393CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease 2 1 in a patient with clinical or biochemical evidence of insuffi cient oxygen delivery, additional interventions and/or surger[.]
CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease 2:1 in a patient with clinical or biochemical evidence of insufficient oxygen delivery, additional interventions and/or surgery is necessary Initial resuscitation involves maintaining patency of the ductus arteriosus with a PGE1 infusion at a rate of 0.01 to 0.05 µg/kg per minute Intubation and mechanical ventilation are not necessary for all patients Patients usually are tachypneic, but provided that the work of breathing is not excessive and systemic perfusion is maintained without metabolic acidosis, spontaneous ventilation is often preferable in order to achieve adequate systemic perfusion and balance of Qp and Qs If the initial presentation involved circulatory collapse and end-organ dysfunction, then a period of days may be required to establish stability and allow for the return of vital organ function prior to surgery Patients may require intubation and mechanical ventilation because of apnea secondary to PGE1, presence of a low–cardiac output state, or for manipulation of gas exchange to assist balancing Qp/Qs An Sao2 greater than 90% indicates pulmonary overcirculation—that is, Qp/Qs greater than PVR can be increased with controlled mechanical hypoventilation to induce respiratory acidosis, often necessitating sedation and neuromuscular blockade, and with a minimization of Fio2 to avoid hyperoxic pulmonary vasodilation Although these maneuvers often are successful in maintaining a relatively high PVR and reducing pulmonary blood flow, it is important to remember that these patients have a limited oxygen reserve and may desaturate suddenly and precipitously Controlled hypoventilation reduces functional residual capacity (FRC) and, therefore, also decreases the oxygen reserve Patients who have continued pulmonary overcirculation with high Sao2 and reduced systemic perfusion despite these maneuvers require early surgical intervention to control pulmonary blood flow At the time of surgery, a temporary snare can be placed around either branch of the pulmonary artery to limit pulmonary blood flow effectively Alternatively, if there are important comorbidities that preclude a standard palliative operation (prematurity, intracranial hemorrhage), bilateral pulmonary arterial bands can be placed through a median sternotomy to optimize systemic blood flow Decreased pulmonary blood flow in preoperative patients with a parallel circulation is reflected by hypoxemia with Sao2 less than 75% This may result from restricted flow across a small ductus arteriosus, increased PVR secondary to parenchymal lung disease, or increased pulmonary venous pressure secondary to obstructed pulmonary venous drainage or a restrictive atrial septal defect (ASD) In patients with a later postnatal presentation, blood flow through a restrictive ductus may be augmented by the administration of high-dose PGE1 (0.1–0.2 µg/kg per minute) Patients at this level of prostaglandin delivery should have their airway secured and may benefit from vasopressor therapy to both offset the vasodilating effects of PGE1 and increase the systemic vascular resistance (SVR) to augment pulmonary blood flow Sedation, paralysis, and optimization of mechanical ventilation to maintain an alkalosis may be effective if PVR is elevated Inhaled nitric oxide (iNO) also may be useful in selected cases Systemic oxygen delivery can be optimized by augmenting cardiac output and increasing hematocrit level greater than 40% Among some newborns with HLHS, pulmonary blood flow may be insufficient because mitral valve hypoplasia, in combination with a restrictive or nearly intact atrial septum, severely restricts pulmonary venous return to the heart The newborn is intensely cyanotic and may have a pulmonary venous congestion pattern on chest radiograph Urgent interventional cardiac catheterization with balloon septos- 393 tomy or dilation (or stent placement) of a restrictive ASD may be necessary.123,124 Immediate surgical intervention and palliation are preferred in some centers Increasingly, these patients are being identified prenatally with an option of fetal catheter-based intervention Despite such advances, survival in this subgroup is reduced (between 48% and 69%).124–128 Systemic perfusion is maintained with the use of volume and vasoactive agents Inotropic support is occasionally necessary because of ventricular dysfunction secondary to the increased volume load This may be of particular concern in the neonate who presents as a postnatal diagnosis