ANESTHESIA FOR CLOSED HEART OPERATIONS

Early corrective repair in infancy has significantly reduced the number of noncorrective, palliative closed heart operations. Corrective closed heart procedures include PDA ligation and repair of coarctation of the aorta. Noncorrective closed heart operations include pulmonary artery banding and extracardiac shunts such as the Blalock-Taussig shunt. These procedures are performed without cardiopulmonary bypass. Therefore, venous access and intra-arterial monitoring are important in evaluating and supporting these patients. A pulse oximeter remains an invaluable monitor during intraoperative management.

Ligation of PDA is typically performed through a left thoracotomy, although video-assisted thoracoscopic techniques are increasingly common.^{[251] [252]} Physiologic management is that of a left-to-right shunt producing volume overload. Patients with a large PDA and low PVR generally present with excessive pulmonary blood flow and congestive heart failure. Neonates and premature infants also run the risk of having substantial diastolic runoff to the pulmonary artery, potentially impairing coronary perfusion. Thus, patients range from an asymptomatic healthy young child to the sick ventilator-dependent premature infant on inotropic support. The health of the former patient allows a wide variety of anesthetic techniques culminating in extubation in the operating room. The latter patient requires a carefully controlled anesthetic and fluid management plan. Generally, a trial of medical management with indomethacin and fluid restriction is attempted in the premature infant prior to surgical correction. Transport of the premature infant to the operating room can be especially difficult and potentially hazardous, requiring great vigilance to avoid extubation, excessive patient cooling, and venous access disruption. For these reasons, many centers are now performing ligation in the neonatal ICU.

There is a subset of premature infants with PDAs at institutions without cardiac surgical teams. Ligation of the PDA in these patients requires either transfer of these high risk neonates to a center that has a team that routinely performs the procedure or the availability of a team capable of performing the procedure that is willing to travel to perform the procedure in the neonate's home neonatal intensive care unit (NICU). Gould et al²⁶¹ reviewed the experience with on-site and off-site ligations of a team composed of a pediatric cardiac attending anesthesiologist, a certified registered nurse anesthetist, an attending pediatric cardiothoracic surgeon and fellow, and cardiac operating room nurses. There were no anesthetic-related complications in their group. No differences were found in the incidence of perioperative complications in the procedures in the two sites. This study showed PDA ligations can be performed safely in the NICUs of hospitals lacking on-site pediatric cardiac surgical units, without incurring the risk inherent in transport of critically ill infants. In addition, patient care is continued by the neonatology team most familiar with the child's medical and social history, and the patient's family is minimally inconvenienced.

Complications of PDA ligation include inadvertent ligation of the left pulmonary artery or descending aorta, recurrent laryngeal nerve damage, and excessive bleeding due to inadvertent PDA disruption. After ductal ligation in premature infants, worsening pulmonary compliance can precipitate a need for increased ventilatory support, and manifestations of an acute increase in left ventricular afterload should be anticipated, especially if left ventricular dysfunction has developed preoperatively. PDA ligation has been performed in infants and children using thoracoscopic surgical techniques. This approach has the advantage of limited incisions at thoracoscopic sites, promoting less postoperative pain and discharge from the hospital the same day of surgery.

Coarctation of the aorta is a narrowing of the descending aorta near the insertion of the ductus arteriosus. Obstruction to aortic flow results and may range from severe obstruction with compromised distal systemic perfusion to mild upper extremity hypertension as the only manifestation. Associated anomalies of both the mitral

2040

The surgical approach is through a left thoracotomy, whereby the aorta is cross-clamped and the coarctation repaired with an end-to-end anastomosis, patch aortoplasty, or subclavian patch. During cross-clamping, we usually allow significant proximal hypertension (20% to 25% increase over baseline), based on evidence that vasodilator therapy may jeopardize distal perfusion and promote spinal cord ischemia.^[253] Intravascular volume loading with 10 to 20 mL/kg of crystalloid is given just before removal of the clamp. The anesthetic concentration is decreased, and additional blood volume support is given until the blood pressure rises. Post-repair rebound hypertension due to heightened baroreceptor reactivity is common and often requires medical therapy. After cross-clamping, aortic wall stress due to systemic hypertension is most effectively lowered by institution of beta blockade with esmolol or alpha/beta blockade with labetalol.^[254] Recent work indicates that patients less than 6 years of age should receive a loading dose of 250 to 500 µg/kg of esmolol, followed by an infusion of 250–750 µg/kg/minute, depending on the blood pressure. Despite an esmolol infusion, 25% to 50% of patients have a blood pressure that is above the targeted range, requiring a second drug. Sodium nitroprusside, which increases the calculated aortic wall stress in the absence of beta blockade, is usually chosen as the second drug. Other agents, which may have a greater likelihood of achieving the targeted pressure, include nitroglycerine and nicardipine. Propranolol is useful in older patients but can cause severe bradycardia in infants and young children. Although it actually increases calculated aortic wall stress in the absence of beta blockade by accelerating dP/dT (contractile force), the addition of sodium nitroprusside may be necessary to control refractory hypertension. Captopril or an alternative antihypertensive regimen is begun in the convalescent stage of recovery in those patients with persistent hypertension.

The management of infants undergoing placement of extracardiac shunts without cardiopulmonary bypass centers around goals similar to those of other shunt lesions: balancing pulmonary and systemic blood flow by altering PaCO₂ , PaO₂ , and ventilatory dynamics. Central shunts are usually performed through a median sternotomy, while Blalock-Taussig shunts may be performed through a thoracotomy or sternotomy. In patients in whom pulmonary blood flow is critically low, partial cross-clamping of the pulmonary artery required for the distal anastomosis causes further reduction of pulmonary blood flow and desaturation, necessitating meticulous monitoring of pulse oximetry. Careful application of the cross-clamp to avoid pulmonary artery distortion will help maintain pulmonary blood flow. Under circumstances in which severe desaturation and bradycardia occur with cross-clamping, CPB will be required for the procedure.

Intraoperative complications include bleeding and severe systemic oxygen desaturation during chest closure, usually indicating a change in the relationship of the intrathoracic contents that results in distortion of the pulmonary arteries or kink in the shunt. Pulmonary edema may develop in the early postoperative period in response to the acute volume overload that accompanies the creation of a large surgical shunt. Measures directed at increasing PVR, such as lowering inspired O₂ to room air, allowing the PaCO₂ to rise, and adding positive end-expiratory pressure are helpful maneuvers to decrease pulmonary blood flow until the pulmonary circulation can adjust. Decongestive therapy such as diuretics and digoxin may alleviate the manifestations of congestive heart failure. Under such circumstances, early extubation is inadvisable.

Pulmonary artery banding is used to restrict pulmonary blood flow in infants whose defects are deemed uncorrectable for either anatomic or physiologic reasons. These patients are generally in congestive heart failure with reduced systemic perfusion and excessive PBF. The surgeon places a restrictive band around the main pulmonary artery to reduce PBF. Band placement is very imprecise and requires careful assistance from the anesthesia team to accomplish successfully. Many approaches have been suggested. We place the patient on 21% inspired oxygen concentration and maintain the PaCO₂ at 40 mm Hg, to simulate the postoperative state. Depending on the malformation, a pulmonary artery band is tightened to achieve hemodynamic (e.g., distal pulmonary artery pressure 50%–25% systemic pressure) or physiologic (e.g., p:s approaching 1) goals. Should the attainment of these objectives produce unacceptable hypoxemia, the band is loosened.