PERIOPERATIVE MANAGEMENT OF PATIENTS WITH
CONGENITAL HEART DISEASE:
A MULTIDISCIPLINARY APPROACH
The perioperative care of the
infant, child, and adult with congenital heart disease requires a coordinated,
multidisciplinary approach to patient care that emphasizes teamwork and the
unique contributions of all those involved in the continuum of patient
care—pediatric cardiologist, pediatric
cardiac surgeon, pediatric cardiovascular anesthesiologist, perfusionist,
pediatric intensivist, nurses, advanced practice nurses, physicians assistants,
respiratory therapists, child life therapists, and family members. Each member of the team brings unique
knowledge and perspective to the care of the patient and recognizing and
integrating all members of the team in the ongoing care of the patient is
essential in providing optimal care for these patients. The presence of trainees from medicine,
nursing, respiratory therapy, or other disciplines adds to the size and
complexity of the team caring for the patient, and the roles and
responsibilities of these individuals must be explicitly acknowledged.
Perioperative care encompasses both pre and post operative care of the patient with congenital heart disease. Although many infants and children with congenital heart defects are managed as outpatients until their repairs, some infants or older children with severely abnormal physiology require stabilization and critical care prior to surgery. Many of the basic principles of cardiac intensive care apply to both pre and post operative care and will be considered in this chapter. In addition to supportive care and stabilization, pre operative management includes thorough evaluation of the anatomy and physiology of the heart and the physiologic status of the patient as a whole so that appropriately planned and timed surgery can take place.
Basic principles of pediatric critical medical and nursing care remain relevant in the pediatric congenital cardiac patient. Pediatric cardiac patients are cared for in specialized cardiac intensive care units and in multidisciplinary intensive care units. There is some data that institutions that perform more surgeries have improved outcomes (info here—based on surgeon, unit, hospital?? Is it surgeon numbers that really matter?), Regardless of the focus of the unit, a commitment to ongoing education and training, as well as a collaborative and supportive environment is essential. We feel strongly that a unit dedicated to the care of infants and children is best able to care for these patients. (down on the adult units caring for kids).
Oxygen delivery (DO2) is described
by the following equation: DO2=Qs(CaO2),
where Qs is the systemic cardiac output and CaO2
is arterial O2 content. In
turn, CaO2 (ml/dl) = Hgb (g/dl) * SaO2 * 1.34 (ml/g) +
PaO2 (mmHg) * 0.003 (ml/dl/mmHg) where, Hgb is the hemoglobin
concentration, SaO2 is the arterial O2 saturation, and
PaO2 is the arterial O2 tension. Oxygen utilization (VO2) is Qs(CaO2-CvO2), where CvO2 is the mixed venous oxygen
content. Oxygen delivery is therefore
primarily dependent on systemic cardiac output, hemoglobin concentration, and
oxygen saturation. Dissolved oxygen
(PaO2) makes a small contribution to oxygen delivery.
Ventricular output (Q) is directly related to heart rate and stroke volume. Stroke volume is in turn dependent on preload, afterload, and myocardial contractility. Both pulmonary blood flow (Qp) and systemic blood flow (Qs) are determined by these fundamental forces. In the patient with two ventricles, ventricular interdependence, or the affect of one ventricle on the other, may play a role in pulmonary or systemic blood flow. In some situations, including the post operative state, the pericardium and restriction due to the pericardial space may also play a role in ventricular output.
When evaluating the loading conditions of the heart and myocardial contractility, it is important to consider the two ventricles independently as well as their affect on one another. In previously healthy pediatric patients without heart disease, right atrial filling pressures are commonly assumed to reflect the loading conditions of the left as well as the right ventricle. In the patient with congenital heart disease, this is frequently not true. Pre-existing lesions and the affects of surgery may affect the two ventricles differently. For example, the presence of a right ventricular outflow tract obstruction will lead to hypertrophy of the right ventricle. That right ventricle will be non-compliant, and the right atrial pressure may therefore not accurately reflect the adequacy of left ventricular filling.
