Blood Gas Analysis

Blood gas analysis is a means of determining the amount of oxygen or carbon dioxide being carried in the blood, and in some cases, of discovering the identity of a toxic gas, such as carbon monoxide, that may be present. Also, the determination can be made as to whether the blood is too acidic or too alkaline, which may help the physician in his diagnosis.

Among other functions, blood carries oxygen to the body's tissues and removes carbon dioxide. The blood laden with carbon dioxide passes through the right side of the heart into the lungs and exchanges the carbon dioxide for fresh oxygen. The oxygenated blood is then pumped by the left side of the heart out into the body to repeat the cycle.

The red blood cells, or erythrocytes, carry the blood gases. Hemoglobin, the substance that gives blood its red color, is the molecular substance in the erythrocyte that attaches to oxygen and exchanges it for carbon dioxide.

Carbon monoxide, a colorless, very toxic gas, can displace oxygen in the bloodstream. Hemoglobin has approximately 12 times the affinity for carbon monoxide as it does for oxygen, so it will pick up carbon monoxide if both gases are present. This means that the body does not get the oxygen it needs, and eventually death will occur.

Testing blood gases is a means to determine whether an acid-base (biochemical) disturbance is of respiratory or metabolic origin. Respiratory conditions such as pneumonia, bronchitis, emphysema, or severe asthma can cause the blood to become more acid. Respiratory conditions such as aspirin toxicity, strenuous exercise, fever, or overactive thyroid can cause the blood to be more alkaline. Kidney failure, burns, heart attack, or starvation are the metabolic reasons for the blood to become acid, and liver failure, vomiting, ulcer, or cystic fibrosis cause metabolic alkaline blood.

To determine blood gases, the blood specimen must be taken from an artery (usual blood specimens are taken from a vein) and the blood specimen is placed in ice to prevent any changes in blood gases, and rushed to the laboratory for analysis.