Systemic afterload reduction with agents such as phosphodiesterase inhibitors may improve systemic perfusion, although the reduction in systemic vascular resistance may worsen hypoxemia if this is the primary problem Oliguria and a rising serum creatinine level may reflect renal insufficiency from a low cardiac output Necrotizing enterocolitis is a risk secondary to splanchnic hypoperfusion; we prefer not to enterally feed newborns with a wide pulse width and low diastolic pressure (usually ,30 mm Hg) prior to surgery It is important to evaluate end-organ perfusion and function continuously Postoperative Management The postoperative management of patients with single-ventricle anatomy and physiology will be discussed later in this chapter, in the section detailing postoperative care of newborns with HLHS following stage I palliation Bidirectional Cavopulmonary Anastomosis In this procedure, also known as a bidirectional Glenn (BDG) shunt, the SVC is transected and connected end-to-side to the right pulmonary artery, while the pulmonary arteries remain in continuity Therefore, flow from the SVC is bidirectional into both left and right pulmonary arteries In most situations, the SVC becomes the only source of pulmonary blood flow, and inferior vena cava (IVC) blood returns to the common atrium Performed between age to months, the BDG has proved to be an important early staging procedure in single-ventricle physiology for relieving volume and pressure overload, pulmonary artery distortion, and coronary hypoperfusion associated with an aortopulmonary shunt However, the BDG circulation is not a stable source of pulmonary blood flow in the first few months of life when the PVR is too high to accommodate sufficient passive pulmonary blood flow for tolerable oxygenation The BDG usually is performed on CPB using mild hypothermia with a beating heart Therefore, the complications related to CPB and aortic cross-clamping are minimal, and patients can be weaned and extubated in the early postoperative period.129 In selected cases, the BDG anastomosis can be accomplished without CPB Systemic hypertension is common following a BDG The etiology remains to be determined, but possible factors include improved contractility and stroke volume after the volume load on the ventricle is reduced, and brainstem-mediated mechanisms secondary to the increased systemic and cerebral venous pressure Treatment with vasodilators may be necessary during the early postoperative period Following the BDG anastomosis, arterial oxygen saturation should be in the 80% to 85% range; however, stabilization to this level can take a number of days In addition, positive-pressure ventilation in these patients reduces passive pulmonary blood flow; thus, these patients are generally excellent candidates for early extubation Oxygen saturation frequently improves after 394 S E C T I O N I V Pediatric Critical Care: Cardiovascular Factors Contributing to a Lower-Than- TABLE Anticipated Oxygen Saturation in Patients 36.3 With Single-Ventricle Physiology Etiology Considerations Low Fio2 Low delivered oxygen concentration Failure of oxygen delivery device Pulmonary vein desaturation Ventilation-perfusion defects • Alveolar process (e.g., edema/infection/ atelectasis) • Restrictive process (e.g., effusion/ bronchospasm) Intrapulmonary shunt • Severe RDS • Pulmonary AVM • PA-to-PV collateral vessel(s) g Pulmonary blood flow Anatomic RV outflow obstruction Anatomic pulmonary artery stenosis Increased PVR Atrial level right-to-left shunt Ventricular level right-to-left shunt g Oxygen content Low mixed venous oxygen level • Increased oxygen extraction: hypermetabolic state • Decreased oxygen delivery: low–cardiac output state Anemia AVM, Arteriovenous malformation; Fio2, fractional inspired concentration of oxygen; PA, pulmonary artery; PV, pulmonary vein; PVR, pulmonary vascular resistance; RDS, respiratory distress syndrome; RV, right ventricle extubation Persistent hypoxemia (Sao2 ,70%) can be secondary to a low–cardiac output state (low mixed venous oxygen saturation [Svo2]), low pulmonary blood flow, or lung disease (Table 36.3) Treatment is directed at improving contractility, reducing afterload, and ensuring that the patient has a normal rhythm and hematocrit Increased PVR is an uncommon cause, and iNO is rarely beneficial in these patients.48 This finding is not surprising because PA pressure and resistance and vascular tone are not high enough following this surgery to see a demonstrable benefit from iNO Persistent profound hypoxemia should be investigated in the catheterization laboratory to evaluate hemodynamics, to look for residual anatomic defects that might limit pulmonary flow, such