Illustrative case: At 21 days of life, a 28-week infant who has gone from noninvasive support to re-intubation should not be labeled with “worsening bronchopulmonary dysplasia (BPD)” and left there. The more useful question is narrower: Is a patent ductus arteriosus causing clinically important pulmonary overcirculation and systemic steal, or is the murmur distracting the team from another deterioration?
Consider a very low birth weight infant recovering from respiratory distress syndrome who develops recurrent apnea, a rising FiO₂ requirement, diffuse haziness on chest radiography, cardiomegaly, bounding pulses, and a wide pulse pressure. A continuous murmur makes PDA highly plausible. It does not, by itself, establish that the PDA is hemodynamically significant or that closure will improve the current illness.
Start with causality, not the murmur
The arterial blood gas shows inadequate ventilation, but hypercapnia does not identify the mechanism. Pulmonary edema from a large left-to-right shunt, pneumonia, atelectasis, airway or ventilator complications, evolving lung injury, and pulmonary hypertension can all worsen gas exchange in this setting.
| Pattern | Findings that support it | Discriminating next question |
|---|---|---|
| PDA-related pulmonary overcirculation | Cardiomegaly, increased pulmonary vascular markings, rising oxygen or ventilator needs, bounding pulses, low diastolic pressure | Does echocardiography show an unrestrictive left-to-right shunt with left-heart volume loading or systemic diastolic steal? |
| Late-onset infection | New apnea, tachycardia, temperature instability, feeding intolerance, lethargy, changing secretions, inflammatory or culture abnormalities | Are cultures, examination, laboratory findings, and imaging consistent with infection rather than isolated cardiopulmonary congestion? |
| Airway or parenchymal complication | Abrupt deterioration, asymmetric breath sounds, tube migration, focal collapse, pneumothorax, new infiltrate, or mucus plugging | Is the endotracheal tube correctly positioned, and does the radiograph explain the change? |
| Pulmonary hypertension or another cardiac problem | Pre- and postductal saturation difference, right-heart strain, septal flattening, bidirectional or right-to-left ductal flow, poor ventricular function | Is the ductus functioning as a pressure-relief pathway rather than producing uncomplicated pulmonary overcirculation? |
The practical move is parallel processing: check the airway and ventilator, repeat the examination, assess perfusion and urine output, and investigate late-onset infection when clinically indicated while obtaining the echocardiogram. A PDA can coexist with sepsis or pneumonia; finding one does not exclude the others.
Echo should answer more than “Is the PDA open?”
The 2025 American Academy of Pediatrics report describes hemodynamic significance as a combination of clinical and echocardiographic findings rather than a single magic number. Its suggested framework uses at least two clinical features plus at least one echocardiographic feature. This is a structured approach, not a universal diagnostic law, but it is useful at the bedside and on examinations.
Clinical features include substantial respiratory support, hypotension requiring a vasopressor, persistent oliguria or renal dysfunction, or gastrointestinal and growth concerns such as abdominal distension, feeding intolerance, poor growth despite optimized nutrition, or a history of NEC. In this vignette, respiratory deterioration is concerning; the case does not provide enough information to assume that the infant fulfills the entire clinical framework.
The echo report should specifically address:
- Ductal size and restriction: a minimum diameter greater than about 1.5 mm may support a significant shunt, but size alone is not enough.
- Transductal flow: unrestrictive left-to-right flow, often reflected by a ductal peak velocity below 2 m/s, suggests a substantial shunt.
- Left-sided volume loading: at least moderate enlargement of the left atrium or left ventricle supports pulmonary overcirculation.
- Systemic diastolic steal: decreased, absent, or reversed end-diastolic flow in the abdominal descending aorta supports impaired systemic perfusion.
- Myocardial performance and pulmonary pressure: ventricular systolic and diastolic function, septal geometry, and the direction of ductal flow help determine whether closure is safe.
A common examination error is to treat a ductal diameter or a left-atrial-to-aortic ratio as a treatment command. These measurements can be supportive, but their meaning depends on shunt direction, flow pattern, ventricular response, postnatal age, and the infant’s clinical state.
