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?