as SVC or PA stenosis or a restrictive ASD, and to coil any significant venous decompressing collaterals if present (e.g., SVC to azygous vein) Fontan Procedure Since the original description in 1971130 the Fontan procedure and its subsequent modifications have been successfully used to treat a wide range of single-ventricle congenital heart defects.131 As a child grows after a BDG, the proportion of IVC blood returning to the heart increases, causing systemic oxygen saturations to fall This often occurs around to years of age, prompting Fontan completion This is functionally accomplished by connecting the IVC blood flow directly to the PA The surgical reconstruction is “physiologic” in that the systemic and pulmonary circulations are in series and cyanosis is corrected Since the early 1990s the technique of Fontan completion has changed from the lateral tunnel to an extracardiac conduit Over the past 25 years, the creation of a fenestration (a small opening between the Fontan pathway and the atrium) has gained broader acceptance to reduce postoperative complications However, given current long-term outcome data, it is important to remember that the operation is still palliative rather than curative.130,132 The mortality and morbidity associated with this surgery have declined substantially over the years, and many patients with stable singleventricle physiology can lead reasonably normal lives.133 Postoperative considerations in managing Fontan physiology include targeting a systemic venous pressure of 15 to 20 mm Hg and LA pressure of to 10 mm Hg—that is, a transpulmonary pressure drop of to 10 mm Hg Intravascular volume must be maintained and hypovolemia must be treated promptly Changes in mean intrathoracic pressure and PVR have a significant effect on pulmonary blood flow Pulmonary blood flow has been shown to be biphasic following the Fontan procedure; earlier resumption of spontaneous ventilation is recommended to avoid the detrimental effects of positive-pressure ventilation.134,135 Doppler analysis demonstrates that pulmonary blood flow predominantly occurs during inspiration in a spontaneously breathing patient—that is, when the mean intrathoracic pressure is subatmospheric In many centers, patients after a standard-risk Fontan completion are identified for early extubation (in the operating room or within hours of ICU admission) With proper selection criteria, optimal CPB and anesthesia management, and early extubation, most patients have an uncomplicated course after Fontan completion and can be discharged from the ICU environment within or days In Fontan patients who not meet early-extubation criteria, the method of mechanical ventilation requires thoughtful consideration A tidal volume of to 10 mL/kg with the lowest possible mean airway pressure is optimal If appropriate selection criteria are followed, patients undergoing a modified Fontan procedure will have a low PVR without labile pulmonary vascular resistance Therefore, vigorous hyperventilation and induction of a respiratory or metabolic alkalosis are generally of little benefit in this group A normal pH and Paco2 of 40 mm Hg should be the goal and, depending on the amount of right-to-left shunt across the fenestration, the arterial oxygen saturation usually is in the 80% to 90 % range The fenestration functions as a “pop-off” when forward flow to the pulmonary circulation is impaired, thereby sending blood into the systemic atrium and ventricle As a result, systemic hypoxemia (Sao2) from the right-to-left shunt is the price paid for maintenance of adequate systemic cardiac output The use of positive end-expiratory pressure (PEEP) requires thoughtful consideration based on patient-specific postoperative circumstances The beneficial effects of a PEEP-related increase in FRC, maintenance of lung volume, and redistribution of lung water must be carefully balanced against the possible detrimental effect of an increase in mean intrathoracic pressure on passive pulmonary blood flow A PEEP of to cm H2O, however, rarely has either hemodynamic consequence or substantial effect on effective pulmonary blood flow Alternative methods of mechanical ventilation have been used in these patients High-frequency ventilation has been employed CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease successfully in selected cases, although the potential hemodynamic consequences of the raised mean intrathoracic pressure must be continually evaluated Airway pressure-release ventilation has been shown to be superior in preserving systemic cardiac output when compared with standard pressure/volume control ventilation in patients post-Fontan completion.136 Negative-pressure ventilation can