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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

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preventing and managing the impact of awareness during anaesthesia

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 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
  • 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)

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


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


Muscle relaxants came into clinical use

Anaesthetists started giving lesser amount of anaesthetic agents

levinson study 1965
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
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!

incidence of awareness
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 awareness1
Incidence of Awareness

Cardiac surgery: 1 – 1.5%

Trauma surgery: 11 – 43%

Cesarian section: 0.4%

  • Lack of complete understanding of kinetics & dynamics of drugs
  • Induction of anaesthesia:
    • Coughing
    • difficult intubation
causes associations
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
  • Opioid based anaesthesia / Neuroleptanaesthesia
  • Regional anaesthesia & ‘Light’ GA
  • Muscle relaxants
  • Disconnection / empty vaporiser
  • Caesarian section, Trauma, Cardiac bypass
stages of awareness
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
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
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 memory1
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
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 memory1
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
Preventing Awareness

‘High’ risk patients / situations

Detecting / Monitoring anaesthetic depth intraop


Avoiding certain anaesthetic techniques

Patient information

detection of awareness
Detection of Awareness
  • Clinical signs
  • Clinical experience
  • IFT
  • Lower oesophageal contractility
  • Frontalis EMG
  • Respiratory sinus arrhythmia
  • EEG
    • Raw EEG
    • Processed EEG
      • BiS
      • AEP
isolated forearm technique ift
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
Monitoring Awareness…

Clinical experience

Lower oesophageal contractility

Frontalis EMG

Heart rate variability (Respiratory sinus arrhythmia)

bis bispectral index monitoring
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
  • 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 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


Limitations: hearing impaired; head & neck surgery

other processed eeg monitors
Other processed EEG monitors

Narcotrend Index

Cerebral state index (CSI)


Snap index

dealing with patients who have a history of awareness during anaesthesia
Dealing with patients who have a history of Awareness during Anaesthesia

Take patient seriously

Investigate previous anaesthetic technique & circumstances

Comorbidity / medications


Sedative premed

Intraop ET agent monitoring / BiS

Postop visit

Good Periop records

consequences of unintended awareness during anaesthesia
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.
dealing with patient who complaints of awareness during anaesthesia
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
Modified Brice Interview

What is the last thing you remember before surgery?

What is the first thing you remember after surgery?

Do you remember anything happening during surgery?

Did you have any dreams during surgery?

What is the worst thing about your surgery?

dealing with patient who complaints of awareness during anaesthesia1
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
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