Oxygen therapy is the most important aspect of supportive care in the management of a critically ill child. Knowledge of the physiology of oxygenation is a key to the proper oxygen therapy. High flow systems are more dependable devices for oxygenation and their use needs to be stressed. Patients on oxygen need close monitoring. Ventilatory support and Continuous Positive Airway Pressure (CPAP) is mandatory in some patients in addition to oxygen therapy for the prevention and treatment of hypoxia.