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EEG In Anesthesia EEG In Anesthesia Steven L. Shafer, M.D. Palo Alto VA Health Care System Associate Professor of Anesthesia Stanford University, Palo Alto, California Control of Anesthetic Depth: Integrating Effect Site Anesthetic Concentrations with Measures of Anesthetic Drug Effect

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EEG In AnesthesiaEEG In Anesthesia

Steven L. Shafer, M.D.Palo Alto VA Health Care SystemAssociate Professor of Anesthesia

Stanford University, Palo Alto, California

Control of Anesthetic Depth:Integrating Effect Site Anesthetic Concentrations

with Measures of Anesthetic Drug Effect

EEG In AnesthesiaEEG In Anesthesia

How do we measure anesthetic depth?Blood pressureHeart rateResponse to noxious stimulation

D blood pressure, D heart rate, and movement

How well do these work?How should we titrate anesthetic drugs?

The ASPECT Data BaseThe ASPECT Data Base

Aspect Medical SystemInventor of the “Bispectral Index”

mysteriously called the “BIS”Validating Bispectral Index as a measure of anesthetic

depthMovement in response to noxious stimulation

- in > 300 patients undergoing surgeryRecall, Sedation, Eyelash reflex

- in >100 volunteers

The ASPECT Data BaseThe ASPECT Data Base

Patient trials (movement):ThiopentalPropofolFentanyl/Alfentanil/SufentanilIsofluraneNitrous Oxide

Volunteer trials (recall, sedation, eyelash):PropofolIsofluraneAlfentanilMidazolam

The ASPECT Data BaseThe ASPECT Data Base

Aspect Investigators:Peter Sebel (Emory)Peter Glass (Duke)Carl Rosow (Harvard/MGH)Lee Kearse (Harvard/MGH)Marc Bloom (University of Pittsburgh)Ira Rampil (University of California, San Francisco)Randy Cork (University of Arizona)Mark Jopling (Ohio State University)N. Ty Smith (University of California, San Diego)Paul White (University of Texas at Dallas)

RecallRecallHeart Rate Heart Rate vsvs Blood Pressure Blood Pressure

RecallRecallBIS BIS vsvs Blood Pressure Blood Pressure

RecallRecallBispectral Index Bispectral Index vsvs Concentration Concentration

01

23

45

Effect Site Concentration

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MovementMovementHeart Rate Heart Rate vsvs Blood Pressure Blood Pressure

MovementMovementDD Heart Rate Heart Rate vsvs DD Blood Pressure Blood Pressure

MovementMovementBispectral Index Bispectral Index vsvs Blood Pressure Blood Pressure

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140 Blood Pressure (MAP)

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MovementMovementBispectral Index Bispectral Index vsvs Concentration Concentration

MovementMovementBlood Pressure Blood Pressure vsvs Concentration Concentration

Eyelash ReflexEyelash ReflexBispectral Index Bispectral Index vsvs Concentration Concentration

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4060

80100

BIS0

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Effect Site Concentration

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SedationSedationBispectral Index Bispectral Index vsvs Concentration Concentration

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BIS0

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Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

Most important predictor of movement is the predicted concentration

The EEG, based on the Bispectral Index, offers additional information about the probability of

sedation/eyelash reflexrecallmovement in response to noxious stimulation

Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

The predicted concentration is available to anesthesiologists using many available software programs

IVA-SIM (J. Schüttler)STANPUMP (S. Shafer)STELPUMP (J. Coetzee/R. Pina)

All of the above are available on the WWW at:http://pkpd.icon.palo-alto.med.va.gov

Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

The predicted concentration is the basis of open-loop infusion devices:

Commercially available:Diprifusor®

For research purposesSTANPUMPSTELPUMPIVA-SIMCACI

Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

Closed-loop controlPK/PD models used to predict concentration

effect-site concentration, based on drug interaction models, is the primary feedback for the system

The Bispectral Index adds information about the probability of sedation/recall/movement

Only to the extent supported by the data and prospective validation

In the mean time……….In the mean time……….

