During an emergency—such as a serious accident, possible heart attack, or other life-threatening event—you might be started on oxygen therapy right away.
Otherwise, your doctor will decide whether you need oxygen therapy based on test results. An arterial blood gas test and a pulse oximetry test can measure the amount of oxygen in your blood.
For an arterial blood gas test, a small needle is inserted into an artery, usually in your wrist. A sample of blood is taken from the artery. The sample is then sent to a laboratory, where its oxygen level is measured.
For a pulse oximetry test, a small sensor is attached to your fingertip or toe. The sensor uses light to estimate how much oxygen is in your blood.
If the tests show that your blood oxygen level is low, your doctor may prescribe oxygen therapy. In the prescription, your doctor will include the number of liters of oxygen per minute that you need (oxygen flow rate). He or she also will include how often you need to use the oxygen (frequency of use).
Frequency of use includes when and for how long you should use the oxygen. Depending on your condition and blood oxygen level, you may need oxygen only at certain times, such as during sleep or while exercising.
If your doctor prescribes home oxygen therapy, he or she can help you find a home equipment provider. The provider will give you the equipment and other supplies you need.