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Anesthesia Machine VAPORIZERS

Anesthesia Machine VAPORIZERS. Vaporizers. Convert liquid anesthetic into a volatile inhalation agent Based on laws of physics You must memorize the chemical properties of the volatile agents. Basic Design. Gas enters vaporizer Flow is split Majority is bypassed

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Anesthesia Machine VAPORIZERS

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  1. Anesthesia MachineVAPORIZERS

  2. Vaporizers • Convert liquid anesthetic into a volatile inhalation agent • Based on laws of physics • You must memorize the chemical properties of the volatile agents

  3. Basic Design • Gas enters vaporizer • Flow is split • Majority is bypassed • Some enters vaporizing chamber • Saturated gas leaves chamber • Diluted by bypass gas • Delivered to patient

  4. Applied Physics • Vapor pressure • Dalton’s law • Based on characteristics of agent • Varies with temperature

  5. Applied Physics (con’t) • Boiling point • Vapor pressure equals atmospheric pressure • Latent heat of vaporization • Heat required to change liquid into a vapor • Comes from liquid and environment

  6. Types of Vaporizers • Historic • Copper kettle • Vernitrol • Modern • Ohmeda Tec 4 • Drager Vapor 19.1

  7. Characteristics of Drager and Ohmeda • Variable bypass • Flow over • Temperature compensated • Agent specific • Out of circuit

  8. Copper Kettle and Vernitrol • Measured flow • Bubble through • Non temperature compensated • Multiple agent • Out of circuit

  9. Factors that Effect Output • Flow rate • Accurate at most flows • Lower than dial setting at both extremes of flow • Temperature • Vapor pressure varies with temp • Accurate at 20 - 35o C

  10. Factors Effecting Output (con’t #1) • Intermittent back pressure • Retrograde flow • Higher than dial setting • especially at low flows and high ventilator pressures • Carrier gas composition • N2O causes transient drop

  11. Vaporizer Interlock System • Only 1 vaporizer can be turned on • Gas enters only the “on” vaporizer • Leak of trace gas is minimized • Vaporizers are locked into the circuit

  12. What is the concentration of an anesthetic gas in the vaporizing chamber?

  13. Vapor pressureX 100atmospheric pressure

  14. Vapor Pressures: Isoflurane - 238 Enflurane - 175 Halothane - 241

  15. Isoflurane 238X 100 = 31% 760

  16. Enflurane 175 X 100 = 23% 760

  17. Halothane 241X 100 = 32% 760

  18. Desflurane • Requires special vaporizer • Vapor pressure 664 • Pressurized, heated chamber • 1550 mm / Hg prevents boiling

  19. Liquid to Vapor CC’s of Gas per ml of Liquid • Isoflurane -- 206 • Enflurane -- 210 • Halothane -- 240

  20. How long will your anesthetic gas last?

  21. Vaporizer problem # 1 • You have 15 cc’s of forane liquid and are giving 1% at 3 l / m. How long will it last?

  22. Vaporizer problem # 2 You have: Forane 15 mL X 206 cc / ml = 3090 cc You use: 1% X 3000 = 30 cc / min Therefore: 3090 cc= 103 minutes 30 cc / min

  23. Vaporizer Hazards • Misfilling • Tipping • Dual vaporizers on • Leaks • Free standing vaporizers

  24. Misfilling • Vaporizers are calibrated according to the vapor pressure of the agent • If you fill with an agent with a higher v.p. -- overdose • If you fill with an agent with a lower v.p. -- underdose

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