Respiratory failure is a syndrome rather than a disease and is characterized by the inability of the respiratory system to maintain an adequate gas exchange at rest or during exercise resulting in hypoxemia with or without concomitant hypercarbia. Respiratory system consists of two important components: the lungs which take part in gas exchange and the muscular pump that helps in ventilation. Clinical features in respiratory failure are due to the underlying disease itself; in addition, they also have signs of hypoxemia and hypercapnia. Correction of hypoxemia should be the first priority in the management of respiratory failure, irrespective of the presence or absence of hypercapnia.