383CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease (Box 36 2) The details of the specific considerations for selected lesions are presented in their respective sections The initi[.]
CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease • BOX 36.2 Ten Intensive Care Strategies to Diagnose and Support Low–Cardiac Output States Know in detail the cardiac anatomy and its physiologic consequences Understand the specialized considerations of the newborn and implications of reparative rather than palliative surgery Diversify personnel to include experts in neonatal and adult congenital heart disease Monitor, measure, and image the heart to rule out residual disease as a cause of postoperative hemodynamic instability or low cardiac output Maintain aortic perfusion and improve the contractile state Optimize preload (including atrial shunting) Reduce afterload Control heart rate, rhythm, and synchrony Optimize heart-lung interactions 10 Provide mechanical support when needed (Box 36.2) The details of the specific considerations for selected lesions are presented in their respective sections The initial assessment following cardiac surgery begins with a review of the operative findings This includes details of the operative repair and CPB, particularly total CPB time, myocardial ischemia (aortic cross-clamp), and circulatory arrest or antegrade perfusion times; concerns about myocardial protection; recovery of myocardial contractility; typical postoperative systemic arterial and central venous pressures; findings from intraoperative transesophageal or epicardial echocardiography, if performed; vasoactive medication requirements; and hemostatic management This information guides subsequent examination, which should focus on the quality of the repair or palliation plus a clinical assessment of cardiac output (Box 38.3) In addition to a complete cardiovascular examination immediately upon arrival to the PICU, a routine set of laboratory tests should be obtained, including a chest radiograph, 12- or 15-lead electrocardiography (ECG), blood gas analysis, serum electrolytes and glucose, ionized calcium and lactate measurements, complete blood count, and coagulation profile This information, together with an understanding of the preoperative and postoperative loading conditions of the heart, are • BOX 36.3 Signs of Heart Failure or Low–Cardiac Output States Signs Cool extremities/poor perfusion Oliguria and other end-organ failure Tachycardia Hypotension Acidosis Cardiomegaly Pleural effusions Monitor and Assess Heart rate, blood pressure, intracardiac pressure Extremity temperature, central temperature Urine output Mixed venous oxygen saturation Arterial blood gas pH and lactate Laboratory measures of end-organ function Echocardiography 383 essential for clinical management in the immediate postoperative period Optimizing preload involves more than just giving volume to a hypotensive patient There are numerous considerations to fluid balance involving types of isotonic fluid, ultrafiltration in the operating room, optimal hematocrit, and the use of diuretics or vasopressors Fluid itself can be detrimental if excess extravascular water results in interstitial edema and end-organ dysfunction of vital organs such as the heart, lungs, and brain Occasionally, permitting a right-to-left shunt at the atrial level can optimize preload to the left ventricle in some conditions (discussed later) Maintaining aortic perfusion after CPB and improving the contractile state of the heart with higher doses of catecholamines are reasonable goals, but they may have particularly deleterious consequences in the newborn myocardium after hypothermic CPB The benefits of afterload reduction are well known but, if excessive, may result in hypotension, coronary insufficiency, and cardiovascular collapse Pacing the heart can stabilize the rhythm and hemodynamics, but it also may contribute to dyssynchronous, inefficient cardiac contraction or may induce other arrhythmias Although lifesaving in many instances, mechanical support of the failing myocardium in the form of extracorporeal life support (ECLS) or ventricular assist devices has its own set of limitations and morbidities Almost every treatment approach has its own set of adverse effects Supporting cardiac output in the postoperative patient is a balance between the promise and poison of therapy Monitoring The goal of postoperative monitoring following cardiac surgery primarily focuses on assessing the adequacy of circulatory status and oxygen delivery The level of vigilance in the immediate postoperative period can be optimized by the combination of laboratory values and physical examination findings with data obtained via noninvasive devices and invasive monitoring to assess intracardiac pressures and oxygen saturations Near-infrared spectroscopy (NIRS) provides a noninvasive, continuous estimate of regional oxygen supply and demand that serves as a surrogate