All forms of respiratory support involve one essential element: The gas or gas mixture administered to the patient. Oxygen is an indispensable gas for cellular metabolism and is indicated in cases of hypoxia. Oxygen therapy aims to increase the partial pressure of oxygen in arterial blood by increasing the oxygen concentration of inspired air. In addition to its therapeutic effects, the adverse effects and drawbacks of oxygen should be known. Several methods and devices for the administration of supplementary oxygen are available. Selection of the method should be individualized according to the patient's age and disease, the required inspiratory fraction and the child's possibilities of adaptation. Helium is an inert gas that has a very low specific weight and density. These properties explain its therapeutic effects, mainly in airway obstructions due to various etiologies. Breathing the helium-oxygen mixture (heliox) reduces respiratory effort and improves gas exchange, without significant adverse effects.