Arterial Blood Gases
Arterial blood gases, abbreviated as ABGs, are a series of blood measurements that are ordered as a single test. This test is used mainly to check lung function and acid and alkali levels in the body.
Who is a candidate for the test?
Any time there is a question about breathing problems, oxygen and carbon dioxide exchange, or acid and alkali levels in the body, this test can be helpful. Examples include:
people with shortness of breath due to lung problems
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, such as someone with kidney failure
- people on artificial breathing machines called ventilators. ABGs are done regularly to assure that the machine settings are correct for the person's condition.
How is the test performed?
A blood sample from an artery is needed to do this 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 may be used. The skin over the artery is cleaned first.
Next, a small needle is inserted through the skin and into the artery. The needle is usually hooked up to a syringe lubricated with a small amount of anticoagulant such as heparin. Blood flows into the syringe once the needle is put into the artery.
Firm pressure is applied over the area for a few minutes after the blood is collected to prevent bleeding. Extreme care is taken not to let a bubble of air into the artery, because a bubble could travel to the brain and cause a stroke - a complication not possible with a blood draw from a vein.
The blood is then sent to the lab for analysis.
What is involved in preparation for the test?
Most of the time, there is no preparation needed for this test. A healthcare professional 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 to be within healthy limits. If any of the main values becomes severely abnormal, the person may die.
The pH is an important part of this test. This is a measure of the level of acid in the blood. Acid levels may be too high with:
- kidney failure or damage
- certain cases of uncontrolled diabetes
- exposure to certain toxic substances, such as a drug overdose
- shock, which may occur from heart failure, serious infections, or massive blood or fluid loss
- difficulty breathing, such as in the case of lung infections, asthma, emphysema, or not breathing fast enough
- certain medicines
Acid levels may be too low from:
- certain types of kidney problems
- breathing too fast, such as when a person has a panic disorder
- excessive vomiting
- salt imbalances, which may result from a hormone problem in the body
- certain medicines
If the pH is abnormal, the other parts of the test can help find out the reason. For example, if the acid level in the body is too high, it could be from breathing or metabolism problems. It is crucial to know what is causing the high acid level so that the best treatment can be chosen. 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 medicines.
Oxygen and Carbon Dioxide Levels
Other 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 level of bicarbonate (alkali) in the blood is calculated by the laboratory equipment from the pH and carbon dioxide levels. This level indicates if there is a metabolism problem. The healthcare professional must look at the pH, breathing, and metabolic parts of the test as a whole. This allows him or her to sort out different medical conditions that the person may have.