Patent Ductus Arteriosus (PDA)
By Dr. Namrata Todurkar
Photo Source: hopkinsmedicine.org
Amongst the various unique issues faced by premature babies, Patent Ductus Arteriosus (PDA) is one of the most important and probably the most distressing for families. It may occasionally appear to be a hurdle in the preterm infant’s path to discharge and may prolong the need for breathing support or result in serious conditions like heart failure, chronic lung disease and feed intolerance. Prior to the twenty-first century, almost all PDAs were arbitrarily considered significant and physicians aimed to close them soon after birth. That approach is no longer favoured, and the majority of physicians prefer to watch and wait. In this blog we will mainly discuss the cause for existence of PDA, its symptoms, and its management.
What is a PDA?
The Ductus arteriosus is a blood vessel that connects two large blood vessels emerging from the heart (the pulmonary artery and the aorta). During the development of heart and blood vessels, a few special connections are established in order to utilize the placenta as an organ for oxygen extraction. These are the Patent Foramen Ovale (PFO), the ductus venosus and the ductus arteriosus. All these connections are designed to close spontaneously after birth, the PDA especially closes by contracting its muscles and converting the tube like structure to a fibrous band.
Role of ductus arteriosus in fetal life and after birth:
Before birth, the ductus arteriosus serves a very important purpose of shunting blood away from the lungs (because lungs are fluid filled and the blood vessels within the lungs have high resistance). This function is so much essential that, closure of the ductus in utero may lead to fetal demise. The shunting of blood is directed away from the lungs and towards the aorta so that more blood can be circulated to the placenta for gas exchange.
After birth, fluid within the lung is replaced with air and the blood vessels within the lungs have much lesser resistance. The direction of shunt within the PDA reverses towards the lungs and may cause flooding of the air sacs. As lungs are now the organs for gas exchange and the placenta is no longer available, it is essential to avoid over circulation of lungs. The shunting of blood within PDA can sometimes be substantial and as a result, it can diminish blood flow to the kidneys and intestine (can cause acute kidney injury and necrotizing enterocolitis) The portion of blood, which is diverted in excess towards the lung, ends up in the left side of the heart, who then has to work harder to pump it into the system. Over time, this excess quantity of blood cannot be managed well by the heart and culminates in heart failure.
Why does PDA affect preterm babies more than term born infants?
In full term neonates, the ductus arteriosus stops shunting blood very soon after birth, and by 48 hours of life more than 90 percent of them would have achieved a functional closure. In general, the rate of ductus closure is delayed in preterm infants and the incidence of PDA is inversely related to the gestational age. Almost 90 percent of babies born before 24 weeks of gestation have a PDA. According to many estimates, almost 80 percent of less than 1000gram babies and those born between 25 and 28 weeks gestation have a PDA. Babies born preterm and more than 30 weeks’ gestational age usually close their ductus by the fourth day of life.
The most important reason for the ductus to remain open in a preterm baby is the increased sensitivity of the ductal tissue to circulating chemical mediators called prostaglandins. Compared to their term born peers, preterm babies have a reduced capacity to clear prostaglandins from their circulation and this results in high concentrations. Factors like surfactant administration, infection, excessive fluid administration increase the likelihood of developing a symptomatic PDA. Antenatal administration of steroids decreases the incidence of PDA. Because of the important role played by prostaglandins in keeping the PDA open, inhibitors of prostaglandin production are usually effective in the medical treatment of PDA.
Diagnosis and treatment:
Diagnosis of PDA is done by clinical suspicion, an audible heart murmur in the setting of worsening breathing in the baby. The definitive diagnosis is by targeted neonatal Echocardiography. The presence of PDA is not an indication to treat if it is not causing trouble to the infant. PDA which is large and troublesome is referred to as ‘hemodynamically significant’. Whereas, a small PDA may be left untreated without major issues, a large PDA left open long-term can lead to complications. The larger the left-to-right shunt, greater is the association with necrotizing enterocolitis, intraventricular haemorrhage, acute kidney injury, retinopathy of prematurity, bronchopulmonary dysplasia and increased risk of death. It has been suggested that PDA closure within the first 4 weeks of life may allow for faster weaning of oxygen and ventilatory support in extremely low birth weight infants. Hemodynamically significant PDAs are treated by inhibitors of prostaglandin production like Indomethacin, Ibuprofen or Acetaminophen. Indomethacin is associated with a good success rate in terms of PDA closure but is harmful to the kidneys. Ibuprofen and Acetaminophen are the commonly used agents in the NICU. A baby can require a repeat course of medical treatment if there is no response to the first course. However, if PDA remains large even after 2-3 courses of therapy, it might be an indication for surgical ligation.
Surgical closure of PDA:
Patent Ductus Arteriosus was the first congenital heart condition that was surgically repaired (performed by Dr Robert Gross in 1938). Open surgical ligation produces definitive closure of PDA. But it is associated with a risk of exposure to surgical anesthesia, air leak around the lungs, nerve damage causing complications like vocal cord palsy and resultant increased requirements for tube feedings and respiratory support. Although the results can be excellent in a dedicated cardiac care unit and in expert hands, due to the risks associated with surgery, PDA is more frequently being treated conservatively. Among preterm infants discharged with a persistent PDA, 86% will achieve PDA closure by 1 year of age, and the remainder will require continued observation or surgical closure. With substantial adverse events depicted after surgical ligation and the debate over whether a PDA even needs to be closed, most neonatologists defer surgical ligation even if medical management fails.
Evolving ideas around the management of PDA:
The question of whether to treat a PDA or not is a matter of ongoing controversy. On one hand there is an association between PDA and various illnesses in premature infants, whereas on the other hand medical treatment of PDA has failed to show clinical benefit in terms of duration of mechanical ventilation, incidence of complications like BPD, NEC or change in length of hospital stay. While there have been several studies and thousands of publications on the topic, the decision to treat the PDA is still strongly debated among cardiologists, surgeons, and neonatologists. A survey conducted in the United states of America in 2018 found many disparities between neonatologists and cardiologists concerning the management of PDA in neonates. Most cardiologists believe that PDA closure alters the clinical outcomes in infants born <28 weeks' gestation, while almost half neonatologists surveyed disagree with this statement.
While it is a well-known fact that majority of PDAs close spontaneously, very tiny babies do require medical or surgical intervention to overcome the effects of a significant shunt. Individualized approach to management is possibly the most appropriate way to treat these tiny babies.
Dr. Namrata Todurkar, MBBS, MD (Pediatrics), DNB (Pediatrics). Fellowship in Neonatology from National Neonatology Forum India. Fellow in Neonatal-Perinatal Medicine in University of British Columbia. Areas of interest: Neonatal nutrition, Fluid and Electrolyte Management, Inborn Errors, Neurodevelopmental follow-up of preterm infants. Dr. Todurkar is a volunteer blogger at CPBF.