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Last Updated 8/18/03
Breathing Circuit

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.