for hemodynamics and cerebral and somatic oxygenation It is based on the differential absorption of varying wavelengths of light by hemoglobin as it associates with oxygen to measure oxygen content in a localized tissue bed.22 While data demonstrating a definitive impact on overall outcome are lacking, there are reports that correlate decreased cerebral and/or somatic NIRS with increased mortality, prolonged length of stay (LOS), and worsening neurologic outcomes.23,24 Invasive monitoring of central venous pressure is routine for most patients following cardiac surgery Intracardiac or transthoracic left atrial (LA) catheters are often used to monitor patients after complex reparative procedures Pulmonary arterial (PA) catheters now are seldom used but may be particularly useful if one anticipates postoperative pulmonary hypertension, allowing rapid detection of pressure changes and assessment of the response to interventions LA catheters are especially helpful in the management of patients with ventricular dysfunction, coronary artery perfusion abnormalities, or mitral valve disease The mean LA pressure typically is to mm Hg greater than mean right atrial (RA) pressure, which generally varies between 1- and 6-mm Hg in nonpostoperative pediatric patients undergoing cardiac catheterization In postoperative patients, mean LA and RA pressures are often greater than to mm Hg However, they generally should be less than 15 mm Hg The compliance of the right atrium is 384 S E C T I O N I V Pediatric Critical Care: Cardiovascular • BOX 36.4 Common Causes of Elevated Left Atrial Pressure After Cardiopulmonary Bypass Decreased ventricular systolic or diastolic function Left atrioventricular valve disease Large left-to-right intracardiac shunt Chamber hypoplasia Intravascular or ventricular volume overload Cardiac tamponade Arrhythmia greater than that of the left atrium except in the newborn; thus, pressure elevations in the right atrium of older patients with two ventricles typically are less pronounced Possible causes of abnormally elevated LA pressure are listed in Box 38.4 In addition to pressure data, intracardiac catheters in the right atrium (or a percutaneously placed central venous catheter), left atrium, and pulmonary artery can be used to monitor the oxygen saturation of systemic or pulmonary venous blood and indicate the presence or absence of atrioventricular synchrony Following reparative surgery, patients with no intracardiac shunts and adequate cardiac output may have a mild reduction in RA oxygen saturation to approximately 60% Lower RA oxygen saturation does not necessarily indicate low cardiac output If a patient has arterial desaturation (complete mixing lessons, lung diseases, and so on), the arteriovenous oxygen saturation difference is normally ,30% Hence, even a low RA saturation may be in keeping with appropriate oxygen delivery and extraction Elevated RA oxygen saturation often is the result of left-to-right shunting at the atrial level (e.g., from the left atrium, anomalous pulmonary vein, or left ventricular [LV]-to-RA shunt) Blood in the LA normally is fully saturated with oxygen (i.e., approximately 100%) The two chief causes of reduced LA oxygen saturation are an atrial-level right-to-left shunt and pulmonary venous desaturation from abnormal gas exchange In the absence of left-to-right shunts, PA oxygen saturation is the best representation of the “true” mixed venous oxygen saturation because all sources of systemic venous blood should be thoroughly mixed as they are ejected from the RV When elevated, this saturation is useful in identifying residual significant left-to-right shunts following repair of a VSD The absolute value of the PA oxygen saturation is a predictor of significant postoperative residual shunt In patients following TOF or VSD repair, PA oxygen saturation greater than 80% within 48 hours of surgery with a fractional inspired oxygen concentration (Fio2) less than 0.5 is a sensitive indicator of significant left-to-right shunt (Qp/Qs 1.5) year after surgery.25 Low Cardiac Output Syndrome Although low cardiac output after CPB is often attributable to residual or undiagnosed structural lesions, progressive low–cardiac output states occur A number of factors have been implicated in the development of myocardial dysfunction following CPB, including (1) the inflammatory response associated with CPB, (2) myocardial ischemia from aortic cross-clamping, (3) hypothermia, (4) reperfusion injury, (5) inadequate myocardial protection, and (6) ventriculotomy (when performed) The typical decrease in cardiac index has been well characterized in newborns following an arterial switch operation (ASO).26 In a group of 122 newborns, the median maximal decrease in cardiac index that typically occurred to 12 hours after separation from CPB was 32%, and in of these newborns reached a nadir of the cardiac index lower than L/min per square meter.26 Anticipation of this low