be beneficial by augmenting pulmonary blood flow, but application is cumbersome in the patient with surgical site dressings, and chest tubes typically present after a midline sternotomy.137 Afterload stress is poorly tolerated after a modified Fontan procedure because of the increase in myocardial wall tension and end-diastolic pressure A phosphodiesterase inhibitor such as milrinone may be particularly beneficial Besides being a weak inotrope with pulmonary and systemic vasodilating properties, its lusitropic action assists by improving diastolic relaxation and lowering ventricular end-diastolic pressure, thereby improving effective pulmonary blood flow and cardiac output Complications After the Fontan Procedure Pleuropericardial Effusions The incidence of recurrent pleural effusions and ascites has decreased since the introduction of the fenestrated baffle technique Nevertheless, for some patients, chylous drainage remains a major problem, with associated respiratory compromise, hypovolemia, and possible hypoproteinemia These effusions can occur secondary to injury to the thoracic duct, persistent elevation of systemic venous pressure, or development of extensive lymphatic collaterals Depending on the clinical significance of the drainage, more extensive evaluation may be required, as discussed earlier Rhythm Disturbances Junctional bradycardia after Fontan completion is commonly observed postoperatively and rarely affects cardiac output significantly In the rare circumstance in which that occurs, the use of AAI pacing rapidly addresses the situation Atrial flutter or fibrillation, heart block, and, less commonly, ventricular dysrhythmia may have a significant impact on immediate recovery and on long-term outcome.138 Sudden loss of sinus rhythm initially causes an increase in LA and ventricular end-diastolic pressure and a fall in cardiac output The SVC or PA pressure must be increased, usually with volume replacement, to maintain the transpulmonary gradient Prompt treatment with antiarrhythmic drugs, pacing, or cardioversion is necessary Premature Closure of the Fenestration Not all patients require a fenestration for a successful, uncomplicated Fontan operation Those with ideal preoperative hemodynamics often maintain adequate pulmonary blood flow and cardiac output without requiring a right-to-left shunt across the baffle Similarly, not all Fontan patients who received a fenestration have a right-to-left shunt in the immediate postoperative period These patients are fully saturated following surgery and may have an elevated right-sided filling pressure but nevertheless maintain an adequate cardiac output The challenge is predicting which patients are at risk for low cardiac output after a Fontan procedure and who will benefit from the placement of a fenestration Even patients with ideal preoperative hemodynamics may manifest a significant low–cardiac output state after surgery In a review of 2747 Fontan completions from 68 centers contributing to the Society of Thoracic Surgeons database, 65% received a surgical fenestration at the time of initial operation.139 Premature closure of the fenestration may occur in the immediate postoperative 395 period, leading to a low–cardiac output state with progressive metabolic acidosis and large chest drain losses from systemic venous hypertension Patients may respond to volume replacement, inotrope support, and vasodilation However, if hypotension and acidosis persist, cardiac catheterization and removal of thrombus or dilation of the fenestration may be urgently needed Persistent Hypoxemia Arterial oxygen saturation levels may vary substantially following a modified Fontan procedure Common causes of persistent arterial oxygen desaturation less than 75% include a poor cardiac output with a low Svo2, a large right-to-left shunt across the fenestration, and additional “leak” in the baffle pathway producing more shunting Persistent hypoxemia can also be caused by an intrapulmonary shunt or venous admixture from decompressing vessels draining from the systemic venous baffle to the pulmonary venous system Reevaluation with conventional or bubble contrast echocardiography and cardiac catheterization may be necessary Low Cardiac Output State An elevated LA pressure after a modified Fontan procedure may reflect poor ventricular function from decreased contractility or increased afterload stress, atrioventricular valve regurgitation, or loss of sinus rhythm (Table 36.4) Treatment consists of maintaining the high right-sided filling pressures (to maintain the transpulmonary gradient) and initiating inotropes and vasodilators If a severely low–cardiac output state with acidosis persists, takedown of the