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[.]
Trang 12:1 in a patient with clinical or biochemical evidence of
insuffi-cient 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
balanc-ing Qp/Qs An Sao2 greater than 90% indicates pulmonary
over-circulation—that is, Qp/Qs greater than 1 PVR can be increased
with controlled mechanical hypoventilation to induce respiratory
acidosis, often necessitating sedation and neuromuscular
block-ade, and with a minimization of Fio2 to avoid hyperoxic
pulmo-nary 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
precipi-tously 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
maneu-vers 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
impor-tant comorbidities that preclude a standard palliative operation
(prematurity, intracranial hemorrhage), bilateral pulmonary
arte-rial bands can be placed through a median sternotomy to
opti-mize 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
administra-tion of high-dose PGE1 (0.1–0.2 µg/kg per minute) Patients at
this level of prostaglandin delivery should have their airway
se-cured 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
in-creasing hematocrit level greater than 40% Among some
new-borns 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-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 inter-vention Despite such advances, survival in this subgroup is re-duced (between 48% and 69%).124–128
Systemic perfusion is maintained with the use of volume and vasoactive agents Inotropic support is occasionally necessary be-cause of ventricular dysfunction secondary to the increased vol-ume 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 in-sufficiency 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 in-ferior vena cava (IVC) blood returns to the common atrium Performed between age 3 to 6 months, the BDG has proved to be
an important early staging procedure in single-ventricle physiol-ogy for relieving volume and pressure overload, pulmonary artery distortion, and coronary hypoperfusion associated with an aorto-pulmonary 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 usu-ally 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 ex-tubated 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 eti-ology remains to be determined, but possible factors include im-proved 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
Trang 2extubation Persistent hypoxemia (Sao2 ,70%) can be secondary
to a low–cardiac output state (low mixed venous oxygen
satura-tion [Svo2]), low pulmonary blood flow, or lung disease
(Table 36.3) Treatment is directed at improving contractility,
re-ducing 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
in-vestigated in the catheterization laboratory to evaluate
hemody-namics, 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 satura-tions to fall This often occurs around 2 to 3 years of age, prompt-ing 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 pulmo-nary 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 mor-tality and morbidity associated with this surgery have declined substantially over the years, and many patients with stable single-ventricle 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 5 to 10 mm Hg—that is, a transpulmonary pressure drop of 5 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 detrimen-tal 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 iden-tified for early extubation (in the operating room or within 6 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 1 or 2 days
In Fontan patients who do not meet early-extubation criteria, the method of mechanical ventilation requires thoughtful consid-eration A tidal volume of 8 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 respira-tory 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 3 to 5 cm H2O, however, rarely has either hemodynamic consequence or substantial effect on ef-fective pulmonary blood flow
Alternative methods of mechanical ventilation have been used
in these patients High-frequency ventilation has been employed
TABLE
36.3
Factors Contributing to a
Lower-Than-Anticipated Oxygen Saturation in Patients
With Single-Ventricle Physiology
Etiology Considerations
Low Fi o2 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 obstructionAnatomic 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:
hypermet-abolic state
• Decreased oxygen delivery: low–cardiac output state
Anemia
AVM, Arteriovenous malformation; Fi o 2, fractional inspired concentration of oxygen;
PA, pulmonary artery; PV, pulmonary vein; PVR, pulmonary vascular resistance;
RDS, respiratory distress syndrome; RV, right ventricle
Trang 3successfully in selected cases, although the potential
hemody-namic 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-pres-sure 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
in-hibitor 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
relax-ation 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
de-creased 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
second-ary to injury to the thoracic duct, persistent elevation of systemic
venous pressure, or development of extensive lymphatic
collater-als 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
signifi-cantly In the rare circumstance in which that occurs, the use of
AAI pacing rapidly addresses the situation Atrial flutter or
fibril-lation, 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,
uncompli-cated Fontan operation Those with ideal preoperative
hemody-namics 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
fenestra-tion have a right-to-left shunt in the immediate postoperative
pe-riod These patients are fully saturated following surgery and may
