Chapter 42 Awareness Under Anesthesia
Incidence
1. What is the difference between explicit and implicit memory?
2. Can the incidence of intraoperative awareness be reliably determined in the recovery room? By self-reporting?
3. What are the components of the “structured interview” as used to evaluate the occurrence of intraoperative awareness?
4. When studied prospectively, and when using a structured interview, what is the approximate incidence of intraoperative awareness?
Prevention of awareness
10. What are some conventional monitors used to assess anesthetic depth?
11. What are some limitations of brain function monitors for assessing anesthetic depth and the risk for intraoperative awareness?
12. What measures can be taken to help prevent intraoperative awareness?
13. What are the elements that the Joint Commission recommends to prevent and manage intraoperative awareness?
The ASA’s practice advisory on intraoperative awareness and brain function monitors
15. According to the Practice Advisory from the American Society of Anesthesiologists (ASA) on Intraoperative Awareness and Brain Function Monitoring, what should the preoperative evaluation include to minimize the risk of intraoperative awareness?
16. According to the Practice Advisory from the ASA on Intraoperative Awareness and Brain Function Monitoring, what should the preinduction phase include to minimize the risk of intraoperative awareness?
17. According to the Practice Advisory from the ASA on Intraoperative Awareness and Brain Function Monitoring, what should intraoperative monitoring include to minimize the risk of intraoperative awareness?
18. According to the Practice Advisory from the ASA on Intraoperative Awareness and Brain Function Monitoring, what should intraoperative and postoperative management include to minimize the risk of intraoperative awareness and associated sequelae?
Answers*
Incidence
1. Explicit memory, or conscious memory, refers to the recollection of previous experiences and is equivalent to remembering (intraoperative awareness). Implicit memory, or unconscious memory, is the ability of a patient to respond to commands, yet lack conscious recall of intraoperative events. (737)
2. The incidence of intraoperative awareness is best estimated by formally interviewing patients postoperatively, well after discharge from the postanesthesia recovery room. Patients will not reliably, or voluntarily, report awareness if they were not disturbed by it, or if embarrassed to do so. A structured interview is recommended to evaluate the incidence of awareness. (738)
3. The structured interview consists of the following components: (738)
4. The best estimate for the incidence of intraoperative awareness is 1 to 2 occurences/1000 patients undergoing a general anesthetic. (738)
Eitology and risk factors for intraoperative awareness
5. The three major causes of intraoperative awareness include light anesthesia, increased patient requirements for anesthesia, and anesthetic delivery problems. (738)
6. Risk factors for intraoperative awareness include hemodynamic intolerance of anesthetic drugs; patients that are hypovolemic; patients with limited cardiovascular reserve; ASA Physical Statue 3–5; emergency surgery; administration of small doses of volatile anesthetics; a nitrous oxide or intravenous- based anesthetic; chronic use of alcohol, opioids, amphetamines, or cocaine; genetic resistance to anesthetics; and equipment problems. (738)
7. Cesarean delivery and open heart procedures are associated with an increased risk of intraoperative awareness. (738)
Psychological sequelae
8. Approximately one third of patients who have an episode of intraoperative awareness have late psychological sequelae. (739)
9. Potential psychological sequelae of intraoperative awareness include flashbacks, anxiety/nervousness, loneliness, nightmares, and fear/panic attacks that vary from bothersome to distressing. Some patients develop severe, persistent symptoms (posttraumatic stress disorder) that profoundly interfere with interpersonal relationships and daily activities. (739)
Prevention of awareness
10. Conventional monitors of anesthetic depth include patient movement, tachycardia, hypertension, tearing, perspiration, and clinical instinct. One could also include anesthetic gas analyzers, which assess the dose of volatile anesthetic delivered to the patient. (739)
11. Limitations of brain function monitors include: (1) there is not a unitary mechanism of general anesthesia, and thus various anesthetics are likely to produce unique electrical activity at a given anesthetic depth. Consequently, a unique algorithm to each specific anesthetic regimen would likely be required for optimal correlation between electrical signals in the brain and anesthetic depth; (2) general anesthesia occurs on a continuum without a quantitative dimension, and there is considerable interpatient pharmacodynamic variability to a specific anesthetic. Attempting to translate a conscious or unconscious state into a quantitative number can at best be limited to the art of probability with an expectation of false positive and false negative data; and (3) there is less than an optimal likelihood of cortical electric activity having reliable sensitivity and specificity to a biochemical event which occurs at a distant subcortical structure. (739, 740, Figure 46-1, Figure 46-2)
