, appropriate in 33%, and impossible to judge in the remainder of claims. The standard of care was commonly judged to be appropriate when it occurred during a planned nitrous – narcotic –relaxant technique or if the recall was associated with hypotension requiring discontinuation of anesthetic agents. Recall associated with vaporizer problems, inadequate doses of drugs, and difficult intubation predominantly were judged as substandard care. Interestingly, the classic cues for light anesthesia (hypertension, tachycardia, and patient movement) were absent in most cases. One claim alleged recall despite use of an intraoperative electroencephalograph. Follow-up care was described as adequate in most claims. However, three claim files explicitly described a lack of concern and attention by the anesthesiologist. A lower proportion of recall under general anesthesia claims resulted in payment (56%), compared with awake paralysis claims; however, the amount of payment was similar to awake paralysis claims. The median payment was $20,000 (range, $1,700 to $750,000) compared to a median payment of $105,000 for all other claims (range, $15 to $23,200,000). The lower median payment is consistent with the lower severity of injury and is similar to compensation for awake paralysis, back pain, and emotional distress. Marked
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variability in the range of compensation reflects differences in the geographic distribution, severity of injury, standard of care, and presence of additional injuries (eg, aspiration pneumonia with substandard care). Higher payments have been reported for more severe injuries in which care was substandard. Multiple logistic regression analysis demonstrated that three factors were significantly associated with claims for recall under general anesthesia compared with other general anesthesia claims: no volatile anesthetic agent (odds ratio [OR], 3.20; 95% confidence interval [CI], 1.88-5.46), female gender (OR, 3.08; 95% CI, 1.58-6.06), intraoperative narcotic (OR, 2.12; 95% CI, 1.20-3.74), and intraoperative muscle relaxant (OR, 2.28; 95% CI, 1.22-4.25). Age, ASA status, anesthesia personnel, standard of care, and use of benzodiazepines, barbiturates, and nitrous oxide were not associated with claims for recall during general anesthesia. The association of claims for recall during general anesthesia with anesthetic techniques using opioids, muscle relaxants, and little or no volatile anesthetic is consistent with the known increased incidence of intraoperative awareness with these light anesthetic techniques. However, it is unclear why female gender was associated with a three times higher rate of a recall claim than other claims. This could represent a gender-related increase in propensity for recall during general anesthesia or a greater likelihood to file a claim for recall. Although many reports of intraoperative awareness involve a preponderance of women, this is most likely secondary to light anesthetic techniques, especially for Cesarean section. However, gender-related differences in the requirements for intravenous anesthetics have been reported [44,45]. Women wake up faster from propofol – alfentanil anesthesia [45]. Plasma remifentanil levels, titrated to ensure the lack of a hemodynamic response to a surgical stimulus, were almost twice as high in women as in men [44]. Women may also file claims for emotional injury more often than men. Claims by women in the Closed Claims database involved a lower severity of injury than did claims by men. For instance, the frequency of claims by women for emotional injury was nearly double of that for men (13% vs 7%, respectively). These data suggest that women may be more likely than men to file a claim for recall under general anesthesia. Medicolegal implications in Europe Patterns of litigation related to awareness during anesthesia over the last 20 years have not been the same in the United States and Europe. The incidence of litigation varies widely in European countries. In the United Kingdom, claims related to awareness are more frequent as a proportion of all claims against anesthesiologists than in the United States [46]. Approximately one eighth of legal claims against anesthesiologists in the United Kingdom relate to allegations of awareness during general anesthesia [46]. This may be a result of differences in anesthetic techniques, but it may, alternatively, relate to the fact that low-value claims are more likely to be pursued if the patient is able to obtain all legal costs
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from the state (as in the United Kingdom) than if the risk of litigation is assumed by the plaintiff’s lawyer, whose reimbursement is restricted if the outcome is a low settlement (as in the United States). In contrast, claims for compensation for awareness during general anesthesia have remained low in the rest of Europe. Ranta et al [47] reviewed claims for awareness in Finland during the late 1980s to the early 1990s. In Finland, compensation is paid to a patient for an injury caused by medical treatment, according to the Patient Injury Act. Of 23,363 claims for patient injury, only 391 were for anesthesia-related injuries (1.7% of all malpractice claims), a proportion similar to that in the United States. Only 4 claims were made for awareness under general anesthesia (1% of anesthesia claims). All the patients sustained serious psychological sequelae. They were awarded between 4,000 to 9,600 Finnish marks (approximately $1,000-$2,400). Differences between the experiences in various countries suggest that claims for awareness under anesthesia are markedly influenced by cultural factors.
Future medicolegal implications Malpractice claims for awareness during anesthesia are likely to increase in quantity and amount of payment to the plaintiff in the United States in the future. The trend for an increase in awareness claims in the 1990s may reflect an increase in public knowledge about awareness and intolerance for this type of complication. Recent prominent discussion in the news media and on television is likely to increase litigation. Introduction of a potential monitor for awareness may also increase the risk for litigation and the magnitude of payment.
Prevention of awareness As it is with most complications, the best treatment for awareness is prevention. Most published recommendations are derived from research involving depth of anesthesia, learning, and memory. The major points have been well summarized in other reviews [6,48] but deserve repetition (Box 5).
Box 5. Prevention of awareness Administer amnestic premedicants. Maintain vigilance regarding equipment and monitoring. Minimize use of complete neuromuscular blockade. Supplement nitrous/opiate anesthesia with a potent volatile anesthetic.
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Maintain 0.8 – 1.0 MAC of a potent volatile anesthetic by itself. Administer adequate dose of induction agent. Obtain informed consent for high-risk patients. Mask auditory input. Provide education. Monitor for awareness.