have an elevated right-sided filling pressure but nevertheless
main-tain 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
period, leading to a low–cardiac output state with progressive metabolic acidosis and large chest drain losses from systemic ve-nous 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 shunt-ing 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 echocardiogra-phy 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 maintain-ing the high right-sided fillmaintain-ing pressures (to maintain the trans-pulmonary gradient) and initiating inotropes and vasodilators If
a severely low–cardiac output state with acidosis persists, take-down of the Fontan operation and conversion to a BDG anasto-mosis 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 af-ter BDG and Fontan is associated with high morbidity and mor-tality 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 sys-temic and pulmonary vessels are determined by the relative resis-tance to flow in the two vascular beds and the resisresis-tance 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, contraindica-tions 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 medi-cally unstable Beyond the newborn period, most centers now oc-clude the ductus with a percutaneously inserted vascular umbrella
or by using coils for smaller PDAs In stable patients who are not
Trang 4candidates 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
hospi-tal stay, and decreased incidence of chest wall deformity.147
Healthy asymptomatic patients undergoing surgery can be
extu-bated 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
pe-riods 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
environ-ment 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,
me-tabolism 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 iden-tify 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 stimula-tion 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 cov-ers 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, caus-ing RV volume overload The degree of atrial-level shuntcaus-ing is a function of the difference between right and left ventricular com-pliance as opposed to atrial pressure differential Pulmonary blood
TABLE
36.4 Etiology and Treatment Strategies for Patients With Low Cardiac Output Immediately Following the Fontan Procedure
Increased TPG
Baffle 20 mm Hg
LAp ,10 mm Hg
h TPG 10 mm Hg
Inadequate pulmonary blood flow and preload to left atrium
Increased PVR Pulmonary artery stenosis
Volume replacement Reduce PVR Correct acidosis Inotropic support
Clinical State
High Sa o2/low Sv o2
Hypotension/tachycardia
Core temperature high
Poor peripheral perfusion
SVC syndrome with pleural effusions and
increased chest tube drainage
Ascites/hepatomegaly
Metabolic acidosis
Pulmonary vein stenosis Premature fenestration closure Systemic vasodilationCatheter or surgical intervention
Normal TPG
Baffle 20 mm Hg
LAp 15 mm Hg
TPG normal 5–10 mm Hg
Ventricular failure Systolic dysfunction Diastolic dysfunction AVV regurgitation or stenosis
Maintain preload Inotrope support Systemic vasodilation Establish sinus rhythm or atrioventricular synchrony
Clinical State
Low Sa o2/low Sv o2
Hypotension/tachycardia
Poor peripheral perfusion
Metabolic acidosis
Loss of sinus rhythm
h Afterload stress Correct acidosisMechanical support
Surgical intervention, including takedown to BDG and transplantation
AVV, Atrioventricular valve; BDG, bidirectional Glenn anastomosis; LAp, left atrial pressure; PVR, pulmonary vascular resistance; Sa o 2, systemic arterial oxygen saturation; SVC, superior vena cava; Svo 2, SVC oxygen saturation; TPG, transpulmonary gradient.
Trang 5flow 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
suffi-ciently large, with a synthetic patch Sinus venosus defects
associ-ated with partial anomalous pulmonary venous connection
re-quire 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
anes-thesia can be managed in many ways, but early tracheal
extuba-tion, either in the operating room or in the immediate
postopera-tive period, is the norm Atrial arrhythmias, including atrial
flutter and atrial fibrillation, are rarely seen during the
postopera-tive period Mitral regurgitation may occur in patients who have
undergone repair of an ASD primum Residual ASDs are
uncom-mon, 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 2 years of life to prevent the progression of pulmonary
vascular obstructive disease.155 In patients with established
pulmo-nary vascular disease, the pulmopulmo-nary arteriolar changes may not
recede when the defect is closed In such cases, there may be
pro-gressive 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
atri-otomy 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
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 ma-neuvers that increase pulmonary blood flow
Persistent CHF and an audible murmur postoperatively, evi-dence of low cardiac output, or the need for extensive inotropic support intraoperatively suggest that a residual or previously un-recognized additional VSD is continuing to place a volume and pressure load on the ventricles When PVR is increased preopera-tively, 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 place-ment of the septal patch Transesophageal echocardiography per-formed 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 addi-tion, 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 7 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 hyper-tension.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 single-patch or two-single-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 poten-tial complications of ASD and VSD closures are seen in these