Fontan operation and conversion to a BDG anastomosis or other palliative procedure might be lifesaving Central venoarterial extracorporeal membrane oxygenation (VA ECMO) support in this instance may be an effective bridging strategy to urgent reoperation Emergent cannulation to VA ECMO late after BDG and Fontan is associated with high morbidity and mortality and is generally contraindicated.140,141 Patent Ductus Arteriosus Pathophysiology The ductus arteriosus is a fetal vascular communication between the main pulmonary artery at its bifurcation and the descending aorta below the origin of the left subclavian artery When patent, it provides a simple shunt between the systemic and pulmonary arteries The magnitude and direction of flow between the systemic and pulmonary vessels are determined by the relative resistance to flow in the two vascular beds and the resistance of the ductus itself With a large, nonrestrictive ductus and low PVR, the pulmonary blood flow is excessive and the volume load of the left heart is large Systolic and diastolic flow away from the aorta may steal blood from vital organs and compromise end-organ function at many sites.142 In addition, overcirculated lungs and elevated LA pressure increase the work of breathing.143,144 Critical Care Management Although the patent ductus arteriosus (PDA) of premature infants can often be closed medically with indomethacin, contraindications to use of this agent (e.g., intracranial hemorrhage, renal dysfunction, and hyperbilirubinemia) may require surgical closure of the defect.145 Thoracotomy and surgical ligation of the ductus arteriosus are standard in term and preterm infants who are medically unstable Beyond the newborn period, most centers now occlude the ductus with a percutaneously inserted vascular umbrella or by using coils for smaller PDAs In stable patients who are not 396 S E C T I O N I V Pediatric Critical Care: Cardiovascular TABLE Etiology and Treatment Strategies for Patients With Low Cardiac Output Immediately Following 36.4 the Fontan Procedure Low Cardiac Output Etiology Treatment Inadequate pulmonary blood flow and preload to left atrium Increased PVR Pulmonary artery stenosis Volume replacement Reduce PVR Correct acidosis Inotropic support Pulmonary vein stenosis Premature fenestration closure Systemic vasodilation Catheter or surgical intervention Ventricular failure Systolic dysfunction Diastolic dysfunction AVV regurgitation or stenosis Maintain preload Inotrope support Systemic vasodilation Establish sinus rhythm or atrioventricular synchrony Loss of sinus rhythm h Afterload stress Correct acidosis Mechanical support Surgical intervention, including takedown to BDG and transplantation Increased TPG Baffle 20 mm Hg LAp ,10 mm Hg h TPG 10 mm Hg Clinical State High Sao2/low Svo2 Hypotension/tachycardia Core temperature high Poor peripheral perfusion SVC syndrome with pleural effusions and increased chest tube drainage Ascites/hepatomegaly Metabolic acidosis Normal TPG Baffle 20 mm Hg LAp 15 mm Hg TPG normal 5–10 mm Hg Clinical State Low Sao2/low Svo2 Hypotension/tachycardia Poor peripheral perfusion Metabolic acidosis AVV, Atrioventricular valve; BDG, bidirectional Glenn anastomosis; LAp, left atrial pressure; PVR, pulmonary vascular resistance; Sao2, systemic arterial oxygen saturation; SVC, superior vena cava; Svo2, SVC oxygen saturation; TPG, transpulmonary gradient candidates for an interventional cardiology approach (by nature of the length of the PDA), video-assisted thoracoscopic surgery (VATS) can be used.146 Advantages of VATS compared with open thoracotomy include decreased postoperative pain, shorter hospital stay, and decreased incidence of chest wall deformity.147 Healthy asymptomatic patients undergoing surgery can be extubated in the operating room, allowing many options for anesthetic management However, the fragile premature infant with severe lung disease may require mechanical ventilation for protracted periods after ligation of the ductus arteriosus Fentanyl, pancuronium, oxygen, and air constitute a common anesthetic regimen for this procedure.148 Many centers will bring the operative room environment to this patient population, performing the surgical ligation in the neonatal intensive care unit Management of the premature infant in the operating room requires special considerations of gas exchange, hemodynamic performance, temperature regulation, metabolism and glucose management, and drug and oxygen toxicity Thoracotomy and lung retraction usually decrease lung compliance and increase oxygen and ventilatory requirements A transient rise in systemic blood pressure with ligation of the ductus arteriosus may increase LV afterload or