A disposable breathing circuit is adapted to be connected between a disposable face mask and a vacuum source for delivering fresh gas to the face mask and for scavenging waste gas exhaled from the face mask. The breathing circuit includes a fresh gas supply limb and an exhalation limb and a scavenging limb coupled to the exhalation limb. The scavenging limb includes a one-way valve to prevent re-breathing, a flexible flow-through reservoir bag used to store exhaled gas, and an output tube adapted to be coupled between the flow-through reservoir bag and the vacuum source.
