118: Patent Ductus Arteriosus

I. DEFINITION

The ductus arteriosus is a large vessel that connects the main pulmonary trunk (or proximal left pulmonary artery) with the descending aorta, some 5–10 mm distal to the origin of the left subclavian artery. In the fetus, it serves to shunt blood away from the lungs and is essential (closure in utero may lead to fetal demise or pulmonary hypertension). In full-term healthy newborns, functional closure of the ductus occurs rapidly after birth. Final functional closure occurs in almost half of full-term infants by 24 hours of age, in 90% by 48 hours, and in all by 96 hours after birth. Patent ductus arteriosus (PDA) refers to the failure of the closure process and continued patency of this fetal channel.

II. INCIDENCE

The incidence varies according to means of diagnosis (eg, clinical signs vs echocardiography).

1. Factors associated with increased incidence of PDA

   1. Prematurity. The incidence is inversely related to gestational age. PDA is found in ∼45% of infants <1750 g; in infants weighing <1000 g, the incidence is closer to 80%.

   2. Respiratory distress syndrome (RDS) and surfactant treatment. The presence of RDS is associated with an increased incidence of a PDA, and this is correlated with the severity of RDS. After surfactant treatment, there is an increased risk of a clinically symptomatic PDA; moreover, surfactant may lead to an earlier clinical presentation of a PDA.

   3. Fluid administration. An increased intravenous fluid load in the first few days of life is associated with an increased incidence of PDA.

   4. Asphyxia.

   5. Congenital syndromes. PDA is present in 60–70% of infants with congenital rubella syndrome. Trisomy 13, trisomy 18, Rubinstein-Taybi syndrome, and XXXXX (Penta X) syndrome are associated with an increased incidence of PDA.

   6. High altitude. Infants born at a high altitude have an increased incidence of PDA.

   7. Congenital heart disease. A PDA may occur as part of a congenital heart disease (eg, coarctation, pulmonary atresia with intact septum, transposition of the great vessels, or total anomalous pulmonary venous return).

2. Factors associated with a decreased incidence of PDA

   1. Antenatal steroid administration

   2. Intrauterine growth restriction

   3. Prolonged rupture of membranes

III. PATHOPHYSIOLOGY

In the fetus, the ductus is essential to divert blood flow from the high-resistance pulmonary circulation to the descending aorta. After birth, functional closure of the ductus occurs within hours (but up to 3–4 days). The patency of the ductus depends on the balance between the various constricting effects (eg, of oxygen) and the relaxing effects of various substances (most importantly: prostaglandin E's). The effects of oxygen and prostaglandins vary at different gestational ages. Oxygen has less of a constricting effect with decreasing gestational age. However, the sensitivity of the ductus to the relaxing effects of prostaglandin E₂ is greatest in immature animals (and decreases with advancing gestational age). In term infants, responsiveness is lost shortly after birth, but this does not occur in ...