1. Premedication. Amnestic agents (benzodiazepines, scopolamine, and so on) should be a strong consideration, especially if the anesthesiologist anticipates or encounters a patient in whom light anesthesia is required. 2. Vigilance regarding equipment and monitoring. There is no greater charge in our profession than vigilance, and this is especially true when it comes to awareness. Although end-tidal gas concentration monitoring did not impact the incidence of awareness in one study [9], the anesthesiologist may not have adjusted the concentrations of volatile agents to high enough levels to prevent recall. Equipment should be maintained and serviced by appropriate personnel, and the anesthesiologist should check the machine. Attention should be paid to checking and filling the vaporizer. TIVA represents different problems, but again vigilance is the key—maintain an adequate volume in the syringe, ensure the flow of drug into the patient, and use computerized pumps with appropriate volume and pressure alarms. 3. Neuromuscular blockade. Movement is the best indicator we have of light anesthesia or its impedance [6,48]. By abolishing it, muscle relaxants put patients at risk for awareness. We should therefore avoid the ‘‘need’’ to paralyze every patient. As such, neuromuscular blockers should only be used when necessary. In most cases, complete paralysis is not required. Patients can open their eyes with modest, but not total, neuromuscular blockade. Because explicit recall is abolished at lower doses than responsiveness to verbal commands [4,25], assessing and maintaining a lack of responsiveness to the verbal command ‘‘open your eyes’’ may help prevent recall at critical phases of surgery (such as separation from cardiopulmonary bypass). 4. Nitrous/opiate. Nitrous/opiate anesthesia should be supplemented with a potent volatile agent to decrease the high incidence of awareness with this technique (up to 6% in a recent study) [24]. At subanesthetic concentrations, nitrous oxide was shown to suppress memory and learning, though to a lesser extent than isoflurane [49]. Opiates may decrease the amount of volatile agent needed to prevent awareness by providing analgesia, but by themselves they do nothing to prevent learning and memory. In addition, they are unpredictable at producing unconsciousness [26].
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5. Adequate concentration of volatile anesthetic. If potent volatile agents are to be used alone, it has been suggested they be maintained at least at 0.8 to 1.0 MAC [6]. Eger et al [50] found that the patients who expressed fear about remembering their anesthetic had end-tidal values of approximately 0.5 MAC. They suggested that perhaps values of at least 0.75 MAC be maintained to abolish fearful memories, attributed to inadequate anesthesia. In actuality, the optimal doses may never be known because studies that have established MAC awake at 0.3 to 0.6 were conducted on healthy volunteers [4,5]. Surgical stimulus will probably necessitate higher doses to prevent movement and subsequent awareness. Given that it is ethically unacceptable to lower doses purposefully in surgical patients to elucidate these doses, they will probably never be established. 6. Adequate dose of induction agent. If possible, give more than just a ‘‘sleep dose’’ of the intravenous induction agent if it is to be immediately followed by succinylcholine and intubation. If a difficult intubation is encountered, supplemental doses of an induction agent should be given. 7. Discuss the possibility of awareness with patients at high risk. Patients undergoing cardiac surgery or emergency Cesarean section are at high risk for awareness. Although some anesthesiologists believe this only increases anxiety during an already stressful time, it may prevent a lawsuit if awareness occurs, and, more important, it may put the postoperative patient at ease that he or she is not crazy. As a result, the patient may bring attention to it and receive appropriate psychiatric treatment. 8. Mask auditory input. Consider covering ears to mask auditory input. In their interviews with 26 patients who were referred because of intraoperative awareness, Moerman et al [34] found that auditory perception and the sensation of paralysis were most frequently mentioned. Derogatory remarks by staff in the operating room should be strongly discouraged. Unfortunately, patients tend to remember ‘‘shock’’ words such as beached whale, beautiful body, or quotes about the stock market! 9. Education. It is hoped that improved education about awareness will result in more sympathetic responses from medical staff. In his review of 187 patients who reported awareness, Cobcroft [33] found that understanding of awareness and its proper management by medical personnel was poor or totally lacking. Postoperative interviews should include inquiries about awareness. Most (65%) patients fail to inform their anesthesiologist that they had intraoperative recall [34]. This is unfortunate because acknowledgment of what happened and prompt referral to psychological therapy may reduce the likelihood of long-term emotional sequelae [9]. 10. Monitoring specifically for awareness. Anesthetic depth has traditionally been monitored indirectly by assessing movement or changes in hemodynamics. However, movement cannot occur in the paralyzed patient, and signs of autonomic responsiveness (eg, hypertension and tachycardia) often do not occur in patients with intraoperative awareness
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[23,27]. Assessment of responsiveness to verbal commands is not frequently performed. In addition, use of end-tidal gas monitoring also does not prevent awareness [9]. Therefore, a monitor that specifically measures the depth of anesthesia has been advocated. The Bispectral Index Scale (BIS; Aspect Medical Systems, Newton, MA), the first to gain Food and Drug Administration approval as an electroencephalogrambased monitor of anesthetic effect, has been advocated as a potential monitor for awareness [51]. BIS has been shown to be efficacious as an indicator of the level of sedation, the probability of responsiveness to command during anesthesia, and the probability of recall [26,52,53]. Awareness during anesthesia has occurred despite BIS monitoring, though it is mostly associated with high BIS levels (greater than 65). [54] However, its efficacy in actually preventing awareness has not been convincingly demonstrated and is under investigation in Australia. One limitation of the BIS is that thresholds indicated by its values may not be independent of different combinations of anesthetics [55,56]. Vernon et al [56] found that although BIS was a better predictor of patient movement than hemodynamic changes, their findings suggested that different anesthetics have different effects on BIS. Similarly, Lysakowski et al [57] found that although the hypnotic effect of propofol is enhanced by analgesic concentrations of m-agonist opioids, the BIS did not show the increased hypnotic effect. Another method of monitoring depth of anesthesia in commercial development is the auditory evoked potential. Current reports suggest it may be better at determining the point of actual loss of consciousness [58]. Other interesting methods recently reported include techniques using approximate entropy [59] and Shannon entropy [60]. Several arguments favor use of an awareness monitor. Though rare, awareness under anesthesia occurs frequently enough to warrant placing a monitor to prevent it. Clinical methods of detecting awareness (ie, changes in vital signs) are not a reliable means for prevention. Although the original purpose for the BIS monitor was to aid in decreasing the risk for awareness, it is also being touted as a means to reduce the amount of anesthetic given, in turn decreasing recovery times. Those in opposition to BIS argue that it may in fact increase the risk for awareness for two reasons. First, concern has been voiced over the use of everdecreasing amounts of anesthetic agents to speed up recovery time using the BIS as a guide [51]. By doing so, we may dangerously encroach on the line of overly light anesthesia, increasing the risk for awareness, especially with changing surgical stimulus. Second, because BIS values can vary from patient to patient with a particular technique and with different anesthetic techniques, titrating to a predetermined value may leave the occasional patient under-anesthetized. A report of a patient having explicit intraoperative recall at a BIS level of 47 has been published [61]. Given these critiques, the development of a universally acceptable device will have to meet stringent conditions. Drummond [49] suggested that to be a satisfactory awareness monitor, any monitor should have sensitivity and specificity approaching 100%. Because of the extremely low
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incidence of awareness under anesthesia, the device must absolutely separate the two states in question (aware vs unaware). Otherwise, it may result in more events than it prevents. In addition, the critical thresholds between aware and unaware must not vary between patients [49]. In other words, the values that indicate these critical thresholds should not change with different anesthetic agents or disease states. Unfortunately, in contrast to other areas within the field of anesthesia, our understanding of awareness and consciousness has moved along slowly. The terms too deep or too light are still used on a daily basis without an objective value given to them. Devices that attempt to monitor the depth of consciousness have been investigated by many but leave us with more questions than answers. Therefore, no monitor is available that can guarantee that a patient will be unaware during anesthesia. In summary, awareness during general anesthesia is estimated to have an incidence of 0.10% to 0.20%. The most common causes of awareness are light anesthesia, increased anesthetic requirement, or machine malfunction/misuse of technique. Awareness is a frightening experience and may result in post-traumatic stress disorder. Medical malpractice litigation is infrequent but may be increasing. At present, there is no proven monitor for awareness.
