The reservoir bag should be at least 4 to 6 times the patient's tidal volume. Tidal volume is often quoted as 10-20 mL/kg. The middle value, 15 mL/kg, is commonly used in small animals. If 15 mL/kg is multiplied by 4 and 6 then 60 and 90, respectively, become constants.

Breathing systems are classified into two broad categories: Rebreathing circuits and Non-rebreathing (NRB) circuits.

Unfortunately, there are no standard of care guidelines available for cleaning breathing circuits in veterinary medicine, so it is going to be strictly the decision of the individual hospital to do what they feel is best.