Hemodynamically Significant Patent Ductus Arteriosus in Low-Birth-Weight Infants: Fact or Fiction?

Abstract

Both the ductus arteriosus and foramen ovale provide a means whereby blood flow in the fetus is diverted away from the high-resistance pulmonary vascular bed to the much lower resistance systemic circulation. At birth or soon thereafter the pulmonary vascular bed experiences a substantial degree of vasodilation and lowering of vascular resistance by mechanisms presently unknown, whereas systemic vascular resistance increases. The former occurs in order to permit the dramatic rise in pulmonary artery blood flow that is necessary for initiation of lung function and thus the exchange of respiratory gases, to replace the function of the placenta. In concert with these changes in lung function and pulmonary blood flow is the anatomic closure of the foramen ovale and the functional closure of the ductus arteriosus. However, in contrast to the foramen ovale, the ductus arteriosus generally remains patent for some time after birth. Whereas this patency is of little consequence to the well term infant [1], it may result in substantial problems in the preterm infant due to the magnitude of the left-to-right shunt that may occur. This chapter discusses the patent ductus arteriosus (PDA) in the preterm infant, pointing out present-day problems in our understanding of its role in neonatal illness and thus in the care and treatment of the preterm infant, in particular the infant of less than 1,500 g birth weight.