A system for unilateral lung ventilation includes an endotracheal tube and a blocking device for blocking the bronchus of a non-ventilated lung to prevent a ventilation medium from entering the lung. The blocking device includes an inflatable member supported by a catheter having an inflation lumen for inflating the inflatable member. The catheter includes at least one lung treatment lumen for delivering a therapeutic agent to the non-ventilated lung. An inner channel within the main channel and a side branch provide a guideway for the blocking device within the tube. A valve may be included to close the side branch when the blocking device is removed from the inner channel for parallel flow of ventilating gas in the main and inner channels. A method of using the system provides for ventilation/perfusion (V/Q) matching by respectively delivering cooled air and nitric oxide to the non-ventilated and ventilated lungs.