anesthesiology information

112/04/08112/04/08 Liu, Chih-Min Liu, Chih-Min 11

Awareness Awareness During AnesthesiaDuring Anesthesia

Do You Remember…?Do You Remember…?


References References Awareness during anesthesiaAwareness during anesthesia

• Anesthesiology Clinics of North AmericaAnesthesiology Clinics of North America Volume 20 • Number 3 • September 2002 Volume 20 • Number 3 • September 2002 Awareness with recall during general anesthesia – InciAwareness with recall during general anesthesia – Inci

dence and risk factorsdence and risk factors• Anesth AnalgAnesth Analg 86: 1084-1089, 1998 86: 1084-1089, 1998

Awareness during anesthesiaAwareness during anesthesia• AnethesiologyAnethesiology 2000; 92: 597-602 2000; 92: 597-602

BIS Monitoring to Prevent Awareness during General ABIS Monitoring to Prevent Awareness during General Anesthesianesthesia• AnethesiologyAnethesiology 2001; 94:520-2 2001; 94:520-2

Awareness detected by auditory evoked potential moAwareness detected by auditory evoked potential monitoringnitoring• BJABJA 91 (2): 209-2 (2003) 91 (2): 209-2 (2003)


Before talking about it…Before talking about it…

Did you ever forget anything…?Did you ever forget anything…?• Patients are concerned that they would Patients are concerned that they would

not be asleep during their surgery not be asleep during their surgery ( more then 50%) ( more then 50%)

• For anesthesiologists, awareness under For anesthesiologists, awareness under anesthesia ranks second only to death anesthesia ranks second only to death as a “dreaded” complication as a “dreaded” complication


DefinitionsDefinitions

ConsciousnessConsciousness• ‘‘The state of being conscious; The state of being conscious;

awareness of one’s own existence, awareness of one’s own existence, sensation, thoughts, surroundings, etc’sensation, thoughts, surroundings, etc’

AwarenessAwareness• ‘‘Having knowledge, conscious, Having knowledge, conscious,

cognizant’ cognizant’


Incidence of awareness during Incidence of awareness during anesthesiaanesthesia

General surgeryGeneral surgery• 1960: 1.2%1960: 1.2%• 2000: 0.11% to 0.16%2000: 0.11% to 0.16%

Cardiac surgeryCardiac surgery• 1977: 5.8%1977: 5.8%• 1998: 0.3%1998: 0.3%

Other types of surgeryOther types of surgery• Major traumaMajor trauma

High from 11% up to 43% High from 11% up to 43% • Obstetric surgery (C/S)Obstetric surgery (C/S)

1968: 11.8%1968: 11.8% 1991: 0.9%1991: 0.9%


Patient perceptions of awareness Patient perceptions of awareness

Most common Most common • Sounds and conversation – 89% to 100% Sounds and conversation – 89% to 100% • Sensation of paralysis - 85% Sensation of paralysis - 85% • Anxiety and panic Anxiety and panic • Helplessness and powerlessness Helplessness and powerlessness • Pain - 39% Pain - 39%

Least common Least common • Visual perceptions Visual perceptions • Intubation or tube Intubation or tube • Feeling the operation without painFeeling the operation without pain


After-effects of Awareness During After-effects of Awareness During General AnesthesiaGeneral Anesthesia

Mental after-effectsMental after-effects• Muscle relaxationMuscle relaxation• PainPain• Fear of dyingFear of dying

Medico-legal after-effectsMedico-legal after-effects


Mental after-effectsMental after-effects

37% of patients were responded with…37% of patients were responded with…• DisbeliefDisbelief• IgnoranceIgnorance• Anger Anger

14% of patients were told…14% of patients were told…• ““just a bad dream”just a bad dream”• ““all in your imagination”all in your imagination”• ““were med or hallucinating”were med or hallucinating”• ““had a seventh sense”had a seventh sense”


Then…there wereThen…there were Sleep disturbances Sleep disturbances

• fear when falling asleep fear when falling asleep Repetitive nightmares Repetitive nightmares

• 52.4% 52.4% Anxiety and panic attacks Anxiety and panic attacks

• 55% 55% Depression Depression Flashbacks Flashbacks Avoidance of medical care Avoidance of medical care Preoccupation of deathPreoccupation of death Post-traumatic stress disorder (PTSD) Post-traumatic stress disorder (PTSD)

• 14.3% to 22% 14.3% to 22% • From months (20m) to years (17y)!From months (20m) to years (17y)!


Medico-legal after-effectsMedico-legal after-effects

Very large compensations…Very large compensations…• USD 1,000 to 600,000USD 1,000 to 600,000

Risk factorsRisk factors• No volatile agents usedNo volatile agents used• FemaleFemale• Obstetric or gynecology procedureObstetric or gynecology procedure• Opioid only Opioid only • Muscle relaxantMuscle relaxant


Causes of AwarenessCauses of Awareness

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



Machine malfunction or misuse of techniMachine malfunction or misuse of technique que • Failure to check equipment Failure to check equipment • Vaporizer and circuit leaks Vaporizer and circuit leaks • Intravenous infusion errors Intravenous infusion errors • Accidental administration of muscle relaxanAccidental administration of muscle relaxan

t to awake patient t to awake patient



Increased anesthetic requirements Increased anesthetic requirements • Variability in anesthetic requirements for intVariability in anesthetic requirements for int

ravenous agents ravenous agents • Increased anesthetic requirement because Increased anesthetic requirement because

of chronic alcohol, opioid, and cocaine abusof chronic alcohol, opioid, and cocaine abusee


