28 Initial Treatment of Critically Ill Neonates with Cardiac Defects
In this chapter, the general features, clinical symptoms, and treatment principles for congenital heart defects that become symptomatic in neonates are discussed. In addition, the specific measures for the initial treatment of the most common defects are presented.
The incidence of congenital heart defects is said to be 6 to 11 per 1,000 live births. Nearly half of these children require surgery or interventional catheterization within the first year of life.
The different congenital heart defects typically become manifest at different times. Important times at which congenital heart defects become symptomatic are the closure of the ductus arteriosus for ductal-dependent cardiac defects or the drop in pulmonary vascular resistance for shunt defects.
Leading symptoms of congenital heart defects in neonates are:
Heart failure or cardiogenic shock (usually in the first or second week of life if there is left heart obstruction; for shunt defects typically not until after the drop in pulmonary resistance at the age of 2 to 8 weeks)
Other symptoms that indicate a congenital heart defect in neonates are a murmur or arrhythmia (rarely as the primary symptom of a congenital heart defect).
The characteristic signs of heart failure in neonates are:
Tachypnea, dyspnea, thoracic retractions, possibly pulmonary edema
Difficulty feeding, failure to thrive, increased sweating
Pallor, prolonged capillary refill time
The symptoms of heart failure in neonates are similar to the clinical symptoms of sepsis. Many neonates with heart failure are therefore first treated for suspected sepsis.
Especially cardiac defects with left heart obstruction (hypoplastic left heart syndrome, critical aortic stenosis, or coarctation of the aorta) can become manifest as early as the first 2 weeks of life with the clinical symptoms of cardiogenic shock.
The hyperoxia test is used to distinguish between cardiac and pulmonary cyanosis. In patients with pulmonary cyanosis, the oxygen saturation increases markedly after oxygen is given, while oxygen saturation usually does not significantly improve in those with cyanotic heart defects. Both pre- and postductal oxygen saturation should be measured. Cardiac cyanosis is the result of either reduced lung perfusion due to a right-to-left shunt or intracardiac mixing of systemic and pulmonary venous blood. Cyanosis can also very rarely be caused by methemoglobinemia. Cyanosis caused by the central nervous system must also be considered (e.g., central apnea in premature neonates or after cerebral hemorrhage).
If there is not an adequate increase in oxygen saturation in a cyanotic neonate in the hyperoxia test, a congenital heart defect with ductal-dependent lung perfusion must be assumed. If the diagnosis cannot be immediately confirmed or ruled out by echocardiography, an attempt at treating it with intravenous prostaglandin E1 is justified.
A heart murmur in a neonate is always suggestive of a congenital heart defect. Innocent murmurs are less common in this age group than in older children. While stenoses of the semilunar valves or AV valve insufficiency can already be detected immediately after birth due to a loud systolic murmur, the typical VSD murmur, for example, cannot be auscultated until after the pulmonary resistance has dropped and the pressure gradient between the left and right ventricles increases. It should also be noted that there may be no indicative heart murmur in some critical heart defects (e.g., d-TGA simplex, coarctation of the aorta).
Arrhythmias are relatively rarely the first symptom of a congenital heart defect. An AV block, for example, occurs frequently in association with an l-TGA. Supraventricular tachycardias due to accessory conduction pathways occur more frequently with an Ebstein anomaly.
28.1.3 Hemodynamic Situation
The congenital heart defects that become symptomatic in neonates can be divided into six groups (Table 28.1).
Critical aortic stenosis, hypoplastic left heart syndrome, interrupted aortic arch, critical coarctation of the aorta
Critical pulmonary stenosis, pulmonary atresia with intact ventricular septum, pulmonary atresia with VSD, pronounced form of tetralogy of Fallot, severe Ebstein anomaly, tricuspid atresia with pulmonary atresia or high-grade pulmonary stenosis
Truncus arteriosus communis, total anomalous pulmonary venous connection, univentricular heart
Large VSD, complete AVSD, large PDA, aortopulmonary window
Severe mitral regurgitation, severe tricuspid regurgitation (Ebstein anomaly), aortico-left ventricular tunnel.
A ductal-dependent defect is a congenital heart defect in which survival depends on the persistence of a patent ductus arteriosus. Ductal-dependent systemic circulation must be distinguished from ductal-dependent pulmonary circulation. In ductal-dependent systemic circulation, there is a high-grade obstruction of the left heart. To ensure sufficient systemic perfusion, the systemic circulation must be supplied with blood from the pulmonary circulation across the patent ductus arteriosus.
In ductal-dependent pulmonary circulation, there is a corresponding high-grade right heart obstruction. Perfusion of the pulmonary circulation depends on blood supply from the aorta across the patent ductus arteriosus.
In parallel circulations (d-TGA), survival depends on shunts (especially a sufficiently large atrial shunt) between the two circulations.
In cardiac defects with complete intracardiac mixing of blood, cyanosis is often only relatively mild, as excessive pulmonary blood flow is often present simultaneously, which leads to pulmonary recirculation of the saturated blood. Heart failure usually develops as a result of the excessive pulmonary blood flow.
Cardiac defects with a large left-to-right shunt usually do not become symptomatic until the age of about 4 to 6 weeks when the pulmonary resistance has dropped and the shunt between the left and right heart increases. If left heart obstruction is also present (e.g., coarctation of the aorta), the symptoms develop as early as the first week of life.
Cardiac defects with predominant severe valve incompetence are rare diseases. In tricuspid valve diseases, these patients have a duct dependent pulmonary circulation. In left sided valve affection these children present in a low cardiac output state.
