To avoid the cumulative morbidity and mortality associated with initial palliative procedures followed by later repair, primary corrective surgery has become increasingly common for patients with congenital heart disease. One result of this trend is that an increasing number of cardiac surgical procedures are performed on neonates and even on premature infants. Optimal care of these infants requires specialized knowledge of the unique structural and functional characteristics of neonatal organ systems and is best accomplished by a multidisciplinary specialty team including cardiology, cardiac surgery, nursing, neonatology, anesthesia, and critical care. The purpose of this chapter is to review general principles of care for these infants. The physiology and surgical procedures pertinent to specific defects are discussed in Chapters 6 through 8. Medications commonly used in the postoperative period are discussed in Chapter 12.

Cardiac surgical procedures are classified as to whether they are open or closed and whether they are corrective or palliative (Table 13-1). “Open” refers to a procedure in which cardiopulmonary bypass is used; bypass is not used in “closed” procedures. Palliative procedures are performed in patients in whom complete correction of the cardiac defects is not possible or not feasible because of comorbidities. Palliated patients have residual intracardiac shunting or other hemodynamic abnormalities. In most institutions, palliative procedures are performed only on infants with a functional single ventricle (eg, hypoplastic left heart syndrome, tricuspid atresia) or on those with poorly developed pulmonary arteries.

Most corrective procedures, such as for truncus arteriosus or transposition of the great arteries, are performed by use of cardiopulmonary bypass. Bypass diverts blood from the operative field while maintaining circulation, adds oxygen and removes carbon dioxide from the blood, and facilitates cooling and subsequent warming. Venous blood from both superior and inferior vena cavae is siphoned to a reservoir of the heart-lung bypass machine, which also collects blood drained from the operative field by suction catheters (Figure 13-1). Blood is pumped through an oxygenator, a heat exchanger (for cooling or warming), and a filter and then is returned to the patient’s ascending aorta through an aortic cannula. The patient is always fully anticoagulated with heparin while on bypass.

Hypothermia extends the safe duration of cardiopulmonary bypass in neonates and infants. Metabolic activity and thus oxygen consumption decrease at cooler temperatures. “Deep” hypothermia involves cooling from 17°C to 22°C. For many years, surgeons combined deep hypothermia with either low-flow bypass (25% to 50% of normal flow) or, more commonly, with no bypass flow, arresting the heart (deep hypothermic circulatory arrest). Deep hypothermic circulatory arrest provided the surgeon with a bloodless and relaxed heart free of multiple cannulas that may distort the surgical field. This technique allowed intricate surgical procedures to be performed and markedly improved survival of infants with complex congenital defects. Unfortunately, neurologic and developmental morbidities are increasingly being recognized in survivors of deep hypothermic circulatory arrest (Chapter 14), and longer duration of circulatory arrest is associated with a greater incidence of adverse neurologic outcomes. Alternate perfusion strategies include moderate hypothermia (22°C to 30°C) with normal or increased pump flow or deep hypothermia with intermittent perfusion. Another approach used during aortic arch reconstruction is antegrade cerebral perfusion, which involves directing blood flow specifically to the cerebral circulation via a cannula in the innominate artery. Further clinical studies and continued refinements in technique are necessary to optimize neurologic outcomes.

Although cardiopulmonary bypass allows for correction of complex cardiac defects, morbidity associated with its use impacts care of the postoperative patient, particularly neonates. Blood cells are damaged by exposure to excessive shear forces and to artificial surfaces. Despite filtration, microembolization of gas bubbles and platelet clumps occurs. Nonpulsatile perfusion and hypothermia per se may also incite injury. Tissue ischemia is present to some extent, and subsequent reperfusion injury occurs. These and other factors combine to stimulate a systemic inflammatory response, consisting of activation of the complement system, leukocytes and the endothelium. Together with induction of cytokines, chemokines, and endotoxin, this results in increased capillary permeability, tissue edema, and multisystem dysfunction. Total body water increases, transient myocardial dysfunction occurs, pulmonary vascular resistance may increase, gas exchange is impaired, and stress and hormonal responses often cause fluid and electrolyte abnormalities. This response is exaggerated in newborn infants compared to older children and results in a decrease in cardiac output that often peaks 6 to 12 hours after bypass. To limit this systemic inflammatory response, steroids are usually administered in the operating room, and various ultrafiltration techniques are used during rewarming or after cardiopulmonary bypass to remove excess water and small-molecular-weight inflammatory mediators. Hemodilution may occur in part because of the priming volume required in the bypass circuit. This decreases oxygen delivery, decreases oncotic pressure resulting in further fluid extravasation, and dilutes clotting factors, contributing to postoperative coagulopathy. Maintenance of a hematocrit of about 25% to 30% during bypass seems to be optimal for hypothermia-induced alterations in blood viscosity and also for maintaining oncotic pressure and oxygen-carrying capacity.

