Described is a therapeutic gas delivery device (200), in combination with a ventilator allowing for delivery of combined flow of breathing gas and therapeutic gas, the gas delivery device comprising an inlet to connect to a source of therapeutic gas (103), an outlet to connect to a device that introduces breathing gas and the therapeutic gas to a patient, at least one binary control valve (109) in fluid communication with the inlet and outlet that delivers a constant flow of the therapeutic gas, at least one proportional control valve (107) in fluid communication with the inlet and outlet that delivers a variable flow of the therapeutic gas, wherein the binary control valve and the proportional control valve are in parallel flow paths, a control system (115) that delivers the therapeutic gas through one or more of the binary control valve and the proportional control valve, wherein the control system is configured to deliver the therapeutic gas to a patient in an amount proportional to a flow of breathing gas.
