Residency · Residency · Pediatrics
Patent Ductus Arteriosus in the Preterm Infant
Overview
The ductus arteriosus is a normal fetal vascular structure connecting the pulmonary artery to the descending aorta, allowing blood to bypass the uninflated fetal lungs. In term infants, functional closure occurs within 24-72 hours of birth, with anatomic closure complete by 2-3 weeks. In preterm infants, however, the ductus frequently fails to close due to immaturity of ductal smooth muscle and heightened sensitivity to prostaglandins. The incidence of patent ductus arteriosus (PDA) is approximately 30% in very low birth weight infants and rises to 60-70% in extremely low birth weight infants under 1000 grams.
Pathophysiology of Ductal Closure
During fetal life, ductal patency is maintained by low arterial oxygen tension, circulating prostaglandins (PGE2 and PGI2), and nitric oxide. After birth, postnatal closure is driven by the rising PaO2 that causes ductal smooth muscle constriction, declining prostaglandin levels as the placental source is removed and pulmonary metabolism increases, and decreased prostaglandin receptor sensitivity in mature ductal tissue. The problem in preterm infants is that their ductal tissue is more sensitive to the dilating effects of PGE2 and simultaneously less responsive to the constrictive stimulus of oxygen. When the ductus fails to close, the result is left-to-right shunting from the high-pressure aorta into the lower-pressure pulmonary artery.
Hemodynamic Consequences
The left-to-right shunt through a PDA has two major hemodynamic consequences: pulmonary overcirculation and systemic hypoperfusion. Excess blood flow to the lungs causes pulmonary edema, worsens respiratory distress syndrome, and contributes to the development of bronchopulmonary dysplasia. Simultaneously, "diastolic steal" -- the preferential flow of blood through the low-resistance ductus during diastole -- reduces blood flow to the systemic organs. The kidneys suffer decreased perfusion with resulting oliguria. The gastrointestinal tract experiences mesenteric ischemia with increased risk of necrotizing enterocolitis. The brain experiences fluctuating cerebral blood flow with increased risk of intraventricular hemorrhage. In severe cases, coronary perfusion may be compromised. A chronically large PDA produces volume overload with progressive left atrial and ventricular dilation, eventually leading to congestive heart failure.
Clinical Presentation
The classic murmur of PDA is continuous or systolic, best heard at the left upper sternal border, though it may be absent in very preterm infants due to low pulmonary vascular resistance and equalized pressures. Bounding peripheral pulses with widened pulse pressure reflect the diastolic runoff through the ductus. A hyperdynamic precordium may be palpable. Respiratory deterioration manifests as increasing ventilatory support requirements or inability to wean FiO2 or CPAP. Hepatomegaly indicates severe heart failure. Oliguria and feeding intolerance reflect end-organ hypoperfusion from systemic steal. Some PDAs are clinically silent and detectable only by echocardiography.
Echocardiographic Assessment
Echocardiography is the gold standard for diagnosis and assessment of hemodynamic significance. Key parameters include ductal diameter (greater than 1.5 mm is generally considered significant), direction and pattern of shunt flow (left-to-right, bidirectional, or right-to-left), the left atrium-to-aortic root ratio (greater than 1.5 suggests significant left-sided volume overload), diastolic flow reversal in the descending aorta or mesenteric/renal arteries indicating steal, left ventricular output and dilation, and mitral valve E/A ratio. There is no universal definition of a "hemodynamically significant PDA" (hsPDA); it is generally established by a combination of echocardiographic findings and clinical symptoms.
Management Approaches
Conservative Management
There is a growing paradigm shift toward conservative (watchful waiting) management of PDA in preterm infants. The rationale is that many PDAs close spontaneously, even in very preterm infants. Supportive measures include fluid restriction (120-140 mL/kg/day), diuretics for pulmonary edema (though furosemide should be used cautiously as it increases PGE2 production), optimization of respiratory support, and tolerance of a moderate shunt if the infant is stable and growing. Observational data suggest no difference in BPD or mortality between conservative and active treatment approaches for many infants.
Pharmacologic Closure
Indomethacin
Indomethacin is a non-selective cyclooxygenase (COX) inhibitor given intravenously at 0.1-0.2 mg/kg every 12-24 hours for 3 doses, with dosing adjusted by postnatal age. It achieves ductal closure in approximately 70-80% of cases. Side effects include transient renal dysfunction with oliguria, decreased platelet function, and intestinal perforation (particularly when given concurrently with dexamethasone). Indomethacin also has cerebral blood flow-stabilizing properties that may reduce IVH, which led to studies of prophylactic administration.
Ibuprofen
Ibuprofen is another non-selective COX inhibitor, given as a 10 mg/kg IV loading dose followed by 5 mg/kg for 2 additional doses at 24-hour intervals. It has similar efficacy to indomethacin but carries lower risk of renal side effects and NEC. Oral ibuprofen may be as effective as the IV formulation with fewer side effects.
