scavenging system a&a pg 356 to reduce exposure to waste anesthetic gases can be active or...
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Scavenging System A&A Pg 356
To reduce exposure to waste anesthetic gases
Can be active or passive scavenging system
Active Scavenging System
Connected to a vacuum that sucks the waste gases out of the machine…concerns?
Runs through a drop down line, through pipes in the ceiling, and outside –must be turned on!
Expensive, maintenance required
Passive Scavenging System
Uses pressure in circuit to expel gases from the machine, out through a hole in the wall
Must be room adjacent to the outside
Scavenging System
Activated charcoal cartridge Cheaper than installing a scavenger
Is mobile
Easy to use with little maintenance
Example: F/air canister
Must be discarded after 12 hours of use or a gain of 50 grams
Down side: do not absorb nitrous oxide
Oxygen Flow Rates
Mask Induction: 2-3 L/min for < 10 kg
3-5 L/min for > 10 kg
Chamber Induction: 5 L/min
*Your inhalant will most likely be at 5% too
Intubated patient:
Rebreathing system: 40 ml/kg/min
Note: this may be increased if you are inducing, changing anesthetic depth, or recovering patient
Rebreathing O2 Flow Rate Calculation
Ex: If your patient is 25 kg, what should their O2 flow rate be?
Flow meter measures in L/min:
Ex: 16 lb patient
If you calculate < 0.8 L/min round up to 0.8 L/min
Non-Rebreathing System
Used for patients weighing < 7 kg
Attach the clear, plastic hose to the fresh gas inlet (this tube comes from the vaporizer outlet port)
Flow of gas differs from rebreathing circuit now!
Fresh gas goes directly to the patient
Exhaled gas comes directly out through a separate hose and goes into a reservoir bag or sent through another tube to be scavenged
What’s Missing??
What parts on the rebreathing system are missing from the non-rebreathing system?
How do we compensate for this?
Non-Rebreathing System
Benefit:
• Less parts = less resistance• Smaller animals need this feature!
Negative:
• Higher amount of oxygen used due to patient not-rebreathing any gas
• Patient is only breathing cool, dry fresh gas• Warm, moist exhaled gases don’t meet
Non-Rebreathing Systems
Jackson-Rees
Norman Mask Elbow
Non-rebreathing Systems
Bain coaxial Ayre’s T-Piece
• Does not have a reservoir bag
http://asevet.com/resources/circuits/index.htm
Universal Bain Block
Oxygen Flow Rate
Non-rebreathing system: 250 ml/kg/min High b/c removal of CO2 is dependent on flow in the
system
Can go up to 600 ml/kg/min!
Note: An inadequate fresh gas supply will result in your patient re-breathing gases…remember, there is no CO2 absorber!
*The higher the flow of gases, the less CO2
breathed in by your patient.
Leak Testing
Performed before every anesthesia to check the system for leaks
The last thing you do on your anesthetic machine
*Hint: this will also tell you if your machine is hooked up correctly
Top three most common leaky parts:
1. Reservoir bag
2. Fresh gas inlet
3. CO2 canister
Leak Testing – Low Pressure Test
Used when oxygen is your carrier gas
Steps: close pop-off valve AND cover end of rebreathing tube with something
Turn on flow meter to 2 L/min and let oxygen fill reservoir bag
Once full, turn down the O2 to 0.2 L/min
Gently squeeze the bag and listen/feel for leaks
If none, maintain a full bag for 30 seconds at 30 cm H2O
If the bag doesn’t hold pressure (remain full), you have a leak!
Things to Consider
Which breathing system may help keep a patient from becoming hypothermic?
Which breathing system is more costly to use?
Which breathing system allows for the quickest change in anesthetic depth?