elevate cerebral perfusion pressure to the detriment of a premature patient Inadvertent ligation of the left pulmonary artery or descending aorta has occurred because the ductus arteriosus often is the same size as the descending aorta The ductus is located near the recurrent laryngeal nerve (RLN), which may be damaged during the procedure In addition to the close relationship of the RLN to the PDA and descending aorta, the RLN has a variable course that may be difficult to identify during dissection Prior reports of PDA ligation performed by open thoracotomy indicate that the incidence of RLN injury is 1.2% to 8.8%.149,150 RLN paralysis causes hoarseness and is not detected until the endotracheal tube is removed The incidence may be reduced by location of the RLN within the thorax prior to ligation or clip placement using direct intraoperative stimulation of the RLN and evoked electromyogram monitoring.151 Ligation of an isolated ductus arteriosus generally results in normal cardiovascular function and reserve several months postoperatively.152 Atrial Septal Defect Pathophysiology There are three anatomic varieties of ASD The most common, ASD secundum, is a defect in the septum primum, which ordinarily covers the region of the foramen ovale ASD primum is a defect of the inferior portion of the atrial septum (endocardial cushion), usually accompanied by a cleft in the anterior leaflet of the mitral valve Sinus venous defects are located near the junction of the right atrium and the SVC or IVC They frequently are associated with a partial anomalous pulmonary venous connection Left-to-right shunting (simple) occurs at the atrial level, causing RV volume overload The degree of atrial-level shunting is a function of the difference between right and left ventricular compliance as opposed to atrial pressure differential Pulmonary blood CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease flow is increased, but generally not enough to make these patients symptomatic during early childhood However, later in life, as the LV becomes less compliant and the LA pressures increase, the left-to-right shunt and volume load increase, and symptoms of CHF may occur In rare patients, the longstanding increase in pulmonary blood flow causes pulmonary vascular obstructive disease.153 Other problems associated with longstanding volume load from an ASD include atrial fibrillation Critical Care Management The defect can be closed primarily with sutures or, if it is sufficiently large, with a synthetic patch Sinus venosus defects associated with partial anomalous pulmonary venous connection require a more extensive patch that also directs the partial anomalous pulmonary venous return into the left atrium These patients are among the healthiest encountered in the cardiac ICU Their anesthesia can be managed in many ways, but early tracheal extubation, either in the operating room or in the immediate postoperative period, is the norm Atrial arrhythmias, including atrial flutter and atrial fibrillation, are rarely seen during the postoperative period Mitral regurgitation may occur in patients who have undergone repair of an ASD primum Residual ASDs are uncommon, but occasionally failure to recognize partial anomalous pulmonary venous return results in a residual left-to-right shunt With the exceptions mentioned, these patients usually have nearly normal cardiovascular function and reserve after repair Ventricular Septal Defect Pathophysiology Defects in the ventricular septum occur at several locations in the muscular partition dividing the ventricles Simple shunting occurs across the ventricular septum The magnitude of pulmonary blood flow is determined by the size of the VSD and the PVR.154 With a nonrestrictive defect, high LV flows and pressures are transmitted to the pulmonary artery Therefore, surgical repair is indicated within the first years of life to prevent the progression of pulmonary vascular obstructive disease.155 In patients with established pulmonary vascular disease, the pulmonary arteriolar changes may not recede when the defect is closed In such cases, there may be progressive PVR elevation.156,157 The growth and development of the pulmonary vascular bed are significant factors in the patient’s ability to normalize pulmonary vascular hemodynamics after surgery.157 When PVR approaches or exceeds systemic vascular resistance, right-to-left shunting occurs through the VSD and the patients develop progressive hypoxemia (Eisenmenger syndrome) Closing the VSD in this circumstance may be contraindicated, as it would result in acute right heart failure without other therapies Critical Care Management The most common septal defect, the perimembranous