cardiac output syndrome (LCOS) and appropriate intervention can much to avert morbidity or the need for mechanical support Mixed venous oxygen saturation, whole-blood pH, and lactate are laboratory measures commonly used to evaluate the adequacy of tissue perfusion and, hence, cardiac output Volume Adjustments After CPB, the factors that influence cardiac output—such as preload, afterload, myocardial contractility, heart rate, and rhythm—must be continuously assessed and manipulated as needed Volume expansion (increased preload) is commonly necessary, followed by appropriate use of vasoactive agents Atrial pressure and the ventricular response to changes in atrial pressure must be evaluated Ventricular response is judged by observing systemic arterial pressure and waveform, heart rate, skin color, peripheral extremity temperature, peripheral pulse magnitude, urine output, core body temperature, and acid-base balance Preserving and Creating Right-to-Left Shunts Selected children with low cardiac output may benefit from strategies that allow right-to-left shunting at the atrial level in the face of expected postoperative RV dysfunction A typical example is early repair of TOF, when the hypertrophied and poorly compliant right ventricle may be further compromised by increased volume load from pulmonary regurgitation secondary to a transannular patch on the RV outflow tract These children will benefit from leaving the foramen ovale patent to permit right-to-left shunting of blood, thus preserving cardiac output and oxygen delivery despite the attendant transient cyanosis When the foramen ovale is not patent or is surgically closed, RV dysfunction can lead to reduced LV filling, low cardiac output, and, ultimately, LV dysfunction In infants and neonates with repaired truncus arteriosus, the same concerns apply and may even be exaggerated if RV afterload is elevated because of pulmonary hypertension Other Strategies Additional strategies to support low cardiac output associated with cardiac surgery in children include the use of atrioventricular pacing for patients with complete heart block or prolonged interventricular conduction delays and asynchronous contraction.27 Appreciation of the hemodynamic effects of positive and negative pressure ventilation may be used to assist cardiac output Avoidance of elevated body temperatures and even inducing hypothermia along with appropriate sedation and even paralysis may provide end-organ protection during periods of low cardiac output and aid in the management of postoperative arrhythmias, such as junctional ectopic tachycardia Mechanical Cardiac Support Perioperative mechanical circulatory support (MCS) can be lifesaving for critically ill children and young adults with CHDs.28,29 The most common form of pediatric MCS is extracorporeal membrane oxygenation (ECMO) ECMO can be used as rescue during extracorporeal cardiopulmonary resuscitation (ECPR), in failure to wean from CPB, or in patients who develop low–cardiac output states postoperatively despite high levels of pharmacologic support.30,31 it is presently less commonly used as a bridge to heart CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease transplantation—it is more often used as a prelude to long-term mechanical assist devices or simply to allow time for decisionmaking.29,32 An analysis of 96,596 operations from 80 centers reporting to the Society of Thoracic Surgeons Congenital Heart Surgery Database showed that MCS was used in 2.4% of cases.33 Children who underwent Norwood procedures (17%) or complex biventricular repairs (14%) were more likely to receive MCS Substantial variation exists in MCS rates across both high- and low-volume centers Overall, 53% of those children who received MCS did not survive to hospital discharge, with mortality greater than 70% for certain operative lesions (truncus arteriosus repair, Ross-Konno operation).33 Despite this high mortality, it is important to recognize that survival would have been virtually zero for those children without MCS In a recent report from the Pediatric Cardiac Critical Care Consortium Registry,34 of the 14,526 eligible medical as well as surgical cardiac ICU hospitalizations, 449 (3.1%) had at least one ECMO run Of these, 329 (3.5%) were surgical and 120 (2.4%) were medical hospitalizations Of the surgical group, 33 (10%) included preoperative ECMO only and 296 (90%) included postoperative ECMO Overall, in-hospital mortality was 48.9% in the surgical group and 63.3% in the medical group; mortality rates for hospitalizations including ECPR were 82.7% (surgical) and 50% (medical).34 Due to improved technology, reliability, and mechanical durability of devices, higher rates of patient survival, reduced adverse events, and limited availability of organs for transplantation, intracorporeal MCS has become an accepted long-term inpatient and outpatient therapy for those with advanced heart failure awaiting heart transplantation.35 