Anesthesiology Information

Awareness During Anesthesia Do You Remember…?

References
Awareness during anesthesia
Anesthesiology Clinics of North America Volume 20 • Number 3 • September 2002
Awareness with recall during general anesthesia – Incidence and risk factors
Anesth Analg 86: 1084-1089, 1998
Awareness during anesthesia
Anethesiology 2000; 92: 597-602
BIS Monitoring to Prevent Awareness during General Anesthesia
Anethesiology 2001; 94:520-2
Awareness detected by auditory evoked potential monitoring
BJA 91 (2): 209-2 (2003)

Before talking about it…
Did you ever forget anything…?
Patients are concerned that they would not be asleep during their surgery ( more then 50%)
For anesthesiologists, awareness under anesthesia ranks second only to death as a “dreaded” complication

Definitions
Consciousness
‘The state of being conscious; awareness of one’s own existence, sensation, thoughts, surroundings, etc’
Awareness
‘Having knowledge, conscious, cognizant’

Incidence of awareness during anesthesia
General surgery
1960: 1.2%
2000: 0.11% to 0.16%
Cardiac surgery
1977: 5.8%
1998: 0.3%
Other types of surgery
Major trauma
High from 11% up to 43%
Obstetric surgery (C/S)
1968: 11.8%
1991: 0.9%

Patient perceptions of awareness
Most common
Sounds and conversation – 89% to 100%
Sensation of paralysis - 85%
Anxiety and panic
Helplessness and powerlessness
Pain - 39%
Least common
Visual perceptions
Intubation or tube
Feeling the operation without pain

After-effects of Awareness During General Anesthesia
Mental after-effects
Muscle relaxation
Pain
Fear of dying
Medico-legal after-effects

Mental after-effects
37% of patients were responded with…
Disbelief
Ignorance
Anger
14% of patients were told…
“ just a bad dream”
“ all in your imagination”
“ were med or hallucinating”
“ had a seventh sense”

Then…there were
Sleep disturbances
fear when falling asleep
Repetitive nightmares
52.4%
Anxiety and panic attacks
55%
Depression
Flashbacks
Avoidance of medical care
Preoccupation of death
Post-traumatic stress disorder (PTSD)
14.3% to 22%
From months (20m) to years (17y)!

Medico-legal after-effects
Very large compensations…
USD 1,000 to 600,000
Risk factors
No volatile agents used
Female
Obstetric or gynecology procedure
Opioid only
Muscle relaxant

Causes of Awareness
Light anesthesia
Nitrous/opioid/relaxant anesthesia
Myocardial depression
Hypovolemia
Cesarean section
Difficult intubation
Premature discontinuation of anesthetic

Causes of Awareness
Machine malfunction or misuse of technique
Failure to check equipment
Vaporizer and circuit leaks
Intravenous infusion errors
Accidental administration of muscle relaxant to awake patient

Causes of Awareness
Increased anesthetic requirements
Variability in anesthetic requirements for intravenous agents
Increased anesthetic requirement because of chronic alcohol, opioid, and cocaine abuse

Causes of Awareness

Prevention of awareness
Administer amnestic premedicants.
Maintain vigilance regarding equipment and monitoring.
Minimize use of complete neuromuscular blockade.
Supplement nitrous/opiate anesthesia with a potent volatile anesthetic.
Maintain 0.8–1.0 MAC of a potent volatile anesthetic by itself.
Administer adequate dose of induction agent.
Obtain informed consent for high-risk patients.
Mask auditory input.
Provide education.
Monitor for awareness.

Methods of detecting awareness
Postoperative interview
Structured
Best
Questions asked during interviews
What is the last thing you remember before going to sleep for the operation?
What is the first thing you remember after waking after the operation?
Do you remember anything in between?
Did you have any dreams?
What is the most unpleasant thing you remember from your operation and anesthesia?

Methods of Monitoring Consciousness During General Anesthesia
Clinical signs
Sympathetic activities: HR, BP, sweating, pupillary dilatation, lacrimation …
Unreliable
Isolated forearm technique
EEG
BIS
AEP

Awareness detected by auditory evoked potential monitoring BJA 91 (2): 209-2 (2003)
Case report
Accidental interruption of drug delivery is a common cause of awareness during general anesthesia
A rapid change of AEP was noted when infusion of anesthetics was stopped

Prevention and Management of Awareness

Conclusions
Incidence in general anesthesia: 0.1-0.2%
Incidence in cardiac surgery: 0.3%
Lower dose of anesthetics are associated with higher incidence of intra-op awareness; insufficient concentration
Standard physiologic monitoring is not reliable, such as AEP or BIS; however, clinical signs are much more unreliable
Psychiatric after-effect of awareness range from no effect to PTSD

Conclusions
There is no evidence that any kind of premedication would affect the incidence of awareness
If prolonged laryngoscopy is required, one should not forget to add the induction agents or inhalation agent
In critical hemodynamic situation, BZD instead of general anesthetics may be acceptable
NMBs should be used as sparingly as possible
If the patient has a history of awareness under anesthesia, it would be wise to use monitor
If the patient has suffered from awareness, psychiatric consultation and follow-up is recommended.

Discussion
Structured post-operative interviews
Best method
however
Large number of patients
Very sick patients: difficult to interview
Feedback information to the anesthesiologists
Education
Incidence from 4% to 1.5% in one study
Changes in drugs dosage
Increase in volatile agents, I.V. anesthetic agents
Decrease in muscle relaxant
BZD?
Have effect on memory but are not likely to be anesthetic

Thanks for your attention!

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Anesthesiology Information

by MedicineAndHealth on Feb 04, 2009

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