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

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),

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.

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

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  BIS reading of 100 is fully awake and alert

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.

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

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

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

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.

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.

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.

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

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.

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.

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 that were 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.

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.

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.

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!

Questions?