Ventricular assist devices (VADs) can support function of the left ventricle (left ventricular assist device [LVAD]), right ventricle (right ventricular assist device [RVAD]), or both (biventricular assist device [BiVAD]) A total artificial heart (TAH) replaces the heart itself VADs have two different mechanisms of blood flow: pulsatile or continuous Continuous flow devices contain an impeller that rotates at high speed to propel blood These include axial flow impellers (e.g., HeartMate II [Thoratec Corp.]), or centrifugal pumps (e.g., HeartWare HVAD [HeartWare Corp.]) Paracorporeal pulsatile devices (e.g., Thoratec PVAD-BiVAD [Thoratec Corp.], Berlin Heart EXCOR BiVAD [Berlin Heart Corp.]) are also used in selected cases Guidelines exist with regard to CPR in children with MCS.35 A more detailed discussion of MCS can be found in Chapter 28 Right Ventriculotomy and Restrictive Physiology Right ventricular restrictive physiology has been demonstrated by echocardiography as persistent anterograde diastolic blood flow into the pulmonary circulation following reconstruction of the RV outflow in infants and children This occurs in the setting of elevated RV end-diastolic pressure and RV hypertrophy when the right ventricle demonstrates diastolic dysfunction with an inability to properly relax and fill during diastole The poorly compliant RV usually is not dilated in this circumstance, and pulmonary valve regurgitation is limited because of the elevated RV diastolic pressure.36,37 The term restrictive RV physiology is also commonly used in the immediate postoperative period in patients who have a stiff, poorly compliant, and sometimes hypertrophied RV The elevated ventricular end-diastolic pressure restricts filling during diastole, causing an increase in RA filling pressure and, ultimately, systemic venous hypertension Because of the phenomenon of ventricular 385 interdependence, changes in RV diastolic function and septal position in turn affect LV compliance and function Factors contributing to diastolic dysfunction include lung and myocardial edema following CPB, inadequate myocardial protection of the hypertrophied ventricle during aortic cross-clamp, coronary artery injury, residual outflow tract obstruction, volume load on the ventricle from a residual VSD or pulmonary regurgitation, and dysrhythmias In many centers, a residual atrial communication is left to mitigate the perioperative sequelae associated with restrictive RV physiology, namely, a low–cardiac output state In such a scenario, patients may be desaturated following surgery (typically in the 75% to 85% range) because of this right-to-left shunting, but they maintain systemic cardiac output while avoiding significant systemic venous hypertension As RV compliance and function improve (usually within to postoperative days), the amount of shunt decreases and both anterograde pulmonary blood flow and Sao2 increase If significant restrictive RV physiology develops in the absence of an unrestrictive atrial communication, a low–cardiac output state with increased right-sided filling pressure (usually 12 mm Hg) ensues Such patients often have cool extremities, oliguria, and metabolic acidosis As a result of the elevated RA pressure, hepatic congestion, ascites, increased chest tube output, and pleural effusions may be evident These patients may be tachycardic and hypotensive, with a narrow pulse pressure Preload must be maintained despite an already elevated RA pressure Significant inotropic support often is required (typically, epinephrine 0.05–0.1 µg/kg per minute) A phosphodiesterase inhibitor, such as milrinone, can be beneficial because of its lusitropic properties; however, one must be cautious in the use of these agents with renal impairment.38 Sedation and paralysis often are necessary for the first 24 to 48 hours to minimize energy expenditure and associated myocardial work Factors that further impair ventricular diastolic filling—such as loss of AV synchrony, accumulation of pleural fluid or ascites, and high tidal volume ventilation with air trapping—should be mitigated early in the postoperative course Mechanical ventilation, either hypoinflation or hyperinflation of the lung, hypothermia, and acidosis can contribute to increased afterload on the right ventricle and pulmonary regurgitation Synchronized intermittent positive-pressure ventilation with the lowest possible mean airway pressure should be the aim, as discussed previously Diastolic Dysfunction Occasionally, there is an alteration of ventricular relaxation, an active energy-dependent process, which reduces ventricular compliance This is particularly problematic in patients with a hypertrophied ventricle undergoing surgical repair, such as TOF or Fontan surgery, and following CPB in some neonates when myocardial edema may significantly restrict diastolic function.37,38 The poorly compliant ventricle with impaired diastolic relaxation has a reduced end-diastolic volume