Can use dosage nomograms:designed on same PK/PD concepts

specific measures of anesthetic depthpharmacokinetics of intravenous anestheticsmodels of drug interaction

Dosage NomogramDosage Nomogram

Vuyk, et al: Pharmacodynamic Interaction of Propofol and Alfentanil

Anesthesiology 83:8-22, 1995

Stanski and Shafer: Quantifying Anesthetic Drug Interaction: Implications for Drug Dosing

Anesthesiology 83:1-5, 1995

Propofol/Alfentanil InteractionPropofol/Alfentanil InteractionVuyk et al, Anesthesiology 83:8-22, 1995Vuyk et al, Anesthesiology 83:8-22, 1995

Intubation

0

100

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0 5 10Propofol IC50 (g/ml)

Alfe

ntan

il IC

50 (n

g/m

l)

Maintenance

0

100

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300

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600

0 5 10 15 20Propofol IC50 (g/ml)

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il IC

50 (n

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Emergence

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0 2 4Propofol IC50 (g/ml)

Alfe

ntan

il IC

50 (n

g/m

l)

““Optimal Dosing”Optimal Dosing”Stanski/Shafer, Anesthesiology 83:1-5, 1995Stanski/Shafer, Anesthesiology 83:1-5, 1995

Time (Minutes)0 120 240 360 480 600

Rec

over

y Pe

rcen

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0255075

100

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ntan

il (n

g/m

l)

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ofol

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ml)

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Maintenance concentrationConcentration on emergence

Maintenance concentrationConcentration on emergence

Propofol (g/kg/min)

Alfentanil (ng/kg/min)

Propofol percent decrement for emergence

Alfentanil percent decrement for emergence

A

B

C

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Dosing Nomogram for TIVA Dosing Nomogram for TIVA

Minutes since beginning of infusion

Infu

sion

rate

s to

mai

ntai

n st

able

pla

sma

conc

entra

tions

0

1

2

3

4

5

( g/kg/hr)Fe

ntan

yl (n

g/m

l)

0.91.21.51.82.12.42.73.0

3.64.56.0

0

100

200

300

400

500

600

( g/kg/min)

Alfe

ntan

il (n

g/m

l)

3.0 2.5 2.25 2.0 1.75

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1.25

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1.0( g/kg/hr)

Suf

enta

nil (

ng/m

l)

0.150.3

0.50.60.70.80.91.0

1.2

1.52.0

0 60 120 180 240 3000

2

4

6

8

( g/kg/min)

Pro

pofo

l ( g

/ml)

255075100120140160180200

250300

Suggested Initial Target

Dosing Nomogram for TIVADosing Nomogram for TIVA

Minutes since beginning of infusion

Infu

sion

rate

s to

mai

ntai

n st

able

pla

sma

conc

entra

tions

0

1

2

3

4

5 ( g/kg/hr)

Fent

anyl

(ng/

ml)

0.91.21.51.82.12.42.73.0

3.64.56.0

0

100

200

300

400

500

600 ( g/kg/min)

Alfe

ntan

il (n

g/m

l)3.0 2.5 2.25 2.0 1.75

1.5

1.25

1.0

0.75

0.25

0.5

0.0

0.2

0.4

0.6

0.8

1.0 ( g/kg/hr)

Suf

enta

nil (

ng/m

l)

0.150.3

0.50.60.70.80.91.0

1.2

1.52.0

0 60 120 180 240 3000

2

4

6

8 ( g/kg/min)

Pro

pofo

l ( g/

ml)

255075100120140160180200

250300

Suggested Initial Target

Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

Conclusions1. Heart rate and blood pressure are poor

predictors of anesthetic depth.2. The best predictor of the probability of

movement, recall, level of sedation, andeyelash reflex is predicted effect siteconcentration.

Requires a model of drug interaction

Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

Conclusions3. The Bispectral Index adds information as a

predictor of:Sedation/eyelash reflexrecallmovement in response to noxious stimulation

4. Nomograms and the Bispectral Analysisare presently available

Application of PK/PD in Support of Application of PK/PD in Support of Total Intravenous AnesthesiaTotal Intravenous Anesthesia

Conclusion5. Open loop systems will be available soon:

Diprifusor®Research Systems

6. Closed-loop systems have been developedfor research purposes:

EEG-Based (Schwilden/Schüttler)Auditory evoked potentials (Kenny)