(also called "ABGs", "gases", "arterial gases").

Blood contains oxygen and carbon dioxide. Oxygen and carbon dioxide are types of gases. When we measure the amount of these gases in the blood stream, we call the laboratory test a "blood gas" measurement. A blood gas test also identifies the amount of acidity in the blood. The balance of acids is reported as the pH.

When the lungs are working properly, oxygen will move into the blood stream and carbon dioxide will move out. When we exhale, we eliminate acids from the body to help keep the pH normal.

Blood gases are measured to evaluate lung function and to assess the effectiveness of the mechanical ventilator.

The acidity of the blood can change for many different reasons. For example, acid levels may rise if the heart, kidney or liver fails. Blood gases also provide important information about the function of other body organs.

Arterial line


Blood gas tests are performed on a small sample of blood taken from an artery. An artery is a blood vessel that carries oxygen rich blood to all of the organs of the body. A small catheter similar to an intravenous can be placed in an artery to make it easy to obtain frequent samples. This is called an arterial line. It allows us to measure blood gases without having to pick the patient with a needle. If the patient does not have an arterial line, a small sample of blood from an oxygen rich capillary can be collected from the earlobe.




Last Updated: October 23, 2014

LHSCPatients, Families & Visitors

Last Updated October 23, 2014 | © 2007, LHSC, London Ontario Canada