Oxygen content (CaO2) is primarily a function of hemoglobin concentration and arterial oxygen saturation. Thus, patients who are cyanotic can achieve adequate oxygen delivery by maintaining a high hemoglobin concentration. Arterial oxygen saturation is commonly affected by inspired oxygen content, by mixed venous oxygen content of blood, by pulmonary abnormalities, and by the presence of a R to L intracardiac shunt. Arterial oxygen content in the patient with a single ventricle and parallel pulmonary and systemic circulations will depend on the relative balance between the circulations as well. In the patient with intracardiac shunt or the single ventricle patient, arterial oxygen content is also affected by the relative resistances of the pulmonary and systemic circuits, as this determines how much blood flows through the lungs relative to the systemic output. Low mixed venous oxygen content contributes to desaturation and suggests increased oxygen extraction due to inadequate oxygen delivery, which in turn is either due to inadequate systemic cardiac output or inadequate hemoglobin concentration.
A thorough understanding of these fundamental principles of cardiac outpu and oxygen delivery is essential for the perioperative care of the patient with congenital heart disease.
An understanding of the anatomy and pathophysiology of the congenital cardiac lesion under consideration allows one to determine the pre-operative care or resuscitation needed and to predict the expected post-operative recovery.
Children with acyanotic heart disease may have one (or more) of three basic defects: 1) left-to-right shunts (e.g., atrial septal defect, ventricular septal defect); 2) ventricular inflow/outflow obstructions (e.g., aortic stenosis, coarctation of the aorta); and 3) primary myocardial dysfunction (e.g., cardiomyopathy) (Table 22-1). These lesions may lead to decreased systemic oxygen delivery by causing maldistribution of flow with excessive pulmonary blood flow (Qp) and diminished systemic blood flow (Qs) (Qp/Qs >1), by impairing oxygenation of blood in the lungs caused by increased intra and extravascular lung water, and decreasing ejection of blood from the systemic ventricle.
In infants
with left-to-right shunts, pulmonary blood flow (Qp)
increases as pulmonary vascular resistance (Rp) decreases from the high levels
present perinatally. (37,132) If Qp is sufficiently
increased, pulmonary artery pressure may also increase, particularly with left
to right shunts distal to the tricuspid valve, such as large VSD or truncus
arteriosus. As pulmonary flow increases,
left ventricular volume overload may occur with cardiac failure, decreased
systemic output, pulmonary congestion and edema. Over time, increased Qp
leads to a series of pulmonary microvascular changes which first produce
reversible pulmonary vasoconstriction and later fixed pulmonary vascular
disease (see Chapter 4 on 'Regulation of Pulmonary Vascular Tone'). As Rp increases over time, Qp
decreases (Table 22-3). The primary determinant of pulmonary blood flow is
pulmonary vascular resistance. In
patients with increased and reactive Rp,
Pulmonary
overcirculation can lead to congestive heart failure through several
mechanisms. Increased Qp leads to left
(systemic) ventricular volume overload and raises left ventricular end
diastolic, left atrial, and pulmonary venous pressures. The increases in pulmonary artery and
pulmonary venous pressures raise the pulmonary hydrostatic pressure gradient
and these promote transudation of fluid into the interstitial space and
ultimately lead to alveolar edema. Right
ventricular end diastolic pressure, and hence, right atrial and systemic venous
pressures, are also elevated. Venous
return may be decreased. High systemic
venous pressure contributes to interstitial edema and may lead to decreased
organ perfusion. The maldistribution of
flow with reduced Qs is accompanied by a reduction in renal blood flow and
resultant stimulation of the renin-angiotensin system (see Chapter 5 on Renal
Function in Heart Disease). Fluid
accumulation is aggravated by sodium and water retention by the kidney.
