**9. Premature neonates with a large PDA**

a. Prevalence.

Significant PDA with CHF occurs in 15% of prematures with a birth weight of less than 1,750 g and in 40% to 50% of those with a birth weight of less than 1,500 g.

b. Pathophysiology

244 Congenital Heart Disease – Selected Aspects

surgical team.

1. Norwood operation

years.

**9. Premature neonates with a large PDA** 

a. Prevalence.

gas to attain a fraction of inspired oxygen of 0.17 to 0.19. PVR can also be increased by maintaining the hematocrit at greater than 0.40, a state that optimizes oxygencarrying capacity and increases the viscosity of the blood. Although these medical management strategies may provide temporary palliation, infants with marked pulmonary overcirculation and systemic hypoperfusion benefit from early surgical correction, because the methods to reverse this situation have limited effectiveness. Infants with HLHS who are born with a severely restricted or no inter-atrial communication, a rare occurrence, have profound hypoxemia. In fact, morbidity and mortality remain high in the subset of patients with an intact or very restrictive atrial septum. (10) The severe restriction of blood flow across the atrial septum results in a life-threatening situation and these patients, which present with severe cyanosis and hemodynamic instability, require urgent postnatal cardiac catheterization to relieve the septal obstruction and improve oxygenation. (11) Relief of the obstruction can be achieved by a balloon atrial septostomy or blade septostomy at the time of cardiac catheterization or a surgical atrial septectomy. The tenuous condition of these infants makes each of these interventions high risk. The choice of intervention depends on the severity of the obstruction, the infant's cardiac anatomy and physiology, and the experience of the available medical and

2. Surgical: Three options are available in the management of these infants:do nothing or choose one of two surgical options. The surgical options are the Norwood operation (followed by a Fontan operation) and cardiac transplantation. The

> a. The first-stage Norwood operation is performed on the neonate. This operation consists of (1) division of the MPA and closure of the distal stump, (2) a right-sided Gore-Tex shunt (usually a 4-mm tube) to provide PBF, (3) excision of the atrial septum ( for adequate interatrial mixing), and (4) construction of a new aortic arch between the proximal main pulmonary artery (MPA) and the hypoplastic ascending aorta and aortic archm using an aortic or pulmonary artery allograft. The surgical

> b. A cavopulmonary shunt ( or bidirectional Glenn operation) is carried out

c. A modified Fontan operation is carried out when the patient is a year and a half old. Overall survival after the Fontan operation is about 50% at 4

2. Cardiac transplantation is considered to be the procedure of choice in some centers. The transplantation is not a cure for the defect but creates a lifelong

Significant PDA with CHF occurs in 15% of prematures with a birth weight of less than

surgical procedure of choice remains controversial.

mortality rate is 35% or higher.

at 6 months of age. Mortality is less than 5%.

medical problem, the threat of infection and rejection.

1,750 g and in 40% to 50% of those with a birth weight of less than 1,500 g.

This is a special problem in premature infants who have been recovering from hyaline membrane disease. With improvement in oxygenation the PVR drops rapidly, but the ductus remains patent because its responsiveness to oxygen is immature in the premature newborn infant. The resulting large L-R ductal shunt makes the lungs stiff, and weaning the infant from ventilator and oxygen therapy becomes difficult. Infants who remain on ventilators for a long time develop bronchopulmonary dysplasia with resulting pulmonary hypertension ( cor pulmonale) and right-sided heart failure.

	- 1. The history usually reveals that a premature infant with hyaline membrane disease has made some improvement during the first few days after birth, but this is followed by inability to wean the infant from the ventilator or a need to increase ventilator settings or oxygen requirement in 4-to 7-day-old premature infants. Apneic spells or episodes of bradycardia may be initial signs in infants who are not on ventilators.
	- 2. Bounding peripheral pulses and a hyperactive precordium are usually present. The classic continuous murmur of PDA at the ULSB is diagnostic, but the murmur is sometimes systolic only at the middle and upper LSB. Premature infants who are fluid overloaded or retaining fluid may also present with the hyperdynamic precordium, an ejection systolic murmur, bounding pulse, and wide pulse pressure.
	- 3. The ECG is usually normal.
	- 4. Chest x-ray films show cardiomegaly and evidence of pulmonary edema or pulmonary venous congestion in addition to varying degrees of the lung disease.
	- 5. 2D echo study confirms the diagnosis. It provides anatomic information about the diameter, length, and shape of the ductus. The Doppler study of the ductus ( with the sample volume placed at the pulmonary end of the ductus) provides important functional information such as ductal shunt patterns ( pure L-R, bidirectional, or predominant R-L shunt), pressure in the PA, and magnitude of the ductal shunt or pulmonary perfusion status. An indirect estimate of the magnitude of the shunt can be made by the LA and LV dimensions.
	- 1. Indomethacin ( a prostaglandin synthetase inhibitor), 0.2 mg/kg IV every 12 hours for up to three doses, may be used on selected cases. A second course is occasionally necessary for adequate ductal closure. Contraindications to the use of indomethacin include (1) BUN over 25 mg/dL or creatinine levels over 1.8 mg/dL, (2) a platelet count below 80,000/mm³, (3) a bleeding tendency ( including intracranial hemorrhage), (4) necrotizing enterocolitis, and (5) hyperbilirubinemia.
	- 2. A European study showed that ibuprofen given IV ( 10 mg/kg followed by 5 mg/kg every 24 hours, two times), starting on the 3rd day of life, was as effective as indomethacin ( 0.2 mg/kg IV every 12 hours, three times), with a lower incidence of oliguria and a less deleterious effect on the cerebral blood flow than indomethacin. However, ibuprofen is not approved for use in premature PDA in this country.

