An arterial blood gas, or ABG, is a lab test that takes blood from an artery and measures how much oxygen and carbon dioxide is in the bloodstream. There are three main reasons for the results of the test to show high levels of carbon dioxide. In each one, the lungs cannot get rid of the carbon dioxide.
Chronic Bronchitis
Chronic bronchitis is the inflammation of the bronchi airway. It is referred to as a chronic obstructive pulmonary disease, or COPD. People with this disease have a cough that produces mucus for at least three months out of the year and for two consecutive years. As explained by Elizabeth Corwin, Ph.D. in "Handbook of Pathophysiology," this disease causes cells in the bronchi to make too much mucus and it stops the cilia from working. Cilia are hair-like structures that line the bronchi. They move in a coordinated way and push foreign substances out of the respiratory tract. But because bronchitis paralyzes the cilia, the mucus accumulates. This creates an environment for infection and inflammation, which leads to swollen tissues. Oxygen enters the lungs so the red blood cells can deliver it throughout the body in exchange for carbon dioxide. But the inflammation of chronic bronchitis makes it hard for people to exhale. Carbon dioxide builds up in the bloodstream.
Emphysema
Emphysema is the second type of COPD. Dr. Corwin writes in "Handbook of Pathophysiology" that this disease destroys the collagen and elastin fibers in the lung. As a result, the lungs are not elastic like they should be. They lose what is called their "elastic recoil." This is similar to a rubber band that can no longer snap back into shape, that can no longer recoil. This loss of elastic recoil can be in just one part of the lungs or throughout the lungs. No elasticity means the air cannot leave the lungs and airways collapse. Like chronic bronchitis, this leads to carbon dioxide building up in the blood.
Respiratory Failure
This disorder means the red blood cells cannot exchange oxygen for carbon dioxide, so they do not get to deliver oxygen throughout the body. But it also means that the carbon dioxide stays in the bloodstream, and its levels increase. This is life-threatening and many times, people will need mechanical ventilation, according to Brian Gehlbach, M.D., Assistant Professor of Medicine at the University of Chicago in "The Merck Manual for Healthcare Professionals." Common causes of respiratory failure include adult respiratory distress syndrome (ARDS), hypoperfusion and atelectasis. In ARDS, bacteria release toxins that damage the lung capillaries and areas of the lungs. Protein, parts of cells and fluid can now enter the lungs, and people have difficulty breathing. Hypoperfusion means the tissues are not getting enough blood and oxygen. This includes the respiratory muscles, as explained by Dr. Gehlbach. In atelectasis, part of the lung or the entire lung collapses.
References
- "Handbook of Pathophysiology"; Elizabeth Corwin, MSN, Ph.D., FNP; 2000
- The Merck Manual for Healthcare Professionals: Other Types of Respiratory Failure
- The Merck Manual for Healthcare Professionals: Acute Hypoxemic Respiratory Failure (AHRF, ARDS)