References [1] McCleane GJ, Cooper R. Nature of pre-operative anxiety. Anaesthesia 1990;45:153 – 5. [2] Macario A, Weinger MN, Truong P, Lee J. Which clinical anesthesia outcomes are both common and important to avoid? the perspective of a panel of expert anesthesiologists. Anesth Analg 1999;88:1085 – 91. [3] Calverley RK. Anesthesia as a specialty: past, present and future. In: Barasch PG, Cullen BF, Stoelting RK, editors. Clinical anesthesia. Philadelphia: JB Lippincott; 1989. p 6 – 7. [4] Chortkoff BS, Eger EI II, Crankshaw DP, Gonsowski CT, Dutton RC, Ionescu P. Concentrations of desflurane and propofol that suppress response to command in humans. Anesth Analg 1995; 81:737 – 43. [5] Dwyer R, Bennett HL, Eger EI II, Heilbron D. Effects of isoflurane and nitrous oxide in subanesthetic concentrations on memory and responsiveness in volunteers. Anesthesiology 1992;77: 888 – 98. [6] Ghoneim MM. Awareness during anesthesia. Anesthesiology 2000;92:597 – 602. [7] Ghoneim MM, Block RI. Learning and consciousness during general anesthesia: an update. Anesthesiology 1997;87:387 – 410. [8] Liu WHD, Thorp TAS, Graham SG, Aitkenhead AR. Incidence of awareness with recall during general anesthesia. Anaesthesia 1991;46:435 – 7. [9] Sandin RH, Enlund G, Samuelsson P, Lennmarken C. Awareness during anaesthesia: a prospective case study. Lancet 2000;355:706 – 11. [10] Crawford JS. Awareness during operative obstetrics under general anaesthesia. Br J Anaesth 1971;43:179 – 82. [11] Lyons G, Macdonald R. Awareness during Caesarean section. Anaesthesia 1991;46:62 – 4. [12] Phillips AA, McLean RF, Devitt JH, Harrington EM. Recall of intraoperative events after general anaesthesia and cardiopulmonary bypass. Can J Anaesth 1993;40:922 – 6. [13] Ranta S, Jussila J, Hynynen M. Recall of awareness during cardiac anaesthesia: influence of feedback information to the anaesthesiologists. Acta Anaesthesiol Scand 1996;40:554 – 60.
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[14] Bogetz MS, Katz JA. Recall of surgery for major trauma. Anesthesiology 1984;61:6 – 9. [15] Lubke GH, Kerssens C, Phaf H, Sebol PS. Dependence of explicit and implicit memory on hypnotic state in trauma patients. Anesthesiology 1999;90:670 – 80. [16] Gilron I, Solomon P, Plourde G. Unintentional intraoperative awareness during sufentanil anaesthesia for cardiac surgery. Can J Anaesth 1996;3:295 – 8. [17] Harris TJB, Brice DD, Hetherington RR, Utting JE. Dreaming associated with anaesthesia: the influence of morphine premedication and two volatile adjuvants. Br J Anaesth 1971;43: 172 – 8. [18] Kelly JS, Roy RC. Intraoperative awareness with propofol-oxygen total intravenous anesthesia of microlaryngeal surgery. Anesthesiology 1992;77:207 – 9. [19] King H, Ashley S, Brathwaite D, Decayette J, Wooten D. Adequacy of general anesthesia for Cesarean section. Anesth Analg 1993;77:84 – 8. [20] Russell IF. Comparison of wakefulness with two anaesthetic regimens: total IV balanced anaesthesia. Br J Anaesth 1986;58:965 – 8. [21] Sandin R, Nordstro¨m O. Awareness during total IV anaesthesia. Br J Anaesth 1993;71:782 – 7. [22] Schultetus RR, Hill CR, Dharamraj CM, Banner TE, Berman LS. Wakefulness during Cesarean section after anesthetic induction with ketamine, thiopental, or ketamine and thiopental combined. Anesth Analg 1986;65:723 – 8. [23] Ranta S, Laurila R, Saario J, Ali-Melkkila T, Hynynen M. Awareness with recall during general anesthesia: incidence and risk factors. Anesth Analg 1999;86:1084 – 9. [24] Utting JE. Awareness clinical aspects. In: Rosen M, Lunn JN, editors. Consciousness, awareness and pain in general anaesthesia. London: Butterworths; 1987. p 171 – 9. [25] Dwyer R, Bennett HL, Eger EI II, Peterson N. Isoflurane anesthesia prevents unconscious learning. Anesth Analg 1993;21:837 – 43. [26] Glass PS, Bloom M, Kearse L, Rosow C, Sebel P, Manberg P. Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfentanil in healthy volunteers. Anesthesiology 1997;86:836 – 47. [27] Domino KB, Posner KL, Caplan RA, Cheney FW. Awareness during anesthesia: a closed claims analysis. Anesthesiology 1999;90:1053 – 61. [28] Vuyk J, Iim T, Engbers FHM, Burm AGL, Vletter AA, Bovill JG. Pharmacodynamics of alfentanil as a supplement to propofol or nitrous oxide for lower abdominal surgery in female patients. Anesthesiology 1993;78:1036 – 45. [29] Bernards CM, Kern C, Cullen BF. Chronic cocaine administration reversibly increases isoflurane minimum alveolar concentration in sheep. Anesthesiology 1996;85:91 – 5. [30] Johnstone RE, Kulp RA, Smith TC. Effects of acute and chronic ethanol administration on isoflurane requirement in mice. Anesth Analg 1975;54:277 – 81. [31] Stoelting RK, Creasser CW, Martz RC. Effect of cocaine administration on halothane MAC in dogs. Anesth Analg 1975;54:422 – 4. [32] Blacher RS. On awakening paralyzed during surgery: a syndrome of traumatic neurosis. JAMA 1975;234:67 – 8. [33] Cobcroft MD, Forsdick C. Awareness under anaesthesia: the patients’ point of view. Anaesth Intens Care 1993;21:837 – 43. [34] Moerman N, Bonke B, Oosting J. Awareness and recall during general anesthesia: facts and feelings. Anesthesiology 1993;79:454 – 64. [35] Osterman JE, Hopper J, Heran WJ, Keane TM, van der Kolk BA. Awareness under anesthesia and the development of posttraumatic stress disorder. Gen Hosp Psychiatry 2001;23:198 – 204. [36] Domino KB. Closed malpractice claims for awareness during anesthesia. ASA Newsl 1996;60:14 – 7. [37] Osterman JE, van der Kolk BA. Awareness during anesthesia and posttraumatic stress disorder. Gen Hosp Psychiatry 1998;20:274 – 81. [38] American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th edition. Washington, DC: American Psychiatric Association; 2000. p. 465 – 8. [39] Wang M. The psychological consequences of explicit and implicit memories of events during
