Function of Inspiratory and Expiratory Unidirectional
Valves
Two unidirectional valves are used in each circle system to ensure that
gases flow toward the patient in one breathing tube and away in the
other. The inspiratory valve prevents backflow through the inspiratory
limb during expiration and the expiratory valve prevents backflow through
the expiratory limb during inspiration. Dead space ventilation occurs
in those sections of the circuit where bidirectional flow (i.e., both
inspiratory and expiratory flow) is possible. Therefore, the unidirectional
valves minimize dead space to the part of the breathing circuit that
extends from the Y-piece to the patient.
The corresponding movements of the inspiratory and expiratory valves can observed in the simulation.
CO2 Absorber Function
Soda lime or Baralyme is used to absorb CO2 exhaled by the patient.
Note that, for efficiency, the CO2 absorbent is positioned such that
only gas being redirected to the patient is scrubbed. An indicator dye
will turn blue/purple as the CO2 absorbent becomes exhausted. The absorption
of CO2 molecules in the canisters can be observed in the simulation.
High fresh gas flows will wash away all CO2. This is most clearly demonstrated by turning the fresh gas flow to maximum or by pressing the oxygen flush in the simulation.