12. Suggestions for the prevention of intraoperative awareness include premedication with an amnesic drug such as a benzodiazepine, giving adequate doses of drugs to induce anesthesia, avoiding muscle paralysis unless necessary, and administering a volatile anesthetic at a dose of 0.7 MAC or more with monitoring of end-tidal levels to ensure delivery of adequate levels of a volatile anesthetic. (740)
13. The Joint Commission’s recommendations to prevent and manage intraoperative awareness include development and implementation of an anesthesia awareness policy, staff education, informed consent for high-risk patients, timely maintenance of anesthesia equipment, postoperative follow-up of all patients who have undergone general anesthesia, and postoperative counseling for patients with awareness. (740)
Brain function monitoring
14. The results of trials which evaluated the effect of brain function monitoring on the incidence of intraoperative awareness are mixed. The best evidence is derived from four sources: a randomized controlled trial in high-risk patients for which the incidence of awareness was reduced by 82% in patients monitored with a brain function monitor; a nonrandomized cohort comparison with historical control subjects for which the incidence of awareness was reduced by 77% in patients monitored with a brain function monitor; a prospective nonrandomized study for which there was no reported effect of a brain function monitor on the incidence of awareness; and a randomized trial that compared the bispectral index (BIS) to end-tidal gas monitoring and reported no difference in the incidence of definite awareness between the two groups. (740, 741)
The ASA’s practice advisory on intraoperative awareness and brain function monitors
15. According to the ASA’s Practice Advisory on Intraoperative Awareness and Brain Function Monitoring, the preoperative evaluation for preventing intraoperative awareness should include the identification of potential risk factors for intraoperative awareness, an interview of the patient and review of past medical records, and obtaining informed consent for those patients at high risk for intraoperative awareness. (741, Table 46-2)
16. According to the ASA’s Practice Advisory on Intraoperative Awareness and Brain Function Monitoring, the preinduction phase of anesthesia should include the use of a checklist for machine/equipment function, verification of function of intravenous access and infusion equipment, and consideration of a preoperative benzodiazepine for the patient. (741, Table 46-2)
17. According to the ASA’s Practice Advisory on Intraoperative Awareness and Brain Function Monitoring, intraoperative monitoring should include multiple modalities to monitor the depth of anesthesia (clinical, conventional monitors, and brain function monitoring on a case-by-case basis). (741, Table 46-2)
18. According to the ASA’s Practice Advisory on Intraoperative Awareness and Brain Function Monitoring, intraoperative and postoperative management should include consideration of a benzodiazepine if the patient unexpectedly becomes conscious, a postoperative visit, consideration of a structured interview to determine the patient’s anesthetic experience, an occurrence report to continuous quality improvement, and offering the patient psychological counseling. (741, Table 46-2)
Medicolegal sequelae of awareness
19. The large disparity between the incidence of awareness and actual malpractice claims is multifactorial and includes the nature and severity of the injuries associated with awareness, as well as the medicolegal and injury compensation system. (742)
20. Factors influencing a patient’s decision to initiate a malpractice claim are poor communication between the patient and physician, unmet expectations, and financial pressure on the patient. One study reported that 50% of potential plaintiffs had a poor relationship with their physician. (742)
Data from the ASA closed claims project
21. Claims for intraoperative awareness represent a small fraction (2%) of all malpractice claims in the Closed Claims database. (742)
22. Factors associated with a malpractice claim for intraoperative awareness in the Closed Claim database include female gender, ASA physical class 1 and 2, less than 60 years of age, elective surgery, and obesity. (742)
23. The two main causes of intraoperative awareness in the Closed Claims database were light anesthesia and anesthetic delivery problems. (743, Table 46-3)
