Test 1 part VI (Anesthesia Machine) Flashcards
What is the SPDD Schematic?
Supply, Processing, Delivery, and Disposal
Refers to how gases get to the anesthesia machine. Involves pipeline and cylinders.
Supply
Oxygen is a stored as a ______ at a temperature of _____ deg C.
Liquid; -160 degrees C
Refers to how the anesthesia machine prepares the gases before they are delivered to the patient.
Processing
Refers to how the prepared gases are brought to the patient.
Delivery
Refers to how the gases are removed from the OR
Disposal
What are the 5 tasks of O2?
- Proceeds to the fresh gas flow meter
- Powers the O2 flush (35-75 L/min)
- Activates the fail-safe valve (occludes N2O if low O2 pressure is present)
- Activates the O2 low pressure alarm
- Compresses the bellows of mechanical ventilation
What is the minimum FGF required to prevent rebreathing?
2-3 x minute ventilation (or a minimum fresh gas flow of 5L/min)
Occurs when there is no rebreathing of any exhaled gases.
-Lack unidirectional valves
-Lack soda lime CO2 absorption
-FGF determines the amount of rebreathing
-Resistance and WOB is low
Non-Rebreathing Systems (rare)
-NO Reservoir or Unidirectional Valves
-NO rebreathing (must have FGF >6 L/min)
-Ex: Open drop/NC/Face Mask
-Patients have access to the atmosphere
Open
-Has a Reservoir
-NO Rebreathing
-CO2 is eliminated by dilution and exclusion
-Ex: Circle system at high FGF (must be > Minute Ventilation) or non-rebreathing system
-Ex: Mapleson and Bain System
-Good for peds patients due to low resistance to flow
Semi-Open
-Has a reservoir
-Partial rebreathing
-CO2 is absorbed (soda lime) and excluded (unidirectional valves)
-Ex: Circle System at low FGF (less than Minute Ventilation)
Semi-Closed
-Has a reservoir
-Complete rebreathing
-Ex: Circle system at extremely low FGF with APL Valve closed
Closed
Defines breathing circuits by the presence or absence of a reservoir bag and the degree to which rebreathing occurs.
Mapleson Classification of Breathing Circuits
_____ and ____ systems are not capable of being semi-closed or closed because they do not have a way to eliminate CO2 by chemical absorption and lack valves to eliminate CO2 rebreathing by exclusion.
Mapleson and Bain
A system that prevents the rebreathing of CO2, while allowing the rebreathing of other gases.
-Can be Semi-open, Semi-closed, or Closed
-Inspiratory & expiratory unidirectional valves enforce flow pattern, all exhaled gasses are directed through CO2 absorbent, low FGF technique
Circle System
Allows venting of excess gas from breathing system into the waste gas scavenging system – adjusted to provide controlled ventilation – fully open (min) during spontaneous ventilation
<30 to prevent barotrauma
Adjustable Pressure Limiting (APL) Valve
Maintains a reserve volume of gasses from the anesthesia machine – serves as a safety device bc of its distensibility
Reservoir Bag
What are the advantages to using the Circle System?
- Constant inspired concentrations
- Conservation of respiratory tract heat/humidity
- Minimal OR pollution
- Useful for closed/low flow/semi-open configurations
- Low resistance
What are the disadvantages of the Circle System?
- Relatively complex
- potential for disconnections
- malfunction of unidirectional valves (open rebreathing; closed occlusion)
- less portable
- increased dead space
Prevent the circle system from contributing to apparatus dead space. Failure of these to seal converts a large volume of the circuit into apparatus dead space, resulting in rebreathing!!
Unidirectional Valves
The only apparatus dead space in the Circle System is:
The distal limb of the Y-connector and any tube or mask between it and the patient’s airway!!
What components make up the High Pressure System?
Cylinder to the first stage regulator.
-Hanger yoke, yoke block with check valves, cylinder pressure gauge, cylinder pressure regulators
-Cylinder Regulator = 45 psi
What are the components of the Intermediate Pressure System?
