1. PACU presentation 5/14/08 -S. Zaghi MD
Anesthesia Awareness
PACU presentation
5/14/08
-S. Zaghi MD

2. Definition Definition of Anesthesia:
Anesthesia is a state in which the patient feels no pain. This may range from blocking the sensation of one small part of the body to total unconsciousness.
Definition of Anesthesia Awareness:
"unintended intra-operative awareness" occurs during general anesthesia, when a patient has not had enough general anesthetic or analgesic to prevent consciousness.

3. Definition Anesthesia Components of Anesthesia Unconsciousness Amnesia
+/- Muscle
Relaxation
Analgesia

4. Definition How is Anesthesia “measured”
Classically done by measuring concentrations of inhaled anesthetic agents like: sevoflorane, desflorane.

5. Definition Basic Concept of MAC
Defn: MAC = Miniumum Alveolar Concentration of inhaled agent where at 1MAC, 50% of targets do not move to surgical stimulus.
MAC for Iso:
MAC for Sevo: 2.2
MAC for Des: 6.6

6. Definition 1 1.3 Advanced understanding of MAC MAC values are additive
Addition of N2O oxide
Use of narcotics, benzodiazepines, etc..
MAC values are patient specific
Age
ETOH acute
Hypothermia
Pregnancy
Drugs
Hyponatremia 1
1.3

7. MAC Aware
.3 MAC – concentration at which 50% of patients lose consciousness
Bell Curve – 50% is obviously not enough!
Awareness .3 .7

8. Importance
Patient Experience

9. Importance
Clip of AWAKE

10. Importance No reason to use monitors that are not effective…
Cost: $$ 360 million in BIS probe cost/year

11. Incidence .1 -.2% of all patients undergoing general anesthesia.
21 million patients have GETA,
Calculated 20-40K/yr experience
Even be higher in children
Incidence calculated for patients who received general anesthesia.
regional anesthesia (ie epidural) does not count for awareness

12. Risk Factors Risk Factors .
Routine use of paralytics (double incidence from .1% to .18%)
TIVA
Light anesthesia for sake of turnover
Hemodynamic instability
Procedures: Obstetric / Cardiac / Trauma
Patient Age
H.o of difficult airway
Limited cardiac reserve
H.o of substance abuse (chronic ETOH, anxiolytics, cocaine) .

13. Experiences What is experienced: Audio (48%)
Not being able to breath (48%)
Pain (30%) from the ET tube to severe pain from incision

14. Etiologies
Class 1: pt specific altered increase in expression of anesthetic receptors
Class 2: patient can’t tolerate anesthetic
Class 3: pt. hemodynamics are masked:
Class 4: anesthetic delivery failure

15. Detection Hemodynamic
Typical indicators of physiologic and motor response, such as high blood pressure, heart rate, or movement, lacrimation,
Movement masked by the use of paralytic agents to achieve necessary muscle relaxation.

16. Detection
BIS monitor
Processed EEG from a single frontal electrode, into a numerical unit less value.
Values range from 0 – 100, and represent absence of brain activity to awake state
Usually aim for numbers for surgical anesthesia and aim in decreasing awareness. BIS <40 represent a deep hypnotic state.

17. Outcomes PTSD (30%) “worst experience of my life” vs uncomfortable
Unable to ascertain why some people the experience leads to PTSD others less so.
May remember these events in the PACU, on the floor or even once they are discharged.

18. Treatment Reassurance
Honest discussion with the patient about the risk factors of awareness
Why awareness occurred, and likelihood of reoccurrence.
Pt should inform future anesthesiologist that has had awareness
Some patients should be referred for psychological evaluation and treatment/counseling
ASADatabase of awareness AwarenessDB.org (

19. Prevention
Premedication with versed (amenstic) if anticipate light anesthesia
Ensure patient is asleep prior to intubation (appropriate doses)
Ensure frequent machine checks and fxn
Watch discussions in the OR
When giving beta blockers or antiHTN – worry about masking awareness
Avoid paralysis unless needed.

20. B-UnAware study design
2000 “high risk” patients, randomized to ETAG vs BIS 40-60; both ETAG and BIS values computer recorded at 1sec intervals for later comparison.
Avidan MS, et al. Anesthesia awareness and the Bispectral Index. The New England Journal of Medicine 358, (11), : 2008.

21. B-UnAware “High Risk” Minor Criteria Major Criteria:
long term use of Narcotics/ETOH/cocaine/
EF <40%
h.o Anesthesia awareness, h.o difficult intubation
ASA 4 or 5
Aortic Stenosis/ open heart surgery / ESLung Disease /
Minor Criteria
perioperative use of BBlockers
COPD, BMI >30
tobacco 2packs/day

22. B-UnAware
Questionnaires where reviewed by blinded reviewers for specificity for intraoperative events. If two of three where in agreement but another was not, then a fourth expert was brought into to evaluate.
Then based on events, expert asked to identify when in normal intraoperative course the awareness could have occurred( to hence identify BIS or ETAG concentration]

23. B-Unaware
Results
90% (1754)of enrolled patients completed entire protocol.
4 patients had definite awareness, 2 in the BIS group and 2 in the ETAG group. Overall incidence of .2%
5 patients had possible awareness – often times recalled in only one interview point, often the 3rd most distal interview date. 4 BIS and 1ETAG overall incidence of .6%,
Of the 1754 patients who did not have awareness
55% (964) of them had BIS values that where sustained over 60
75% (1315) of them had ETAG that where over .7

24. B-UnAware Experiences

25. B-UnAware Experience Definite Definite Possible Possible
Notice how the Turquoise line (BIS) consistently in range, but awareness still occurred