Test used to determine the oxygen, carbon dioxide, and acid content of the blood. A blood gas is used to evaluate the status of the infant’s lungs. If the lungs are not working properly, the concentration of oxygen gas in the blood will be low and the concentration of carbon dioxide will be high. The amount of acid in the blood reflects both lung and heart function. Physicians use the blood gas to help them evaluate a sick newborn infant.
Blood gas can be obtained from three sources: arterial blood, capillary blood or venous blood. Arterial blood (blood taken from an artery) is the most accurate and useful way to measure blood gases because it most closely reflects the lung function. Capillary blood (blood taken by pricking a finger or heel) is often easier to obtain than arterial blood, but does not give as accurate a measure of oxygen concentration in the blood as the arterial blood sample does. Venous blood (blood taken from a vein) is used the least often and yields values that least closely reflect lung function, but may still be useful.