and stroke volume b-Adrenergic antagonists and calcium channel blockers add little to the treatment of this condition In fact, hypotension or myocardial depression produced by these agents often outweighs any gain from slowing the heart rate Calcium channel blockers are relatively contraindicated in neonates and small infants because of their dependence on transsarcolemmal flux of calcium to both initiate and sustain contraction A gradual increase in intravascular volume to augment ventricular capacity, in addition to the use of low doses of inotropic 386 S E C T I O N I V Pediatric Critical Care: Cardiovascular agents, is of modest benefit in patients with diastolic dysfunction Tachycardia must be avoided and AV synchrony maintained to optimize diastolic filling time and decrease myocardial oxygen demands If low cardiac output persists despite treatment, vasodilators can be carefully attempted to alter systolic wall tension (afterload) and thus decrease the impediment to ventricular ejection Because the capacity of the vascular bed increases after vasodilation, simultaneous volume replacement is often necessary A noncatecholamine inodilator with vasodilating and lusitropic (improved diastolic state) properties, such as milrinone, is useful under these circumstances in contrast with other inotropic agents.39 Pharmacologic Support General principles of pharmacologic support in the neonatal and pediatric patient center on the recognition of the developmental limitations of the neonatal myocardium and the well-described reductions in cardiac output to 12 hours after separation from CPB.26 Despite ongoing development and maturity of adrenergic receptors and L-type calcium channels, catecholamine-based inotropic agents and vasodilators are efficacious in this population Other nonvasoactive agents serve as adjuncts to optimizing postoperative hemodynamics and fluid balance The combination of a low-dose inotrope and an afterload reducing agent—or, more commonly, a phosphodiesterase inhibitor—has been shown to decrease the occurrence of postoperative LCOS following CPB.39 It should be understood that the need for vasoactive and inotropic support varies greatly among patients recovering from cardiac surgery and even over time for an individual patient progressing through the postoperative care continuum The intensity of pharmacologic support employed must be constantly evaluated One must not embrace a false sense of security when caring for a patient with adequate cardiac output when this requires disproportionate pharmacologic support The current approach is to employ the lowest level of inotropic and vasoactive support necessary for the achievement of hemodynamic goals Due to advances in preoperative stabilization, anesthetic strategies, surgical technique, myocardial protection, and CPB, it is not uncommon for a patient to return to the PICU requiring only low doses of milrinone or epinephrine or no pharmacologic support at all A detailed discussion of cardiovascular pharmacology is beyond the scope of this chapter but can be found in Chapter 31 surgically In these cases, the use of pulmonary vasodilator strategies augments only residual or undiagnosed shunts and increases the volume load on the heart Several factors peculiar to CPB may raise PVR: pulmonary vascular endothelial dysfunction, microemboli, pulmonary leukostasis, excess thromboxane production, atelectasis, hypoxic pulmonary vasoconstriction, and adrenergic events all have been suggested to play a role in postoperative pulmonary hypertension Postoperative pulmonary vascular reactivity has been related not only to the presence of preoperative pulmonary hypertension and left-to-right shunts but also to the duration of total CPB The threat of postoperative pulmonary hypertensive crises can be partially addressed by providing surgery at earlier ages, pharmacologic interventions, and other postoperative management strategies (Table 36.1) Pulmonary Vasodilators Nitric oxide (NO) is the mainstay of therapy in patients with pulmonary hypertension requiring critical care NO is a vasodilator formed by the endothelium from l-arginine and molecular oxygen in a reaction catalyzed by NO synthase NO then diffuses to the adjacent vascular smooth muscle cells, where it induces vasodilation through a cyclic guanosine monophosphate-dependent pathway.42,43 Because NO exists as a gas, it can be delivered by inhalation to the alveoli and, hence, to the adjacent blood vessels Once it diffuses across the wall of the pulmonary blood vessels, NO enters the vascular lumen There, it is rapidly inactivated by hemoglobin, resulting in selective pulmonary vasodilation Inhaled NO (iNO) has advantages over intravenously administered vasodilators that may cause systemic hypotension and increase intrapulmonary shunting Inhaled NO lowers pulmonary artery pressure in a number of diseases without the unwanted effect of systemic hypotension This effect is especially