CHAPTER 29 Awareness During Anesthesia
The current classifications of memory include both implicit, or unconscious memory, and explicit, or conscious memory. Explicit memory refers to the conscious recollection of specific intraoperative events that took place during general anesthesia, also called anesthetic awareness. Recall can only be determined after surgery. These memories can occur with or without pain and can range from vivid recollections to vague memories. It was reported in 2008 that subjective auditory perceptions represented 50% of intraoperative awareness experiences. By contrast, implicit memory reflects changes in behavior or performance secondary to an anesthetic experience without the ability to specifically recall the event. The 2006 American Society of Anesthesiologists’ (ASA) practice advisory regarding intraoperative awareness excludes dreaming as anesthetic awareness.
Estimates of awareness during anesthesia in nonobstetric and noncardiac surgeries are approximately 0.1% to 0.2%. Whenever lighter anesthesia is provided, the incidence increases. During cardiac surgery the incidence ranges from 1.1% to 1.5%. A higher incidence is also seen in obstetric (0.4%) and trauma cases (11% to 43%). Interestingly, although the use of anesthetic techniques associated with increased awareness (e.g., nitrous-narcotic) has decreased, the claims against anesthesiologists for awareness are increasing, recently accounting for 2% of all claims. This claim rate rivals other common complications such as aspiration pneumonia and myocardial infarction.