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24 Cards in this Set
- Front
- Back
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RESISTANCE TO FLOW CAN BE MINIMIZED BY
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-reducing the length of the circuit, increasing the diameter of the circuit, eliminating unnecessary valves, maintaining laminar flow, avoiding sharp bends
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CLASSIFIED BASED ON WHETHER PRESSENCE OR ABSENCE OF
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-gas reservoir bag, rebreathing of exhaled gases, means to chemically neutralize CO2, unidirectional valves
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OPEN SYSTEM
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-no gas reservoir bag, no rebreathing of exhaled gases, no neutralization of CO2, no unidirectional valves
**ex - nasal cannula, open drop ether, blow by |
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SEMI OPEN SYSTEM
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-gas reservoir is present, no rebreathing and no neutralization of CO2, unidirectional valve may or may not be present, high FGF (2-3x minute ventilation)
ex- mapleson systems |
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SEMI CLOSED SYSTEM
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-always has a reservoir bag, allows for partial rebreathing of exhaled gases, neutralization of CO2, 3 unidirectional valves (APL, inspiratory, and expiratory), FGF is less than minute ventilation, **a type of circle system
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CLOSED SYSTEM
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-always has a reservoir bag, allows for total rebreathing of exhaled gases, neutralization of CO2, contains unidirectional valves, flow of 150- 500ml/min for physiological req
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MAPLESON CLASSIFICATION
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-A, B, C, D, E, F
-ALL have source of fresh gas, corrugated tubing, and adjustable pressure limiting valve (APL) DIFFERENCES ARE - location of APL valve, fresh gas input, and presence or absence of reservoir bag ALL are semi open systems |
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MAPLESON SYSTEMS
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ALL non rebreathing systems lack unidirectional valves and soda lime and co2 absorbers, SO amount of rebreathing is highly dependent on fresh gas flows, work of breathing is low in all b/c there are no unidirectional valves or absorbers to create resistance to flow
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HOW DO NRB SYSTEMS WORK?
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-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 FG 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. One objection is that the circuit must be reconfigured between cases, with the possibility of error
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ADVANTAGES AND DISADVANTAGES OF MAPLESON SYSTEMS
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Advantages:
Simplicity of design Portability Ability to change anesthetic depth rapidly Lack of rebreathing of exhaled gases Disadvantages Lack of conservation of heat & moisture Limited ability to scavenge waste gases High requirements of fresh gas flow |
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WHICH MAPLESON CIRCUIT DOES NOT HAVE A RESERVOIR BAG
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mapleson E
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MAPLESON A
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Most efficient design during spontaneous ventilations since a fresh gas flow rate equal to minute ventilation will be enough to prevent rebreathing
FGF into reservoir bag Overflow valve will open if maximum pressure is reached |
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MAPLESON B
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Fresh gas inlet and APL valve are close together to reduce rebreathing
No common clinical use |
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MAPLESON C
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Much like the Mapleson B but has a shorter expiratory limb
No common clinical application Can be used during controlled ventilation |
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MAPLESON D
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Fresh gas inlet and overflow valve are opposite of Mapleson A
Fresh gas flow forces alveolar gas away from the patient toward the APL valve |
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BAIN SYSTEM
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-modified example of mapleson D
-co axial tubing- the benefit is humidification of exhaled gases Fresh gas flow required to prevent rebreathing: Spontaneous: 2 times minute ventilation (300 ml/kg/min) Controlled : 70 ml/kg/min |
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DISADVANTAGES OF THE BAIN SYSTEM
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Disadvantages
Increased resistance to breathing Unrecognized disconnection Inner tube may kink Pethick’s Test – used to check the patency of the inner fresh gas flow tubing Occlude the patient’s end of the circuit Close APL valve Fill the circuit using the oxygen flush valve Release the occlusion at the patient’s end and open the APL valve. A Venturi effect flattens the reservoir bag if the inner tube is patent |
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MAPLESON E
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Modified with no reservoir bag
**the only one without a reservoir bag |
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MAPLESON F
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Jackson Reese modification of the Mapleson E system (Ayres T-Piece)
APL valve is on the distal end of the reservoir bag Minimal dead space and low resistance to breathing |
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DISADVANTAGES OF MAPLESON F
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-short tube, if it becomes occluded it has nowhere to go
Disadvantages Lack of humidification High fresh gas inflow to prevent rebreathing High airway pressures and barotrauma if the APL valve becomes occluded |
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MAPLESON CIRCUIT EFFICIENCY
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For CV: D>B>C>A
Dead Bodies Can’t Argue For SV: A>D>C>B All Dogs Can Bite |
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CIRCLE SYSTEMS
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Can be converted to semi-open, semiclosed or closed dependent on fresh gas flow
Uses chemical neutralization of CO2 Conservation of moisture & body heat Allows mechanical ventilation using attached ventilators Allows for adjustment of ventilatory pressure Easily scavenged to avoid pollution of OR environment |
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IMPORTANT FOR CIRCLE SYSTEMS
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-Incompetent valve will allow rebreathing of CO2
Hypercarbia Failure of ETCO2 waveform to return to baseline APL valve Controls the amount of gas in the system |
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ADVANTAGES AND DISADVANTAGES OF CLOSED SYSTEMS
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Advantages:
Maintains humidification Less pollution of waste gas since maintained in system (APL closed) Disadvantages: Unknown gas concentrations Unpredictable amounts of oxyge |