28.1.4 Diagnostic Measures
Oxygen saturation should be measured both preductally (right hand) and postductally (lower limb). If there is ductal-dependent systemic circulation, the (postductal) oxygen saturation measured in the legs is lower than the (preductal) saturation in the right hand.
Because the brachiocephalic trunk (except in the rare cases of a lusoria artery) branches off from the aortic arch well before the ductus arteriosus, it is safe to assume that the saturation measured in the right hand is equivalent to preductal saturation.
Blood Gas Analysis
Metabolic acidosis is the typical finding of severe heart failure and cardiogenic shock.
The hyperoxia test is used to distinguish between cardiac or pulmonary central cyanosis. The cyanotic patient is allowed to breathe 100% oxygen for a few minutes. In pulmonary cyanosis, the cyanosis disappears or is clearly reduced and there is a relevant increase in arterial partial oxygen pressure. In cardiac cyanosis, the partial oxygen pressure remains largely unchanged, as the cardiac right-to-left shunt or inadequate pulmonary perfusion cannot be compensated by the administration of oxygen.
If possible, an echocardiography examination is preferable to a hyperoxia test. One reason is that a hyperoxia test is associated with diagnostic uncertainty. On the other hand, in ductal-dependent defects, the ductus arteriosus can theoretically close when oxygen is administered. In addition, by lowering the pulmonary resistance as a result of administering oxygen to a patient with a shunt defect, pulmonary blood flow can increase and exacerbate heart failure.
Pulse and Blood Pressure in all Limbs
A difference in blood pressure between the right arm (preductal) and the lower limbs (postductal) or pulses in the lower limbs that cannot be palpated are leading findings of coarctation of the aorta or an interrupted aortic arch.
In a large patent ductus arteriosus, there may be no difference in blood pressure between the upper and lower halves of the body even with relevant coarctation of the aorta or interrupted aortic arch.
Echocardiography is the diagnostic method of choice. It allows all significant cardiac defects that become symptomatic in the neonatal period to be reliably diagnosed.
The treatment principles for the various groups of congenital heart defects are presented below. The specific treatments of the individual heart defects in the neonatal period are then described.
Cardiac defects with ductal-dependent systemic circulation
In ductal-dependent systemic circulation, an attempt must be made to allow as much blood flow as possible from the pulmonary circulation to reach the systemic circulation via the patent ductus arteriosus. The treatment principles of ductal-dependent systemic circulation are:
Maintain patency of the ductus arteriosus with a prostaglandin E1 infusion (initial dosage 50 to 100 ng/kg/min).
Lower systemic resistance:
Reduce afterload: for example, with sodium nitroprusside infusion.
If catecholamines are needed: Give milrinone and/or dobutamine (vasodilatative effects); avoid vasoconstrictive catecholamines (noradrenaline).
Increase pulmonary resistance, increase pulmonary artery pressure:
Avoid additional oxygen.
Aim for mild metabolic acidosis (pH 7.35).
Aim for mild hypoventilation (pCO2 around 60 mmHg).
In case of pulmonary edema, give intravenous furosemide, apply high PEEP; reduce prostaglandin E1 to a minimum (e.g., 10 ng/kg/min)
The uncritical administration of oxygen and hyperventilation in patients with ductal-dependent systemic circulation can lead to acute decompensation of the hemodynamic situation.
Cardiac defects with ductal-dependent pulmonary circulation
In ductal-dependent pulmonary circulation, the situation is reversed. The following measures can be useful to allow as much blood as possible to flow from the systemic circulation to the pulmonary circulation via the patent ductus arteriosus:
Maintain patency of the ductus arteriosus with a prostaglandin E1 infusion (initial dosage 50 to 100 ng/kg/min).
Lower pulmonary resistance:
Aim for mild metabolic alkalosis (use buffering is necessary) (pH 7.45–7.5).
Adjust ventilation for mild hyperventilation (pCO2 around 35 mmHg).
Increase systemic resistance, increase systemic pressure by:
possibly also adrenaline infusion.
Maintain rather high dosage of prostaglandin E1.
Prostaglandin E1 is given to maintain patency or reopen the ductus arteriosus in neonates with a ductal-dependent defect. Due to its short half-life, it must be administered continuously intravenously. The initial dosage is between 50 and 100 ng/kg/min. Depending on the effect, the dosage can then be gradually reduced to a minimum of 5 to 10 ng/kg/min.
The most common adverse effects are:
Apnea (administer in readiness for intubation)
Cortical hyperostosis, periostitis only after long-term administration
Practical tip: When using prostaglandin, a second venous access should always be available to ensure the ability to administer prostaglandin immediately via the other access if the first one is dislocated. The second access can also be used for volume substitution in case of acute hypotension.
Cardiac defects with parallel circulations
The only example of this kind of heart defect is a d-TGA. Its treatment is described in the specific treatment section.
Cardiac defects with complete intracardiac mixing of blood
The different cardiac defects in this group are also described in the specific treatment section.
Cardiac defects with a large left-to-right shunt
When the pulmonary resistance drops, the left-to-right shunt and pulmonary blood flow increase. Heart failure develops, which must be treated conservatively (diuretics, ACE inhibitors, beta blockers, possibly digoxin or catecholamines) until corrective surgery is performed. To prevent lowering the pulmonary resistance and thus increasing excessive pulmonary blood flow, no additional oxygen should be administered.
Cardiac defects with severe valve incompetence
In left-sided lesions, inotropic support (dubutamine, milrinone) together with adequate afterload reduction (sodium nitroprusside infusion) should be installed. In right-sided lesions, lowering the pulmonary vascular resistance together with inotropic support (milrinone) should be achieved (i.e. additional oxygen).