Patent Ductus Arteriosus

The ductus arteriosus is a fetal blood vessel connecting the pulmonary artery with the aorta. Before birth, the placenta oxygenates the blood and the fetal lungs offer high resistance to blood flow, so the ductus diverts much of the right ventricular output away from the lungs. After birth, lung expansion lowers pulmonary vascular resistance. Rising oxygen tension and falling prostaglandin synthesis normally constrict and close the ductus within 48–72 hours. When it remains open, blood usually moves from the higher-pressure aorta into the pulmonary artery: a left-to-right shunt. That extra pulmonary flow can increase respiratory workload. The same shunt can reduce effective systemic perfusion because blood is “run off” from the aorta into the pulmonary circulation. A small PDA may cause little or no clinical effect; a hemodynamically significant PDA can produce pulmonary over-circulation, systemic hypoperfusion, or both. Closure is therefore based on the infant’s condition and echocardiographic findings, not on the presence of a murmur alone.