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Awareness during anesthesia Pete H. Spitellie, MD, Megan A. Holmes, MS, Karen B. Domino, MD, MPH* Department of Anesthesiology, University of Washington School of Medicine, Box 356540, Health Sciences Building, Room BB 1457, 1959 NE Pacific Street, Seattle, WA 98195-6540, USA
The number of patients who have preoperative anxiety over possibly ‘‘waking up’’ in the middle of surgery has increased dramatically over the last decade. McCleane and Cooper [1] found that more than 50% of 247 patients were concerned that they would not be asleep during their surgery. Even after having an adequate anesthetic, 25% were still worried about being asleep with future anesthetics [1]. With increased media coverage, these anxieties are not likely to go away anytime soon. For the patient, awareness or recall while under general anesthesia is a frightening experience that can lead to debilitating emotional injury and even post-traumatic stress disorder. For anesthesiologists, awareness under anesthesia ranks second only to death as a ‘‘dreaded’’ complication [2]. This chapter reviews the incidence, etiology, psychological sequelae, medicolegal consequences, and prevention of awareness during anesthesia.
Incidence and etiology of awareness The history of awareness during anesthesia is as old as the specialty itself. During the first successful administration of ether, William Morton’s patient reported being aware during the surgical procedure, but without pain. Oliver Wendell Holmes soon suggested the term anaesthesia to describe this state of temporary insensibility [3]. Performing surgery with little or no pain was such an advancement that awareness was not an issue. It was not until the advent and widespread use of neuromuscular blockade that awareness became a concern. Neuromuscular blockade could prevent patient movement, the most common sign of light anesthesia. Because the anesthetic concentrations needed to prevent awareness are lower than those necessary to prevent movement, [4,5] the patient is usually amnestic at the time of movement. Deepening the anesthetic at this
* Corresponding author. E-mail address: [email protected] (K.B. Domino). 0889-8537/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S 0 8 8 9 - 8 5 3 7 ( 0 2 ) 0 0 0 0 5 - 6
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point usually prevents awareness. After more than a century since the first anesthetic and almost 60 years since the introduction of neuromuscular blockers, the situation has changed little and there is still no guaranteed method for determining anesthetic depth in a paralyzed patient. Much of the research on incidence awareness has been conflicting and remains controversial. Ghoniem [6,7] suggests there are basically two camps in the modern anesthesia world. In the conservative camp are those who feel that consciousness and recall occur rarely and that when it does, it is generally explainable (ie, light anesthesia) and does not represent a widespread phenomenon. In the liberal camp are those who feel that the documented clinical reports of consciousness and explicit recall under general anesthesia are just the tip of the iceberg. The true incidence of awareness and recall, at least in the United States, is unknown. The incidence of awareness in noncardiac, nonobstetric surgery in Europe is 0.1% to 0.2% [8,9]. Of 18,785 patients, Sandin et al [9] found the incidence of awareness was 0.18% in those in whom neuromuscular blocking drugs were used and 0.10% in the absence of such drugs. Approximately half the episodes of awareness were reported in the recovery room, and the rest were reported 7 to 14 days after surgery [9]. Higher incidences of awareness has been reported in patients undergoing Cesarean section (0.4% incidence) [10,11], cardiac surgery (1.5% incidence) [12,13], or treatment for trauma (as high as 11%-43% incidence) [14]. The increased incidence is generally the result of intentionally light anesthesia because of the patient’s limited cardiac reserve, hypovolemia, or hypotension or for fear of decreasing uterine tone and increasing blood loss during obstetric procedures. Lyons and Macdonald [11] showed a decrease in the incidence of awareness during Cesarean section from 1.3% to 0.4% after a change in anesthetic technique to include isoflurane throughout the operation rather than nitrous oxide alone after delivery. In addition, the incidence of awareness in trauma surgery patients may have decreased to that for noncardiac, nonobstetric patients [15] perhaps because of improved resuscitation of the trauma patient, which in turn has allowed more appropriate use of amnestic/anesthetic agents. The anesthetic technique is important in the pathogenesis of awareness during anesthesia. Several case reports and small clinical studies have suggested that intraoperative awareness is more likely to occur during anesthesia based on nitrous oxide and intravenous agents (eg, opioids, propofol, benzodiazepines, and barbiturates) and is less likely to occur when potent volatile anesthetics are used [16 –22]. Ranta et al [23] found that the doses of propofol and isoflurane were smaller in patients with awareness than in those who did not have recall during general anesthesia. When nitrous oxide 70% is used alone, there is a 2% incidence of recall [24]. Volatile anesthetics are markedly more effective than nitrous oxide in reducing recall. Responsiveness to commands was impaired in volunteers at 0.2 minimum alveolar concentration (MAC) and lost at 0.4 MAC [5,25]. Recall of ‘‘shock’’ words also disappeared at 0.4 MAC. Because surgical stimulation may increase arousal, volatile anesthetic levels greater than 0.8 MAC are recommended to prevent recall [6]. Explicit recall is also abolished at lower doses of intravenous anesthetics than is responsiveness to verbal commands [4,26].
