Prevention of intraoperative
Awareness in High-Risk Surgical
Population
NEJM August 2011
Intraoperative Awarenss
Plan
Awareness – Defintion
 BIS
 Previous Studies
 Journal Article
 Conclusion & Recommendations

Awareness

Explicit Memory
◦ Active
◦ Intentional or conscious recollection of prior
experiences as assessed by tests

Implicit Memory
◦ Passive
◦ Perception without conscious recall. Patient
denies recall but may remember “something”
under hypnosis

Deliberate
◦ Regional/Local Anaesthesia. Waking of patient
during neurosurgical procedures
Stages of Awareness

Griffith and Jones described 5 stages of
perception during general anaesthesia with
memory of intra-operative events
1.
2.
3.
4.
5.
Conscious perception with explicit memory
Conscious perception without explicit memory
Dreaming
Subconscious perception with implicit memory
No perception and no implicit memory
Modified Brice Questionnaire
Were you expecting to be completely asleep for this operation (please circle)? YES / NO
1. What is the last thing you remember before going to sleep (please tick one
box)?
-Being in the pre-op area
☐
-Seeing the operating room
☐
-Being with family
☐
-Hearing voices
☐
-Feeling mask on face
☐
-Smell of gas
☐
-Burning or stinging in the IV line ☐
-Other [Please write below]:
2. What is the first thing you remember after waking up (please tick one box)?
-Hearing voices
☐
-Feeling breathing tube
☐
-Feeling mask on face
☐
-Feeling pain
☐
-Seeing the operating room
☐
-Being in the recovery room
☐
-Being with family
☐
-Being in ICU
☐
-Nothing
☐
-Other [Please write below]:
Modified Brice Questionnaire
3. Do you remember anything between going to sleep and waking up (please tick
box)?
-No ☐
-Yes: -Hearing voices
☐
-Hearing events of the surgery
☐
-Unable to move or breathe
☐
-Anxiety/stress
☐
-Feeling pain
☐
-Sensation of breathing tube
☐
-Feeling surgery without pain
☐
-Other [Please write below]
4. Did you dream during your procedure (please tick box)?
-No ☐ -Yes ☐
-What about [Please write below]:
5. Were your dreams disturbing to you (please tick box)?
-No ☐ -Yes ☐
6. What was the worst thing about your operation (please tick box)?
-Anxiety
☐
-Pain
☐
-Recovery process
☐
-Unable to carry out usual activities ☐
-Awareness
☐
-Other [Please write below]:
What is BIS?

Google says
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British Interplanetary Society
A Scottish band (Sci-fi Steven and John Disco)
A bank the Nazis used to launder money
Bishops Stortford Train Station
Bispecitral index monitoring
BIS

Frontotemporal EEG
trace

Fed into Algorithm to give
a dimensionless number
0-100

100= “normal” cortical
activity

0 = cortical electrical
silence
BIS

Essentially a group of healthy individuals were
anaesthetised/sedated

Fixed end points were assigned from
consciousness to unconsciousness using
different agents

The EEG changes were analysed and from this
an algorithm created to give a number
Previous Studies

AIM 2004
◦ Assessed incidence
◦ 1-2/1000 in USA

B-AWARE 2004
◦
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2503 high risk for awareness patients
BIS vs no BIS
82% reduction with BIS
2/1225 vs 11/1238
Previous Studies

SAFE-1 Trial 2000/2002
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Incidence of Awareness in Sweden
1.8/1000 with NMB
1/1000 without NMB
18/11,785  explicit recall
9 interviewed 2 years later  4 severely
disabled due to PTSD
Previous Studies

SAFE-2 Trial 2004
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Sweden
BIS vs No BIS
Used historical control
2/4945 vs 14/7826
Reduction of 77%
Prevention of Intraoperative Awareness in a
High-Risk Surgical Population

High-Risk?
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Planned open heart surgery
Aortic Stenosis
Pulmonary Hypertension
Use of Opiates
Use of Benzodiazepines
Use of anticonvulsant drugs
Daily Alcohol consumption
ASA 4
End-stage lung disease
History of intraoperatuve awareness
History of anticipated difficult intubation
Cardiac ejection fraction <40%
Marginal exercise tolerance
Study
USA over 3 sites
 GA with Iso-, Sevo-, Desflurane
 5713 patients
 Anaesthetist presented with envelope
informing of which arm patient
randomised to

◦ Patient, postop interviewer, expert reviewer
and statistician blinded
Procedure

BIS applied to everyone
◦ In non BIS the number was not available to the
anaesthetist but recorded

In BIS arm
◦ Alarm set for >60 & <40

In Non BIS
◦ Alarm set for Age adjusted MAC <0.7 & >1.3

BIS and ETAC electronically recorded at 1
minute intervals
Post op
Interview at 72 hours and 30 days using
Modified Brice Questionnaire
 If some awareness was suspected they
were further contacted and asked
additional questions

Results

Of 5713
◦ 49 reported “memories”
◦ 9 definite intraoperative awarenss 1.6/1000
◦ 27 had definite or possible intraoperative
awareness 4.7/1000


BIS
◦ Definite 7/2861
◦ Possible 12/2861
ETAC
◦ Definite 2/2852
◦ Possible 6/2852
Results
Results

5 out of the 9 who had definite awareness
had BIS values <60 and Age Adjusted
MAC >0.7
Discussion

Results not as expected

Trial does not support superiority of the
BIS over ETAC for prevention of
intraoperative awareness

Suggest not to decrease Anaesthetic agent
upon BIS value alone
Limitations
1.
2.
3.
4.
Limited to High risk patients
Only one EEG derived monitored tested
Compared BIS vs ETAC when
combination may be better
Possible desentisation to protocol due
to multiple false alarms sounds
Further Investigation
NAP 5
 SNAP 1
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