Many infants diagnosed with congenital heart disease are managed as outpatients before undergoing surgery, but those with ductal-dependent circulations need supportive critical care before proceeding with surgical intervention. In general, cyanotic infants can be stabilized by administration of PGE₁ and other supportive measures before intervention. Surgery or catheter-based intervention can be scheduled on a semielective basis after careful evaluation is complete. Two exceptions are noteworthy: (1) emergency surgery is necessary for neonates with obstructed total anomalous pulmonary venous return, and (2) neonates with d-transposition of the great arteries and a restrictive patent foramen ovale often need emergency balloon atrial septostomy because of profound hypoxemia. This procedure can be performed at the bedside with echocardiographic guidance. After successful septostomy, these infants are usually stable, and corrective surgery can be performed soon thereafter if end-organ damage has not occurred.

Infants who present with shock because of left heart obstructive lesions (eg, coarctation of the aorta, hypoplastic left heart syndrome) can usually be stabilized by administration of PGE₁ and other supportive care. These infants may have sustained end-organ damage because of decreased perfusion, most commonly to the kidneys or liver. Deferring surgery while organ function recovers allows for complete evaluation (including neurologic) of the infant and decreases surgical morbidity and risk. However, surgical intervention should be undertaken if there is evidence of ongoing organ injury despite maximal medical therapy.

All personnel responsible for care of the infant after surgery must understand the anatomic defects and be familiar with the preoperative evaluation and course. Upon return from the operating room, information must be provided regarding the following:

• 
  

  Intraoperative findings, especially if the anatomy is different than what was on the preoperative diagnosis list

  
  
• 
  

  The exact procedure(s) performed

  
  
• 
  

  Length of time on cardiopulmonary bypass, including aortic cross-clamp time, level of hypothermia, and circulatory arrest times

  
  
• 
  

  Available postoperative hemodynamic and echocardiographic data, especially regarding residual lesions

  
  
• 
  

  Complications, including arrhythmias and bleeding (including blood product administration)

  
  
• 
  

  Location of catheters, tubes, and temporary pacing wires

  
  
• 
  

  Vasoactive infusions and other medications

  
  
• 
  

  Airway and ventilatory status (anesthetic agents and status of neuromuscular blockade are also summarized, as is the timing of the last doses of analgesic and sedative agents)

The personnel transporting the infant must work harmoniously with staff in the cardiac intensive care unit (ICU) to ensure a careful and efficient admission of the patient to the ICU. A standard template for handoff of care from the operating room to ICU is helpful. Maintenance of adequate oxygenation and ventilation and uninterrupted delivery of vasoactive drugs are critically important. About 15 minutes after the patient is placed on the ventilator (or earlier if clinically indicated), initial laboratory studies should be obtained. This often includes arterial blood gas, complete blood count, serum electrolytes and glucose, ionized calcium, and coagulation profile. A chest radiograph and often an electrocardiogram are obtained as soon as possible.

A comprehensive assessment should be performed as soon as possible, including a physical examination focusing on cardiovascular and respiratory function, as should a review of data from bedside monitors, postoperative orders, and laboratory data as available. The family should be updated and allowed to visit as soon as is feasible.

Although variation exists among institutions, most infants have continuous monitoring of their heart rate, rhythm, blood pressure, oxygen saturation, and respiratory rate after cardiac surgery. Most infants have an arterial line. End-tidal CO₂ monitoring is valuable in patients who are mechanically ventilated. Near-infrared spectroscopy (NIRS) monitoring estimates the oxygen saturation in tissues (regional oxygen saturation [rSO₂]) by comparing the tissue’s absorption of two wavelengths of light corresponding to hemoglobin-carrying oxygen and hemoglobin without oxygen. NIRS leads placed on the forehead and in the paravertebral region over a kidney allow assessment of oxygen delivery to the brain and kidneys, respectively. Changes in head rSO₂ correlate closely with changes in mixed venous saturation.

Infants who have been on cardiopulmonary bypass usually have one or more intracardiac catheters for monitoring and infusions. Temporary pacing wires are often placed on the epicardial surface of the atrium and/or ventricle. The data obtained allow more precise measurement of hemodynamic variables, thereby providing a rational basis for therapy. Nevertheless, the information obtained should be viewed as an adjunct to rather than a substitute for careful serial physical examinations to assess cardiac output.

