Definition: Arterial blood gas is the concentration of oxygen and carbon dioxide carried in arterial blood.
Arterial blood gas analysis is a test in which blood is taken from an artery in your wrist to evaluate how effective your lungs are in bringing oxygen to the blood and removing carbon dioxide from it.
Since arteries lie deeper under the skin than veins, most technicians will inject a local anesthetic prior to drawing blood for the ABG test. Without a local anesthetic, this procedure can be very painful.
If you are taking a blood thinner or any other type of medication that prevents or reduces clotting of the blood, be sure to tell your doctor prior to the procedure.
Source: Coping with COPD by Elaine Fantle Shimberg