Patent Ductus Arteriosus (PDA)

Why is this topic important?

Patent Ductus Arteriosus (PDA) is one of the commonest cardiovascular problems encountered in premature infants and a frequent MRCPCH examination topic. Candidates should understand its physiology, clinical features, diagnosis and management.

Definition

The ductus arteriosus is a normal fetal blood vessel connecting the pulmonary artery to the descending aorta.

Patent Ductus Arteriosus occurs when the ductus fails to close after birth, resulting in persistent left-to-right shunting of blood.

Key MRCPCH Facts

Common in preterm infants.
Incidence increases with decreasing gestation.
Large PDAs may cause heart failure and respiratory deterioration.
A PDA may close spontaneously, particularly in more mature infants.
Echocardiography is the gold standard for diagnosis.

Pathophysiology

Fetal Circulation

In fetal life:

Pulmonary vascular resistance is high.
Most right ventricular output bypasses the lungs through the ductus arteriosus.

After Birth

Normally:

Pulmonary vascular resistance falls.
Oxygen tension rises.
Ductus constricts and closes.

If the duct remains patent:

Blood flows from the aorta to the pulmonary artery.
Pulmonary overcirculation develops.
Increased pulmonary blood flow returns to the left atrium and ventricle.
This may lead to respiratory compromise and heart failure.

Risk Factors

Neonatal Factors

Prematurity
Respiratory distress syndrome
Extreme low birth weight

Maternal Factors

Rubella infection
Maternal diabetes

Other Factors

Excessive fluid administration
Chronic lung disease

Clinical Features

Small PDA

May be asymptomatic.

Possible findings:

Soft systolic murmur
Incidental echocardiographic finding

Significant PDA

Increasing oxygen requirement
Tachypnoea
Recurrent apnoea
Difficulty weaning respiratory support
Feeding intolerance
Poor weight gain

Classical Signs

Continuous or systolic murmur
Bounding pulses
Hyperdynamic precordium
Wide pulse pressure

Investigations

Echocardiography

Gold standard investigation.

Assesses:

Ductal size
Direction of shunting
Cardiac chamber enlargement
Haemodynamic significance

Chest X-Ray

May show:

Cardiomegaly
Pulmonary plethora
Pulmonary oedema

Blood Gas

May demonstrate:

Respiratory acidosis
Increased oxygen requirement

Management

Conservative Management

Appropriate for many infants.

Includes:

Careful fluid management
Optimising respiratory support
Monitoring clinical status

Medical Treatment

Common medications:

Ibuprofen
Indomethacin
Paracetamol (selected situations)

These promote ductal closure.

Surgical or Catheter Closure

Consider if:

Significant PDA persists
Medical treatment fails
Ongoing respiratory compromise

Complications

Respiratory

Prolonged ventilation
Chronic lung disease

Cardiovascular

Heart failure
Pulmonary overcirculation

Gastrointestinal

Increased risk of NEC

Neurological

Possible association with IVH in extremely preterm infants

Common Exam Traps

Trap 1

Not every PDA requires treatment.

Many close spontaneously.

Trap 2

A murmur may be absent despite a significant PDA.

Trap 3

Bounding pulses and wide pulse pressure are important clinical clues.

Trap 4

Echocardiography, not clinical examination alone, determines haemodynamic significance.

One Minute Revision

Common in preterm infants.
Left-to-right shunt.
Bounding pulses.
Wide pulse pressure.
Echocardiography confirms diagnosis.
Management: observe, medical treatment or closure.

Suggested References

BAPM Guidance
RCPCH Guidance
BNF for Children
Nelson Textbook of Pediatrics
Illustrated Textbook of Paediatrics
Rennie & Roberton's Textbook of Neonatology

Disclaimer

These notes are intended for MRCPCH revision and educational purposes only. They do not replace local, national or institutional guidelines. Clinical decisions should always be based on current guidance, senior advice and individual patient circumstances.

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