A method and apparatus for respirating a patient in which the apparatus has a circulation device for circulating a gas in one direction and a conduit system, a pressure control device for varying a pressure of the gas and the conduit system in accordance with the desired respirating pattern, a sensor for measuring a flow of the gas and a composition of the gas, at least one supply line for a component of the gas, and a discharge line connected to the conduit system. The discharge line has a first valve for discharging the gas out of the conduit system, a second valve behind the first valve and a third valve in spaced relation to a behind the second valve.
