Blood gases are all the gases present in a dissolved form in the blood, such as oxygen or carbon dioxide. However, they are specifically called blood gases when a test of these gases performed on a blood sample, more frequently on an artery, to study the blood that is taking on oxygen in the lungs. This is also referred to as gas analysis. This sample is usually taken in the radial artery and can be a little more painful than taking a conventional blood sample, as the artery is deeper than a superficial vein. The study of the concentration of these gases can detect many diseases that cause a decrease in the amount of exchanges made between the air and the blood in the pulmonary alveoli.