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When a patient has been found to be aware during general anesthesia, the cause is usually traceable to one of three factors: light anesthesia, machine malfunction or misuse of a technique, or increased anesthetic requirement (Box 1) [6]. At times the anesthesiologist may be purposefully trying to administer light anesthesia, or it can happen accidentally. Occasionally, certain patient characteristics (limited cardiac reserve, hypovolemia/hypotension, emergency Cesarean section) and intraoperative factors make it difficult to use anesthetic agents without deleterious consequences for the patient. Failure to repeat the induction dose during a difficult intubation is a relatively common cause of awareness [27]. At other times the anesthesiologist may try to awaken the patient more quickly by decreasing recovery from general anesthesia, thereby improving discharge times. This may dangerously approach the point of overly light anesthesia and possible awareness. Box 1. Causes of Awareness Light anesthesia Nitrous/opioid/relaxant anesthesia Myocardial depression– hypovolemia Cesarean section Difficult intubation Premature discontinuation of anesthetic Machine malfunction or misuse of technique Failure to check equipment Vaporizer and circuit leaks Intravenous infusion errors Accidental administration of muscle relaxant to awake patient Increased anesthetic requirements Variability in anesthetic requirements for intravenous agents Increased anesthetic requirement because of chronic alcohol, opioid, and cocaine abuse Awareness may also be the result of machine malfunction or misuse/ misinterpretation of a technique (Box 1). Machine malfunction and equipment failure are less common now than they used to be. With improved technology (ie, end-tidal gas analysis), unknowingly giving an unintentional diminished dose as a result of an empty vaporizer or tubing leak should never happen. However, even with modern sophisticated equipment, misuse and failure still occur. Sandin and Nordstrom [21] report five cases of awareness with total intravenous anesthesia (TIVA). In that report, examples of a misused technique, misused equipment, and increased drug requirements for the patient were given. TIVA presents a different and difficult problem in this area. There are no end-tidal equivalents such as measuring plasma levels in real time. Even with computerized target-controlled delivery devices, plasma concentrations can vary considerably
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from the set point [28]. In addition, there is significantly more inter-individual pharmacokinetic variability between patients than with volatile agents. However, to date no difference has been shown in awareness incidence between TIVA and inhalational agents. The third cause of awareness is that some patients may have increased anesthetic requirements (Box 1). Many drugs have altered kinetics and potency in patients on different medications. It is entirely possible that some patient populations may have altered responses to general anesthetic and amnestic agents. Chronic use of alcohol, opiates, and cocaine may increase the dose requirements of anesthetic agents [29 –31]. Chronic cocaine exposure increased MAC of isoflurane in sheep by approximately 25% [29]. Chronic ethanol administration also increased MAC in mice by a similar amount [30].
Psychological sequelae of awareness Awareness during anesthesia is a frightening experience. Patients who experience awareness and recall during anesthesia describe auditory perceptions (eg, sounds and conversations in the operating room), the sensation of paralysis, anxiety, panic, helplessness, and powerlessness (Box 2) [32 – 35]. Pain has been reported in up to 40% of patients with awareness during anesthesia [34]. Visual perceptions and feeling the endotracheal tube being placed or feeling the operation without pain are less commonly reported [34]. Patient testimonials describing the sensation of suffocation, being buried alive, overwhelming pain, and inability to escape or signal their distress are particularly chilling. One account from a patient is described below [36]: ‘‘I remember feeling the cold plastic tube being inserted down the back of my throat. I remember trying to cough, talk, open my eyes, and do anything to signal that I was awake. At that point, I began to panic and I could feel my heart racing. I was crying inside, but no one noticed my tears. The sensation and memory were similar to what I have read about people being buried alive.’’
Box 2. Patient perceptions of awareness Most common Sounds and conversation Sensation of paralysis Anxiety and panic Helplessness and powerlessness Pain Least common Visual perceptions Intubation or tube Feeling the operation without pain
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Awareness that one is awake and paralyzed creates an overwhelming sense of anxiety and panic, and the inability to alert the surgical team that he or she is awake leaves the patient feeling helpless. The inability to take action to escape the experience leads to a failure of the normal fight or flight response, preventing active coping and increasing the likelihood of passive coping or dissociation [37]. Nonparalyzed patients are less likely to experience anxiety during an episode of awareness. As many as 70% of patients with intraoperative awareness experience unpleasant aftereffects including sleep disturbances, dreams and nightmares, and flashbacks and anxiety during the day [34,35,37]. Nonparalyzed patients may be less likely to develop aftereffects than paralyzed patients. Sometimes these effects are so severe and persistent that post-traumatic stress disorder (PTSD) develops (Box 3). The primary features of PTSD are defined by three clusters of symptoms: intrusive and distressing thoughts and images recalling the traumatic event, avoidance of stimuli that may prompt memory of the trauma, and increased autonomic arousal and generalized anxiety [38]. In the months and years after the awareness episode, PTSD manifests itself in the form of panic attacks, distressing flashbacks of the event during the day, exaggerated startle response, difficulty concentrating, recurrent nightmares, and insomnia. Patients often feel betrayed by their doctors and nurses, which results in general distrust of medical personnel. This leads to avoidance of physicians and hospitals and of other places and situations that may remind them of the surgery [35].
Box 3. Psychological sequelae of awareness Sleep disturbances Nightmares Anxiety and panic attacks Flashbacks Avoidance of medical care Post-traumatic stress disorder
The predisposing factors for the development of PTSD are unknown, though a number of factors have been associated with the disorder. In the patient with awareness during anesthesia, full recall of the awareness episode, the sensation of pain during awareness, the experience of paralysis, and an underlying psychiatric disorder may increase the risk for PTSD [39]. An abnormal biologic response to trauma and female gender may also play a role. Many people recover from PTSD, with symptoms decreasing over an average period of a few months to a few years. However, 10% to 25% of patients experience chronic PTSD [40]. Early diagnosis and treatment are important in those with PTSD. Untreated, it can lead to comorbid depression, agoraphobia, or
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substance abuse [35,39,40]. It has also been associated with higher rates of hypertension, peptic ulcer, and infectious disease [41]. Consultation or debriefing by the anesthesiologist after an awareness episode has been shown to be effective in preventing prolonged traumatic reaction. The anesthesiologist should listen carefully to the patient’s account and show concern about what the patient has experienced (Box 4). It is essential to provide a reasonable explanation of why the awareness occurred and reassurance that the probability of a re-occurrence in future procedures is slight [39]. Sandin et al [9] found that with repeated discussion and information, nightmares, anxiety, and flashbacks resolved within 3 weeks in 18 patients with intraoperative awareness. Therefore, frequent contact with the patient should be made to monitor psychological sequelae and to provide interpersonal support during the first few weeks after awareness.
