1. 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

2. 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

3. 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

4. Rebreathing O 2 Flow Rate Calculation Ex: If your patient is 25 kg, what should their O 2 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

5. 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

6. What’s Missing??  What parts on the rebreathing system are missing from the non-rebreathing system? How do we compensate for this?

7. 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

8. Non-Rebreathing Systems Jackson-Rees Norman Mask Elbow

9. Non-rebreathing Systems Bain coaxial Ayre’s T-Piece Does not have a reservoir bag http://asevet.com/resources/circuits/index.htm

10. Universal Bain Block

11. Oxygen Flow Rate  Non-rebreathing system: 250 ml/kg/min  High b/c removal of CO 2 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 CO 2 absorber! *The higher the flow of gases, the less CO 2 breathed in by your patient.

12. 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

13. 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 O 2 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!

14. 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?