Prevention of awareness Prevention of awareness 1.1. Administer amnestic premedicants. Administer amnestic premedicants. 2.2. Maintain vigilance regarding equipment and monitoriMaintain vigilance regarding equipment and monitori

ng. ng. 3.3. Minimize use of complete neuromuscular blockade. Minimize use of complete neuromuscular blockade. 4.4. Supplement nitrous/opiate anesthesia with a potent Supplement nitrous/opiate anesthesia with a potent

volatile anesthetic. volatile anesthetic. 5.5. Maintain 0.8–1.0 MAC of a potent volatile anesthetic bMaintain 0.8–1.0 MAC of a potent volatile anesthetic b

y itself. y itself. 6.6. Administer adequate dose of induction agent. Administer adequate dose of induction agent. 7.7. Obtain informed consent for high-risk patients. Obtain informed consent for high-risk patients. 8.8. Mask auditory input. Mask auditory input. 9.9. Provide education. Provide education. 10.10. Monitor for awareness.Monitor for awareness.


Methods of detecting awarenessMethods of detecting awareness

Postoperative interviewPostoperative interview• Structured Structured • Best Best

Questions asked during interviewsQuestions asked during interviews1.1. What is the last thing you remember before going to What is the last thing you remember before going to

sleep for the operation?sleep for the operation?

2.2. What is the first thing you remember after waking after What is the first thing you remember after waking after the operation?the operation?

3.3. Do you remember anything in between?Do you remember anything in between?

4.4. Did you have any dreams?Did you have any dreams?

5.5. What is the most unpleasant thing you remember from What is the most unpleasant thing you remember from your operation and anesthesia?your operation and anesthesia?


Methods of Monitoring Consciousness Methods of Monitoring Consciousness During General AnesthesiaDuring General Anesthesia

Clinical signsClinical signs• Sympathetic activities: HR, BP, sweating, puSympathetic activities: HR, BP, sweating, pu

pillary dilatation, lacrimation … pillary dilatation, lacrimation … • Unreliable Unreliable

Isolated forearm techniqueIsolated forearm technique EEGEEG

• BISBIS• AEPAEP


Awareness detected by auditory Awareness detected by auditory evoked potential monitoringevoked potential monitoring

BJA 91 (2): 209-2 (2003)BJA 91 (2): 209-2 (2003)

Case reportCase report Accidental interruption of drug Accidental interruption of drug

delivery is a common cause of delivery is a common cause of awareness during general anesthesiaawareness during general anesthesia

A rapid change of AEP was noted A rapid change of AEP was noted when infusion of anesthetics was when infusion of anesthetics was stoppedstopped


Prevention and Management of AwarenessPrevention and Management of Awareness


Conclusions Conclusions

1.1. Incidence in general anesthesia: 0.1-Incidence in general anesthesia: 0.1-0.2% 0.2%

2.2. Incidence in cardiac surgery: 0.3%Incidence in cardiac surgery: 0.3%3.3. Lower dose of anesthetics are associated Lower dose of anesthetics are associated

with higher incidence of intra-op with higher incidence of intra-op awareness; insufficient concentrationawareness; insufficient concentration

4.4. Standard physiologic monitoring is not Standard physiologic monitoring is not reliable, such as AEP or BIS; however, reliable, such as AEP or BIS; however, clinical signs are much more unreliableclinical signs are much more unreliable

5.5. Psychiatric after-effect of awareness Psychiatric after-effect of awareness range from no effect to PTSDrange from no effect to PTSD


Conclusions Conclusions

6.6. There is no evidence that any kind of premedication woulThere is no evidence that any kind of premedication would affect the incidence of awareness d affect the incidence of awareness

7.7. If prolonged laryngoscopy is required, one should not forIf prolonged laryngoscopy is required, one should not forget to add the induction agents or inhalation agentget to add the induction agents or inhalation agent

8.8. In critical hemodynamic situation, BZD instead of general In critical hemodynamic situation, BZD instead of general anesthetics may be acceptableanesthetics may be acceptable

9.9. NMBs should be used as sparingly as possibleNMBs should be used as sparingly as possible10.10. If the patient has a history of awareness under anesthesiIf the patient has a history of awareness under anesthesi

a, it would be wise to use monitora, it would be wise to use monitor11.11. If the patient has suffered from awareness, psychiatric coIf the patient has suffered from awareness, psychiatric co

nsultation and follow-up is recommended.nsultation and follow-up is recommended.


Discussion Discussion Structured post-operative interviewsStructured post-operative interviews

• Best methodBest method• howeverhowever

Large number of patientsLarge number of patients Very sick patients: difficult to interviewVery sick patients: difficult to interview

Feedback information to the anesthesiologistsFeedback information to the anesthesiologists• EducationEducation

Incidence from 4% to 1.5% in one studyIncidence from 4% to 1.5% in one study• Changes in drugs dosageChanges in drugs dosage

Increase in volatile agents, I.V. anesthetic agentsIncrease in volatile agents, I.V. anesthetic agents Decrease in muscle relaxantDecrease in muscle relaxant

BZD?BZD?• Have effect on memory but are not likely to be Have effect on memory but are not likely to be

anesthetic anesthetic


Thanks for your attention! Thanks for your attention!