Blood gases measure the level of oxygen and carbon dioxide in the blood. Venous BG are drawn from a vein, as opposed to arterial BG which are drawn from an artery (oxygenated vs deoxygenated blood). So checking to make sure your DS's blood is picking up and carrying around enough oxygen and not building up too much carbon dioxide. BG results can also indicate problems with pH and will be combined with the results of the other blood tests to give a more comprehensive result.

Good luck in your search for answers. Regardless of any diagnosis, your DS is still the same perfect little boy; a diagnosis just allows you to better understand his development and assist him to reach his full potential.