Anesthesia AwarenessAnesthesia Awareness

PACU presentationPACU presentation

5/14/085/14/08

-S. Zaghi MD-S. Zaghi MD

DefinitionDefinition

Definition of Anesthesia:Definition of Anesthesia: Anesthesia is a state in which the patient feels no Anesthesia is a state in which the patient feels no

pain. This may range from blocking the sensation of pain. This may range from blocking the sensation of one small part of the body to total unconsciousness.one small part of the body to total unconsciousness.

Definition of Anesthesia Awareness:Definition of Anesthesia Awareness: "unintended intra-operative awareness" occurs "unintended intra-operative awareness" occurs

during general anesthesia, when a patient has not during general anesthesia, when a patient has not had enough general anesthetic or analgesic to had enough general anesthetic or analgesic to prevent consciousness.prevent consciousness.

DefinitionDefinition

Components of AnesthesiaComponents of Anesthesia

Amnesia

Analgesia

Unconsciousness

Anesthesia+/- Muscle Relaxation

DefinitionDefinition

How is Anesthesia “measured”How is Anesthesia “measured”Classically done by measuring concentrations of Classically done by measuring concentrations of

inhaled anesthetic agents like: sevoflorane, inhaled anesthetic agents like: sevoflorane, desflorane.desflorane.

DefinitionDefinition

Basic Concept of MACBasic Concept of MACDefn: MAC = Miniumum Alveolar Concentration of Defn: MAC = Miniumum Alveolar Concentration of

inhaled agent where at 1MAC, 50% of targets do inhaled agent where at 1MAC, 50% of targets do not move to surgical stimulus.not move to surgical stimulus.

MAC for Iso: 1.1MAC for Iso: 1.1MAC for Sevo: 2.2MAC for Sevo: 2.2MAC for Des: 6.6MAC for Des: 6.6

DefinitionDefinition

Advanced understanding of MACAdvanced understanding of MACMAC values are additiveMAC values are additive

Addition of N2O oxideAddition of N2O oxide Use of narcotics, benzodiazepines, etc..Use of narcotics, benzodiazepines, etc..

MAC values are patient specificMAC values are patient specific AgeAge ETOH acuteETOH acute HypothermiaHypothermia PregnancyPregnancy DrugsDrugs HyponatremiaHyponatremia 1 1.3

MAC AwareMAC Aware.3 MAC – concentration at which 50% of patients .3 MAC – concentration at which 50% of patients

lose consciousnesslose consciousness

Bell Curve – 50% is obviously not enough!Bell Curve – 50% is obviously not enough!

.3 .7

Awareness

ImportanceImportance

Patient ExperiencePatient Experience

ImportanceImportance

Clip of AWAKEClip of AWAKE

ImportanceImportance

No reason to use monitors that are not No reason to use monitors that are not effective…effective…

Cost:Cost:$$ 360 million in BIS probe cost/year$$ 360 million in BIS probe cost/year

IncidenceIncidence

.1 -.2% of all patients undergoing general .1 -.2% of all patients undergoing general anesthesia.anesthesia.

21 million patients have GETA, 21 million patients have GETA, Calculated 20-40K/yr experienceCalculated 20-40K/yr experience

Even be higher in childrenEven be higher in children Incidence calculated for patients who received Incidence calculated for patients who received

general anesthesia. general anesthesia. regional anesthesia regional anesthesia (ie epidural)(ie epidural) does not count for awareness does not count for awareness

Risk FactorsRisk Factors Risk Factors Risk Factors

Routine use of paralytics Routine use of paralytics (double incidence from .1% to .18%)(double incidence from .1% to .18%)

TIVATIVA Light anesthesia for sake of turnoverLight anesthesia for sake of turnover Hemodynamic instabilityHemodynamic instability Procedures: Obstetric / Cardiac / TraumaProcedures: Obstetric / Cardiac / Trauma Patient AgePatient Age H.o of difficult airwayH.o of difficult airway Limited cardiac reserveLimited cardiac reserve H.o of substance abuse H.o of substance abuse (chronic ETOH, anxiolytics, cocaine)(chronic ETOH, anxiolytics, cocaine)

..

ExperiencesExperiences

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

from incisionfrom incision

EtiologiesEtiologies

Class 1Class 1: pt specific altered increase in : pt specific altered increase in expression of anesthetic expression of anesthetic

receptors receptors

Class 2Class 2: patient can’t tolerate anesthetic: patient can’t tolerate anesthetic

Class 3Class 3: pt. hemodynamics are masked: : pt. hemodynamics are masked:

Class 4Class 4: anesthetic delivery failure: anesthetic delivery failure

DetectionDetection

HemodynamicHemodynamic Typical indicators of physiologic and motor Typical indicators of physiologic and motor

response, such as response, such as high blood pressure, heart high blood pressure, heart rate, or movement, lacrimation, rate, or movement, lacrimation,

Movement masked by the use of paralytic agents Movement masked by the use of paralytic agents to achieve necessary muscle relaxation.to achieve necessary muscle relaxation.