Acetaminophen (Paracetamol)
Acetaminophen inhibits the peroxidase component of prostaglandin synthase through a different mechanism than traditional NSAIDs. It is given at 15 mg/kg IV or orally every 6 hours for 3-7 days. Emerging evidence suggests closure rates similar to ibuprofen. Its advantages include fewer renal and gastrointestinal side effects and oral availability. However, long-term neurodevelopmental safety data remain limited.
| Agent | Dose | Schedule | Closure Rate | Key Side Effects |
|---|---|---|---|---|
| Indomethacin | 0.1-0.2 mg/kg IV | q12-24h x 3 doses | 70-80% | Renal dysfunction, platelet dysfunction, intestinal perforation |
| Ibuprofen | 10 mg/kg then 5 mg/kg IV | q24h x 3 doses | 70-80% | Less renal toxicity than indomethacin |
| Acetaminophen | 15 mg/kg IV/PO | q6h x 3-7 days | Similar to ibuprofen | Fewer renal/GI effects; limited long-term safety data |
Surgical Ligation
Surgical ligation is indicated when pharmacologic treatment fails, when medical therapy is contraindicated (active NEC, renal failure, significant bleeding), or when hemodynamic instability requires urgent intervention. The procedure involves open thoracotomy with clip application or ligation. Risks include pneumothorax, chylothorax, recurrent laryngeal nerve palsy, and post-ligation cardiac syndrome (hypotension and oxygenation failure occurring in the first 6-12 hours post-operatively in approximately 30% of infants). Observational studies suggest associations between ligation and BPD, retinopathy of prematurity, and neurodevelopmental impairment, though these associations are confounded by indication bias.
Catheter-Based Closure
Transcatheter device closure is an emerging option for small preterm infants, with devices now available for infants as small as 700 grams. The Amplatzer Piccolo Occluder is FDA-approved for premature infants weighing 700 grams or more with hemodynamically significant PDA. Advantages include avoidance of thoracotomy and potentially fewer complications, though the procedure requires an experienced interventional cardiologist and cardiac catheterization laboratory.
The Treatment Controversy
A major paradigm shift has occurred in PDA management, with many centers now adopting conservative management as the default approach. The PDA-TOLERATE trial demonstrated that early routine treatment did not reduce BPD or death compared to a conservative approach. There is growing concern that treatment of PDA may cause more harm than the PDA itself in many cases. However, the counter-argument holds that large, persistent PDAs in symptomatic ELBW infants likely do warrant intervention. The current approach at many centers is to treat only when there is a large PDA with clear clinical impact that has failed to respond to conservative measures.
<image>An echocardiographic illustration showing a parasternal short-axis view of a preterm heart with a patent ductus arteriosus, with color Doppler demonstrating left-to-right shunting from the aorta to the pulmonary artery. Include labeled anatomical structures (aorta, main pulmonary artery, ductus) and an adjacent diagram showing the hemodynamic consequences of the left-to-right shunt including pulmonary overcirculation and systemic steal.</image>
<image>A comparative diagram showing three management strategies for PDA in preterm infants: conservative management (fluid restriction, supportive care, watchful waiting), pharmacologic closure (indomethacin, ibuprofen, acetaminophen with their mechanisms of action on prostaglandin synthesis), and surgical/interventional approaches (thoracotomy ligation, catheter-based device closure). Flowchart format with decision points and outcomes.</image>
Clinical Pearls
Not every PDA needs treatment, and many close spontaneously even in very low birth weight infants. The absence of a murmur does not exclude a hemodynamically significant PDA in a ventilated preterm infant, as equalized pressures may eliminate the pressure gradient that generates the murmur. Diastolic flow reversal in the descending aorta on echocardiography is one of the most important markers of hemodynamic significance and systemic steal. Concurrent indomethacin and dexamethasone must be avoided due to the increased risk of spontaneous intestinal perforation. Furosemide paradoxically increases PGE2 production and may delay ductal closure; chlorothiazide or hydrochlorothiazide are preferred alternative diuretics. Acetaminophen is increasingly used as first-line pharmacotherapy due to its favorable side-effect profile, though long-term safety data remain limited. Post-ligation cardiac syndrome occurs in approximately 30% of infants undergoing surgical ligation, and anticipatory hemodynamic support should be planned.
References
- Hamrick SEG, et al. Patent Ductus Arteriosus of the Preterm Infant. Pediatrics. 2020;146(5):e20201209.
- Clyman RI, et al. PDA-TOLERATE Trial. J Pediatr. 2019;213:41-48.e6.
- Ohlsson A, et al. Ibuprofen for the treatment of PDA in preterm or low birth weight infants. Cochrane Database Syst Rev. 2020;(1):CD003481.
- Dang D, et al. Comparison of oral paracetamol versus ibuprofen in premature infants with PDA. PLoS One. 2013;8(10):e77888.
- Sathanandam S, et al. Amplatzer Piccolo Occluder clinical trial for percutaneous closure of the PDA in premature infants. Catheter Cardiovasc Interv. 2020;96(6):1266-1276.
