**8. Hypoplastic left heart syndrome**


Evaluation and Emergency Treatment of

Criticlly Ill Neonate with Cyanosis and Respiratory Distress 243

of balance between systemic and pulmonary blood flow. (4)

volume load on the right ventricle.

cardiac output.

Sildenafil could be a reasonable alternative to PGE1 for maintaining DA patency, since it can also prevent and reverse DA closure through a mechanism that is distinct, and eventually safer, from the PGE1 mechanism. (9) An audible murmur and adequate peripheral perfusion provide evidence of ductal patency; however, Doppler echocardiography is needed to confirm flow. Once the ductus is open, the rate of infusion may be reduced to decrease the risk for potential adverse effects. Unrestricted blood flow through the ductus arteriosus is necessary for systemic perfusion. Sometimes even a temporary discontinuation of the prostaglandin infusion is possible, with careful monitoring of blood pressure and urine volume as well as frequent echocardiographic examinations, in order to enable maintenance

The pulmonary/systemic (p/s) ratio preoperatively is dictated by the adequacy of the interatrial communication. An infant with a mildly restrictive interatrial communication may have balanced circulation and remain in a clinically stable condition as long as the ductus arteriosus remains open. Oxygen saturations of 75% to 85% by pulse oximetry suggest adequate balance between systemic and pulmonary blood flow. Ventilatory support may be needed for apneic episodes or tenacious secretions, both common adverse effects of treatment with prostaglandin E1. Judicious use of inotropic support is initiated if evidence of low cardiac output is detected. Infusion of dopamine at a rate of 3 to 5 µg/kg per minute usually results in improved ventricular function. High-dose inotropic support should be used with caution because it can result in increased SVR and cause a shift in the p/s ratio to greater than 1. In our institution we do not recommend the use of dopamine as a "standard" since we consider it a "dirty" drug with a lot of potential unexpected effects. Diuretics may be necessary to help alleviate the increased

Infants with an unrestrictive inter-atrial communication may be in a stable condition initially, but signs of congestive heart failure may develop as the PVR (pulmonary vascular resistance) decreases. When oxygen saturations are approximately 90%, systemic blood flow may be reduced, resulting in tissue hypoperfusion, metabolic acidosis, and a low cardiac output state. In infants with high oxygen saturation and evidence of tissue hypoperfusion, controlled mechanical ventilation is often initiated to improve the p/s ratio and systemic

Severe tricuspid regurgitation (TR) could be another issue that complicates the life of the intensivist dealing with a newborn with HLHS. Good preoperative management with mechanical ventilation in order to lower the degree of TR results

The goal of respiratory management is to increase pulmonary vascular resistance and decrease systemic vascular resistance. The p/s ratio can be manipulated by increasing PVR by increasing the PaCO2. PaCO2 can be increased by adding supplemental inspired carbon dioxide, a potent pulmonary vasoconstrictor, to the ventilator circuit. This approach for increasing PaCO2 is preferred over hypoventilation, which may lead to atelectasis. PVR can also be increased by decreasing the concentration of inspired oxygen by adding supplemental nitrogen

in a better short-term prognosis of stage 1 Norwood operation. (4)

