The fetal lungs are collapsed, and blood passes from the right atrium directly into the left atrium through the foramen ovale: an open conduit between the paired atria, or through the ductus arteriosus: a shunt between the pulmonary artery and the aorta.
By Deborah Leader, RN. Updated January 21, 2016. Hypercapnia is a condition that occurs when there is too much carbon dioxide in the blood. While it is sometimes caused by things such as hypoventilation or a narcotic drug overdose, a much more common cause is COPD. If you have COPD, it's important to know the hypercapnia symptoms, as well as the treatments available.
Third, the majority of carbon dioxide molecules (85 percent) are carried as part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H2CO3).