Ratio of arterial oxygen tension to inspired oxygen fraction

This test measures the difference between the amount of oxygen in the blood, and the amount of oxygen that is inhaled while breathing. This test measures the extent of decreased lung function.

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:

• ARDS - Acute respiratory distress syndrome
• Transfusion related acute lung injury

Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.

Do not exercise before this test.

Before an arterial blood draw, the healthcare worker may check blood circulation to your arm or leg. Tell the healthcare worker if you use supplemental oxygen as this may affect the test results.

An artery in the wrist is the most common site to draw arterial blood. However, an artery at the inside bend of the arm or groin may be used. The area will be swabbed clean with antiseptic. Anesthetic may be used to numb the skin over the area where the blood will be drawn. A needle is used to puncture the skin. You will be asked to hold very still while your blood is collected. When enough blood is collected, the needle will be removed.

If you have an existing arterial catheter, a blood sample may be collected from that catheter.

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the procedure. Inform the person doing the procedure if you feel that you cannot continue with the procedure.

If you receive anesthetic to numb the skin before an arterial blood draw, you may feel discomfort at the location where the anesthetic needle is inserted into the skin. You may feel discomfort as the needle used to draw your blood is inserted into the skin, and you may have cramping at the site during the procedure. Inform the person doing the test if you feel faint or nauseated or if the discomfort is severe.

If blood is collected from an existing catheter inserted into an artery, you will feel little or no discomfort.

If blood was drawn from an artery in your arm or leg, cotton will be placed over the site and held firmly for at least five minutes to stop the bleeding. Bleeding may continue beyond five minutes if you are using medications or supplements that thin your blood or have a medical condition that causes excessive bleeding. When bleeding has stopped, a bandage will be placed firmly over the site and should be left on for 30 to 60 minutes. You should rest for at least 15 minutes after the test. Avoid heavy use of the arm or leg from which the blood was drawn for 24 hours after the blood is collected.

If blood was drawn from an existing catheter inserted into an artery, there are no special instructions for you after this test.

You have the right to help plan your care. To help with this plan, you must learn about your health condition and how it may be treated. You can then discuss treatment options with your caregivers. Work with them to decide what care may be used to treat you. You always have the right to refuse treatment.