Box 4. Management of awareness during anesthesia Patient interview Validate the events Empathize Provide explanation Provide reassurance Maintain contact to monitor psychologic sequelae Refer to psychologist or psychiatrist if symptoms persist
Unfortunately, debriefing by the anesthesiologist does not resolve symptoms in all patients, and referral to a psychologist may be necessary. In addition, many patients do not report their awareness episodes, fearing disbelief on the part of physicians [34,42]. By the time these patients seek treatment, they have most likely been experiencing traumatic stress symptoms for an extended period of time. Many arrive seeking help for a comorbid somatization disorder, such as a gastrointestinal problem, or seeking relief from chronic anxiety, and underlying PTSD is discovered only after many tests and consultations [35]. Treatment for those with PTSD is often challenging and the PTSD may never be resolved completely, but a number of techniques have been shown to be effective in reducing symptoms. Psychotherapy can be beneficial for those who have experienced trauma. It has been suggested that for the greatest impact, cognitive-behavioral therapy should be combined with anxiety management techniques and direct confrontation of the event by the patient [40,41]. Another option is psychopharmacologic intervention. Antidepressants, especially selective serotonin reuptake inhibitors, have been shown to significantly reduce PTSD symptoms of intrusion and avoidance and of depression and anxiety [40]. Other agents, such as benzodiazepines and mood stabilizers, have produced mixed results. Eye movement desensitization and reprocessing allows reprocessing of the traumatic event while enabling the patient to develop a sense of mastery and
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control over the memories [35]. Each of these treatment modalities has been shown to have some effect when used alone, but the greatest improvement occurs when pharmacotherapy is used in conjunction with other types of treatment [41].
Medicolegal consequences of awareness during anesthesia Although awareness under general anesthesia may result in serious emotional injury and post-traumatic stress disorder, for most patients this awareness results in no litigation. However, a few patients file a medical malpractice claim as a result of their injury. Physician –patient communication, severity of the outcome, expected compensation for damages, and sociocultural factors all influence whether a malpractice claim is filed. Because of the implicit bias that emotional injuries are less severe and less documentable than physical injuries, the relatively low payment for an emotional rather than a physical injury may deter plaintiff attorneys from pursuing claims for intraoperative awareness [43].
Medicolegal implications in the United States The medicolegal ramifications of intraoperative awareness in the United States have been recently described by the American Society of Anesthesiologists (ASA) Closed Claims Project [27] and are summarized below. Awareness claims account for 100 of 5480 (1.8%) claims in the ASA Closed Claims Project database, a proportion similar to that for burns, aspiration pneumonia, myocardial infarction, hepatic dysfunction, and renal failure. Compared with all other claims, awareness claims involved more women (78% of awareness claims vs 59% of all other claims), patients younger than 60 (82% for awareness claims vs 74% for all other claims), and patients undergoing elective surgery (82% of awareness claims vs 75% for all other claims). Claims for awareness in the Closed Claims database fall into two categories: awake paralysis, that is, the inadvertent paralysis of an awake patient (22 claims), and recall under general anesthesia, that is, patient recall of events during general anesthesia (78 claims). Claims for recall during anesthesia represent typical cases of awareness during anesthesia. The proportion of claims for awareness in the Closed Claims database has increased since the 1970s, mostly because of an increase in claims for recall under general anesthesia (Fig. 1). The proportion of claims for awake paralysis has remained relatively constant. Most claims for awake paralysis were related to intravenous infusion errors or syringe swaps. The periods of highest risk were in the pre-induction and induction periods, when a muscle relaxant was administered instead of a sedative or hypnotic agent. Reviewers considered most cases of awake paralysis to be examples of substandard anesthesia care, though the paralysis was promptly recognized and appropriately managed. Ninety-six percent of awake paralysis closed claims were judged to represent substandard care by the anesthesiologist,
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Fig. 1. Proportion of claims for awareness in the Closed Claims database in each decade. The proportion of claims for awareness increased in the 1980s and 1990s compared with the 1970s because of an increase in claims for recall under general anesthesia ( P < 0.05).
