The device has an intubation tube (2), a gas mixing chamber and a pressure generator (4,4'). A selection element with respect to the target fraction of the returned breathing gas from its residual fraction or vice-versa is provided between the intubation tube and the mixing chamber and a target feed connection (7) is connected to a controlled delivery regulator (9) with a target fraction reservoir. An independent claim is also included for a method of reusing and admixing a target fraction in a gas mixture.