Pulmonary edema reduces CaO2 through increased intrapulmonary shunting in the lungs. In addition to pulmonary overcirculation, other causes of pulmonary edema in patients with acyanotic heart disease include left ventricular inflow- or outflow obstruction and diastolic dysfunction of the left ventricle. These children demonstrate an increased respiratory rate, diffuse rales and increased work of breathing. The chest x-ray demonstrates diffuse interstitial and alveolar infiltrates.
Diastolic and to a lesser extent systolic dysfunction decrease oxygen delivery in patients with cardiomyopathy.50,77 Diastolic dysfunction raises LVEDP and pulmonary venous pressures ultimately leading to pulmonary edema. Systolic dysfunction decreases ejection fraction and systemic output. Cardiomyopathy represents the primary defect in a variety of heritable and inflammatory heart diseases (See Chapter 47 on Heritable Heart Disease and 44 on Inflammatory Heart Disease). Patients with structural congenital heart defects may also develop myopathic changes in the heart . Graham et al.(32,51,58,73) have shown that cardiomyopathy may be produced by volume or pressure overload depending on the type of defect (Table 22-4). The myopathic changes will be important both pre and post-operatively.
Children with cyanotic heart disease have a right-to-left shunt and therefore always demonstrate systemic arterial desaturation. 95 As with acyanotic heart disease, there may be some combination of shunt, obstruction, and myopathic changes, all of which must be considered. Infants with cyanotic heart disease may be divided into two physiologically distinct groups, those with decreased pulmonary blood flow and those with increased pulmonary blood flow.
Ductal Dependent
Pulmonary Blood Flow (Decreased Pulmonary Blood Flow)
These patients have decreased systemic venous blood entering the pulmonary circulation. Patients in this group may have obstruction to flow from the pulmonary ventricle either at the outlet (e.g., Tetralogy of Fallot, Pulmonary Atresia) or inlet (e.g., Tricuspid Atresia). Patients whose pulmonary blood flow is dependent on a patent ductus arteriosus may present with severe hypoxemia and acidosis as the ductus closes. With decreased Qp and the obligatory presence of an atrial or ventricular septal defect, the blood in the systemic ventricle consists of desaturated systemic venous blood (via the septal defect) and a smaller volume of saturated pulmonary blood (Qp/Qs < 1). The decreased Qp results in decreased oxygen uptake from the lungs, and thus decreased systemic oxygen delivery. In the initial stages, Qs may be normal. If systemic oxygen delivery remains inadequate, anaerobic metabolism and myocardial dysfunction develop, resulting in a further reduction in oxygen delivery. The end result can be severe hypoxemia and acidosis. Patients with decreased Qp require a stable conduit for pulmonary blood flow and a high hemoglobin concentration (> 14 mg/dl) to maximize oxygen content CaO2) and oxygen delivery (D02).
Ductal Dependent
Systemic Blood Flow (Increased Pulmonary Blood Flow)
Patients with ductal dependent systemic blood flow have increased pulmonary blood flow but decreased systemic blood flow due to obstruction of systemic output which can occur at a variety of locations. (61,114,116) These infants may have acceptable arterial saturation but develop decreased oxygen delivery as a result of decreased systemic output (i.e., hypoplastic left heart syndrome, interrupted aortic arch, co-arctation.) Patients may present with profound shock due to dramatic reduction in systemic perfusion and oxygen delivery if the ductal flow is inadequate. Systemic blood flow in patients with severe left ventricular outflow obstruction is dependent on flow through a patent ductus arteriosus into the aorta distal to the obstruction.
The degree to which infants and children will require pre-operative stabilization will depend on the nature and severity of the lesion, the degree to which the lesion has affected the myocardial function, and the presence of other organ system involvement. Many of the concepts involved in pre-operative stabilization will be applicable to post operative care.
Preoperative stabilization of the ill infant or child focuses on
establishing adequate oxygen delivery through manipulation of total cardiac
output, Qp, Qs, hemoglobin concentration, and oxygen
saturation. Additionally, any
abnormalities of other organ systems, such as pneumonia, renal insufficiency,
or seizures, must be evaluated and corrected if possible.