in contrast to 37% of all other closed claims. One case for which the care by the anesthesiologist was judged to be appropriate involved mislabeling of a syringe in the pharmacy. Payments were made in a greater proportion of awake paralysis claims (76%) than in all other claims (59%), consistent with the judgment of substandard care. However, payments for awake paralysis claims were lower than those for all other claims, with a median payment of only $10,250 (range, $1,000 to $215,000), reflecting the low severity of injury. Claims for recall during general anesthesia were more diverse. Most of the cases of recall originated during the maintenance phase of anesthesia. In contrast to awake paralysis, the anesthesia care in claims for recall during anesthesia was judged to be substandard in 44%, appropriate in 33%, and impossible to judge in the remainder of claims. The standard of care was commonly judged to be appropriate when it occurred during a planned nitrous – narcotic –relaxant technique or if the recall was associated with hypotension requiring discontinuation of anesthetic agents. Recall associated with vaporizer problems, inadequate doses of drugs, and difficult intubation predominantly were judged as substandard care. Interestingly, the classic cues for light anesthesia (hypertension, tachycardia, and patient movement) were absent in most cases. One claim alleged recall despite use of an intraoperative electroencephalograph. Follow-up care was described as adequate in most claims. However, three claim files explicitly described a lack of concern and attention by the anesthesiologist. A lower proportion of recall under general anesthesia claims resulted in payment (56%), compared with awake paralysis claims; however, the amount of payment was similar to awake paralysis claims. The median payment was $20,000 (range, $1,700 to $750,000) compared to a median payment of $105,000 for all other claims (range, $15 to $23,200,000). The lower median payment is consistent with the lower severity of injury and is similar to compensation for awake paralysis, back pain, and emotional distress. Marked
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variability in the range of compensation reflects differences in the geographic distribution, severity of injury, standard of care, and presence of additional injuries (eg, aspiration pneumonia with substandard care). Higher payments have been reported for more severe injuries in which care was substandard. Multiple logistic regression analysis demonstrated that three factors were significantly associated with claims for recall under general anesthesia compared with other general anesthesia claims: no volatile anesthetic agent (odds ratio [OR], 3.20; 95% confidence interval [CI], 1.88-5.46), female gender (OR, 3.08; 95% CI, 1.58-6.06), intraoperative narcotic (OR, 2.12; 95% CI, 1.20-3.74), and intraoperative muscle relaxant (OR, 2.28; 95% CI, 1.22-4.25). Age, ASA status, anesthesia personnel, standard of care, and use of benzodiazepines, barbiturates, and nitrous oxide were not associated with claims for recall during general anesthesia. The association of claims for recall during general anesthesia with anesthetic techniques using opioids, muscle relaxants, and little or no volatile anesthetic is consistent with the known increased incidence of intraoperative awareness with these light anesthetic techniques. However, it is unclear why female gender was associated with a three times higher rate of a recall claim than other claims. This could represent a gender-related increase in propensity for recall during general anesthesia or a greater likelihood to file a claim for recall. Although many reports of intraoperative awareness involve a preponderance of women, this is most likely secondary to light anesthetic techniques, especially for Cesarean section. However, gender-related differences in the requirements for intravenous anesthetics have been reported [44,45]. Women wake up faster from propofol – alfentanil anesthesia [45]. Plasma remifentanil levels, titrated to ensure the lack of a hemodynamic response to a surgical stimulus, were almost twice as high in women as in men [44]. Women may also file claims for emotional injury more often than men. Claims by women in the Closed Claims database involved a lower severity of injury than did claims by men. For instance, the frequency of claims by women for emotional injury was nearly double of that for men (13% vs 7%, respectively). These data suggest that women may be more likely than men to file a claim for recall under general anesthesia. Medicolegal implications in Europe Patterns of litigation related to awareness during anesthesia over the last 20 years have not been the same in the United States and Europe. The incidence of litigation varies widely in European countries. In the United Kingdom, claims related to awareness are more frequent as a proportion of all claims against anesthesiologists than in the United States [46]. Approximately one eighth of legal claims against anesthesiologists in the United Kingdom relate to allegations of awareness during general anesthesia [46]. This may be a result of differences in anesthetic techniques, but it may, alternatively, relate to the fact that low-value claims are more likely to be pursued if the patient is able to obtain all legal costs
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from the state (as in the United Kingdom) than if the risk of litigation is assumed by the plaintiff’s lawyer, whose reimbursement is restricted if the outcome is a low settlement (as in the United States). In contrast, claims for compensation for awareness during general anesthesia have remained low in the rest of Europe. Ranta et al [47] reviewed claims for awareness in Finland during the late 1980s to the early 1990s. In Finland, compensation is paid to a patient for an injury caused by medical treatment, according to the Patient Injury Act. Of 23,363 claims for patient injury, only 391 were for anesthesia-related injuries (1.7% of all malpractice claims), a proportion similar to that in the United States. Only 4 claims were made for awareness under general anesthesia (1% of anesthesia claims). All the patients sustained serious psychological sequelae. They were awarded between 4,000 to 9,600 Finnish marks (approximately $1,000-$2,400). Differences between the experiences in various countries suggest that claims for awareness under anesthesia are markedly influenced by cultural factors.
Future medicolegal implications Malpractice claims for awareness during anesthesia are likely to increase in quantity and amount of payment to the plaintiff in the United States in the future. The trend for an increase in awareness claims in the 1990s may reflect an increase in public knowledge about awareness and intolerance for this type of complication. Recent prominent discussion in the news media and on television is likely to increase litigation. Introduction of a potential monitor for awareness may also increase the risk for litigation and the magnitude of payment.
Prevention of awareness As it is with most complications, the best treatment for awareness is prevention. Most published recommendations are derived from research involving depth of anesthesia, learning, and memory. The major points have been well summarized in other reviews [6,48] but deserve repetition (Box 5).
Box 5. Prevention of awareness Administer amnestic premedicants. Maintain vigilance regarding equipment and monitoring. Minimize use of complete neuromuscular blockade. Supplement nitrous/opiate anesthesia with a potent volatile anesthetic.
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Maintain 0.8 – 1.0 MAC of a potent volatile anesthetic by itself. Administer adequate dose of induction agent. Obtain informed consent for high-risk patients. Mask auditory input. Provide education. Monitor for awareness.
1. Premedication. Amnestic agents (benzodiazepines, scopolamine, and so on) should be a strong consideration, especially if the anesthesiologist anticipates or encounters a patient in whom light anesthesia is required. 2. Vigilance regarding equipment and monitoring. There is no greater charge in our profession than vigilance, and this is especially true when it comes to awareness. Although end-tidal gas concentration monitoring did not impact the incidence of awareness in one study [9], the anesthesiologist may not have adjusted the concentrations of volatile agents to high enough levels to prevent recall. Equipment should be maintained and serviced by appropriate personnel, and the anesthesiologist should check the machine. Attention should be paid to checking and filling the vaporizer. TIVA represents different problems, but again vigilance is the key—maintain an adequate volume in the syringe, ensure the flow of drug into the patient, and use computerized pumps with appropriate volume and pressure alarms. 3. Neuromuscular blockade. Movement is the best indicator we have of light anesthesia or its impedance [6,48]. By abolishing it, muscle relaxants put patients at risk for awareness. We should therefore avoid the ‘‘need’’ to paralyze every patient. As such, neuromuscular blockers should only be used when necessary. In most cases, complete paralysis is not required. Patients can open their eyes with modest, but not total, neuromuscular blockade. Because explicit recall is abolished at lower doses than responsiveness to verbal commands [4,25], assessing and maintaining a lack of responsiveness to the verbal command ‘‘open your eyes’’ may help prevent recall at critical phases of surgery (such as separation from cardiopulmonary bypass). 4. Nitrous/opiate. Nitrous/opiate anesthesia should be supplemented with a potent volatile agent to decrease the high incidence of awareness with this technique (up to 6% in a recent study) [24]. At subanesthetic concentrations, nitrous oxide was shown to suppress memory and learning, though to a lesser extent than isoflurane [49]. Opiates may decrease the amount of volatile agent needed to prevent awareness by providing analgesia, but by themselves they do nothing to prevent learning and memory. In addition, they are unpredictable at producing unconsciousness [26].
