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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
Dr. Subbiah Chelliah MBBS, DA (UK), FRCA (UK), DESA (Sweden)
Kovai Medical Centre & Hospitals, Coimbatore
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
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
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!
Reported incidence of awareness varies and is difficult to determine
Cardiac surgery: 1 – 1.5%
Trauma surgery: 11 – 43%
Cesarian section: 0.4%
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
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
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
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
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
Category generation, free association, stem completion tests are used
Conflicting study results
Positive suggestions intraop: stop smoking, faster recovery
‘High’ risk patients / situations
Detecting / Monitoring anaesthetic depth intraop
Avoiding certain anaesthetic techniques
Lower oesophageal contractility
Heart rate variability (Respiratory sinus arrhythmia)
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
Cerebral state index (CSI)
Take patient seriously
Investigate previous anaesthetic technique & circumstances
Comorbidity / medications
Intraop ET agent monitoring / BiS
Good Periop records
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
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?
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