1. Awareness During Anesthesia
Do You Remember…?
2018/11/15
Liu, Chih-Min

2. 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: , 1998
Anethesiology 2000; 92:
BIS Monitoring to Prevent Awareness during General Anesthesia
Anethesiology 2001; 94:520-2
Awareness detected by auditory evoked potential monitoring
BJA 91 (2): (2003)
2018/11/15
Liu, Chih-Min

3. 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
2018/11/15
Liu, Chih-Min

4. Definitions Consciousness Awareness
‘The state of being conscious; awareness of one’s own existence, sensation, thoughts, surroundings, etc’
Awareness
‘Having knowledge, conscious, cognizant’
2018/11/15
Liu, Chih-Min

5. 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%
2018/11/15
Liu, Chih-Min

6. 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
2018/11/15
Liu, Chih-Min

7. After-effects of Awareness During General Anesthesia
Mental after-effects
Muscle relaxation
Pain
Fear of dying
Medico-legal after-effects
2018/11/15
Liu, Chih-Min

8. 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”
2018/11/15
Liu, Chih-Min

9. Then…there were Sleep disturbances Repetitive nightmares
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)!
2018/11/15
Liu, Chih-Min

10. 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
2018/11/15
Liu, Chih-Min

11. Causes of Awareness Light anesthesia
Nitrous/opioid/relaxant anesthesia    
Myocardial depression
Hypovolemia    
Cesarean section    
Difficult intubation    
Premature discontinuation of anesthetic   
2018/11/15
Liu, Chih-Min

12. 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   
2018/11/15
Liu, Chih-Min

13. Causes of Awareness Increased anesthetic requirements
Variability in anesthetic requirements for intravenous agents    
Increased anesthetic requirement because of chronic alcohol, opioid, and cocaine abuse
2018/11/15
Liu, Chih-Min

14. Causes of Awareness
2018/11/15
Liu, Chih-Min

15. 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.
2018/11/15
Liu, Chih-Min

16. 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?
2018/11/15
Liu, Chih-Min

17. Methods of Monitoring Consciousness During General Anesthesia
Clinical signs
Sympathetic activities: HR, BP, sweating, pupillary dilatation, lacrimation …
Unreliable
Isolated forearm technique
EEG
BIS
AEP
2018/11/15
Liu, Chih-Min

18. 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
2018/11/15
Liu, Chih-Min

19. Prevention and Management of Awareness
2018/11/15
Liu, Chih-Min

20. 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
2018/11/15
Liu, Chih-Min

21. 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.
2018/11/15
Liu, Chih-Min

22. 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
2018/11/15
Liu, Chih-Min

23. Thanks for your attention!
2018/11/15
Liu, Chih-Min