Awareness during Anesthesia

MEMORY is not a single entity. Current classification distinguishes between two types: explicit, or conscious memory, and implicit, or unconscious memory. Explicit memory refers to the conscious recollection of previous experiences. Implicit memory, by contrast, refers to changes in performance or behavior that are produced by previous experiences but without any conscious recollection of those experiences. 1Explicit memory is equivalent to “remembering” (e. g. , can you remember what you did last Tuesday evening? ). In the case of an anesthetized patient, one might ask the patient in the postoperative period “can you remember hearing any words or sounds during your operation? ” (i. e. , a recall test) or “which of the following words were played to you during surgery? ” (a recognition test). As an example of implicit memory, consider the following scenario. Patients were exposed during anesthesia to a list of words containing the word “pension. ” Postoperatively, when they were presented with the three-letter word stem “PEN___” and were asked to supply the first word that came to their minds beginning with those letters, they gave the word “pension” more often than “pencil” or “peninsula” or others. The term “awareness” will be used to describe explicit memory during anesthesia. The incidence of awareness during anesthesia and surgery is best estimated by formally interviewing patients postoperatively. Patients, particularly those who were not unduly disturbed by their experiences, may not voluntarily report them without being asked directly. 2Some patients also may not recall events shortly after surgery but may recall them 1–2 weeks after surgery. 3It is also possible that some patients may need a detailed and extensive interview to “jog” their memories for the intraoperative experience. 4When a structured interview was used in a large series of patients, the incidence of awareness in nonobstetric and noncardiac surgical cases was 0. 2%. 2The incidence is greater, however, when light anesthesia is used: the incidence in cardiac surgery ranges from 1. 1–1. 5%. A higher incidence also has been reported for obstetric cases (0. 4%) and major trauma cases (11–43%), and this incidence varies according to the dose of anesthetic administered. 5The incidence of intraoperative recall is 2% when 70% nitrous oxide (N2O) alone is used for anesthetic maintenance. 6This incidence is not reduced by intermittent boluses of opioids. 4Nevertheless, Jones 7estimates that only 0. 01% of patients report pain while being aware. It is probable that opioids, together with N2O, provide sufficient analgesia to decrease complaints from pain. Some or all of the quoted estimates about the incidence of awareness may need to be updated. Patients also may recall dreams, some of which are disturbing. Dreams may be recalled more often than actual events. For example, in Utting’s 6series of 500 patients anesthetized with N2O, the incidence of dreams that the patients considered to be the worst features of their perioperative experiences was 7%versus 2% for recall of intraoperative events. Utting 6proposed a continuum, with adequate anesthesia resulting in complete amnesia, lighter anesthesia resulting in dream recall, and still lighter anesthesia resulting in explicit recall. Awareness usually is associated with one of three situations (fig. 1): The pain was like that of a tooth drilled without local anesthetic—when the drill hits a nerve. Multiply this pain so that the area involved would equal a thumb-print, then pour a steady stream of molten lead into it. This quotation is from a physician describing her almost unbearable pain when she was aware during a cesarean section. 11There is no doubt that pain during surgery is the most distressing feature of awareness. Other frequent complaints are the ability to hear events during surgery, sensations of weakness or paralysis, and feelings of helplessness, anxiety, panic, and impending death. The patients also may be tormented, if they were in an obtunded state, by doubts about whether what they experienced really happened or whether there is something wrong with their minds 12 (fig. 1). For some patients, awareness may cause temporary after effects, including sleep disturbances, nightmares, and daytime anxiety, which subside eventually. Nevertheless, there may remain a fear that awareness may happen again if they require anesthesia in the future. In some patients, post-traumatic stress disorder develops, marked by repetitive nightmares, anxiety, and irritability; a preoccupation with death; and a concern with sanity that make the patients reluctant to discuss their symptoms. 12It is not apparent why post-traumatic stress disorder develops in some patients and not in others. Patient personality, predisposition to mental disease, emotional response to illness, and reason for surgery may be factors. There are also medicolegal consequences to awareness. Domino et al. 13recently analyzed claims from the American Society of Anesthesiologists Closed Claims Project. Claims for awareness during anesthesia accounted for 2% of all claims. This incidence was similar to rates of claims for such familiar complications after anesthesia as aspiration pneumonia and myocardial infarction. Claims were more likely in females and with the nitrous oxide–opioid–relaxant technique. The amount of compensation was small, a median of 18, 000. Payments for awareness claims also show interesting variability from one country to another. Although sizable payments have been reported in the United Kingdom, low payments have been reported in Finland. Social, cultural, or other factors may be important. If a patient complains of awareness, a detailed account of the experience should be obtained (table 1). Although there have been cases of fraudulent claims and mistaken recall of events during emergence from anesthesia, 14most claims are genuine and credibility can be established easily. The patient should be assured that the anesthesiologist believes their account and sympathizes with their suffering. Denial of the authenticity of the patient’s experience may adversely influence the patient’s psychologic recovery and may turn the patient toward litigation. Some explanation of what happened and its reasons should be given;e. g. , necessity to administer light anesthesia in the presence of significant cardiovascular instability. The patient should be reassured about nonrepetition of the same mishap with future anesthetics because the details will be in the patient’s records and will guide the anesthesiologist managing subsequent anesthetics. An apology should be given, and it is possible to apologize without admitting liability. The patient should be offered psychologic or psychiatric support. The details of the interview should be recorded in the patient’s chart, and the surgeon, the patient’s nurse, and the hospital lawyer or the physician’s insurer should be notified. Subsequently, the patient should be visited daily during the hospital stay to look for and treat psychologic sequelae;e. g. , sleep disturbances, daytime anxiety, among others. After the patient is discharged, frequent contacts by telephone should be made until the patient is judged to be fully recovered. Referral to a psychiatrist or psychologist should not be delayed; there is anecdotal evidence that early counseling may reduce the incidence of post-traumatic stress disorder. 15Prevention of recall of events during anesthesia should be feasible in most cases. The following methods should be effective (table 1): The waking of patients during anesthetic administration is an uncommon complication, though alarming to patients and anesthesiologists alike. When we consider that approximately 20 million general anesthetics are administered each year in the United States, the incidence of one case in 500 anesthetics corresponds to 40, 000 cases of awareness annually. Awareness appears to be a dose-related phenomenon, and the risk is greatest when muscle relaxants are used. Its most-feared consequence is post-traumatic stress disorder. Management of a case of awareness should be precise, detailed, and documented, but compassionate. Measures to prevent awareness include avoidance of “overly” light anesthesia, gaining more knowledge about anesthetic requirements of patients, and development of methods to detect consciousness during anesthesia.