Manipulation of Qp and Qs and the balance
between the pulmonary and systemic circulations is achieved by manipulation of
the preload, afterload, and inotropic state of the right and left
ventricle. Pulmonary vascular resistance
is affected by pH, alveolar pO2, lung volume (atelectasis or overdistension),
noxious stimuli, hematocrit, and many medications. The patient with excessive pulmonary blood
flow and consequent low systemic oxygen delivery can be managed with maneuvers
to increase pulmonary vascular resistance (Rp), which will lead to decreased Qp and increased Qs.
In the patient with ductal dependent pulmonary or systemic blood flow,
the balance of pulmonary and systemic flow can be manipulated by manipulation
of pulmonary vascular resistance or the systemic vascular resistance if needed.
Afterload reduction may improve
myocardial function by decreasing ventricular wall tension, thus improving
stroke volume and decreasing myocardial oxygen consumption. .
Systemic vascular resistance can be lowered by agents that vasodilate
(milrinone, dobutamine) and by avoiding agents that raise SVR (high dose
dopamine, epinephrine, norepinephrine) or situations that raise SVR (pain,
agitation). Patients with left to
right shunts and
Children
with
The myopathic ventricle requires a greater than normal preload to maintain output. If the infant presents with CHF, pulmonary edema, and a stable systemic blood pressure, diuretics may be useful to reduce LVEDP and relieve pulmonary edema without compromising ventricular output. On the other hand if the infant with a myopathic ventricle presents with hypoperfusion, hypotension and acidosis, carefully titrated fluid administration may be necessary to optimize preload and increase cardiac output.
Inotropic drugs increase
contractility at least in the short term.
Unfortunately, inotropic drugs which increase cytosolic Ca++
concentration may also impair relaxation of the heart and decrease ventricular
compliance (see Chapter 2 on
Treatment of
pulmonary edema without pulmonary overcirculation are directed at increasing
both oxygen content and delivery. These children will benefit from oxygen
administration to treat the hypoxia and diuretic therapy to reduce the
intravascular volume and left atrial pressure.
Positive pressure ventilation with positive end expiratory pressures
(PEEP) can improve end expiratory lung volume, decrease intrapulmonary shunting
by opening collapsed alveoli, improve compliance, increase tidal volume and
decrease the work of breathing. (59) In addition, increased intrathoracic
pressure with positive pressure ventilation and PEEP reduces
Post operative care requires a thorough understanding of the anatomic defect, the pathophysiology of the pre-operative heart as well as any other organ system involvement, the anesthetic regimen used, cardiopulmonary bypass issues, and the details of the operative procedure. Invasive and non-invasive monitoring and laboratory or radiographic monitoring is tailored to the needs of the individual patient and will depend on the lesion, the repair, and expected post-operative issues.
Patients who require mechanical ventilation post-operatively do so for a variety of reasons: airway control, abnormal lung function, reduction of oxygen delivery needs, assurance of stability during the immediate post operative period, because of the affect of positive pressure ventilation on cardiac loading conditions, or due to neurologic concerns or residual anesthesia. Mechanical ventilation, either in the operating room or the intensive care unit, is continued until there is adequate hemostasis, the heart rate and rhythm are stable and close to normal for age, cardiac output is adequate with minimal inotropic support, oxygen saturation is adequate and lung function is close to normal, and the patient is awake enough to have adequate respiratory drive and airway protective reflexes. Depending on a number of factors, these conditions may be met in the operating room or the intensive care unit much later in the post-operative course.
Cardiopulmonary interactions can exert important influences on the hemodynamics of the post operative patient but must be evaluated critically and optimized for the specific patient situation. For example, while early extubation and spontaneous ventilation after Fontan operation is often thought to improve hemodynamics, if atelectasis or hypoventilation occurs, pulmonary vascular resistance will increase, and hemodynamics will be adversely affected.
