While still on the mother's womb a baby's lungs are not needed to supply oxygen because the baby receives its oxygen via the mother's lungs and placenta. Since a baby's lungs do not provide any oxygen, there is no need for energy to be expended pumping blood to the lungs. The ductus arteriosus is a blood vessel that is present in all babies while still in the womb that allows blood to bypass the pathway to the lungs; it allows blood to flow from the pulmonary artery to the aorta.
When the baby is born and the umbilical cord is cut, the lungs are now needed to supply oxygen. The lungs expand, their blood vessels relax to accept more flow and the ductus arteriosus usually closes within the first hours of life. On occasion, however, the ductus arteriosus does not close on its own and this is referred to as a patent ("patent" means open) ductus arteriosus (PDA). While this condition is much more often seen in premature babies, it may also appear in term infants.
The symptoms of PDA depend on the size of the ductus and how much blood flow it carries. After birth, the pressures and resistance are much tighter in the aorta than the pulmonary artery, so if a ductus arteriosis is present, blood will flow from the aorta into the pulmonary artery. This extra blood flow into the lungs can overload the lungs and put an additional burden on the heart to pump this extra blood. This situation may not be well tolerated in a premature baby who already has problems related to immaturity of the lungs themselves. These babies may need more support from the ventilator and have symptoms of congestive heart failure.
A newborn with a patent ductus arteriosus, may have:
However, if the patent ductus arteriosus is not large, it may cause absolutely no symptoms at all and may be detected only upon further evaluation of a heart murmur. Even in the absence of symptoms, the turbulent flow of blood through the patent ductus arteriosus puts a person at a higher risk for a serious infection known as endocarditis.
Because of turbulent blood flow from the high pressure aorta to the low pressure pulmonary artery, a PDA causes a characteristic heart murmur that is heard on physical exam. The presence of the characteristic murmur along with symptoms of heart failure in a premature infant most frequently leads to the diagnosis of patent ductus arteriosus. The chest X-ray will show an enlarged heart and evidence of an excessive amount of blood flow to the lungs (except in older children, where an x-ray may appear normal). An echocardiogram is performed to confirm the diagnosis. This will demonstrate the size of the ductus arteriousus and will demonstrate if the heart chambers have become enlarged due to the extra blood flow.
In a newborn, the PDA still has the potential to close on its own without intervention. Thus, in newborns, additional time may be allowed for this to happen if the heart failure can be easily managed. If symptoms are severe, such as in a premature infant, or if it is felt unlikely to close on its own, medical or surgical closure is pursued.
If a PDA is still present beyond the newborn period, it will generally never close on its own. Closure is recommended in such cases to prevent the future risk of endocarditis.
In newborns, a medication such as indomethacin or ibuprofen can be given. These medications are given in the stomach and can constrict the muscle in the wall of the PDA and promote closure. These drugs do have side effects, however, such as kidney injury or bleeding, so not all babies can receive them. Because of the potential side effects, the baby must have lab values checked before medications can be given. If the lab values are not normal or if the medications do not work, surgery can be performed and the PDA tied off (ligated).
Medications are generally only successful in newborn patients. In older infants and children, treaments include surgery or closure in the cardiac catheterization laboratory with a device or coil.
During the cardiac catheterization procedure, the patient is sedated and catheters are placed into blood vessels in the groin. The catheters are then fed to the heart and pictures are taken of the ductus arteriosus with dye (called an angiogram). Two methods can be used to close the ductus. If it is small, a coil may be placed within the vessel which will expand to block the blood flow. If the ductus is larger, a flexible device can be placed within the ductus as a "plug".
During surgery, a small incision is made between the ribs on the left side and the ductus arteriosus is tied and cut. Surgical closure of the patent ductus arteriosus can be performed at any age, and is specifically recommended in some situations such as a very large PDA or other unusual anatomy.
The risk of complications with any of these treatments is low, determined mostly by how ill the child is prior to treatment.
In some cases, having a patent ductus arteriosus can be a good thing. Some babies have heart defects that require the patent ductus arteriosus to remain open for them to survive. In some heart defects, such as pulmonary atresia (an underdeveloped or blocked pulmonary valve), the PDA supplies the only adequate source of blood flow to the lungs so that oxygen can be delivered to the blood. In these patients, the ductus arteriosus supplies blood to the lungs from the aorta.
In other anomalies, such as underdeveloped or severely narrowed aorta (like that seen in hypoplastic left heart syndrome), the PDA is crucial to allow adequate blood flow to the body. In these patents, the ductus arteriosus supplies blood to the body from the pulmonary artery.
Medication is given intravenously (IV) to keep the PDA open and requires the baby to be closely monitored in the intensive care unit. This allows stabilization of the newborn until more definitive treatment, usually surgical, can be carried out.