Fresh gas flow

In Anaesthesia, fresh gas flow is the mixture of medical gases and volatile anaesthetic agents which is produced by an anaesthetic machine and has not been recirculated. The flow rate and composition of the fresh gas flow is determined by the anaesthetist.

Typically the fresh gas flow emerges from the common gas outlet, a specific outlet on the anaesthetic machine to which the breathing attachment is connected.

Open circuit forms of equipment, such as the Magill attachment, require high fresh gas flows (e.g. 7 litres/min) to prevent the patient from rebreathing their own expired carbon dioxide. Recirculatin (rebreather) systems, use soda lime to absorb carbon dioxide, so that expired gas becomes suitable to re-use. With a very efficient recirculation system, the fresh gas flow may be reduced to the patient's minimum oxygen requirements (e.g. 250ml/min), plus a little volatile as needed to maintain the concentration of anaesthetic agent.

Increasing fresh gas flow to a recirculating breathing system can reduce carbon dioxide absorbent consumption. There is a cost/benefit trade-off between gas flow and use of adsorbent material when no inhalational anaesthetic agent is used which may have economic and environmental consequences.[1]