Monitoring of mechanical ventilation and pulmonary adequacy is accomplished via physical examination, non-invasive monitoring of oxygen saturation and end tidal carbon dioxide, attention to lung mechanics, blood gases, and chest radiographs. The need for tracheal suctioning and the quality and quantity of secretions should be followed as well.
Once patients are weaned from mechanical ventilation, care must be taken to avoid atelectasis. Infants and young children typically will move and cry spontaneously, but older children and adolescents frequently will need assistance with sitting and standing, and will need encouragement to deep breathe and move. Incentive spirometry and a guided program of progressive ambulation is essential and should be initiated as soon as physiologically safe.
The routine evaluation of the cardiovascular system after surgery depends on a combination of physical exam, non invasive monitoring, and invasive monitoring.
Repeated physical examination is an essential part of the evaluation following cardiac surgery. Although a vital part of patient assessment, physical examination remains the least quantifiable and most subjective. Distal extremity temperature, capillary refill and peripheral pulses suggest the adequacy of tissue perfusion. A prolongation of capillary refill greater than 3 - 4 seconds indicates poor systemic perfusion. Changes in the character of murmur or attenuation of a shunt murmur may reflect significant changes in the child’s condition. The child should (frequently) be examined for changes in cardiorespiratory status.
Noninvasive monitoring includes examination, pulse oximetry, central and peripheral temperatures, and surface ECG monitoring. The surface ECG provides information on heart rate and rhythm. Cool extremities with normal or rising rectal temperature suggests decreasing and inadequate systemic cardiac output.
Before invasive monitoring is planned, the risk-benefit ratio of catheter placement should be considered. Vascular catheters are commonly placed in the operating room, and include central venous catheters, right atrial catheters, left atrial catheters, pulmonary artery catheters, and arterial catheters. Central venous or right atrial catheters provide right-sided filling pressures, as well as information about tricuspid valve function. They enable indirect assessment of cardiac output by providing systemic venous oxygen saturation119, and they provide a site for infusion of pharmacologic agents. Because of their relative safety and extraordinary utility, most cardiac surgery patients will have a central venous/right atrial line. Central venous catheterization can be obtained by percutaneous cannulation of the internal jugular vein or by placing the catheter directly into the right atrial appendage at the time of surgery.
Left atrial catheterization provides measurement of pressures in the left side of the heart, information about mitral valve function, and measurement of left atrial desaturation due to right-to-left shunting in the lung. The indications for left atrial catheter placement are abnormal mitral valve function, abnormalities of left ventricular diastolic and/or systolic function, and abnormal lung parenchyma. Left atrial catheter placement carries the serious risk of introduction of air into the systemic arterial circulation. This can be kept to a minimum by careful management of these lines, the use of air filters, and appropriate education of the care team. The recent introduction of intraoperative echocardiography has resulted in a more selective use of left atrial lines.145
Pulmonary artery catheters provide access for measurement of pulmonary pressures, pulmonary arterial saturation, and cardiac output.46,71 Indications include the risk of pulmonary hypertension, residual left-to-right shunts, and decreased cardiac output. Pulmonary artery catheters should be used in children whose postoperative pulmonary artery pressure is greater than 1/2 systemic arterial pressure and in children who are at a high risk for pulmonary artery hypertension (Table 22-6). Pulmonary artery catheters are placed during surgery through the right ventricular outflow tract and advanced into the main pulmonary artery. Contraindications for pulmonary artery catheter placement are a large right ventricular outflow tract patch or any anatomic condition which will not allow placement of the catheter through a muscle bundle.