A right atrial (RA) catheter may be advanced via a central vein or placed through the RA appendage. RA catheters are used to measure central venous pressure, which may reflect intravascular volume status. In addition to volume overload, other causes of increased RA pressure include decreased right (or single) ventricular compliance, tricuspid valve regurgitation or a residual left ventricular to RA shunt, and cardiac tamponade. RA saturation can also be measured but may not represent a true mixed venous sample because of streaming of venous inflow within the atrium and because it is mixed with left atrial blood in the single-ventricle patient. When blood can be obtained from a site that is a reasonable estimate of mixed venous saturation (the superior vena cava is usually the best source), an arteriovenous oxygen saturation difference of less than 30% indicates adequate cardiac output.

A left atrial (LA) catheter may be placed via the LA appendage or through the right superior pulmonary vein. The LA pressure provides indirect data regarding functioning of the systemic ventricle as long as the systemic atrioventricular valve is neither regurgitant nor stenotic. LA pressure also rises and falls with intravascular volume status. The oxygen saturation in the LA should be about 100%. Decreased LA saturation can be caused by right-to-left atrial shunting or by pulmonary venous desaturation secondary to abnormal gas exchange (eg, atelectasis).

Echocardiography is used frequently in the ICU to assess postoperative status. Intraoperative transesophageal examination evaluates residual lesions as well as ventricular function, outflow tract obstruction, valve regurgitation, and possibly pulmonary arterial pressure. At times of clinical deterioration in the ICU, emergent echocardiography is useful to assess all of the above as well as shunt function and the presence of pericardial effusion.

Cardiovascular

Decreased Cardiac Output

Myocardial dysfunction is common after surgery in young infants, especially neonates. One or more of the following factors may be involved:

• 
  

  Preoperative myocardial dysfunction—This is most common in patients with left heart obstructive lesions, such as aortic coarctation.

  
  
• 
  

  Effects of cardiopulmonary bypass—As discussed in the preceding text, a prominent systemic inflammatory response frequently occurs and may adversely affect myocardial function. Inadequate myocardial perfusion can occur during surgery. Finally, a ventriculotomy, if performed, may lead to regional myocardial dysfunction. If these intraoperative events lead to a low-output state, their effects usually peak 6 to 12 hours after surgery. Physical examination will disclose tachycardia, hypotension, and cool extremities with decreased perfusion. Decreased urine output, lactic acidosis, low head rSO₂, edema, and pleural effusions may be present. It is critically important to anticipate this reproducible and potentially lethal phenomenon and to intervene immediately. Infusion of volume and administration of inotropic and afterload reducing agents are often necessary. Serial physical examinations and frequent evaluation of hemodynamic and metabolic data are necessary to assess the response to therapeutic interventions.

  
  
• 
  

  Residual anatomic lesions—The operative assessment of cardiac anatomy and function is done by direct inspection, blood gas and pressure measurements, and imaging. The use of transesophageal echocardiography in the operating room after surgery has reduced the incidence of unsuspected residual anatomic lesions. Nevertheless, if the postoperative course does not conform to that expected, investigation should be undertaken to assess for residual or previously undiagnosed anatomic defects. This certainly includes echocardiography but may also involve magnetic resonance imaging and/or cardiac catheterization.

  
  
• 
  

  Arrhythmias—Abnormal heart rhythms, such as atrioventricular block and tachycardias, are relatively common in the postoperative period and may contribute to inadequate cardiac output. Diagnosis and treatment of rhythm disorders is discussed in Chapter 10. The neonate is relatively dependent on a physiologic heart rate and an atrial contribution to ventricular filling (“atrial kick”) to maintain cardiac output. Therefore, bradycardia associated with atrioventricular block will markedly decrease cardiac output, and pacing should be instituted promptly via the transthoracic pacing wires. Junctional ectopic tachycardia is the most common tachyarrhythmia and results in loss of atrioventricular synchrony. Infants who are symptomatic from rapid heart rates should be treated immediately.

  
  
• 
  

  Electrolyte and hormonal disturbances—Hypocalcemia and hypomagnesemia depress myocardial contractility and should be treated appropriately. It has been postulated that administration of glucocorticosteroids improves refractory hemodynamic instability in stressed neonates who may have an inappropriate or abnormal adrenal response to stress after cardiac surgery. Similarly, decreased concentrations of triiodothyronine, the biologically active hormone in cardiac myocytes, may contribute to low cardiac output syndrome after bypass; some have advocated administration of triiodothyronine. Neither of these therapies has been shown to be efficacious in a clinical trial, but both are used empirically at times.

  
  
• 
  

  Anemia—Increasing the hemoglobin concentration improves the oxygen-carrying capacity of blood and may benefit patients with low levels of cardiac output. Transfusing cyanotic patients up to a hemoglobin concentration of 14 to15 g/dL may be helpful.