defect, is often repaired through the tricuspid valve (TV) from a right atriotomy However, lesions in the inferior apical muscular septum or those high in the ventricular outflow tract may require a left or right ventriculotomy If so, postoperative ventricular function may be impaired Concomitant RV muscle bundle resection can further impair ventricular function Before repair, measures that decrease PVR may appreciably increase left-to-right shunting in patients with a nonrestrictive defect and may increase the degree of CHF Postoperative RV or LV failure may be a manifestation of the preoperative status of the myocardium, a result of the ventriculotomy and CPB, or both 397 Small infants who fail to thrive, who are malnourished, and who have significant CHF preoperatively may have excessive lung water and may require prolonged mechanical ventilation postoperatively.158 Such infants may have limited intraoperative tolerance for anesthetics that depress the myocardium or for maneuvers that increase pulmonary blood flow Persistent CHF and an audible murmur postoperatively, evidence of low cardiac output, or the need for extensive inotropic support intraoperatively suggest that a residual or previously unrecognized additional VSD is continuing to place a volume and pressure load on the ventricles When PVR is increased preoperatively, the increase in RV afterload caused by closure of the VSD may be poorly tolerated, leading to the need for inotropic support of the heart and measures to decrease PVR Rarely, ventricular outflow tract obstruction is caused by placement of the septal patch Transesophageal echocardiography performed in the operating room is an important tool in diagnosing this problem so that it can be addressed prior to complete separation from CPB Aortic regurgitation caused by prolapse of one of the aortic valve cusps can develop in subaortic or subpulmonic VSDs In addition, heart block may occur after patch closure of a VSD Temporary pacing may be needed to maintain an adequate heart rate and cardiac output Generally a permanent pacemaker is indicated when there is evidence of pacemaker dependence beyond to 10 days.159 Critical Care Management for Late Postoperative Care In the absence of residual VSDs, outflow obstruction, or heart block, most of these patients regain relatively normal myocardial function, especially if the VSD is repaired early.160 However, a small percentage of patients, especially those in whom a large defect was repaired late in childhood, continue to have some degree of ventricular dysfunction and some pulmonary hypertension.161 Atrioventricular Canal Defects Pathophysiology The endocardial cushion defect, or complete common AV canal, consists of defects in the atrial, ventricular, and atrioventricular septa and the AV valvular tissue All four chambers communicate and share a single common AV valve The atrial and ventricular shunts communicate volume and systemic pressures to the right ventricle and pulmonary artery The ventricular shunt orifice usually is nonrestrictive (simple shunt); therefore, PVR governs the degree of excess pulmonary blood flow Left AV valve regurgitation and direct left-ventricular-to-right-atrial shunting may further contribute to atrial hypertension and total left-to-right shunting Critical Care Management Surgical repair of this lesion consists of division of the common AV valve and closure of the ASD and VSD with either a singlepatch or two-patch repair technique In addition, the left AV valve (and sometimes the right AV valve) requires suture approximation and resuspension of the separated portions Prior to surgical repair, these patients have large left-to-right shunts As a result of their high pulmonary blood flows, they have CHF and increased pulmonary vascular reactivity Myocardial depressants and therapies that decrease PVR and thereby increase shunt flow may be poorly tolerated before repair The occasional patients, especially older children and those with trisomy 21, may have developed true pulmonary vascular disease All of the potential complications of ASD and VSD closures are seen in these ... rarely beneficial in these patients.48 This finding is not surprising because PA pressure and resistance and vascular tone are not high enough following this surgery to see a demonstrable benefit... heart increases, causing systemic oxygen saturations to fall This often occurs around to years of age, prompting Fontan completion This is functionally accomplished by connecting the IVC blood... of breathing.143,144 Critical Care Management Although the patent ductus arteriosus (PDA) of premature infants can often be closed medically with indomethacin, contraindications to use of this