dioxide absorber canister (C) is connected
to a breathing bag (B), the fresh gas supply (F), the patient
(P) and a pressure-relief valve (V).
breathes to-and-fro into the circuit. Expired carbon dioxide is
absorbed by the soda-lime. Excess gas is vented when necessary via
the pressure-relief valve.
with the original horizontal canister is that, unless it is tightly
packed, the soda-lime tends to settle and allow channeling of the
gas above the granules:
This can lead
to substantial rebreathing and can be avoided by ensuring that the
soda-lime is tightly packed using a nylon pot scrub pad. An alternative,
and superior, approach usually used in large animal systems is to
use a vertical canister so that channeling cannot occur:
- The position
of the canister close to the patient's head is a major inconvenience.
- The to-and-fro
pattern of breathing causes the soda lime to become more rapidly
exhausted at the patient end of the canister, leading to inefficiency
in soda-lime use and a progressive increase in apparatus dead
of gas can lead to rebreathing with horizontal canisters.
Little used in small animals, but is still useful for field anesthesia
of large animals, where portability of the equipment may be a major