Arterial catheterization is required in all children who undergo surgery for congenital heart disease and allows for continuous blood pressure monitoring as well as repeated measurements of a variety of laboratory studies,
Support of the cardiovascular system is directed at optimizing cardiac output and oxygen delivery. This is accomplished by optimization of heart rate, preload, afterload, and intropy, and is guided by invasive, non-invasive, and laboratory monitoring. When cardiac output measurement is not available, mixed venous oxygen saturation trends can provide information regarding the adequacy of oxygen delivery. Studies have demonstrated that mixed venous saturations are a reliable and early indicator of cardiovascular dysfunction and failure to measure this may worsen outcomes in some situations.8 A decreasing mixed venous oxygen saturation, despite escalating support, indicates abnormal convalescence and the need for aggressive intervention. Another indicator of failing oxygen delivery is the development of lactic acidosis... The sequential evaluation of serum lactate levels provides important assessment of the adequacy of oxygen delivery. Lactate levels are usually high immediately after surgery but should decrease to < 2.0 mmol/L if oxygen delivery is adequate.30 Persistent elevation of lactate requires evaluation. Metabolic acidosis that is not accompanied by elevated lactate is usually a hyperchloremic metabolic acidosis (non anion gap metabolic acidosis) and generally resolves without treatment.
Post operative bleeding is the result of inadequate surgical hemostasis or of coagulopathy, either due to residual heparin, to dilutional effects, or to disseminated intravascular coagulation. If bleeding is not corrected after correction of coagulopathy or if the blood loss is greater than 10 cc/kg/hour, surgical bleeding should be considered and exploration strongly considered. Chest tubes and mediastinal drainage tubes must be kept clear and patent if there is ongoing bleeding in order to prevent the occurrence of cardiac tamponade.
Heparin
induced thrombocytopenia (HIT) is increasingly recognized in the pediatric
population. HIT is the most common
drug-induced thrombocytopenia in adults, complicating 1-4% of full-dose
exposures to standard heparin. We have
reported as similar rate of occurrence of HIT in a pediatric cardiac surgical
population. In HIT, the platelet fall
is usually 40-50% and the thrombocytopenia is moderate (30-100). The onset is 5-10 days after first exposure
to heparin and hours to 2-3 days with re-exposure. Thrombosis may localize to
sites of pre-existing pathology (CVLs, shunts, surgical repairs) and be
present in unusual locations. Less
common presentations include delayed thrombocytopenia (2-3 weeks),
heparin-induced skin necrosis (SQ sites), adrenal infarction/hemorrhage, heparin resistance and anaphylactoid reactions.
Antibody (PF4) ELISAs are
sensitive but not specific. Positive
ELISAs are found in 40-60% of asymptomatic adult re-operative cardiac surgery
patients. A recent abstract found them
in 31/64 children (median age 29 months) undergoing re-operative cardiac
surgery, only 1 of whom had clinical HIT.
Unfortunately a negative ELISA does not exclude HIT. More specific for clinical HIT are functional
assays based on in vitro heparin-dependent platelet activation (14C
serotonin release, heparin-dependent platelet aggregation, lumi-aggregometry). Unfortunately functional assays are less
sensitive and often negative or indeterminate in the first 24-48 hours of
HIT. Both assays usually become negative
in about 3 weeks, making it difficult to diagnose previous HIT.
If HIT is diagnosed, all
heparin (lines, flushes, heparin-coated catheters, low molecular weight
heparins) must be stopped. Platelet
transfusion should be AVOIDED (transfusion may precipitate thrombosis) as
should warfarin in the acute phase of HIT.
Use of alternative anticoagulation is imperative in pre-existing or new
thrombosis and should be strongly considered for prophylaxis. Argatroban, a hepatically-excreted, synthetic
anti-thrombin with a t 1/2 of ~ 40-50 minutes, is presently our
choice. Usual dose is 2mg/kg/min by continuous
infusion. Anticoagulation is monitored
by either PTT (target 1.5 – 3.0 x normal) or by ACT (target on ECMO 180-200).
