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 tube, a flexible flow-through exhalation bag, an exhalation tube disposed between the face mask and an entry port of the exhalation bag, and a scavenging tube disposed between an exit or of the exhalation bag and the vacuum source. The exhalation tube includes a one-way valve to prevent re-breathing.
