What is patent ductus arteriosus (PDA)?

In foetal life, a special blood vessel connects the circulation from the lungs to the arteries, supplying the rest of the body. This is called the arterial duct or ductus arteriosus.  After birth, normally this vessel spontaneously closes and separates the two circulations. In very preterm babies the duct may not close immediately and for some it persists – for which the medical term used is patent ductus arteriosus (or PDA).

If the PDA is only partially open, there may not be any symptoms or consequences for the baby. However, if the opening is larger, blood flow to the lungs can increase and the heart must pump more than usual to compensate this condition. This can occasionally lead to potential health problems such as respiratory complications, heart failure, or a reduced blood supply to the kidneys, the intestines, and the brain.

If left without treatment many PDAs eventually close but the healthcare team will weigh up the benefits and disadvantages of any health issues that may be made worse by the presence of a PDA.

Who is affected and what are the risk factors?

The earlier a preterm baby is born, the more likely it is to be affected by health issues resulting from PDA. For example, approximately four out of ten babies born before 34 weeks of gestation are estimated to develop a PDA.

What is the cause?

Foetal Circulation: While the foetus is in the womb, its oxygen needs are met by the mother. Oxygen from the mother passes through the placenta, along the umbilical vein and is pumped to the heart of the baby through a blood vessel called the ductus venosus. From there it is pumped to the rest of the body. The fetus does not need blood to pass through the lungs before birth, so it flows straight into the major artery (Aorta) through the ductus arteriosus. After blood has delivered the oxygen to the body of the foetus, the blood returns to the heart and is pumped back to the umbilical cord and placenta to be re-oxygenated.

In term-born babies, the ductus arteriosus closes rapidly after birth as it is no longer necessary. When breathing starts, blood flow through the ductus arteriosus falls off and increasing levels of oxygen encourage it to close. For some preterm babies, this closing process is delayed. If it remains widely open, then the heart must pump blood to both the lungs and the aorta at the same time leading to a range of health issues.

How is it diagnosed?

Most babies with a PDA have a heart murmur, which the the healthcare team will identify during their examination. Other symptoms include apnoea, abnormal blood pressure, changes in heart rate, and difficulties in breathing. Additionally, the oxygen saturation may decrease and carbon dioxide levels may increase in the blood, all of which are picked up using routine montoring in the NICU. Some times the heart size increases a little on X-ray. Using ultrasound, echocardiography can identify a PDA and monitor how well it responds to therapy.

How is it managed?

Sometimes PDA resolves without causing any serious problems, termed spontaneous closure. Often careful attention to fluid balance is all that is required.

Several drugs may be used to try to encourage a PDA to close, usually indometacin or ibuprofen, In some situations, surgery may be needed to close the PDA.

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