Exposed to pipeline pressure.
-Pipeline inlets, check valves, pressure gauges, ventilator power inlet, oxygen pressure-failure devices, flow meter valve, oxygen second-stage regulator, flush valve
-Pipeline = 50 psi
What are the components of the Low Pressure System?
Distal to flow meter needle valves.
-Flow meter tubes, vaporizers, check valves, common gas outlet
-Pressures are slightly greater than atm pressure
How to calculate minutes of O2 remaining in the cylinder?
Tank capacity (L)/Full tank pressure (psi) = Contents Remaining (L)/Gauge pressure
Contents Remaining/Flow rate (L/min) = Minutes left before tank expires
What is the color, service pressure (psi), capacity (L), and Pin Position of Oxygen?
Green; 1900; 660; 2-5
What is the color, service pressure (psi), capacity (L), and Pin Position of Nitrous Oxide?
Blue; 745; 1590; 3-5
What is the color, service pressure (psi), capacity (L), and Pin Position of Air?
Yellow; 1900; 625; 1-5
Prevents inadvertent misconnection of gas hoses. Each gas hose & connector are sized & threaded for each individual gas by a series of increasing & decreasing diameters —not fail-proof system
Diameter Index Safety System (DISS)
Prevents inadvertent misplacement of gas cylinders –not fail-proof. Pin configuration on each hanger yoke assembly is unique for each gas. Hanger yoke orients cylinder, provides gas-tight seal, ensures unidirectional flow in the machine
Pin Index Safety System (PISS)
What can cause the PISS to fail?
If pins are missing/removed, or if more than 1 washer is used.
Where is the oxygen flow meter always positioned?
Furthest to the right
How does the O2 pressure fail-safe system work?
Proportionally reduces N2O flow if O2 pressure drops below 20 psi. Limited if pipeline crossover occurs (can still create a hypoxic mixture)
How does the hypoxic proportioning system (link system) work?
Prevents the delivery of a hypoxic mixture with the flow control valves by requiring a 3:1 N20:O2 mixture. Tested by turning on N2O without O2. Final breathing mixtures at the CGO are at least 23-25% O2.
Hypoxia prevention devices and the Fail Safe system only respond to changes in O2 ______, NOT the O2 ______. This is why proper use of a calibrate O2 analyzer in each GA case is of vital importance.
Only respond to changes in O2 pressure or flow, NOT the O2 concentration. Could have pipeline crossover and would only be detected by O2 analyzer.
What are the limitations of the hypoxic proportioning system (Link system)
- O2 pipeline crossover
- Administration of a 3rd gas
- Defective mechanic or pneumatic components
What is the only system that would detect a pipeline crossover?
A calibrated O2 analyzer
A type of O2 analyzer that works via a current generated across 2 electrodes as the O2 tension increases. Must be calibrated daily and replaced over time.
Galvanic Fuel Cell
A type of O2 analyzer that works via increasing O2 tension creating increased magnetic attraction. Self calibrating and faster, lower cost, and low maintenance.
Paramagnetic Analyzer
The tendency of a liquid to evaporate. The more volatile the agent, the faster it will evaporate
Volatility
Inhalational agents are volatile liquids at _____ deg C
20 degrees C (room temp)
The molecules in gas phase of a substance that is liquid at room temp & at 1 atm
Vapor
The conversion of a liquid to a vapor in a closed container. Rate depends on temp, vapor pressure of liquid, and the partial pressure of vapor above evaporating liquid.
Vaporization
Modern vaporizers are made out of what materials?
Metals with high thermal conductivity & capacity (copper)
The energy required to transform molecules from the liquid phase to the gas phase; remaining liquid in container is cooled.
Latent Heat of Vaporization
What are some of the safety features regarding volatile agents and vaporizers?
- Vaporizers are agent-specific and color coded
- Filling connectors are specific to each agent
- Vaporizers are “out of circuit” - they are isolated outside of the breathing system
- Safety interlock system
