Seminars in perinatology
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Seminars in perinatology · Apr 1993
ReviewThe transition from fetal to neonatal circulation: normal responses and implications for infants with heart disease.
The primary function of the circulatory system of both the fetus and newborn is to deliver oxygen to metabolizing organs and return deoxygenated blood to the gas exchange organ to replenish the oxygen and eliminate the waste product CO2. In the fetus, the gas exchange organ is the placenta, and its vascular connections are in a parallel arrangement with the other systemic organs, remote from the pulmonary circulation. In order to supply deoxygenated blood to the placenta and return oxygenated blood to the systemic organs, a series of extracardiac shunts (ductus venosus, ductus arteriosus) and an intracardiac communication (foramen ovale) are necessary. ⋯ Severe right heart obstruction is also well tolerated in the fetus, because the combined fetal cardiac output can be transferred to the aorta, with the ductus arteriosus supplying predominantly lung blood flow. After birth, such "ductal-dependent" pulmonary blood flow can lead to critically low levels of pulmonary blood flow and severe cyanosis with closure of the ductus arteriosus. An understanding of fetal hemodynamics and the acute and chronic changes that occur with transition to the newborn circulation are important for the care of normal newborns and are crucial to the recognition, diagnosis, and management of the newborn with significant congenital heart disease.