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5. Adequate concentration of volatile anesthetic. If potent volatile agents are to be used alone, it has been suggested they be maintained at least at 0.8 to 1.0 MAC [6]. Eger et al [50] found that the patients who expressed fear about remembering their anesthetic had end-tidal values of approximately 0.5 MAC. They suggested that perhaps values of at least 0.75 MAC be maintained to abolish fearful memories, attributed to inadequate anesthesia. In actuality, the optimal doses may never be known because studies that have established MAC awake at 0.3 to 0.6 were conducted on healthy volunteers [4,5]. Surgical stimulus will probably necessitate higher doses to prevent movement and subsequent awareness. Given that it is ethically unacceptable to lower doses purposefully in surgical patients to elucidate these doses, they will probably never be established. 6. Adequate dose of induction agent. If possible, give more than just a ‘‘sleep dose’’ of the intravenous induction agent if it is to be immediately followed by succinylcholine and intubation. If a difficult intubation is encountered, supplemental doses of an induction agent should be given. 7. Discuss the possibility of awareness with patients at high risk. Patients undergoing cardiac surgery or emergency Cesarean section are at high risk for awareness. Although some anesthesiologists believe this only increases anxiety during an already stressful time, it may prevent a lawsuit if awareness occurs, and, more important, it may put the postoperative patient at ease that he or she is not crazy. As a result, the patient may bring attention to it and receive appropriate psychiatric treatment. 8. Mask auditory input. Consider covering ears to mask auditory input. In their interviews with 26 patients who were referred because of intraoperative awareness, Moerman et al [34] found that auditory perception and the sensation of paralysis were most frequently mentioned. Derogatory remarks by staff in the operating room should be strongly discouraged. Unfortunately, patients tend to remember ‘‘shock’’ words such as beached whale, beautiful body, or quotes about the stock market! 9. Education. It is hoped that improved education about awareness will result in more sympathetic responses from medical staff. In his review of 187 patients who reported awareness, Cobcroft [33] found that understanding of awareness and its proper management by medical personnel was poor or totally lacking. Postoperative interviews should include inquiries about awareness. Most (65%) patients fail to inform their anesthesiologist that they had intraoperative recall [34]. This is unfortunate because acknowledgment of what happened and prompt referral to psychological therapy may reduce the likelihood of long-term emotional sequelae [9]. 10. Monitoring specifically for awareness. Anesthetic depth has traditionally been monitored indirectly by assessing movement or changes in hemodynamics. However, movement cannot occur in the paralyzed patient, and signs of autonomic responsiveness (eg, hypertension and tachycardia) often do not occur in patients with intraoperative awareness
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[23,27]. Assessment of responsiveness to verbal commands is not frequently performed. In addition, use of end-tidal gas monitoring also does not prevent awareness [9]. Therefore, a monitor that specifically measures the depth of anesthesia has been advocated. The Bispectral Index Scale (BIS; Aspect Medical Systems, Newton, MA), the first to gain Food and Drug Administration approval as an electroencephalogrambased monitor of anesthetic effect, has been advocated as a potential monitor for awareness [51]. BIS has been shown to be efficacious as an indicator of the level of sedation, the probability of responsiveness to command during anesthesia, and the probability of recall [26,52,53]. Awareness during anesthesia has occurred despite BIS monitoring, though it is mostly associated with high BIS levels (greater than 65). [54] However, its efficacy in actually preventing awareness has not been convincingly demonstrated and is under investigation in Australia. One limitation of the BIS is that thresholds indicated by its values may not be independent of different combinations of anesthetics [55,56]. Vernon et al [56] found that although BIS was a better predictor of patient movement than hemodynamic changes, their findings suggested that different anesthetics have different effects on BIS. Similarly, Lysakowski et al [57] found that although the hypnotic effect of propofol is enhanced by analgesic concentrations of m-agonist opioids, the BIS did not show the increased hypnotic effect. Another method of monitoring depth of anesthesia in commercial development is the auditory evoked potential. Current reports suggest it may be better at determining the point of actual loss of consciousness [58]. Other interesting methods recently reported include techniques using approximate entropy [59] and Shannon entropy [60]. Several arguments favor use of an awareness monitor. Though rare, awareness under anesthesia occurs frequently enough to warrant placing a monitor to prevent it. Clinical methods of detecting awareness (ie, changes in vital signs) are not a reliable means for prevention. Although the original purpose for the BIS monitor was to aid in decreasing the risk for awareness, it is also being touted as a means to reduce the amount of anesthetic given, in turn decreasing recovery times. Those in opposition to BIS argue that it may in fact increase the risk for awareness for two reasons. First, concern has been voiced over the use of everdecreasing amounts of anesthetic agents to speed up recovery time using the BIS as a guide [51]. By doing so, we may dangerously encroach on the line of overly light anesthesia, increasing the risk for awareness, especially with changing surgical stimulus. Second, because BIS values can vary from patient to patient with a particular technique and with different anesthetic techniques, titrating to a predetermined value may leave the occasional patient under-anesthetized. A report of a patient having explicit intraoperative recall at a BIS level of 47 has been published [61]. Given these critiques, the development of a universally acceptable device will have to meet stringent conditions. Drummond [49] suggested that to be a satisfactory awareness monitor, any monitor should have sensitivity and specificity approaching 100%. Because of the extremely low
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incidence of awareness under anesthesia, the device must absolutely separate the two states in question (aware vs unaware). Otherwise, it may result in more events than it prevents. In addition, the critical thresholds between aware and unaware must not vary between patients [49]. In other words, the values that indicate these critical thresholds should not change with different anesthetic agents or disease states. Unfortunately, in contrast to other areas within the field of anesthesia, our understanding of awareness and consciousness has moved along slowly. The terms too deep or too light are still used on a daily basis without an objective value given to them. Devices that attempt to monitor the depth of consciousness have been investigated by many but leave us with more questions than answers. Therefore, no monitor is available that can guarantee that a patient will be unaware during anesthesia. In summary, awareness during general anesthesia is estimated to have an incidence of 0.10% to 0.20%. The most common causes of awareness are light anesthesia, increased anesthetic requirement, or machine malfunction/misuse of technique. Awareness is a frightening experience and may result in post-traumatic stress disorder. Medical malpractice litigation is infrequent but may be increasing. At present, there is no proven monitor for awareness.
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