dramatic in children with cardiovascular disorders and postoperative patients with pulmonary hypertensive crises.41,44,45 Therapeutic uses of iNO in children with CHD abound in the ICU Newborns with total anomalous pulmonary venous connection (TAPVC) frequently have obstruction of the pulmonary venous pathway where it connects anomalously to the systemic TABLE Critical Care Strategies for Postoperative 36.1 Treatment of Pulmonary Hypertension Managing Acute Pulmonary Hypertension in the Intensive Care Unit Encourage Avoid Anatomic investigation Residual anatomic disease Children with many forms of CHD are prone to perioperative elevations in pulmonary vascular resistance (PVR).40 This situation complicates the postoperative course when transient myocardial dysfunction is further challenged by increased RV afterload.41 Although postoperative patients with pulmonary hypertension often are presumed to have active and reversible pulmonary vasoconstriction as the source of their pathophysiology, the intensivist is obligated to explore anatomic causes of mechanical obstruction that impose a barrier to pulmonary blood flow Elevated LA pressure, pulmonary venous obstruction, branch pulmonary artery stenosis, or surgically induced loss of the vascular tree all raise RV pressure and impose an unnecessary burden on the right heart Similarly, a residual or undiagnosed left-to-right shunt raises pulmonary artery pressure postoperatively and must be addressed Opportunities for right-to-left shunt as pop-off Intact atrial septum in right heart failure Sedation/anesthesia Agitation/pain Moderate hyperventilation Respiratory acidosis Moderate alkalosis Metabolic acidosis Adequate inspired oxygen Alveolar hypoxia Normal lung volumes Atelectasis or overdistension Optimal hematocrit Excessive hematocrit Inotropic support Low output and coronary perfusion Vasodilators Vasoconstrictors/increased afterload CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease venous circulation When pulmonary venous return is obstructed preoperatively, pulmonary hypertension is severe and requires urgent surgical relief Use of iNO in this or other settings of suspected pulmonary venous obstruction is contraindicated On the other hand, increased neonatal pulmonary vasoreactivity, endothelial injury induced by CPB, and remodeling of the pulmonary vascular bed in this disease contribute to postoperative pulmonary hypertension Postoperatively in the patient with TAPVC after adequate surgical relief of obstruction, iNO dramatically reduces pulmonary hypertension without adverse changes in heart rate, systemic blood pressure, or vascular resistance Postoperative patients with TAPVC, congenital mitral stenosis, and other pulmonary venous hypertensive disorders associated with low cardiac output are among the most responsive to iNO These infants are born with significantly increased amounts of smooth muscle in their pulmonary arterioles and venules Histologic evidence of muscularized pulmonary veins and pulmonary arteries suggests the presence of vascular tone and capacity for change in resistance at both the arterial and venous sites The increased responsiveness to iNO seen in younger patients with pulmonary venous hypertension may result from pulmonary vasorelaxation at a combination of precapillary and postcapillary vessels Resolving the primary venous obstruction is of utmost importance before using iNO in these lesions Several groups have reported successful use of iNO in a variety of other congenital heart defects following cardiac surgery Inhaled NO is especially helpful when administered during a pulmonary hypertensive crisis.46 Successful iNO use has been described after the Fontan procedure, following late VSD repair, and with a variety of other anatomic lesions for which patients are at risk of developing postoperative pulmonary hypertensive crises.45–47 Oxygen saturation in response to iNO generally does not improve in very young infants who are excessively cyanotic after a bidirectional Glenn anastomosis.48 In these cases, increasing cardiac output and cerebral blood flow will have a much greater impact on arterial oxygenation because elevated pulmonary vascular tone is seldom the limiting factor in the hypoxemic patient after the bidirectional Glenn operation.49 Inhaled NO can be used diagnostically in neonates with RV hypertension after cardiac surgery to discern those with reversible vasoconstriction In patients with Ebstein anomaly, a clinical response to iNO can accurately differentiate between functional and anatomic pulmonary atresia.50 In addition, the use of iNO in such patients can facilitate anterograde pulmonary blood flow and hemodynamic stabilization Failure of the postoperative newborn to respond to iNO should be regarded as strong evidence of anatomic and possibly surgically remediable obstruction.50 If iNO must be discontinued before the pathologic process has been resolved, hemodynamic instability can