The important echo result is not simply “PDA present.” It is “PDA present, with this shunt volume, this systemic effect, and this ventricular response.”
The management fork at 21 days
If the PDA is small and restrictive, with no meaningful left-heart volume loading or systemic steal, it is unlikely to explain the entire deterioration. Continue the search for infection, airway problems, atelectasis, anemia, fluid overload, evolving lung disease, or pulmonary hypertension.
If the study shows a large, unrestrictive left-to-right shunt together with clinical respiratory or systemic consequences, the PDA becomes a credible treatment target. Supportive care still matters: optimize fluid balance, nutrition, electrolytes, respiratory support, and cardiovascular status. Do not respond reflexively with aggressive fluid restriction; evidence that fluid restriction improves outcomes after hsPDA diagnosis is lacking.
The treatment conversation at three weeks requires more nuance than the traditional “murmur plus wide pulse pressure equals indomethacin.” Current evidence does not support routine early closure solely to prevent bronchopulmonary dysplasia or death. The AAP report notes that evidence is insufficient to make firm recommendations for hsPDA management beyond two weeks, when expectant monitoring, medical closure, and procedural closure all remain individualized decisions.
A randomized clinical trial published on February 17, 2026, enrolled infants born at 22–28 weeks who had a protocol-defined PDA identified between 48 hours and 21 days of age. It found no reduction in death or BPD with active medication—acetaminophen, ibuprofen, or indomethacin—compared with expectant management; observed mortality was lower in the expectant-management group. The trial stopped early for futility and safety. That result should discourage reflexive closure, not prohibit rescue treatment in an infant with severe, persistent ductal physiology and ongoing cardiopulmonary compromise. Trial results describe populations; they do not replace physiologic assessment of the individual infant.
For a convincingly hemodynamically important PDA, ibuprofen or acetaminophen may be considered according to local neonatal protocols and the infant’s renal, hepatic, gastrointestinal, and hematologic status, enteral tolerance, and prior treatment. If medication is contraindicated or fails while the infant remains dependent on substantial support, transcatheter or surgical closure may be discussed with neonatology and pediatric cardiology teams experienced in very small infants.
A right-to-left or markedly bidirectional ductal pattern changes the reasoning. It may indicate high pulmonary vascular resistance or pulmonary hypertension rather than uncomplicated pulmonary overcirculation. If the ductus is serving as a pressure-relief pathway, closing it without understanding the pressure physiology could worsen right-heart performance. The first task is to evaluate the pulmonary vascular and cardiac state, not to celebrate ductal closure.
Common traps worth correcting
- “The machinery murmur proves hsPDA.” It is a strong clue, not the hemodynamic diagnosis.
- “The chest radiograph proves PDA.” Cardiomegaly and pulmonary vascular prominence support the hypothesis but are not specific.
- “A PDA explains the apnea.” Apnea in a very preterm infant with new oxygen need still warrants consideration of infection, airway problems, seizures, metabolic disturbance, and worsening lung disease.
- “One echo number decides treatment.” Size, flow, left-heart loading, systemic steal, and ventricular function must be interpreted together.
- “At 21 days, closure is either mandatory or futile.” The evidence is uncertain beyond two weeks; the decision should be selective, physiology-based, and reassessed after other reversible causes are addressed.
Practical takeaways
- Treat new respiratory deterioration at three weeks as a localization problem, not automatically as BPD progression.
- Use the murmur, bounding pulses, wide pulse pressure, and pulmonary congestion to prioritize echocardiography—but not to skip an infection and airway evaluation.
- Ask the echo to describe shunt direction, restriction, left-heart volume loading, systemic diastolic flow, pulmonary pressure, and ventricular function.
- Do not describe a PDA as hemodynamically significant from ductal diameter alone or from a single left-heart measurement.
- At 21 days, discuss closure as a selective rescue strategy, balancing current physiology, treatment risks, and the limits of outcome evidence.
- If ductal flow is right-to-left or bidirectional, evaluate pulmonary hypertension before considering closure.
