Artigo: Awareness during anesthesia

Beverley A. Orser MD PhD, C. David Mazer MD, Andrew J. Baker MD

Published at www.cmaj.ca on Dec. 11, 2007.

DOI:10.1503/cmaj.071761

More than 40 million patients receive anesthesia each year in North America. The risks associated with anesthesia have progressively decreased, but the mechanisms of action of anesthetic drugs remain poorly understood. This lack of knowledge has limited the optimum use of drugs that are currently available and has slowed efforts to develop even safer anesthetics. Many complex and lengthy surgical procedures, often performed on medically compromised patients, have been made possible by modern anesthetic techniques. However, anesthetic drugs, like other medications, have limitations, contraindications and adverse effects.

One of the more common concerns expressed by patients who are about to undergo anesthesia is that they will remember intraoperative events¹. For some, this concern will likely be heightened with the Nov. 30, 2007, release of the movie Awake, about a young patient who experiences intraoperative awareness during cardiac surgery (www.awakethemovie.com). Many anesthesiologists are already reporting an increase in the number of patients raising questions about intraoperative awareness, and surgeons and primary care physicians may also soon be faced with such enquiries. In this commentary, we define the nature of the problem of awareness, identify the risk factors, describe strategies to reduce the incidence of intraoperative awareness and point to resources for further information.

Intraoperative awareness is the unexpected and explicit recall by patients of events that occurred during anesthesia. As many as 1 or 2 in every 1000 patients who receive general anesthesia experience this outcome, and the incidence may be even higher among children^2-4. Most patients who remember intraoperative events do not experience pain; rather, they have vague auditory recall or a sense of dreaming and are not distressed by the experience⁵. However, some patients experience pain, which is occasionally severe. In a study involving 11 785 patients who had received general anesthesia, the incidence of awareness was 0.18% in cases in which neuromuscular blockers were used and 0.10% in the absence of such drugs³. Of the 19 patients who experienced recall, 7 (36%) reported some degree of pain, ranging from soreness in the throat because of the endotracheal tube to severe pain at the incision site³.

Patients may remember these events immediately after surgery, or hours or days later³. According to a study by Samuelsson and colleagues, most cases of awareness are inconsequential, but some patients experience prolonged and unwanted outcomes, including post-traumatic stress disorder or depression⁶. Late psychological symptoms, including nightmares, anxiety and flashbacks, occurred in 15 of 46 patients (33%) who experienced awareness. Reports of intraoperative awareness generally apply only to patients who have received general anesthesia, since painless auditory recall by patients receiving regional (e.g., epidural) anesthesia is not surprising. Patients who receive regional anesthesia often receive medication for sedation and anxiolysis but are usually arousable...

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