Evaluation and Emergency Treatment of

roentgenograms.

polycythemia, sepsis).

Criticlly Ill Neonate with Cyanosis and Respiratory Distress 247

c. Diagnosis: PPHN should be suspected in all term infants who have cyanosis with or without fetal distress, intrauterine growth restriction, meconium-stained amniotic fluid, hypoglycemia, polycythemia, diaphragmatic hernia, pleural effusions, and birth asphyxia. Hypoxia is universal and is unresponsive to 100% oxygen given by oxygen hood, but it may respond transiently to hyperoxic hyperventilation administered after endotracheal intubation or to the application of a bag and mask. A Pao2 gradient between a preductal (right radial artery) and a postductal (umbilical artery) site of blood sampling greater than 20 mm Hg suggest right-to-left shunting through the ductus arteriosus. Real-time echocardiography combined with Doppler flow studies demonstrates right-to-left shunting across a patent foramen ovale and a ductus arteriosus. Deviation of the intraatrial septum into the left atrium is seen in severe PPHN. Tricuspid or mitral insufficiency may be noted on auscultation as a holosystolic murmur and can be visualized echocardiographically together with poor contractility when PPHN is associated with myocardial ischemia. The degree of tricuspid regurgitation can be used to estime pulmonary artery pressure. The 2nd heart sound is accentuated and not split. In asphyxia-associated and idiopathic PPHN , the chest roentgenogram is normal, whereas in PPHN associated with pneumonia and diaphragmatic hernia, it shows the specific lesions of parenchymal opacification and bowel in the chest, respectively. The differential diagnosis of PPHN includes cyanotic heart disease (especially obstructed total anomalous pulmonary venous return) and the associated etiologic entities that predispose to PPHN (e.g., hypoglycemia,

d. Treatment: Therapy is directed toward correcting any predisposing disease ( hypoglycemia, polycithemia) and improving poor tissue oxygenation. The response to therapy is often unpredictable, transient, and complicated by the adverse effects of drugs or mechanical ventilation. Initial management includes oxygen administration and correction of acidosis, hypotension, and hypercapnia. Persistent hypoxia should be

Treatment with inhaled nitric oxide (iNO) is indicated for newborns with an oxygen index (OI) of less than 25. Nitric oxide (NO) is an endothelially derived gas signaling molecule that relaxes vascular smooth muscle and that can be delivered to the lung by means of an inhalation device **.** In 2 large, randomized trials, NO reduced the need for extracorporeal membrane oxygenation (ECMO) by approximately 40%. Although these trials led to the US Food and Drug Administration (FDA) approving iNO as a therapy for persistent pulmonary hypertension of the newborn (PPHN), iNO did not reduce mortality, the length of hospitalization, or the risk of neurodevelopmental impairment. A randomized study confirmed that beginning iNO at a milder or earlier point in the disease course (for an oxygenation index of 15-25) did not decrease the incidence of ECMO and/or death or improve other patient outcomes, including the incidence of neurodevelopmental impairment.The use of iNO has not been demonstrated to reduce the need for ECMO in newborns with congenital

managed with intubation and mechanical ventilation.

shock. Multiorgan involvement may be present. Myocardial ischemia, papillary muscle dysfunction with mitral and tricuspid regurgitation, and cardiac stunning produce cardiogenic shock with decreased pulmonary blood flow, tissue perfusion, and oxygen delivery. The hypoxia is quite labile and often out of proportion to the findings on chest

3. If the medical treatment is unsuccessful or if the use of indomethacin is contraindicated, a surgical ligation of the ductus is indicated. The standard operative approach to the PDA has been through a posterolateral thoracotomy. The safety, effectiveness, and minimally invasive nature of video-assisted thoracoscopic surgery (VATS) have been reported for premature PDA. Advantages of the technique may include no need to cut the muscle and to spread ribs, thus a reduced compromise of respiratory mechanics and of chest wall deformity.
