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breathin system anesthesia.pptx
- 9. Circle components: fresh gas inflow source, inspiratory & expiratory unidirectional valves, inspiratory and expiratory corrugated tubing, Y connector, overflow (called popoff, adjustable pressure-limiting valve, or APL valve), reservoir bag, carbon dioxide absorbent canister and granules. Resistance of circle systems is less than 3 cm H2O (less than the resistance imposed by the endotracheal tube).
- 10. Circle advantages: •constant inspired concentrations •conserve respiratory heat and humidity -Warming and humidification of the inspired gases •useful for all ages (may use down to 10 kg, about one year of age, or less with a pediatric disposable circuit) •useful for closed system or low-flow •low resistance (less than tracheal tube, but more than a NRB circuit) •Economy of anaesthetic consumption •Reduced atmospheric pollution Circle disadvantages: •increased dead space - Mechanical dead space ends at the point where inspired and expired gas streams diverge (the Y-connector) •malfunctions of unidirectional valves Slow changes in the inspired anaesthetic concentration with low flows and out-of-circuit vaporiser
- 11. Non-rebreathing (Mapleson) breathing circuits All non-rebreathing (NRB) circuits lack unidirectional valves and soda lime carbon dioxide absorption. The amount of rebreathing is highly dependent on dilution of expirations with high fresh gas flow (FGF) in all. Minimum FGF In practice, most anesthetists will provide a minimum 5 L/min for children on up to adults to prevent rebreathing (or 2-3 x minute ventilation [VE], whichever is greater).
- 12. The Bain circuit is a "coaxial" Mapleson D- the same components, but the fresh gas flow tubing is directed within the inspiratory limb, with fresh gas entering the circuit near the mask. The Bain has been shown to add more heat and humidity to inhaled gases than other Mapleson circuits.
- 13. How do NRB’s work? During expiration, fresh gas flow (FGF) pushes exhaled gas down the expiratory limb, where it collects in the reservoir (breathing) bag and opens the expiratory valve (pop-off or APL). The next inspiration draws on the gas in the expiratory limb. The expiratory limb will have less carbon dioxide (less rebreathing) if FGF inflow is high, tidal volume (VT) is low, and the duration of the expiratory pause is long (a long expiratory pause is desirable as exhaled gas will be flushed more thoroughly). All NRB circuits are convenient, lightweight, easily scavenged. A unique hazard of the use of the Bain circuit is occult disconnection or kinking of the inner, fresh gas delivery hose. If this occurs, the entire corrugated limb becomes dead space. This results in respiratory acidosis which is unresponsive to increased minute ventilation.
- 14. The Pethick Test for the Bain Circuit To perform the Pethick test, use the following steps: 1. Occlude the patient's end of the circuit (at the elbow). 2. Close the APL valve. 3. Fill the circuit, using the oxygen flush valve. 4. Release the occlusion at the elbow and flush. A Venturi effect flattens the reservoir bag if the inner tube is patent. Another test - If fresh gas flow is established, and the inner tube is occluded, the flowmeter bobbins (if present) should dip (due to back pressure) if the inner tube is patent.
- 15. Advantages Used during transport of children Minimal dead space low resistance to breathing Scavenging (variable ability, depending on FGF used) Disadvantages High flows required (cools children, more costly) Lack of humidification/heat (except Bain) Possibility of high airway pressures and barotrauma Unrecognized kink of inner hose in Bain Pollution and higher cost