Dedicated One Way Fresh Gas Flow into the Patient Breathing Circuit
All dedicated inhalation sedation flowmeters (Matrx, Porter & Accutron) operate in a similar manner. The fresh (titrated) gases from the flowmeter outlet are ‘split’ into two flow conditions. Due to the bias on the flowmeter non-return valve, a portion of fresh gas is directed into the reservoir bag. This allows provision for patient monitoring.
The exception to this is when using a system such as the Porter Silhouette. Due to the bag tee being capped (with the reservoir bag removed), all titrated gases will pass out of the flowmeter outlet into the Silhouette system. Therefore slightly lower flow rates may be required, the rule of thumb being the 4-5-6 Rule. 4 is used for paediatrics, 5 for average females and 6 for average males. The patient should be monitored closely and flow rates adjusted as required.
There is also a flow of fresh gas from the flowmeter outlet into the breathing system. Once in the breathing system assembly, it is a dedicated one way flow until the expired gases are vented into the source of active draw.
It is not possible for patient expired breathing to re-enter the flowmeter due to the outlet (Bag tee) non-return valving, aided by the positive pressure flow of fresh gases from the flowmeter.
This effectively results in no internal contamination of the fresh gas hosing or reservoir bag.