Chapter 61 Patent Ductus Arteriosus
PATHOPHYSIOLOGY
The ductus arteriosus is a large vessel that connects the main pulmonary trunk (or left pulmonary artery) with the descending aorta approximately 5 to 10 mm from the origin of the left subclavian artery. Patent ductus arteriosus (PDA) is the persistent patency of the ductus arteriosus after birth, which results in the shunting of blood directly from the aorta (higher pressure) into the pulmonary artery (lower pressure). This left-to-right shunting causes the recirculation of increased amounts of oxygenated blood in the lungs, which raises demands on the left side of the heart. The additional effort required of the left ventricle to meet this increased demand leads to progressive dilation and left atrial hypertension. The cumulative cardiac effects cause increased pressure in the pulmonary veins and capillaries, which results in pulmonary edema. The pulmonary edema leads to decreased diffusion of oxygen and hypoxia, with progressive constriction of the arterioles in the lungs. Pulmonary hypertension and failure of the right side of the heart ensue if the condition is not corrected through medical or surgical treatment. Most PDAs are a left-to-right shunting of blood, but right-to-left ductal shunting may occur with associated pulmonary disease, left-heart obstructive lesions, and coarctation of the aorta. Closure of the PDA depends primarily on the constrictor response of the ductus to the oxygen tension in the blood. Other factors affecting ductus closure include the action of prostaglandins, pulmonary and systemic vascular resistances, the size of the ductus, and the condition of the infant (premature or full-term). PDA occurs more frequently in premature infants; it is also less well tolerated in these infants, because their cardiac compensatory mechanisms are not as well developed and left-to-right shunts tend to be larger.
INCIDENCE
1. Precise incidence varies depending on gestational age and according to the means of diagnosing (clinical signs as opposed to echocardiography).
2. Approximately 5% to 10% of infants with PDAs have additional cardiac defects (coarctation of the aorta, ventricular septal defect, aortic stenosis).
3. PDA is present in 60% to 70% of infants with congenital rubella infection.
4. PDA occurs 2 to 3 times more often in girls than in boys.
5. PDA is found in approximately 45% of infants <1750 g; and in infants <1000 g, the incidence is 80%.
CLINICAL MANIFESTATIONS
The disorder may be manifest at birth, but usually it is first noticed on days 1 to 4 of life. Manifestations of PDA in premature infants are often clouded by other problems associated with prematurity (e.g., respiratory distress syndrome). Signs of ventricular overload are not apparent for 4 to 6 hours after birth. Infants with small PDAs may be asymptomatic; infants with large PDAs may manifest signs of congestive heart failure (CHF):
1. Persistent murmur (systolic, then continuous; heard best at left upper sternal border)
2. Hyperactive precordium (result of increased left ventricular stroke volume)
3. Prominent to bounding pulses
4. Wide pulse pressure (higher than 25 mm Hg)
5. Decreased mean arterial blood pressure
6. Tachypnea (respiratory rate higher than 70 breaths/min)
7. Increased ventricular requirement (associated with pulmonary problems)
8. Tachycardia (apical pulse higher than 170 beats/min); usually associated with congestive heart failure
COMPLICATIONS
1. Cardiovascular: arrhythmias (digitalis toxicity)
2. Respiratory: concurrent pulmonary disorder (e.g., respiratory distress syndrome or bronchopulmonary dysplasia), pulmonary hemorrhage
3. Gastrointestinal (GI): necrotizing enterocolitis, GI hemorrhage (decreased platelet count), failure to thrive, decreased blood flow to intestines with use of indomethacin
4. Renal: hyperkalemia (decreased urinary output), decreased blood flow to kidneys with indomethacin
5. Hematologic: sepsis secondary to impaired white blood cell motility with use of indomethacin
LABORATORY AND DIAGNOSTIC TESTS
1. Echocardiography—two-dimensional echocardiographic visualization of the ductus with Doppler measurements is sensitive and specific for identifying PDA; M-mode measurements of left atrial to aortic root ratio greater than 1.4:1 in full-term infants or greater than 1.0 in preterm infants (caused by increased left atrial volume as a result of left-to-right shunt)
2. Doppler color flow mapping—to evaluate blood flow and its direction
3. Chest radiographic study—prominent or enlarged left atrium and left ventricle (cardiomegaly); increased pulmonary vascular markings
4. Electrocardiography (ECG)—findings vary with degree of severity: no abnormality noted with small PDA; left ventricular hypertrophy is typically seen as tall R waves in V6 with large PDA, limited value in assessment
5. Cardiac catheterization—performed only when further evaluation of confusing echocardiographic or Doppler findings is needed or when additional defects are suspected to be present
MEDICAL AND SURGICAL MANAGEMENT
Interrupting the left-to-right flow of blood is the goal of management for the uncomplicated PDA. When the shunt is hemodynamically significant, conservative measures may be tried initially. Conservative management consists of fluid restriction and medications. Furosemide (Lasix) is used along with fluid restriction to promote diuresis and minimize the effects of cardiovascular overload. Fluid restriction alone is unlikely to cause PDA closure and, in combination with diuretics, may lead to electrolyte abnormalities and dehydration as well as caloric deprivation, which impairs growth.
