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3. Breathing systems

3. Breathing systems. R1 문은진. Definition. Assembly of components which connects the patient’s airway to the anesthetic machine Providing the final conduit for the delivery of anesthetic gases to the patient. Classification. Insufflation Open – drop anesthesia Draw-over anesthesia

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3. Breathing systems

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  1. 3. Breathing systems R1 문은진

  2. Definition • Assembly of components which connects the patient’s airway to the anesthetic machine • Providing the final conduit for the delivery of anesthetic gases to the patient

  3. Classification • Insufflation • Open – drop anesthesia • Draw-over anesthesia • Mapleson circuits • The circle system • Resuscitation system

  4. Insufflation • The blowing of anesthetic gases across a patient’s face • Avoids direct connection between a breathing circuit and a patient’s airway • Because children resist the placement of a face mask or an IV line, insufflation is valuable • CO2 accumulation is avoided with insufflation of oxygen & air at high flow rate(>10 L/m) under H & N draping at ophthalmic surgery • Maintain arterial oxygenation during brief periods of apnea

  5. Open- drop anesthesia • Not used in modern medicine • A highly volatile anesthetic is dripped onto a gauze–covered mask applied to the patient’s face (vaporization->lowers mask temp.>moisture condensation->drop in anesthetic vapor pr.)

  6. Draw-over anesthesia

  7. Draw-over anestheaia • Nonrebreathing circuits • Use ambient air as the carrier gas • Inspired vapor and oxygen concentrations are predictable & controllable • Advantage; simplicity, portability • Disadvantage; absence of reservoir bag -> not well appreciating the depth of TV during spontaneous ventilation

  8. Disadvantages of the insufflation & draw-over systems • Poor control of inspired gas concentration & depth of anesthesia • Inability to assist or control ventilation • No conservation of exhaled heat or humidity • Difficult airway management during head & neck surgery • Pollution of the operating room with large volumes of waste gas

  9. Mapleson circuits • Incorporating additional components - breathing tubes - fresh gas inlets - adjustable pressure limiting (APL) valves - reservoir bag

  10. A. Breathing tubes • Corrugated breathing tubes - connect the components of the Mapleson circuit to the patient • Large diameter of tubes (22mm) - low resistance pathway - potential reservoir for anesthetic gases

  11. B. Fresh gas inlet • gases(anesthetics with oxygen or air) from the anesthesia machine -> enter the circuit through the fresh gas inlet • the relative position of fresh gas inlet - a key differentiating factor in Mapleson circuit performance

  12. C. Adjustable pressure limiting valve(pressure-relief valve, pop-off valve) • Allowing gases to exit the circuit through an APL valve -> control pressure build up • Fully open the APL valve during spontaneous ventaillation ! -> for remaining circuit pressure negligible throughout inspiration and expiration • Partial closure of the APL valve limits gas exit -> permitting positive circuit pressure during reservoir bag compressions

  13. D. Reservoir bag(breathing bag) • Reservoir of anesthetic gas and a method of generating positive-pressure ventilation • Phase Ⅰ; the nominal 3L capacity of an adult reservoir bag is achieved • Phase Ⅱ; Pr rises rapidly to a peak • Phase Ⅲ; plateau or even a slight decrease in Pr --- ceilling effect ! -> help to protect the patient’s lungs against high airway pressures

  14. Performance characterisitcs of MC • Lightweight, inexpensive, simple • Breathing circuit efficiency - depends on the fresh gas flow required eliminating CO2 rebreathing • Mapleson A • CO2 exhaled into breathing tube or directly vented through open APL valve • Most efficient for spontaneous ventilation. • Mapleson D • Interchanging APL valve and fresh gas inlet ->FGF forces alveolar air away from pt. toward the APL valve -> efficient during controlled ventilation • Bain circuit • Retains heat and humidity • Decrease the circuit’s bulk • Possibility of kinking or disconnection of the fresh gas inlet tubing

  15. The circle system

  16. A. carbon dioxide absorbent • Eliminating CO2 in exhaled gas to prevent hypercapnea • CO2 absorbent(sodalime, barium hydroxide lime) -> containing hydroxide salt -> neutralizing carbonic acid

