<unk> , also known as supplemental<unk> , is the use of<unk>  as medical treatment. Acute indications for therapy include hypoxemia (low blood<unk>  levels), carbon monoxide toxicity and cluster headache. It may also be prophylactically given to maintain blood<unk>  levels during the induction of anesthesia.<unk>  is often useful in chronic hypoxemia caused by conditions such as severe COPD or cystic fibrosis.<unk>  can be delivered via nasal cannula or face mask, or via high pressure conditions such as in endotracheal intubation or hyperbaric chamber. It can also be given through bypassing the airway, such as in ECMO therapy.<unk>  is required for normal cellular metabolism. However, excessively high concentrations can result in<unk>  toxicity, leading to lung damage and respiratory failure. Higher<unk>  concentrations can also increase the risk of airway fires, particularly while smoking.<unk>  can also dry out the nasal mucosa without humidification. In most conditions an<unk>  saturation of 94–96% is adequate, while in those at risk of carbon dioxide retention saturations of 88–92% are preferred. In cases of carbon monoxide toxicity or cardiac arrest, saturations should be as high as possible. While air is typically 21%<unk>  by volume,<unk>  can increase O2 content of air up to 100%. The medical use of<unk>  first became common around 1917, and is the most common hospital treatment in the developed world. It is currently on the World Health Organization's List of Essential Medicines. Home<unk>  can be provided either by<unk>  tanks or<unk>  concentrator.
Oxygen therapy
Asthma spacer
Bubble CPAP
Pulmonary rehabilitation
Positive airway pressure
Continuous positive airway pressure
Nicotine nasal spray
Balneotherapy