Circle System Circuit

The essential features of the circle absorber are: a carbon dioxide absorber canister (C), breathing bag (B), unidirectional inspiratory (Vi) and expiratory (Ve) valves, fresh gas supply (F) and pressure-relief valve (V). The absorber is connected to the patient via corrugated hoses and a Y-piece (not shown) attached to the inspiratory and expiratory valves (Vi and Ve).

The position of the breathing bag and pressure-relief valve may vary in relation to the absorber, but the above is a common and satisfactory arrangement.

Inspiration:
Inspiration causes the expiratory valve to close, and gas flows from the breathing bag to the patient via the inspiratory limb of the circuit. Anaesthetic is taken up from the in-circuit vaporiser (VIC), if fitted.

Expiration:
The inspiratory valve closes and gas flows into the breathing bag via the expiratory limb. Carbon dioxide is absorbed by the soda lime canister. Excess gas is vented when necessary via the pressure-relief valve.