Recently, it was necessary to ask several outpatients to a have what is called an arterial blood gas (ABG) drawn. This is generally not a test that can be done in the office because it must be analyzed quickly using expensive lab equipment. The patients involved at first did not understand the need for the test and I thought that it would be helpful to instruct any reader who needs this test done.

The ABG test is done with a sample of blood which must be drawn from an artery not a vein. The most common site is the artery in the wrist on the side of the thumb. If you place your finger tips on this spot you can feel the artery pulsing. Drawing the blood from this artery is no more painful than a venous blood draw if done by an experienced technician or physician.

The reason to get this test is to check not only on the oxygen content of the blood, but also the carbon dioxide level. To check the oxygen level we often use something called a pulse oximeter which is usually placed on the finger. This device gives us the amount of blood saturated by oxygen in the body. This technique does not tell us about the carbon dioxide in the blood. Knowing the level of carbon dioxide in the blood of any given patient can be critical and lifesaving. The pulse oximeter does not give us this information.