Gas Man® Understanding Inhalation Kinetics

Through Computer Simulation

© Copyright 1980 - 2005, James H Philip, all rights reserved

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Gas Man® Understanding Inhalation Kinetics

Through Computer SimulationJames H. Philip, M.E.(E.), M.D.

Anesthesiologist andDirector of Anesthesia Technology,

Brigham and Women's HospitalAssociate Professor of Anaesthesia,

Harvard Medical SchoolMedical Liaison, Partners Biomedical EngineeringPresident, Society for Technology in Anesthesia

Everything profitable I ever invented is owned by Brigham and Woman’s Hospital(Edwards Vigilance CCO, Baxter-Bard InfusOR Pump, IVAC-Alaris Signature Pump

Perkin-Elmer Life Watch™ CO2 Monitor)

Gas Man® Understanding Inhalation Kinetics

Through Computer SimulationJames H. Philip, M.E.(E.), M.D.

Anesthesiologist andDirector of Anesthesia Technology,

Brigham and Women's HospitalAssociate Professor of Anaesthesia,

Harvard Medical SchoolMedical Liaison, Partners Biomedical EngineeringPresident, Society for Technology in Anesthesia

I have performed funded research on Sevoflurane, Desflurane, IsofluraneI have a financial interest in Gas Man® and Med Man Simulations, Inc.

UVM owns a Gas Man® Site License.

I wrote Gas Man® in 1980 because

"Uptake and distribution of anesthetic gases

is virtually incomprehensible"

wroteLawson: Gas Man Review, Anesthesia and Analgesia, August 1991

Pharmacokinetics is important !

Pharmacokinetics is important !

Pharmacokinetics explainswhat goes onfrom vaporizer to brain

Crucial to clinical practice

Goal

Inhalation Kinetics is not understood 1

1 Lawson D. Gas Man Review. Anes & Analg 8/91Cited: 1990 ABA In-Training Exam resultsCA3 resident graduates from US Medical Schoolsanswered 47% of questions incorrectly !

The Model = path of anesthetic tensionVaporizer

Breathing Circuit

Alveoli (lungs)

Arterial Blood

Tissues (VRG [brain], MUS,FAT)

Venous blood (coming back to lungs)

Alveoli (lungs, again)

Breathing Circuit (to be rebreathed)

The Model = path of anesthetic tensionVaporizer (DEL = delivered conc)

Breathing Circuit (Inspired on monitor)

Alveoli (lungs) (Expired on monitor)

Arterial Blood (not measured)

Tissues (VRG [brain], MUS,FAT)VRG = Vessel-rich = lots of blood flow = fast

Venous blood (coming back to lungs)

Alveoli (lungs, again)

Breathing Circuit (to be rebreathed)

Electrical model for inhalation kinetics

P = Partial Pressure or Tension (electrical V or E)

F = Gas Flow = Conductance (electrical G = 1/R)

C = Capacitance (electrical C)

= Anesthetic flow (electrical current = I)

CFRC

FFGF FVA

CCKT

DELP

CFAT

MUSF

FFAT

CMUS

CVRG

FVRG

IP E VRGPAPDEL

P P=

Electrical model for inhalation kinetics

P = Partial Pressure or Tension (electrical V or E)

F = Gas Flow = Conductance (electrical G = 1/R)

C = Capacitance (electrical C)

= Anesthetic flow (electrical current = I)

CFRC

FFGF FVA

CCKT

DELP

CFAT

MUSF

FFAT

CMUS

CVRG

FVRG

IP E VRGPAPDEL

P P=

Too Complicated

Inhalation Kinetics is not understood 1

1 Lawson D. Gas Man Review. Anes & Analg 8/91Cited: 1990 ABA In-Training Exam resultsCA3 resident graduates from US Medical Schoolsanswered 47% of questions incorrectly !

Gas Man® teaches inhalation kinetics effectively and enjoyably 2

2. Garfield JM, Paskin S, Philip JH. An evaluation of the effectiveness of a computer simulation of anesthetic uptake and distribution as a teaching tool. Med Educ. 1989; 23:457-462.

Gas Man Splash Screen

.9

Gas Man for WIN & MAC

More info:www.gasmanweb.com

Gas Man® results are correct

(A) Wash-in 360 minutes = 6 hr

15 minutes

(B) Wash-out

after breathing 1 MAC for 1 hr.

(C) Wash-out after breathing

1 MAC for 2 h.

(D) Wash-out after breathing

1 MAC for 4 h.

(E) Washout after breathing

1 MAC for 12 h.

According to:

Bouillon T, Shafer S. Editorial – Hot air or full steam ahead? An empirical pharmacokinetic model of potent inhaled agents. Brit J. Anaes. 84:429-431 2000.

GAS MAN® can be used two ways

Follow the book

GAS MAN® can be used two ways

Play and Explore

Follow the book

GAS MAN® can be used two waysFollow the book

Perform specific experiments

Learn the model's structure

Observe the model's behavior

Understand the structure-behavior relationship

Learn to predict & control behavior of model & patient

Learn to predict & control expired anesthetic tension

GAS MAN® can be used two waysFollow the book

Play

The Model - Gas Man® Picture

The Model - Compartments and Flows

VaporizerBreathingCircuit Lungs

Blood

------Tissues------BrainVRG

Mus FatVenousBlood

FGFFreshGasFlow

Alv(Lung)Vent

CardiacOutput

The Model - Return Flows

BreathingCircuit Lungs Venous

Blood

The Model - From Vaporizer to Brain !

Vaporizer

Brain(VRG)

Measurements we make

BreathingCircuit Lungs

Vaporizer

Setting Inspired Expired

BrainEEG,

BIS, PSI?HR,BP

Time, Uptake, and Delivered Liters and $

Questions on Model ?

5 minute course in inhalation kinetics

CONCEPTS

1. Tissue tensions (partial pressures) equalize (=)Tissue concentrations equilibrate (≠)

2. The One Compartment ModelStep Response is an exponentialLung wash-in (exponential - = 0.5 min) Tissue wash-in (another exponential - = 3 min)

3. Sequential Compartmentsdelays add to each otherBreathing circuit + Alveoli + Tissue

4. The Alveolar Tension Curve

A. Initial Rise - Alveolar Wash-In

B. Knee - Equilibration with Blood

C. Tail - Venous Return