ABG - Arterial Blood Gases

Introduction

Arterial blood gases, called 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 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 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 machines are set correctly.

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. 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 lab for analysis. 

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.
pH Level
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:

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

breathing troubles, such as lung infections, asthma, emphysema, or not breathing fast enough

certain medicines

Acid levels may be too low from:

dehydration

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.
Bicarbonate Level
The part of the test that measures the bicarbonate level in the blood will determine whether there is a metabolism problem.
Other minor parts of the test may be monitored by a doctor in certain situations.
The doctor must look at the pH, breathing, and metabolic parts of the test as a whole. This allows the doctor to sort out different problems in a person's body.