Anesthesia machine and breathing systems

1. Anesthesia machine and breathing systems Chaiyapruk Kusumaphanyo, M.D.

2. Content outline • Anesthesia machine component • Gas supply • Safety measures and alarms • Vaporizer • Breathing systems/circuits • Carbon dioxide absorbent • Ventilator • Scavenging system

3. Before using machine • Pre-use check of components 1. calibration of oxygen analyzer 2. low-pressure circuit leak test 3. oxygen flush positive-pressure leak test 4. circle system leak test 5. workstation self-test

4. Machine components • Three circuit within machine 1. high-pressure 2. intermediate-pressure 3. low-pressure • Fail-safe valve

5. >>14-26 psi (low) Machine components • High-pressure circuit oxygen cylinder 2200 psi >> 45 psi N2O cylinder 750 psi >> 45 psi • Intermediate-pressure circuit oxygen cylinder 45 psi N2O cylinder 45 psi oxygen pipeline 50 psi N2O pipeline 50 psi

6. Machine components • Low-pressure circuit from flow control valve to common gas outlet

7. Fail-safe valve • aka. Pressure sensor shut-off valve, oxygen failure protection device • Located downstream from N2O supply • An interface between Oxygen and N2O • Shuts off or proportionately decrease N2O supply if oxygen supply declines • Audible alarm if oxygen supply drops to e.g. 30 psi

8. Proportioning system • Oxygen and N2O flow control valves connected to each other mechanically or pneumatically • Link-25 system (minimum 25% oxygen) • Sensitive oxygen ratio controller • Oxygen analyzer is mandatory

9. Pipeline supply source • Primary gas supply • Through pipeline inlet connections • Gas-specific fittings with DISS (diameter index safety system) Silbermann DISS

10. Cylinder supply source • E-size cylinders hung with hanger yoke assembly • PISS (pin index safety system) • Gas-tight seal and unidirectional flow • Pressure gauge • Pressure regulator • Turn off when not in use

11. PISS • Pin position

12. PISS oxygen N2O CO2 nitrogen air

13. Flow meter assembly • Glass flow meter (Thorpe tube) and the float • Electronic flow meter • Proportioning system

14. Oxygen flush valve • Deliver flow 35-75 L/min (50 psi) • Bypass the vaporizer • Can cause high pressure in low-pressure circuit >> barotrauma • Incompetent flush valve >> awareness

15. Vaporizer • Vapor pressure • Latent heat of vaporization • 4 types: variable bypass : desflurane : cassette : injection

16. Vaporizer • Factors affecting delivery accuracy :flow rate :temperature :carrier gas composition :altitude

17. Anesthesia breathing circuits • 2 types : Mapleson systems : circle (absorption) system

18. Mapleson systems • Type A-B-C-D-E (F added later) • Components : face mask : pop-off valve : reservoir tubing : fresh gas inflow tubing : reservoir bag

19. Light-weighted • Spontaneous/controlled ventilation • Convenient • Easily sterilized • Low resistance • High FGF Bain circuit

20. Circle breathing system • 7 primary components : 1. fresh gas inflow source 2. insp. & exp. unidirectional valves 3. insp. & exp. Corrugated tubes 4. Y-piece 5. APL (adjustable pressure-limiting) valve 6. reservoir bag 7. CO2 absorbent

21. Circle breathing system • Heavy and bulky • Expensive • More connections • Lower FGF • Higher resistance • Low anesthetics cost and pollution • Stable anesthetic concentration • Heat and moisture conservation

22. Circle breathing system • Can be semi-open, semi-closed or closed depending on FGF • Semi-open >>no rebreathing, very high flow • Semi-closed >>some rebreathing • Closed >>inflow gas exactly matches that being taken up, complete rebreathing of exhaled gas after CO2 absorption with APL valve closed

23. CO2 absorbents • Ideal absorbents: 1. lack of reactivity with common anesthetics 2. lack of toxicity 3. low resistance (size 4 -8 mesh) 4. low cost 5. ease of handling 6. efficient CO2 absorption

24. 80% Ca(OH)2 >80% Ca(OH)2 80% Ca(OH)2 15% water 20% Ba(OH)2 CaCl2 13-18% water 4% NaOH silica Ca2SO4 + polyvinylpyrrolidine 1% KOH Soda lime Baralyme Amsorb Plus® Forms of CO2 absorbents • Soda lime • Baralyme • Calcium hydroxide lime (Amsorb®)

25. Amsorb Plus® • Alkali-free • Lack of production of CO and compound A • Reduced possibility of fire in breathing circuit • Less absorptive capacity • Expensive

26. Chemical reactions CO2 + H2O  H2CO3 H2CO3 + 2NaOH(KOH)  Na2CO3 (K2CO3) + 2H2O + heat Na2CO3(K2CO3) + Ca(OH)2  CaCO3 + 2NaOH(KOH) Colorless ethyl violet violet pH<10.3 Soda lime

27. Chemical reactions Ba(OH)2 + 8H2O + CO2 BaCO3 + 9H2O + heat 9H2O + 9CO2  9H2CO3 9H2CO3 + 9Ca(OH)2  CaCO3 + 18H2O + heat Colorless ethyl violet violet pH<10.3 Baralyme

28. Anesthesia ventilators • Power source • Drive mechanism and circuit designation • Cycling mechanism • Bellow classification • Modes of ventilation VC (most common used) PC PS

29. Scavenging systems • Collection and removal of waste anesthetic gas from the OR NIOSH Recommendations for Trace Gas Levels Criteria for a Recommended Standard: Occupational Exposure to Waste Anesthetic Gases and Vapors. Washington DC, US Department of Health, Education, and Welfare, March 1977.

30. Scavenging systems • 5 components

31. Health risks due to waste gases • Abortion • Multiple sclerosis? (Swedish survey) • Psychomotor performance impairment

32. Machine and workstation • Machine proper • Vaporizer • Monitoring devices • Ventilator • Electronic data records • “anesthesia workstation”

33. ศึกษาเพิ่มเติมใน http://vam.anest.ufl.edu ลงทะเบียนฟรี แล้วเข้าใช้ได้เลย