Indomethacin (Indocin) may be used if fluid management and diuretics fail to significantly decrease the left-to-right ductal shunting. Indomethacin, a prostaglandin synthetase inhibitor, promotes closure of the ductus. It works best in newborns younger than 13 days old and has been shown to be effective as late as 1 month of age. Its side effects include transitory changes in renal function, increased incidence of occult blood loss via the GI tract, and inhibition of platelet function for 7 to 9 days. Prophylactic administration of indomethacin soon after birth in very premature infants has also been advocated to decrease the incidence of PDA, intraventricular hemorrhage, and mortality. However, uncertainty exists about routine early prophylactic use of indomethacin because of the possible negative effects of the drug on neonatal vasoregulation and cerebral blood flow. Contraindications for the use of indomethacin are as follows:
1. Blood urea nitrogen (BUN) levels higher than 30 mg/dl
2. Creatinine levels higher than 1.5 mg/dl to 2.0 mg/dl
3. Urine output of less than 0.6 ml/kg/hr over the preceding 8 hours
4. Platelet count lower than 50,000/mm3, because it prolongs platelet activity
6. Clinical or radiographic evidence of necrotizing enterocolitis
The more immature the ductus, the greater the chance of its reopening. In one study, 23% of infants who were delivered before 26 weeks of gestation demonstrated reopening; in contrast, only 9% of those delivered between 26 and 27 weeks demonstrated reopening if the ductus was found to be closed by echocardiography after treatment with indomethacin. Early treatment leads to a higher rate of permanent ductus closure. If the ductus reopens, a second course of indomethacin treatment may be used.
Ibuprofen is another prostaglandin synthetase inhibitor that has been shown to be equally effective in closing the ductus. It does not appear to reduce the mesenteric and renal blood flow as much as indomethacin and is associated with fewer renal side effects. There is less experience with the use of ibuprofen as compared to indomethacin. It has not been studied sufficiently in preterm infants of less than 27 weeks’ gestation, and, to date, the intravenous product has not been readily available.
The use of digitalis is controversial and is contraindicated in premature infants. Digitalis is not useful because myocardial contractility is increased rather than reduced in infants with PDA. Digitalis increases the force of contraction of the heart, increases the stroke volume and cardiac output, and decreases cardiac venous pressures. It is used to treat CHF and selected cardiac arrhythmias. Using digoxin (digitalis) in combination with indomethacin may increase the infant’s susceptibility to the toxic effects of digoxin.
Medical management also includes prophylactic administration of antibiotics to prevent bacterial endocarditis. In older children, there are no exercise restrictions if no evidence of pulmonary hypertension is present.
Increasing positive end expiratory pressure is helpful in managing infants with PDA. When end expiratory pressure is added, the degree of left-to-right shunting through the ductus is decreased; as a result, systemic blood flow increases.
A low hematocrit has been shown to aggravate left-to-right shunting by lowering the resistance of blood flow through the pulmonary vascular circulation. Increasing the hematocrit above 40% to 45% will decrease excessive shunting through the PDA and help systemic oxygenation when perfusion is limited. Conservative management therapies usually only delay the ultimate need for PDA closure.