	- 1. The neonate is critically ill in the first few hourse to days of life, with mild cyanosis, tachycardia, tachypnea, and pulmonary crackles.
	- 2. Poor peripheral pulses and vasoconstricted extremities are characteristic. The S2 is loud and single. Heart murmur is usually absent, but a grade 1 to 3/6 ejection systolic murmur may be present over the precordium.
	- 3. The ECG shows RVH. Rarely, left ventricular hypertrophy (LVH) pattern is present because V5 and V6 electrodes are placed over the dilated RV.
	- 4. Chest x-ray films show pulmonary venous congestion or pulmonary edema. The heart is only mildly enlarged.
	- 5. The arterial blood gas determination reveals severe metabolic acidosis in the presence of a slightly decreased Po2, a characteristic finding of this condition.
	- 6. Echo findings are diagnosticand usually obviate cardiac catheterization. Severe hypoplasia of the aorta and aortic annulus and the absent or distorted mitral valve are usually imaged. The LV cavity is diminutive. The RV cavity is markedly dilated, and the tricuspid valve is large.A partially constricted PDA may be imaged.
	- 7. Progressive hypoxemia and acidosis result in death, usually in the first month of life.
	- 1. Preoperatively the goal is to achieve adequate systemic oxygen delivery. Patency of the ductus arteriosus is critical for survival until surgery. Blood flow to the pulmonary and systemic circulations should be nearly balanced (goal p/s ratio of 1). The immediate therapy for all infants with HLHS is an intravenous infusion of prostaglandin E1 (PGE1) in order to pharmacologically manipulate the ductus arteriosus (DA) and maintain ductal patency. A continuous infusion of the prostaglandin is initiated, preferably through a central catheter, at a rate of 0.05 to 0.1 µg/kg per minute. However, numerous side effects are associated with PGE1 infusion such as respiratory depression, fever, lethargy, irritability, myoclonic jerks, flushing, edema, pyloric stenosis, hyperostosis, necrotizing enetrocolitis, as well as structural remodeling of the DA and the pulmonary vessels, with a reported incidence of these complications ranging from 10 to 40%. (7,8) In the future

the atrial septum is frequently intact other than the PFO.

tachycardia, tachypnea, and pulmonary crackles.

systolic murmur may be present over the precordium.

because V5 and V6 electrodes are placed over the dilated RV.

pulmonary edema.

heart is only mildly enlarged.

c. Clinical manifestations

imaged.

life. d. Management

1. HLHS includes a group of closely related anomalies characterized by hypoplasia of the left ventricul (LV) ( from atresia or severe stenosis of the aortic and/or mitral valves) and hypoplasia of the ascending aorta and aortic arch. The LA is small, and

2. During fetal life the pulmonary vascular resistance (PVR) is higher than the systemic vascular resistance (SVR), and the dominant RV maintains normal perfusing pressure in the descending aorta through the ductal R-L shunt, even in the presence of the nonfunctioning hypoplastic LV. However, difficulties arise after birth, primarily from two factors: (1) reversal of the vascular resistance in the two circuits with the SVR higher than the PVR, and (2) closure of the PDA. The end result is a marked decrease in systemic cardiac output and aortic pressure, resulting in circulatory shock and metabolic acidosis. An increase in PBF in the presence of the nonfunctioning LV results in an elevated LA pressure and

1. The neonate is critically ill in the first few hourse to days of life, with mild cyanosis,

2. Poor peripheral pulses and vasoconstricted extremities are characteristic. The S2 is loud and single. Heart murmur is usually absent, but a grade 1 to 3/6 ejection

3. The ECG shows RVH. Rarely, left ventricular hypertrophy (LVH) pattern is present

4. Chest x-ray films show pulmonary venous congestion or pulmonary edema. The

5. The arterial blood gas determination reveals severe metabolic acidosis in the presence of a slightly decreased Po2, a characteristic finding of this condition. 6. Echo findings are diagnosticand usually obviate cardiac catheterization. Severe hypoplasia of the aorta and aortic annulus and the absent or distorted mitral valve are usually imaged. The LV cavity is diminutive. The RV cavity is markedly dilated, and the tricuspid valve is large.A partially constricted PDA may be

