The therapeutic medical gases include

oxygen at ambient pressure

oxygen at hyperbaric pressure

helium-oxygen mixtures (heliox) 

nitric oxide. 

Heliox is occasionally used to partially relieve the increased work of breathing due to partial upper airway obstruction. Nitric oxide is administered as a direct, selective pulmonary vasodilator.

The primary goal of oxygen therapy is to prevent or correct hypoxemia or tissue hypoxia. Table 57-1 identifies classic categories of hypoxia. Oxygen therapy alone may not correct either hypoxemia or hypoxia. Continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) may be required to recruit collapsed alveoli. Patients with profound hypercapnia may require ventilatory assistance. High concentrations of oxygen may be indicated for conditions requiring removal of entrapped gas (eg, nitrogen) from body cavities or vessels. The short-term inhalation of increased concentrations of oxygen is relatively free of complications.