Surgical Management
Surgery is indicated if the ductus arteriosus remains hemodynamically significant after indomethacin therapy or if indomethacin use is contraindicated. Surgical management consists of PDA ligation. Two major groups of children have been identified as requiring this surgery. The first includes infants with CHF, usually premature neonates who did not respond to indomethacin therapy. Children older than 6 months of age whose ductus did not close spontaneously (and who are at risk for pulmonary hypertension and subacute endocarditis) make up the second group. Both groups require a left thoracotomy incision. Bypass is unnecessary. Infants are usually at greater risk for complications, so the PDA is doubly ligated in a comparatively quick procedure. For older children, surgery is advised during their preschool years and is performed by dividing the ductus between clamps and suturing the ends closed. Coil closure of the PDA to plug the ductus during cardiac catheterization or video-assisted transthoracic endoscopic closure of the PDA can also be performed, but its use is limited by the size of the patient and the diameter of the PDA.
The hemodynamic results of PDA ligation are truly curative, in contrast to the palliative procedures of many heart surgeries. Closure decreases the pulmonary flow while increasing the systemic flow, creating normal hemodynamics. Unfortunately, if severe pulmonary hypertension existed before surgery, closure will not reverse this process.
After an infant’s first birthday, the most common treatment for a PDA is occlusion at cardiac catheterization. Today the most common device used for PDA occlusion is a spring occluding coil. Coil occlusion is best suited to close PDAs with an internal diameter of less than 2.5 mm. If the PDA is larger, alternative techniques should be used.
NURSING INTERVENTIONS
1. Monitor cardiac and respiratory status (may need to monitor as often as every hour during acute phase).
2. Observe and report signs of changes in cardiac status (color, vital signs, peripheral perfusion, level of consciousness, activity level, signs of CHF).
3. Observe and report signs of respiratory distress and changes in respiratory status.
4. Monitor and report responses to ventilator assistance.
5. Assess for and maintain optimal hydration status.
6. Promote and maintain optimal body temperature.
7. Monitor action and side effects of medications.
8. Monitor response to and side effects of blood transfusions.
9. Promote process of attachment between parents and infant.
10. Provide developmentally appropriate stimulation activities (see the relevant section in Appendix F).
Preoperative Care
1. Allow parents to express feelings; despite its being relatively minor heart surgery, PDA repair is still overwhelming to parents.
2. Prepare child for surgery by obtaining assessment data.
3. Because older child is usually of preschool age, prepare him or her accordingly; do not tell child that surgery will make him or her “feel better,” because child is usually asymptomatic.
Postoperative Care
1. Monitor child’s or infant’s cardiac status (see the Cardiovascular Assessment section in Appendix A).
2. Monitor for and report signs and symptoms of complications.
3. Treat chylothorax if present.
4. Provide intensive pulmonary toilet.
5. Provide intensive pain control, because pain with thoracotomy incision is usually greater than that with median sternotomy.
6. Monitor child’s response to medications.
7. Provide emotional support to infant or child during hospitalization.
Discharge Planning and Home Care
1. Instruct parents to observe for and report signs of cardiac or respiratory distress.
2. Instruct parents about administration of medications.
3. Provide parents with name of physician or nurse to contact for medical or health care follow-up.
4. Instruct parents about principles of infection control and well-child care (e.g., use of prophylactic medications before dental care).
5. Encourage and instruct parents about providing developmentally appropriate stimulation activities (see the relevant section in Appendix F).
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Jaillard S, et al. Consequences of delayed surgical closure of patent ductus arteriosus in very premature infants. Ann Thorac Surg. 2006;81(1):231.
Lott JW. Assessment and management of the cardiovascular system. Kenner C, et al. Comprehensive neonatal nursing, ed 3, Philadelphia: WB Saunders, 2003.
Shah S, Ohlsson A. Ibuprofen for the prevention of patent ductus arteriosus in preterm and/or low birth weight infants. Cochrane Database Syst Rev. 25(1), 2006. CD004213
