Definition Arterial blood gases (ABG) are a series of blood measurements that are ordered as a single test. This test is primarily used to check lung function and acid levels in the body.
Who is a candidate for the test? There are many potential candidates for this test. This test is helpful any time there is a question about breathing problems, oxygen and carbon dioxide exchange, or acid levels in the body. Examples include:
people with rapid breathing due to heart or blood conditions
people who are unconscious
people who are suspected of having too much or too little acid in the body. An example would be people with kidney failure, who usually have too much acid in the body.
people on artificial breathing machines called ventilators. ABG's are done regularly to assure that the machines are set correctly.
How is the test performed? A blood sample from an artery is needed to perform the test. In most cases, an artery on the palm side of the wrist is used to get the blood. Sometimes, an artery in the groin or other area is used to get blood. The skin over the artery is first cleaned. Next, a small needle is inserted through the skin and into the artery. The needle is usually hooked up to a syringe. Blood flows into the syringe once the needle is put into the artery. Pressure is applied over the area after the blood is collected to prevent bleeding. The blood is then sent to the laboratory for analysis.
What is involved in preparation for the test? No preparation is generally needed for this test. A doctor will give any instructions if needed.
What do the test results mean? There are several values that are measured in an ABG. Each of the values has a set range that is considered normal. If any of the main values becomes severely abnormal, it may result in death.
The pH is one of the main parts of this test. This is a measure of the level of acid in the blood. Acid levels may be too high with:
salt imbalances, which may be from a hormone problem in the body
certain medications
If the pH is abnormal, the other parts of the test can help determine the reason. For example, if the acid level in the body is too high, it could be from breathing or metabolism problems. It is important to know what is the cause of the high acid level, as the treatment is often different. If the acid level is too high because of a breathing problem, the person may need extra oxygen or even a ventilator. If the acid level is too high from metabolism problems, a person may need to be hooked up to a blood-filtering machine, or may need antibiotics or other drugs.
The breathing parts of the test are the oxygen and carbon dioxide levels in the blood. The job of the lungs is to take in oxygen and get rid of carbon dioxide. If some type of breathing or respiratory problem is present, these values will be abnormal. The oxygen level can also be used to check if a person is getting enough oxygen or whether they need extra oxygen.
The part of the test that measures the bicarbonate level in the blood will determine whether there is a metabolism problem. If a metabolism problem is present, this value will be abnormal.
There are other minor parts of the test that may be monitored by a doctor in certain situations.
The doctor must look at the pH, breathing, and metabolic parts of the test together. This allows the doctor to sort out different problems in a person's body.
Author: Adam Brochert, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