  17. A. carbon dioxide absorbent • Increasing hydrogen ion concentration - Color conversion of a pH indicator dye -> 50-70% has changed color -> absorbent should be replaced • Absorbent granules can absorb and later release significant amounts of volatile anesthetic -> delay induction or emergence • The drier the soda lime, the more absorb and degrade volatile anesthetics ; Desflurane be broken down to carbon monoxide -> clinically significant carbon monoxide poisoning

  18. B. Carbon dioxide absorbers • Bulky, double canister permit -more complete CO2 absorption -less frequent changes -lower gas flow resistance • Patient’s TV should not exceed the air space between absorbent granules(=50% of the absorber’s capacity) • Dust trap - collect dust and moisture

  19. C. Unidirectional valves • Function as check valves • Contain a ceramic or mica disk resting horizontally on an annular valve seat • Forward flow -> disk upward -> gas proceed through the circuit • Reverse flow -> push disk against its seat -> preventing reflux

  20. C. Unidirectional valves • Inhalation - Open the inspiratory valve - Breath a mixture of fresh and exhaled gas - Pass through the CO2 absorber - Simultaneously, expiratory valve close (preventing rebreathing of exhaled gas) • Exhalation - Open the expiratory valve - Vented through the APL valve or rebreathed by the Pt after passing through the absorbers - Closure of the inspiratory valve (preventing expiratory gas from mixing with fresh gas)

  21. Optimization of circle system design • Unidirectional valves • Close to the pt ; prevent back flow into inspiratory limb • Not placed in the Y-piece • The fresh gas inlet • Between the absorber and the inspiratory valve • APL valve • Immediately before the absorber; conserve absorption capacity, minimize venting of fresh gas • Reservoir bag • Locating in the expiratory limb; resistance to exhalation is decreased

  22. Performance characteristics of the circle system-A. Fresh gas requirement • At low fresh gas flows(<1L) With absorber- preventing rebreathing of CO2 • At fresh gas flows>5L rebreathing so minimal – absorber is unnecessary • the greater FGF , the less time for a change in fresh gas anesthetic concentration • Higher flows - speed induction, recovery - compensate for leaks in the circuit - decrease the risks of unanticipated gas mixture

  23. Performance characteristics of the circle system- B. Dead space • Part of TV that does not undergo alveolar ventilation • Unidirectional valve • Apparatus dead space is limited to the area distal to the point ins-exp gas mixing at the Y-piece • Breathing-tube length does not affect dead space

  24. Performance characteristics of the circle systemC. Resistance • Unidirectional valves and absorber - increase circle system resistance (at high RR, large TV)

  25. Performance characteristics of the circle system-D. Humidity and heat conservation • Medical gas – dehumidified gases at room temp. • Exhaled gas – saturated with water at body temp. • The heat and humidity of inspired gas - depend on the relative proportion of rebreathed gas to fresh gas • Absorbent granules- significant source of heat and moisture in the circle system

  26. Performance characteristics of the circle system-E. Bacterial contamination • Slightly risk of microorganism retention in circle system component -> respiratory infections in subsequent Pt • Bacterial filters are incorporated into the breathing tubes or at the Y- piece

  27. Resuscitation breathing systems • Resuscitation bags(AMBU bags or bag-mask units) - used for emergency ventilation - simplicity, portability, ability to deliver almost 100% oxygen - contain nonrebreathing valve

  28. The Pt valve open • Allow gas flow • from the ventilation bag to the pt. • Exhalation ports in this valve • Venting exhaled gas to atmosphere • Rebreathing is prevented • Intake valve • Close during bag compression, permitting positive ventilation • Connecting a reservoir->prevent the entrapment of room air • Reservoir valve assembly-two unidirectional valves • Inlet valve; allow ambient air to enter the ventilation bag if FGF is inadequate to maintain reservoir filling • Outlet valve; venting oxygen if FGF is excessive

  29. Disadvantage • Require high fresh gas flows to achieve a high FIO2 • Proportional to the oxygen concentration • Proportional to flow rate of the gas mixture supplied to the resuscitator • Inversely proportional to the MV delivered to the Pt. • Exhaled moisture – cause valve sticking -The end-

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