One factor that influences the severity of high blood pressure in the lungs, or pulmonary hypertension, is the amount of oxygen in the adjacent small air sacks of the lung. The amount of oxygen in the air sacks is more important than the amount of oxygen in the blood flowing through the lungs or the body. We know this is true because children with heart defects that cause low levels of oxygen in the blood (low oxygen saturation measurements) do not have tight lung vessels, or pulmonary hypertension if the amount of oxygen in the air sacks is normal.

The small arteries of the lung constrict and the blood pressure in the lungs increases when the amount of oxygen in the air sacks is low (alveolar hypoxia). This process may occur in the presence of lung disease. For example, in patients with a lung infection (pneumonia), the small arteries in the most infected areas constrict so more blood flows to the areas of lung that are less infected. The small arteries in the lung also constrict when an individual travels to a higher altitude where the amount of oxygen they breathe is relatively low.

The small arteries of the lung may relax in some patients with pulmonary hypertension when they breathe supplemental oxygen, even if their oxygen saturation measurements are normal in room air. Thereby, supplemental oxygen may be an effective therapy for some patients. Supplemental oxygen may also help to prevent an increase in blood pressure in the lungs of some patients by helping them maintain a normal or increased amount of oxygen in the air sacks of their lungs.

Blow by oxygen may not deliver as much oxygen to the lungs as a properly positioned nasal cannula or face mask. However, blow by devices will likely deliver more oxygen into the lungs than a cannula or mask if the patient is unable or unwilling to keep them in place.

Many individuals with pulmonary hypertension have normal oxygen saturation measurements while breathing room air. They do not need extra oxygen to maintain adequate oxygen saturation measurements or to sustain life. As a result, blow by oxygen can be safely used for these patients, even if the supply of oxygen is transiently removed, or is only used part-time.

Blow by oxygen may not be appropriate for some patients with pulmonary hypertension. Blow by oxygen should not be used for patients with lung disease who have low oxygen levels in the lung and blood if it does not sufficiently increase the amount of oxygen in the blood to a normal level. Further, blow by oxygen alone will not alleviate problems with airway obstruction in patients with obstructive sleep apnea, or help patients who do not breathe adequately while they are sleeping.

Patients and parents of patients should discuss with their care provider whether blow by oxygen might be an acceptable therapy for them or their child.