When a physician needs information on how efficiently a patient’s lungs are functioning, an arterial blood gas (ABG) can provide the answer. The ABG is a blood test. Performance of a routine blood test requires blood taken from a vein, often from the area near the elbow crease.
For an ABG test, however, blood is drawn from an artery instead of a vein, and it is analyzed immediately for oxygen (O2) content, carbon dioxide (CO2), and pH, a measure of acidity. The radial artery in the wrist is a frequent site for ABG sampling. The ABG gives information about the arterial blood’s oxygen and carbon dioxide content, as well as the blood’s acidity.
Because the lungs are responsible for the extraction of oxygen from the outside air as well as for the removal of carbon dioxide, analysis of the artery sample for those gases indicates how well the lungs are functioning. The main function of the respiratory system is to carry out respiration.
Respiration provides the body’s vital organs with oxygen and allows for removal of accumulated waste products, primarily acid. After the blood sup-ply passes though the lungs and picks up oxygen, it becomes oxygen (O2) rich and carbon dioxide (CO2) poor. The oxygen-rich blood is then pumped by the heart to the entire body—via the arteries—in order to supply organs with needed oxygen. Although an ABG is not a routine test in outpatient asthma management, it is frequently used in intensive care settings. If a person is suffering a severe asthmatic exacerbation, the ABG will reveal decreased oxygen and carbon dioxide.
If the asthma worsens further, carbon dioxide may rise, and the pH will drop, indicating a dangerous buildup of acid. Such a scenario may indicate life-threatening asthma. If such is the case, respiratory failure will ensue from continued carbon dioxide accumulation and oxygen deprivation; treatment includes life support with a ventilator. Patients on ventilator assistance may require frequent ABG monitoring to assist physicians in selecting optimal ventilator settings and to ensure adequate oxygen delivery to vital organs.