An assembly of devices dedicated to the short-term delivery of precise amounts of nitric oxide (NO), also known as nitrogen monoxide, to the respiratory tract of patients for the treatment of severe respiratory failure, particularly when a primary delivery system cannot be used (functions as a backup system). It typically includes a computerized main unit that delivers NO to gases that are to be breathed by the patient via a ventilator or other respiratory device/system and which also monitors this gaseous mixture, and tubing.