DetectionDetection

BIS monitorBIS monitor Processed EEG from a single frontal electrode, Processed EEG from a single frontal electrode,

into a numerical unit less value. into a numerical unit less value. Values range from 0 – 100, and represent Values range from 0 – 100, and represent

absence of brain activity to awake state absence of brain activity to awake state Usually aim for numbers 40- 60 for surgical anesthesia Usually aim for numbers 40- 60 for surgical anesthesia

and aim in decreasing awareness. BIS <40 represent a and aim in decreasing awareness. BIS <40 represent a deep hypnotic state.deep hypnotic state.

OutcomesOutcomes

PTSD (30%)PTSD (30%) ““worst experience of my life” vs worst experience of my life” vs

uncomfortable uncomfortable Unable to ascertain why some people the experience Unable to ascertain why some people the experience

leads to PTSD others less so.leads to PTSD others less so.

May remember these events in the PACU, May remember these events in the PACU, on the floor or even once they are on the floor or even once they are discharged.discharged.

TreatmentTreatment

ReassuranceReassurance Honest discussion with the patient about the risk Honest discussion with the patient about the risk

factors of awarenessfactors of awareness Why awareness occurred, and likelihood of reoccurrence.Why awareness occurred, and likelihood of reoccurrence. Pt should inform future anesthesiologist that has had Pt should inform future anesthesiologist that has had

awarenessawareness

Some patients should be referred for psychological Some patients should be referred for psychological evaluation and treatment/counselingevaluation and treatment/counseling

ASADatabase of awareness AwarenessDB.org ASADatabase of awareness AwarenessDB.org (http://depts.washington.edu/awaredb/)(http://depts.washington.edu/awaredb/)

PreventionPrevention

Premedication with versed Premedication with versed (amenstic)(amenstic) if if anticipate light anesthesiaanticipate light anesthesia

Ensure patient is asleep prior to intubation Ensure patient is asleep prior to intubation (appropriate doses)(appropriate doses)

Ensure frequent machine checks and fxnEnsure frequent machine checks and fxn Watch discussions in the ORWatch discussions in the OR When giving beta blockers or antiHTN – When giving beta blockers or antiHTN –

worry about masking awarenessworry about masking awareness Avoid paralysis unless needed.Avoid paralysis unless needed.

B-UnAwareB-UnAware

study designstudy design 2000 “high risk” patients, randomized to ETAG vs BIS 2000 “high risk” patients, randomized to ETAG vs BIS

40-60; both ETAG and BIS values computer recorded 40-60; both ETAG and BIS values computer recorded at 1sec intervals for later comparison. at 1sec intervals for later comparison.

Avidan MS, et al. Anesthesia awareness and the Bispectral Index. The New England Journal of Medicine 358, (11), 1097-1108: 2008.

B-UnAwareB-UnAware

““High Risk”High Risk” Major Criteria: Major Criteria:

long term use of Narcotics/ETOH/cocaine/long term use of Narcotics/ETOH/cocaine/ EF <40%EF <40% h.o Anesthesia awareness, h.o difficult intubationh.o Anesthesia awareness, h.o difficult intubation ASA 4 or 5ASA 4 or 5 Aortic Stenosis/ open heart surgery / ESLung Aortic Stenosis/ open heart surgery / ESLung

Disease / Disease /

Minor CriteriaMinor Criteria perioperative use of BBlockersperioperative use of BBlockers COPD, BMI >30COPD, BMI >30 tobacco 2packs/daytobacco 2packs/day

B-UnAwareB-UnAware Questionnaires where reviewed by blinded reviewers Questionnaires where reviewed by blinded reviewers

for specificity for intraoperative events. If two of three for specificity for intraoperative events. If two of three where in agreement but another was not, then a fourth where in agreement but another was not, then a fourth expert was brought into to evaluate.expert was brought into to evaluate. Then based on events, expert asked to identify Then based on events, expert asked to identify

when in normal intraoperative course the when in normal intraoperative course the awareness could have occurred( to hence identify awareness could have occurred( to hence identify BIS or ETAG concentration]BIS or ETAG concentration]

B-UnawareB-UnawareResultsResults

90% (1754)of enrolled patients completed entire 90% (1754)of enrolled patients completed entire protocol.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 5 patients had possible awareness – often times recalled in only one interview point, often the 3rd recalled in only one interview point, often the 3rd most distal interview date. 4 BIS and 1ETAG most distal interview date. 4 BIS and 1ETAG overall incidence of .6%, overall incidence of .6%,

Of the 1754 patients who did not have awarenessOf the 1754 patients who did not have awareness 55% (964) of them had BIS values that where 55% (964) of them had BIS values that where

sustained over 60sustained over 60 75% (1315) of them had ETAG that where over .775% (1315) of them had ETAG that where over .7

B-UnAware ExperiencesB-UnAware Experiences

B-UnAware ExperienceB-UnAware Experience

Definite

Definite

Possible

Possible

Notice how the Turquoise line (BIS) consistently in range, but awareness still occurred