Prevention of intraoperative awareness in a high-risk surgical population

1. Prevention of intraoperative awareness in a high-risk surgical population Rachel Brunette RN, BSN, SRNA Oakland University-Beaumont Graduate Program of Nurse Anesthesia

2. Avidan, MS; Burnside, BA; Glick, D:Jacobsohn, E; Zhang, L. (2011) Prevention of Intraoperative Awareness in a High Risk Surgical Population. The New England Journal of Medicine 365(7), 591-600.

3. Anesthesia awareness • Awareness during anesthesia occurs in 20,000–40,000 patients out of the 20 million US surgeries performed each year (between 0.1% and 0.2%) • Defined as the experience and explicit recall of sensory perceptions during surgery. May lead to PTSD.

4. About the trial • Published in the New England Journal of Medicine Aug 18, 2011 • The study was randomized, evaluator blinded on 6,041 patients at three major medical centers. • Univeristy of Chicago, Washington University in St. Louis, University of Manitoba

5. BIS MONITORING • Provides depth of consciousness and sedation monitoring • Uses multiple EEG signal processing • Single number represents actual number of cerebral electrical activity • Low probability of Recall/Memory 40-60 • BIS reading of 100 is fully awake and alert

6. ETAC • End-tidal anesthetic-agent concentration for the prevention of awareness • An audible alarm was set to indicate when the ETAC fell below 0.7 or exceeded 1.3 age-adjusted MAC • If alarm settings were unavailable for ETAC, alarms were set for inspired anesthetic agents.

7. WHY? • Simple protocol based interventions can decrease perioperative complications. • If BIS monitor is effective then technology can be used to clinically benefit patients and prevent intraoperative awareness

8. Who? • Patients 18 yo or older • Undergoing elective surgery with the use of Isoflurane, Sevoflurane, or Desflurane. • High Risk for intraoperative awareness (See table 1) • Drug tolerance, fat distribution, age, obesity • Pts with dementia, unable to provide written consent, or history of CVA with residual neurological deficits excluded

9. Study Design • 6,100 pre-randomized designations generated electronically in blocks of 100. • Labels indicated BIS or ETAC and sealed in opaque numbered envelopes. • Informed consent was obtained • Anesthesia providers were aware of patients’ group assignments but the patients, postoperative interviewers, expert reviewers, and statistician were not

10. Procedure • BIS sensor was applied to forehead of each patient • ETAC group had monitors configured to conceal the BIS number. • Anesthesia practitioners in both groups were able to view the ETAC • Sign was placed on the anesthesia machines reminding practitioners to check the BIS or ETAC value. • Practitioners could decrease anesthetic administration at their discretion if a patient’s condition was hemodynamically unstable • Results recorded on Metavision electronically with a minimum of every one minute.

11. Questionnaire • Intraoperative awareness was assessed by a modified Brice questionnaire. (designed to evaluate intraop awareness under anesthesia) • Evaluated within 72 hours after surgery and at 30 days post extubation • If patients reported memories from “going to sleep” to “waking up” they were contacted by a different evaluator. • Referred to a psychologist • Three experts independently reviewed the responses and determined if the patient had definite awareness, possible awareness, or no awareness.

12. Hypothesis • Null hypothesis=BIS protocol is not superior to the ETAC protocol in preventing intraoperative awareness • Alternative hypothesis= BIS protocol is superior in preventing intraoperative awareness.

13. Methods • Chi-square test- compares observed data we would expect to obtain according to specific hypothesis • Fishers exact test-used to determine if there are non-random associations between two categorical variables. • Unpaired Mann-Whitney U test- (rank sum test) Nonparametric test that compares two unpaired groups • Unpaired student’s t-test-Used to compare two small sets of quantitative data when samples are collected independent or one another. • Modified intention-to-treat analysis was performed • P-values <0.05 were considered to indicate statistical significance

14. Patients • Of an estimated 49,000 patients screened, 6,041 were enrolled. • 25-month period from May 2008-May 2010 • 5,809 patients were included in the trial of whom 5713 (98.3%) completed at least one postoperative interview and were included in the primary outcome analysis.

15. Results • 49 patients reported memories of the period between “going to sleep” and “waking up” at the end of surgery. • Experts determined that 9 patients had definite intraoperative awareness and 27 patients had definite or possible awareness. • There were fewer cases of awareness in the ETAC group than BIS group.

16. Results • A total of 7 or 2,861 patients (0.24%) in the BIS group compared with 2 of 2,852 (0.07%) in the ETAC group thatwere interviewed postoperatively had definite awareness. • Superiority of the BIS protocol was not demonstrated • 19 cases of definite or possible intraoperative awareness (o.66%) occurred in the BIS group, as compared with 8 (o.28%) in the ETAC group.

17. Results • The patients who experienced awareness or possible awareness did not have either a BIS>60 or ETAC values less than 0.7 age-adjusted MAC. • No major differences in doses of sedative, hypnotic, opioid analgesic, or neuromuscular blocking drugs administered between the two groups.

18. Limitations • ETAC protocol was evaluated against only one of many EEG monitors. • Practitioners may become desensitized to audible alerts. • Some patients were not interviewed due to not awakening and passed away before the initial interview. • Unidentified risk factors such as genetic resistance to anesthetic agents could have been unequally distributed between the two groups.

19. Summary • Anesthesia awareness is not extremely common but a very serious complication of surgery • Graphs on the study were difficult to view on this study • Only tested one monitor • VIGALENCE IS KEY!

20. Questions?