Oxygen therapy, also called supplemental oxygen, is when oxygen gas (O) is used for medical treatment by giving the gas to the patient for inhalation. It can be used for ilnesses like hypoxia, carbon monoxide toxicity, and cluster headaches. It can be used over a long time for people who suffer with illnesses that lower oxygen levels in the blood like COPD and cystic fibrosis. It can be given in a few different ways such as through a nasal cannula, face mask, or inside a hyperbaric chamber. Oxygen levels need to be high enough for respiration to keep a patient healthy and for normal cell metabolism.