Transcript BiSpectral Index monitoring (BiS)

Preventing and Managing the impact
of Awareness during Anaesthesia
Dr. Subbiah Chelliah MBBS, DA (UK), FRCA (UK), DESA (Sweden)
Consultant Anaesthesiologist,
Kovai Medical Centre & Hospitals, Coimbatore
Awareness during Anaesthesia
• Awareness:
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Definition
Brief history
Incidence
Causes
Associations
Stages
• Prevention:
– Detecting Awareness
– Preventing Awareness
• Consequences of intra-op awareness
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PTSD
Public awareness
Dealing with patients who complain of awareness during anaesthesia
Medico legal aspects
Definition
• Awareness is the conscious experiencing of an
event at the time that it occurs. (Guerra 1986)
• Recall denotes the retention of an event in
memory after it has occurred. (Guerra 1986)
1895
• Horace Wells attempted to demonstrate
N2O to physicians at MGH, Boston
• Patient moved & cried out!
• Surgeons considered the demonstration a
failure
• Patient had no recall of his operation
1896
• W.T.G. Morton demonstrated the use of
Ether in the same venue
• Patient did not move
• Surgeons considered it a ground breaking
success!
• Morton’s patient Gilbert Abbot, reported
that he had been aware during his surgery,
while experiencing no pain
1943
• Muscle relaxants came into clinical use
• Anaesthetists started giving lesser
amount of anaesthetic agents
Levinson study (1965)
• 10 pts undergoing dental extraction with ether; shortly after
induction, the anaesthetist called to the surgeon ‘STOP THE
OPERATION, I don’t like the patient’s color. His/her lips are
turning too blue. I am going to give a little oxygen!’
• One month later, probed for assimilation of crisis by hypnosis
• 4/10 patients were able to quote verbatin the words spoken by
the anaesthetist; 4 more showed evidence of having registered
the event, in the form of emotional distress
Levinson study
• Obvious methodological flaws: no controls,
non-randomisation, absence of double blind
study, asking leading questions
• Thirty years later, Levinson repeated this
study but failed to replicate his original
findings!
General Anaesthesia is not an all or
nothing phenomenon!
Incidence of Awareness
Reported incidence of awareness varies and is
difficult to determine
• Swedish study: 0.06%
• American academic centres: 0.13%
• Overall incidence: ~0.2%
• Conscious awareness with pain: 1 in 20,000 –
40,000 anaesthetics
Incidence of Awareness
• Cardiac surgery: 1 – 1.5%
• Trauma surgery: 11 – 43%
• Cesarian section: 0.4%
Causes
• Lack of complete
understanding of kinetics
& dynamics of drugs
• Induction of anaesthesia:
– Coughing
– difficult intubation
Causes / Associations
Patient factors:
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Limited cardiac reserve (ASA IV & V)
On going blood loss / hypotension
Patients on beta blockers, Calcium channel blockers
Drug / alcohol abusers / addicts
Patients on regular opiates /sedative medications
Associations
• Opioid based anaesthesia / Neuroleptanaesthesia
• Regional anaesthesia & ‘Light’ GA
• Muscle relaxants
• Disconnection / empty vaporiser
• Caesarian section, Trauma, Cardiac bypass
Stages of Awareness
Stage 1: Conscious awareness with explicit memory
Stage 2: Conscious awareness without explicit memory
Stage 3: Subconscious awareness with implicit memory
Stage 4: No awareness
Awareness with explicit memory
• Nearly always associated with neuromuscular
blocking drug use
• May or may not be associated with pain
• ‘State of awful helplessness’
• Patients can go on to develop severe unexplained
psychiatric disorder
Awareness without explicit memory
• Tunstall: 9/12 pts showed arm movements during
procedure (IFT) 4/9 appropriately – none recalled
• Russell: 61% were able to move arm to command
(given thio/dtc/nitous/oxygen) – none recalled
• Changes in BP, pulse, sweating & tears were
shown to be poor indicators of awareness
Awareness without explicit memory
• 80% of patients induced with Midazolam &
fentanyl and 70% induced with Midazolam &
Alfentanil showed hand movement
• While breathing low doses of Isoflurane (<0.4%
ET) subjects were able to comprehend and
respond to words
Subconscious awareness with
implicit memory
• Increasing anaesthetic concentration leads to
reduction in working memory, then loss of
conciousness and explicit memory, whereas
implicit memory of intraop events may
remain!!
