Prevention of intraoperative awareness in a high-risk surgical population

Rachel Brunette RN, BSN, SRNAOakland University-BeaumontGraduate 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), 591-600.

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 40-60 BIS reading of 100 is fully awake and alert

ETACEnd-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 olderUndergoing 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 Design6,100 pre-randomized designations

generated electronically in blocks of 100.

Labels indicated BIS or ETAC and sealed in opaque numbered envelopes.

Informed consent was obtainedAnesthesia 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

PatientsOf an estimated 49,000 patients

screened, 6,041 were enrolled. 25-month period from May 2008-

May 20105,809 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.

Results49 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.

ResultsA 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.

ResultsThe 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?