Convalescence after cardiac surgery may be characterized as normal or abnormal. Normal convalescence is recovery that is expected given the pre-operative state of the patient, the procedure performed, and the expected effects of cardiopulmonary bypass or other interventions. Abnormal convalescence is recovery that is prolonged or unexpected given what is known about the patient and the interventions that have been performed. It may be due to unknown or underappreciated abnormal pre-operative anatomy or physiology, to unexpected complications of bypass, to residual anatomic defects, or to abnormalities in other organ systems such as pneumonia or sepsis. It is crucial to identify abnormal convalescence and to characterize it thoroughly so that appropriate intervention can take place in a timely fashion.
The effects of cardiopulmonary bypass (CPB) have been described as a "whole body inflammatory response" because of the generalized activation of complement, neutrophils, cytokines, and other mediators.25 These effects of cardiopulmonary bypass (CPB) and related techniques are discussed in detail in Chapter 21. It is important to appreciate those effects which are anticipated sequelae of CPB and those that suggest abnormal convalescence.
Most congenital heart defects are repaired on cardiopulmonary bypass and require a period of time during which the circulation to the heart is interrupted by aortic cross clamping and infusion of cardioplegia. This provides the surgeon with a still, flaccid heart on which to operate, however, the heart may be "ischemic" during this time. Ischemic injury to myocardium, produced (or unable to be prevented) by the protection used for operative repair, can present serious problems in the postoperative period. Depressed ventricular function in the immediate period following CPB, or inability to wean a patient from CPB, may be due to ischemic injury.150,27 This condition can usually be treated with inotropic support, recognizing that inotropic support following CPB further increases myocardial oxygen demand. For patients with severe ventricular dysfunction, consideration of ventricular extracorporeal support with ECMO (patients less than 5 kg), or with RVAD or LVAD (for selected patients over 5 kg) is reasonable if it is felt that the ventricular dysfunction may be reversible. For the intensive care physician, knowledge of the aortic cross clamp time (ischemic time) and the period of total circulatory arrest is important. These times can be predictive of the degree of postoperative ventricular dysfunction and the amount of support that can be predicted. ??numbers here??
Patients who require extracardiac repair only and patients with simple shunting lesions who require closure (patch or ligature) without valvar involvement should require minimal inotropic support. When performed in the neonatal period, these children may require inotropic support with a single agent. Requirement of multiple agents and increasing inotropic requirements indicate abnormal convalescence. Patients with more complicated perioperative pathophysiology and those who require circulatory arrest will require more intensive myocardial and respiratory support. In the first 24 - 48 hours inotropic support may be generous and escalation of inotropic support should be anticipated in the first 24 hours due to myocardial edema/injury. Failure to respond to moderate increases in inotropic therapy and the need for high levels of inotropic therapy (Dopamine/Dobutamine > 15 µg/kg/min, Milrinone > 1.0 µg/kg/min, Epinephrine > 0.1 µg/kg/min) indicate abnormal convalescence and the need for a thorough investigation.
Pulmonary dysfunction is a common occurrence after cardiopulmonary bypass.35,150 Lung injury is mediated by a variety of mechanisms including an inflammatory response initiated by activation of complement which occurs during cardiopulmonary bypass.69 This also occurs after hypothermic cardiopulmonary bypass which causes complement activation, leukocyte degranulation, an increase in capillary permeability, and widespread endothelial injury (See Chapter 21 on Cardiopulmonary Bypass).23 Microvascular dysfunction with platelet aggregation and mediator release increases pulmonary vascular resistance, extravascular lung water, and airway resistance and decreased lung compliance. All of these increase intrapulmonary fluid and can decrease oxygen delivery.
Management of pulmonary insufficiency in the postoperative period requires an understanding of the physiologic consequences of cardiopulmonary bypass. Pulmonary function tests after cardiopulmonary bypass demonstrate reduced static and dynamic compliance, end expiratory lung volumes less than physiologic FRC, an increase in alveolar-arterial oxygen gradient, and atelectasis.75,156 These abnormalities are related to endothelial injury and interstitial edema and result in alveolar collapse and microatelectasis. Therapy for children with pulmonary insufficiency is directed at reducing atelectasis and improving the ventilation/perfusion mismatch with positive end-expiratory pressure (PEEP) and an inspiratory time adequate to aerate all lung units. Very low PEEP (<4) and very short inspiratory times do not provide adequate lung expansion or aeration of all lung units. Diuresis consistent with the hemodynamic status of the child may encourage the resolution of pulmonary edema and atelectasis.
