Oxygen partial pressure (pO2)

pO2 measures the partial pressure of oxygen dissolved in your blood. It is usually part of an arterial blood gas test and reflects how well oxygen moves from the air in your lungs into your bloodstream, as well as the effect of any oxygen therapy.

A small sample of arterial blood, most often from the wrist, is analyzed promptly to prevent changes from exposure to room air. pO2 is different from oxygen saturation, which reflects the percentage of hemoglobin carrying oxygen.

Clinicians use pO2 to evaluate breathing problems, lung disease, and the response to oxygen therapy or ventilator support. It helps identify low oxygen levels that can occur with conditions such as pneumonia, asthma or COPD flare, heart failure, blood clots in the lungs, and during anesthesia or critical illness.

Your clinician may order it if you are short of breath, have low pulse oximeter readings, or when acid-base balance needs assessment. The test is generally safe; brief discomfort, bruising, or bleeding at the artery puncture site can occur, and rarely there may be infection or vessel spasm.

Your healthcare team interprets pO2 together with pH, pCO2, bicarbonate, oxygen saturation, and your symptoms. A lower pO2 suggests that oxygen transfer from lungs to blood is limited, which can result from lung conditions, infection, fluid in or around the lungs, blood clots, chest wall or muscle problems, or being at higher altitude.

A higher pO2 often reflects supplemental oxygen or hyperventilation. If results are unexpected, your team may repeat the test, review oxygen settings and sampling technique, correlate with imaging or pulmonary testing, and tailor treatment.

Do not adjust oxygen or breathing equipment without medical advice.