A blood test used to determine the amounts of oxygen, carbon dioxide, and acidity in the blood. Information from this test is used to adjust ventilators and therapy for lung diseases. This is one of the most common tests in the ICN, and may be performed using blood from an artery (arterial blood gas [ABG]), vein (venous blood gas [VBG]), or heelstick (capillary blood gas [CBG, "cap gas"]).