BiSpectral Index monitoring _BiS_ by malj

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									   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:
   –   Definition
   –   Brief history
   –   Incidence
   –   Causes
   –   Associations
   –   Stages
• Prevention:
   – Detecting Awareness
   – Preventing Awareness
• Consequences of intra-op awareness
   –   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:
  –   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
•   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)
•   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…

•   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

•   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
•   Awake, a 2007 film about anaesthetic
    awareness


•   Anaesthesia, an award-winning
    horror film about anaesthesia awareness


•   Return, a Korean thriller movie about
    anaesthesia awareness


•   In an episode of Nip/Tuck a woman
    experiences anaesthesia awareness
    while having surgery to repair scarring
    on her face.


•   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!

								
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