The effects of cardiopulmonary bypass on renal function are not completely understood. Cardiopulmonary bypass with hypothermia, non-pulsatile perfusion, and reduced mean arterial pressure causes the release of angiotensin, renin, catecholamines and antidiuretic hormones.44,48,49,66,67,82 These circulating hormones result in reduced renal blood flow. There are no confirmatory studies linking low-flow, low pressure, and non-pulsatile perfusion during CPB with postoperative renal dysfunction,49,67 but reduction in cardiac output in the postoperative period is associated with the development of renal dysfunction. After total circulatory arrest, it is common to observe a period of oliguria or anuria which usually resolves after 24 hours.44,49 This oliguria is seen less frequently in infants whose CPB perfusion flow rates are maintained at 150-200 cc/kg/min during the recovery following circulatory arrest. Treatment of renal dysfunction in the postoperative period includes increasing renal perfusion pressure using inotropic agents. Diuretics are the primary agents for promoting urinary output after cardiopulmonary bypass. Furosemide (1-2 mg/kg) every 6-8 hours induces a vigorous diuresis and reduces renal cortical ischemia associated with cardiopulmonary bypass.66 Continuous infusion of diuretics is useful in patients sensitive to fluid shifts. During the immediate postoperative period diuretics should be used cautiously because of the ongoing capillary leak that is the result of CPB. After resolution of the capillary injury, usually 24-48 hours postoperatively, a vigorous diuresis can be initiated.
Nutrition is an essential component in the care of the postoperative patients. Early aggressive feeding is now advocated for the majority of patients. Early feeding reduces gut translocation of bacteria and decreases the need for total parenteral nutrition and its attendant risks. Feedings are usually begun when bowel sounds are present.. Feedings are withheld in high-risk patients, such as those with severe pre-operative acidosis or those with marginal post-operative hemodynamics.104 In those children, a delay in feeding is usually indicated until the patient has demonstrated resolution of acidosis and organ dysfunction. Necrotizing enterocolitis in the post-operative period can lead to significant morbidity and mortality.81,104 The diagnosis of necrotizing enterocolitis should be considered in any infant with abdominal distention, bloody stools, and pneumatosis intestinalis. Children who cannot tolerate enteral feeds require parenteral nutrition to support caloric needs (see Chapter 17 on Nutrition and Metabolism).
Cardiac
surgical patients are frequently hyperglycemic in the initial post operative
period. Many infants have received
steroids pre and intraoperatively, and all patients have undergone a
physiologically stressful event. There
is evidence in the adult literature that control of hyperglycemia significantly
improves outcome in patients in the intensive care unit (NEJM article). At the present time, there is no data on any
beneficial or detrimental effect of control of hyperglycemia in critically ill
pediatric patients. If blood glucose is
controlled with insulin, care must be taken to avoid hypoglycemia.
THE INFORMATION CONTAINED IN THIS SITE IS NOT INTENDED NOR IMPLIED TO BE A SUBSTITUTE FOR PROFESSIONAL MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF YOUR PHYSICIAN OR OTHER QUALIFIED HEALTH PROVIDER PRIOR TO STARTING ANY NEW TREATMENT OR WITH ANY QUESTIONS YOU MAY HAVE REGARDING A MEDICAL CONDITION. NOTHING CONTAINED IN THE SITE IS INTENDED FOR MEDICAL DIAGNOSIS OR TREATMENT.
This page was created by Laura M. Ibsen, M.D. for the use of Pediatric Residents in training. Comments or suggestions should be forwarded to Dr. Ibsen at ibsenl@ohsu.edu