be expected The withdrawal response to iNO can be attenuated by pretreatment with the type V phosphodiesterase inhibitor sildenafil.51 Sildenafil inhibits the inactivation of cyclic guanosine monophosphate within the vascular smooth muscle cell and has the potential to augment the effects of either endogenous or exogenously administered NO to affect vascular smooth muscle relaxation Sildenafil can be administered in an oral or intravenous (IV) form and has a somewhat selective pulmonary vasodilating capacity while lowering LA pressure and providing a modest degree of systemic afterload reduction in some postoperative children Chronic oral administration of sildenafil to adults with primary pulmonary hypertension improves exercise capacity This phenomenon has 387 also been demonstrated in pediatric patients with a Fontan circulation, perhaps suggesting a broad therapeutic application on older patients after operation for CHD Many other vasodilators have been used with variable success in patients with pulmonary hypertensive disorders requiring critical care IV vasodilators—such as tolazoline, phenoxybenzamine, nitroprusside, and isoproterenol—have little biological basis for selectivity or enhanced activity in the pulmonary vascular bed.52 However, if myocardial contractility is depressed and the afterload reducing effect on the left ventricle is beneficial to myocardial function and cardiac output, then these drugs may be of some value In addition to drug-specific side effects, intravenous vasodilators all have the potential to produce profound systemic hypotension, critically lowering coronary perfusion pressure while simultaneously increasing intrapulmonary shunt, thus limiting their usefulness in the management of acute postoperative pulmonary hypertension In fact, in patients with idiopathic pulmonary hypertension who have adequate LV contractility, the use of a vasopressor may help the RV coronary perfusion pressure, LV preload and systolic interventricular dependence, thus preventing a pulmonary hypertensive crisis Management of Postoperative Bleeding Infants and children undergoing cardiac surgery are at high risk for hemorrhage and need for transfusion CPB is a major thrombogenic stimulus that causes a multifactorial coagulopathy due to dilution and consumption of clotting factors and inactivation of platelets This is further exacerbated by an immature coagulation system and the presence of hypoxia and hypothermia While upward of 79% of children undergoing cardiac surgery will require transfusion,53 the need for transfusion is associated with increased morbidity.54,55 Transfusion criteria for packed red blood cells is determined by balancing the inherent risks associated with transfusion and the need to optimize oxygen delivery in the face of hemodynamic instability However, there are increasing data suggesting that the use of more restrictive transfusion parameters results in less transfusion with no difference in clinical outcome.56 To minimize the need for excessive blood products, careful attention to ongoing bleeding and coagulopathy is necessary Baseline complete blood count and coagulation profile should be measured on return from the operating room Chest tube outputs of 10 mL/kg in the first hour or mL/kg per hour for subsequent hours should prompt aggressive repletion of abnormal clotting factors, initially with platelets and fresh-frozen plasma (FFP), assessment of adequate reversal of anticoagulants, and a discussion with the surgeon When bleeding is resistant to therapy, transfusion of factor concentrates should be considered These include fibrinogen concentrate, prothrombin complex concentrates, or even activated factor VII in selected patients Significant repletion of red blood cells also necessitates the concurrent transfusion of platelets and FFP to avoid further dilution of clotting components Ongoing chest tube output that does not abate despite normalization of factors suggests the possibility of surgical bleeding that could necessitate reexploration Further, while control of postoperative bleeding is the goal, the abrupt cessation of chest tube output—particularly when accompanied by increasing CVP, tachycardia, and hypotension—suggests evolving tamponade Ensuring chest tube patency may be sufficient to reverse the process If not, reexploration of the mediastinum may be necessary ... because of this right-to-left shunting, but they maintain systemic cardiac output while avoiding significant systemic venous hypertension As RV compliance and function improve (usually within to... residual shunt In patients following TOF or VSD repair, PA oxygen saturation greater than 80% within 48 hours of surgery with a fractional inspired oxygen concentration (Fio2) less than 0.5 is... newborns reached a nadir of the cardiac index lower than L/min per square meter.26 Anticipation of this low cardiac output syndrome (LCOS) and appropriate intervention can much to avert morbidity