BREATHING SYSTEMS

BREATHING VS. NONREBREATHING SYSTEMS Also known as a circle system Exhaled gases are re-circulated back to the patient. After exhalation, they go through the unidirectional valve, to the CO2 canister and the reservoir bag, then back through the inhalation valve where they are combined with more fresh gas for the patient to inhale.

BREATHING VS. NON-REBREATHING SYSTEMS Choose a re-breathing system for your patient if the patient is >15lb (7kg) Because re-breathing systems recycle exhaled gases, the O2 flow rates are relatively low. When we recycle, we don’t have to use as much oxygen or anesthetic gas.

Re-breathing Systems Depending on the position of the pop-off valve, we can call a re-breathing system CLOSED OR SEMI-CLOSED CLOSED- the pop-of valve is totally closed. All gases exhaled by the patient remain in the circuit and are re-circulated after the CO2 is absorbed SEMI-CLOSED- the pop-off valve is open or semi-closed. Some gases exhaled by the patient remain in the circuit, some exit through the pop off and into the scavenger

CLOSED Total re-breathing Low oxygen flow rate! Pop off valve is closed SEMI-CLOSED aka partial re-breathing Higher oxygen flow rate than closed system Pop off valve is open letting excess gases be scavenged (in some cases, valve may not be open ALL the way)

RE-BREATHING VS. NON-REBREATHING SYSTEMS In a non-rebreathing system, oxygen flows from the tank to the flowmeter and vaporizer, however the unidirectional inhalation valve is bypassed. Fresh gas enters a hose after the vaporizer and is inhaled by the patient. Exhaled gases exit through a separate hose and into a reservoir bag. There is no entry into the CO2 canister. The gases pass through the pop off valve and into a scavenging system. Most anesthetic machines can be converted back and forth from re-breathing to non-rebreathing systems

BREATHING VS. NONREBREATHING SYSTEMS Choose a non-rebreathing system for your patient if it weighs less than 15lb (7kg). Little to no gas is recycled back to the patient, so O2 flow rate are very high! Since we are being wasteful and NOT recycling, we have to use more oxygen and anesthetic gas The pop-off valve should be all the way open or partially open with a non-rebreathing system.

NON-REBREATHING SYSTEM ADVANTAGES: Great for small patients (< 7 kg) as it offers very little resistance to breathing. Lighter weight than conventional tubing; creates less drag on tube DISADVANTAGES: More expensive as more gas is used. Patients are more susceptible to heat loss without the benefit of the tube within a tube.

NON-REBREATHING Commonly used Bain Co-axial system Tube within a tube Inner tube delivers fresh gas to the patient. Outer tubing conducts gas away from the patient and into a reservoir bag. Since most of the gas is scavenged and does not re-enter the patient, the bag is used to visualize respirations and facilitate manual ventilation. Incoming gases are warmed by exhaled gases

CO2 absorption Not necessary Must have Quickly Slowly Flow rates High Parameters Nonrebreathing Rebreathing CO2 absorption Not necessary Must have Anesthetic depth change Quickly Slowly Flow rates High Low Cost Waste gas Minimal Pop off valve Fully open Open, Closed or partially open Heat and moisture conservation Poor Good Animal size < 7 kg >7 kg, unless pediatric hoses are available

O2 FLOW RATES Depends on the period of anesthesia and the type of system being used Generally, flow rates during induction and recovery are higher because we are trying to achieve a rapid change in anesthetic depth. Chamber induction: 5 L/min Mask induction: animals <10kg = 1-3 L/min animals > 10kg = 3-5 L/min

O2 FLOW RATES MAINTENANCE FLOW RATES NONREBREATHING: REBREATHING 150-200ml/kg/min (ex: Bain Coaxial system) 400-600mL/kg/min (ex: Jackson-Rees) WE COMMONLY USE 250 mL/kg/min at VTI (and we will round up to at least 0.8 L/min) REBREATHING CLOSED: 5-10 mL/kg/min, SEMICLOSED: 20-40 mL/kg/min WE COMMONLY USE 40 mL/kg/min at VTI (and will round up)

LEAK TEST TO BE PERFORMED BEFORE EVERY ANESTHETIC PROCEDURE! Close pop-off valve and cover the patient end of the anesthetic tube Push O2 flush button or turn on flow meter until bag is distended and the pressure on the manometer reads 30cm H20. Turn O2 off and watch the manometer. If the reading drops rapidly, bag deflates rapidly, or a hissing sound is heard, leak is present. If there were no leaks, the pressure would remain constant for at least 30 seconds, despite the O2 being turned off.

LEAK TEST CONT’D Check the hoses, bag, attachments of machine to be sure everything is properly placed When test is over, reopen pop off valve and squeeze the reservoir bag.

RESERVOIR BAGS WEIGHT BAG SIZE 0-3 kgs ½ L 4-7 kgs 1 L 8-15 kgs 2 L