A test for arterial blood gases determines the amount of carbon dioxide, oxygen and carbon monoxide bound to hemoglobin in a volume of blood from an artery. It can also test for the acidity of blood. It is an important test of heart and lung function. The term "blood gases" is a bit of misnomer. There are always dissolved gases in the liquid part of blood that are generally inert, such as nitrogen. What a physician needs to know is whether or not oxygen and carbon dioxide are properly bound to blood in the bloodstream.