7. Progressive hypoxemia and acidosis result in death, usually in the first month of

1. Preoperatively the goal is to achieve adequate systemic oxygen delivery. Patency of the ductus arteriosus is critical for survival until surgery. Blood flow to the pulmonary and systemic circulations should be nearly balanced (goal p/s ratio of 1). The immediate therapy for all infants with HLHS is an intravenous infusion of prostaglandin E1 (PGE1) in order to pharmacologically manipulate the ductus arteriosus (DA) and maintain ductal patency. A continuous infusion of the prostaglandin is initiated, preferably through a central catheter, at a rate of 0.05 to 0.1 µg/kg per minute. However, numerous side effects are associated with PGE1 infusion such as respiratory depression, fever, lethargy, irritability, myoclonic jerks, flushing, edema, pyloric stenosis, hyperostosis, necrotizing enetrocolitis, as well as structural remodeling of the DA and the pulmonary vessels, with a reported incidence of these complications ranging from 10 to 40%. (7,8) In the future Sildenafil could be a reasonable alternative to PGE1 for maintaining DA patency, since it can also prevent and reverse DA closure through a mechanism that is distinct, and eventually safer, from the PGE1 mechanism. (9) An audible murmur and adequate peripheral perfusion provide evidence of ductal patency; however, Doppler echocardiography is needed to confirm flow. Once the ductus is open, the rate of infusion may be reduced to decrease the risk for potential adverse effects. Unrestricted blood flow through the ductus arteriosus is necessary for systemic perfusion. Sometimes even a temporary discontinuation of the prostaglandin infusion is possible, with careful monitoring of blood pressure and urine volume as well as frequent echocardiographic examinations, in order to enable maintenance of balance between systemic and pulmonary blood flow. (4)

The pulmonary/systemic (p/s) ratio preoperatively is dictated by the adequacy of the interatrial communication. An infant with a mildly restrictive interatrial communication may have balanced circulation and remain in a clinically stable condition as long as the ductus arteriosus remains open. Oxygen saturations of 75% to 85% by pulse oximetry suggest adequate balance between systemic and pulmonary blood flow. Ventilatory support may be needed for apneic episodes or tenacious secretions, both common adverse effects of treatment with prostaglandin E1. Judicious use of inotropic support is initiated if evidence of low cardiac output is detected. Infusion of dopamine at a rate of 3 to 5 µg/kg per minute usually results in improved ventricular function. High-dose inotropic support should be used with caution because it can result in increased SVR and cause a shift in the p/s ratio to greater than 1. In our institution we do not recommend the use of dopamine as a "standard" since we consider it a "dirty" drug with a lot of potential unexpected effects. Diuretics may be necessary to help alleviate the increased volume load on the right ventricle.

Infants with an unrestrictive inter-atrial communication may be in a stable condition initially, but signs of congestive heart failure may develop as the PVR (pulmonary vascular resistance) decreases. When oxygen saturations are approximately 90%, systemic blood flow may be reduced, resulting in tissue hypoperfusion, metabolic acidosis, and a low cardiac output state. In infants with high oxygen saturation and evidence of tissue hypoperfusion, controlled mechanical ventilation is often initiated to improve the p/s ratio and systemic cardiac output.

Severe tricuspid regurgitation (TR) could be another issue that complicates the life of the intensivist dealing with a newborn with HLHS. Good preoperative management with mechanical ventilation in order to lower the degree of TR results in a better short-term prognosis of stage 1 Norwood operation. (4)

The goal of respiratory management is to increase pulmonary vascular resistance and decrease systemic vascular resistance. The p/s ratio can be manipulated by increasing PVR by increasing the PaCO2. PaCO2 can be increased by adding supplemental inspired carbon dioxide, a potent pulmonary vasoconstrictor, to the ventilator circuit. This approach for increasing PaCO2 is preferred over hypoventilation, which may lead to atelectasis. PVR can also be increased by decreasing the concentration of inspired oxygen by adding supplemental nitrogen

Evaluation and Emergency Treatment of

b. Pathophysiology

c. Clinical manifestations

on ventilators.

pressure.

3. The ECG is usually normal.

possibility of spontaneous closure.

this country.

be made by the LA and LV dimensions.

Criticlly Ill Neonate with Cyanosis and Respiratory Distress 245

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

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

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

d. Management: For symptomatic infants, either pharmacologic ( indomethacin) or surgical closure of the ductus is indicates. A small PDA that is not causing CHF should be followed up medically for 6 months without surgical ligation because of the

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

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 surgical team.

	- 1. Norwood operation
		- 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 mortality rate is 35% or higher.
		- b. A cavopulmonary shunt ( or bidirectional Glenn operation) is carried out at 6 months of age. Mortality is less than 5%.
		- 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 years.
	- 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 medical problem, the threat of infection and rejection.
