Gas Man ® Understanding Inhalation Kinetics Through Computer Simulation © Copyright , James H Philip, all rights reserved

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Gas Man® Understanding Inhalation Kinetics Through Computer Simulation James H. Philip, M.E.(E.), M.D. Anesthesiologist and Director of Anesthesia Technology, Brigham and Women's Hospital Associate Professor of Anaesthesia, Harvard Medical School Medical Liaison, Partners Biomedical Engineering President, Society for Technology in Anesthesia Everything profitable I ever invented is owned by Brigham and Womans 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 Simulation James H. Philip, M.E.(E.), M.D. Anesthesiologist and Director of Anesthesia Technology, Brigham and Women's Hospital Associate Professor of Anaesthesia, Harvard Medical School Medical Liaison, Partners Biomedical Engineering President, Society for Technology in Anesthesia I have performed funded research on Sevoflurane, Desflurane, Isoflurane I 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" wrote Lawson: Gas Man Review, Anesthesia and Analgesia, August 1991

Gas Man® Site License Residents and Faculty may Make copies Install at work and at home while you are affiliated with U Miami

Pharmacokinetics is important !

Pharmacokinetics explains what goes on from vaporizer to brain Crucial to clinical practice Goal

Inhalation Kinetics is not understood 1 1 Lawson D. Gas Man Review. Anes & Analg 8/91 Cited: 1990 ABA In-Training Exam results CA3 resident graduates from US Medical Schools answered 47% of questions incorrectly !

The Model = path of anesthetic tension Vaporizer 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 tension Vaporizer (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) C FRC F FGF F VA C CKT DEL P C FAT MUS F F FAT C MUS C VRG F I P E P A P DEL PP =

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) C FRC F FGF F VA C CKT DEL P C FAT MUS F F FAT C MUS C VRG F I P E P A P DEL PP = Too Complicated

Inhalation Kinetics is not understood 1 1 Lawson D. Gas Man Review. Anes & Analg 8/91 Cited: 1990 ABA In-Training Exam results CA3 resident graduates from US Medical Schools answered 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:

Gas Man Splash Screen.9 Gas Man for WIN & MAC More info:

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:

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 ways Follow 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 ways Follow the book Play

The Model - Gas Man ® Picture

The Model - Compartments and Flows Vaporizer Breathing Circuit Lungs Blood Tissues Brain VRG Mus Fat Venous Blood FGF Fresh Gas Flow Alv (Lung) Vent Cardiac Output

The Model - Return Flows Breathing Circuit LungsVenous Blood

The Model - From Vaporizer to Brain ! Vaporizer Brain (VRG)

Measurements we make Breathing Circuit Lungs Vaporizer Setting Inspired Expired Brain EEG, BIS, PSI? HR,BP

Time, Uptake, and Delivered Liters and $ Questions on Model ?

The Model

5 minute course in inhalation kinetics

CONCEPTS 1. Tissue tensions (partial pressures) equalize (=) Tissue concentrations equilibrate () 2. The One Compartment Model Step Response is an exponential Lung wash-in ( exponential - = 0.5 min) Tissue wash-in (another exponential - = 3 min) 3. Sequential Compartments delays add to each other Breathing circuit + Alveoli + Tissue

4. The Alveolar Tension Curve A. Initial Rise - Alveolar Wash-In B. Knee - Equilibration with Blood C. Tail - Venous Return