A therapeutic gas delivery device includes a monitor having an inlet and an outlet, a source of therapeutic gas in fluid communication with the monitor inlet, and a gas delivery tube in fluid communication with the monitor outlet. The monitor includes a control valve having a normally open port, a normally closed port, and a common port. The common port is connected to the monitor outlet over a gas line and the normally open port and normally closed port are connected to the monitor inlet and atmosphere. The valve is switchable between a first position wherein the therapeutic gas passes through the monitor and a second position wherein atmospheric air or gas passes through the monitor. A flow sensor is placed in the gas line to measure the flow of gas through the second line and produces a signal indicative of the flow of gas through the gas line. A sensor by-pass tube extends around the flow sensor to allow a predetermined portion of the gas to by-pass the flow sensor. A computer is operatively connected to the flow sensor. The computer may be programmed to control the switching of the control valve in response to signals received from the flow sensor.