An arterial blood gas, or ABG, is a test to measure the levels of oxygen and carbon dioxide in the blood and the acidity of the blood. It is often ordered for people who have respiratory conditions that may cause an imbalance in the level of gases in the blood. A sample of blood is drawn from an artery. A doctor, nurse, respiratory therapist or lab technician, trained specifically in how to take an ABG, should obtain the sample.
Determine the spot from which to get the arterial blood. Arteries used to take an arterial blood gas include the femoral artery in the groin, the brachial artery on the inside of the elbow and the radial artery located on the wrist. The femoral is the largest, but can cause the most complications, such as excessive bleeding. The radial is the most common site to take an arterial blood gas.
Perform an Allen's test if the blood is to be obtained from the radial artery in the wrist to determine collateral circulation. The test helps determine if the ulnar artery, also located in the forearm, is working efficiently. This is done in case the radial artery is damaged taking the blood. With your thumb and middle finger press down on both arteries firmly. Instruct the patient to open and close her hand a few times. Then open the hand. It should be whitish from restricted blood flow. Release the ulnar artery. If the hand turns pink, blood is flowing through the ulnar artery.
Position the patient’s arm palm up, if taking the blood from the radial artery. Feel for the pulse. Unlike veins, which can be seen, the arteries from which to test for blood gases are taken by feel. If you do not feel a good one at one location, select a different spot where you can feel the pulse.
Clean the site with an antiseptic and insert the needle into the skin where you feel the pulse. If you hit the artery, the blood will flow into the syringe. There is no need to pull back on the plunger of the needle. The pressure from the artery causes the blood to flow out. Usually 3 to 5 milliliters is enough blood to run a sample.
Pull the needle out of the artery and immediately apply pressure to the artery with a clean piece of gauze. The artery can bleed and applying direct pressure may limit it. Hold pressure on the site for 5 minutes.
Take the needle off the syringe and place the cap on the syringe. Roll the syringe in between your hands a few times to reduce the chances that the blood will clot before it is analyzed.