• Indirect tests of memory must be used to
demonstrate evidence of implicit memory &
learning
Subconscious awareness with
implicit memory
• Category generation, free association, stem
completion tests are used
• Conflicting study results
• Positive suggestions intraop: stop smoking,
faster recovery
Preventing Awareness
• ‘High’ risk patients / situations
• Detecting / Monitoring anaesthetic depth
intraop
• Drugs
• Avoiding certain anaesthetic techniques
• Patient information
Detection of Awareness
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Clinical signs
Clinical experience
IFT
Lower oesophageal contractility
Frontalis EMG
Respiratory sinus arrhythmia
EEG
– Raw EEG
– Processed EEG
• BiS
• AEP
PRST Score
Isolated Forearm Technique (IFT)
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First used by Tunstall
Isolate forearm with BP cuff before giving NMB
Patients asked to squeeze hand for ‘Yes’
Limitations: time; surgery on the hand
• Even when patients responded, rarely did they
have any memory of this after the operation
Monitoring Awareness…
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Clinical experience
Lower oesophageal contractility
Frontalis EMG
Heart rate variability (Respiratory sinus
arrhythmia)
EEG
BiS (BiSpectral index monitoring)
• Complex EEG parameter under development by
Aspect Medical systems since 1985 using
clinical data from 1500 anaesthetic regimes and
500hrs of EEG signals gathered under
anaesthetics
• Approved by the FDA in 1996
• Several hundred publications to date
BiS
• Direct measure of the effects of anaesthetics
on the brain
• BIS monitoring allows anaesthesia
providers to administer the appropriate
amount of drug that each patient needs
The Bispectral IndexTM (BiS)
Aspect Medical Systems
Auditory Evoked Potential
The early cortical AEP waves called Pa and Nb, which occurs between 20 and 80 ms reflects the activity in the
temporal lobe/primary auditory cortex
( the site of sound registration)
Changes in the latency of these waves ( in particular the Nb wave) are highly correlated with a transition from
awake to loss of consciousness
Mid-latency AEP
AEP
• Limitations: hearing impaired; head & neck
surgery
Other processed EEG monitors
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Narcotrend Index
Cerebral state index (CSI)
Entropy
Snap index
Preventing Awareness
Preventing Awareness
Dealing with patients who have a history
of Awareness during Anaesthesia
• Take patient seriously
• Investigate previous anaesthetic technique &
circumstances
• Comorbidity / medications
• Reassure
• Sedative premed
• Intraop ET agent monitoring / BiS
• Postop visit
• Good Periop records
Consequences of unintended
awareness during Anaesthesia
• Fear of Anaesthesia
• Post Traumatic Stress disorder
• Flashbacks, Anxiety, sustained emotional effects
• Anger / litigation
• Paranoia / loss of confidence / financial loss Anaesthesiologist
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Awake, a 2007 film about anaesthetic
awareness
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Anaesthesia, an award-winning
horror film about anaesthesia awareness
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Return, a Korean thriller movie about
anaesthesia awareness
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In an episode of Nip/Tuck a woman
experiences anaesthesia awareness
while having surgery to repair scarring
on her face.
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Wide Awake, a Korean horror/thriller
movie was mainly about the outcomes
mentally after anaesthesia awareness.
Patient associations / support groups
Dealing with patient who complaints
of Awareness during Anaesthesia
• Don’t trivialise the problem – take patient’s
complaint seriously
• Visit patient as soon as possible, along with
a witness
• Detailed history – modified Brice interview
Modified Brice Interview
1. What is the last thing you remember before surgery?
2. What is the first thing you remember after surgery?
3. Do you remember anything happening during surgery?
4. Did you have any dreams during surgery?
5. What is the worst thing about your surgery?
Dealing with patient who complaints of
Awareness during Anaesthesia
• Document patient’s exact memory
• Attempt to confirm validity of account
• Patient anaesthetic records / theatre
circumstances
• Try to determine cause
• Reassure / offer explanation / document
• Keep a copy of records
• Offer psychological support
• Notify medical defence / hospital admin / patient’s GP
Medico legal aspects
(American closed claims database: 1971 - 2001)
• Small fraction of patients initiate
legal action
• Most of them are women (>70%)
• Cases of intraop awareness with
explicit recall are difficult to defend
• Awards to patients for awareness
with recall range from $1000 $800,000
"Awareness with
analgesia is regrettable;
awareness with pain is
unforgivable"
Thank you!