Supplemental oxygen is prescribed if tests show that the oxygen level in your blood is too low. If the level stays too low for too long, serious problems can occur in many parts of the body. Supplemental oxygen helps to ease your symptoms and prevent future problems by getting more oxygen to the blood. Depending on your test results, you may need oxygen all the time. Or it may only be needed during certain activities, such as exercise or sleep. When oxygen is prescribed, you'll be referred to a medical equipment company. They will set up the oxygen unit and teach you how to use it.