1. PART 3: Breathing Circuit
The system that brings the fresh gas from the vaporizer to the patient and takes the expired gases from the patient to the scavenger.
May contain unidirectional valves, reservoir bag, pop off valve, CO2 canister, negative pressure relief valve, pressure manometer.
Non-rebreathing
System
Rebreathing System

2. Rebreathing System
Set up as a circle system  exhaled gases are recirculated and rebreathed by the patient
New fresh gas is also added in
Used for patients weighing >7kg
Can be used as a closed or semi-closed system
Begins with the fresh gas inlet
Vaporizer outlet port connects to the fresh gas inlet, which connects to the inspiratory unidirectional valve

3. Rebreathing System: Closed
Pop-off valve is completely closed!
Only provides enough oxygen to meet metabolic demands of the patient
Oxygen flow rates (L/min) must be kept very low!!
The volume of gas added to the circuit = the volume of gas used by the patient
*This is very tricky to achieve and is therefore not commonly used

4. Rebreathing System: Semi-Closed
Also known as partial rebreathing system
This is much more common!
Pop-off valve is open or partially closed
This system requires a scavenging system because more oxygen than the patient needs is being provided

5. Unidirectional Valves
One-way valves that allow the flow of fresh gas to enter the inhalation valve and exit the exhalation valve.
Valve is either a rigid disk or a flap that flutters as gas flows past it
Inspiratory/Inhalation valve opens as patient inhales
Fresh gas enters the inspiratory breathing hose, then the ET tube and then the patient’s lungs
Gas exchange occurs now = sleepy patient
02 CO2

6. Unidirectional Valves
CO2 and anesthetic gases are then exhaled and travel up the expiratory breathing hose.
Gas flows through the unidirectional exhalation valve
This valve prevents the expired gases from traveling back to the patient before the CO2
is removed.

7. Breathing Tubes for Rebreathing System
1. Y Tubes
Come in large animal, small animal, and pediatric
Large animal tubes can only be used on large animal machines
2. Universal F-circuit
Come in adult (green-blue) and pediatric (red or green)
Pediatric = patients lbs
Adult = patients weight > 35 lbs
The inspiratory tube is located within the expiratory tube
Each connects to the machine separately at their respective flutter valves
 CO2 absorber

8. F-circuit
Y tubing

9. CO2 Absorber
Exhaled gases flow out of the expiratory breathing tube and
into the CO2 canister
CO2 canisters usually contain calcium hydroxide granules that
selectively absorb CO2 from other gases breathed out.
Example: soda lime granules
“Exhausted” soda lime granules no longer absorb CO2.
patient breathes in CO2

10. HOW DO I KNOW WHEN THE GRANULES ARE EXHAUSTED?
CO2 Absorber
HOW DO I KNOW WHEN THE GRANULES ARE EXHAUSTED?
Color change to violet, off-white or pink depending on the brand.
CO2 saturated granules are hard and brittle; new ones can be chipped and crumbled
Once color becomes abnormal, it is possible that it changes back to normal within hours!
VTI note: Change q 8 hours of use
next, gas flows into the rebreathing bag AND through the pop-off simultaneously 

11. Reservoir Bag- aka rebreathing bag
Expandable bag that fills as gases enter the circuit or as patient exhales
Deflates as patient inhales
Range in size from 0.5 L to 30 L; 1 L increments
Volume of bag should be minimally 60 mL/kg
*This is equal to 6 times their minimum tidal volume

12. Reservoir Bag Calculation
If your patient weighs 15 lbs, how many mLs of air should the bag hold?
How many liters is this?
*Always round up to next highest bag
*If that size doesn’t work for your patient, switch it out!

13. Reservoir Bag Functions
Helps in determining correct ET tube placement movement of bag with breaths = tube in trachea (yay!)
Allows assessment of respiratory rate and depth
Good for when you can’t see your patient
Why can’t you see your patient?!
Allows manual ventilation of the patient
Also known as “giving a breath” or “bagging”

14. Indications for Manual Ventilation
Reverse atelectasis if present; prevent if not
Done by closing pop-off and gently squeezing bag
Performed once q 10 minutes = “sighing” patient
Removal of CO2 and anesthetic that builds up when respirations have decreased in volume
Anesthetics decrease tidal volume up to 50%
Forcing fresh gas in stimulates gas exchange in the alveoli
Assist or control ventilation – especially if in respiratory arrest or “deciding not to breathe”
IPPV

15. Is Your Reservoir Bag the Right Size?
Bags should consistently be ½ to ¾ full upon exhalation
If bag is going from over-inflated to flat =
Bag is too small and doesn’t hold enough oxygen  patient won’t be able to fully inflate lungs on inhalation
AND
Bag will overinflate on exhalation increases pressure in the circuit
If bag is flat during respirations (under-inflated) =
Bag is too big  will not see movements with each breath and wasted space in circuit

16. Pressure Manometer
Measures pressure of gas within the breathing circuit this includes the patient’s lungs
Unit is in cm H20
Should read between 0-2 cm H2O during normal respirations
Pressure increases as system is closed
How do we close the circle and why?
Gauge should never exceed 20 cm H20 in small animals!
Watch manometer while “bagging” patient

17. Pop-off Valve - aka pressure relief valve, exhaust valve
Always kept open for semi-closed system
Allows exhaled gas to leave the breathing circuit and be scavenged
Prevents the build-up of excess gas or pressure within the circuit.
If the pressure were allowed to build up (forgot to open pop-off valve), the alveoli in the lungs could rupture!

18. Pop-off Valve
The degree that the pop off valve is opened changes the flow rate and how full the reservoir bag is.
(semi-closed system)
If you see your reservoir bag unintentionally expanding very quickly- check pop-off!
Only close the pop-off valve when you are currently providing breaths for the patient
Must be opened between breaths!

19. Occlusion Valve This one is safety regulated

20. Negative Pressure Release Valve aka Air Intake Valve
Special feature activated in emergencies
Indicated by a completely empty reservoir bag
1. When an active scavenging system is utilized, if negative pressure is detected in the circuit, this valve opens and allows room air in.
Instances when there is excessive suction
2. O2 flow rate is too low or tank runs out of O2
ALWAYS keep an eye on your oxygen pressure gauge
*Better for the patient to breathe room air than no air