Chapter 77 Tetralogy of Fallot
PATHOPHYSIOLOGY
Tetralogy of Fallot (TOF) is a cyanotic congenital heart defect composed of four structural components: (1) ventricular septal defect (VSD); (2) pulmonic stenosis, which can occur at any level (infundibular, valvular, supravalvular) and causes obstruction of blood flow into the pulmonary arteries; (3) right ventricular hypertrophy; and (4) overriding of the aorta. In children with TOF, the diameter of the aorta is larger than normal, whereas the pulmonary artery is smaller than normal.
The pulmonic stenosis causes portions of the deoxygenated blood from the right ventricle to shunt across the VSD into the aorta (right to left shunt) and results in cyanosis. The degree of cyanosis is related to the severity of the pulmonic stenosis, with more severe cyanosis associated with more severe obstruction. The degree of cyanosis ranges from none (pink TOF) in children with minimal right to left shunting to profound in children with more significant right to left shunting (blue TOF).
INCIDENCE
1. TOF affects boys and girls equally.
2. Incidence is higher with older maternal age.
3. Few affected individuals survive beyond 20 years without surgery.
4. TOF accounts for 8% to 10% of congenital defects and is the most common cyanotic defect beyond the first week of life.
5. For patients with uncomplicated repair, the mortality rate is 2% to 3% during the first 2 years.
CLINICAL MANIFESTATIONS
1. Cyanosis—appears after neonatal period, although children with mild degree of right ventricular outflow obstruction may be acyanotic
2. Hypercyanotic spells during infancy, also known as “tet spells”
3. Clubbing—late sign seen in unrepaired older children
4. Initially normal blood pressure—can increase after several years of marked cyanosis and polycythemia in unrepaired older children
5. Preference for classic squatting position—decreases venous return from lower extremities and increases pulmonary blood flow and systemic arterial oxygenation during spells or after exercise; rarely seen now owing to earlier repair of the defect
6. Anemia (if severe hypoxia and polycythemia are present)—contributes to worsening of symptoms
7. Decreased exercise tolerance
8. Murmur (systolic ejection murmur at upper left sternal border)
COMPLICATIONS
Postoperative complications
1. Bleeding—especially prominent in children with polycythemia
3. Low cardiac output or heart failure
4. Pleural effusion (surgical complication related to multiple cardiac procedures)
5. Phrenic nerve damage (surgical complication related to multiple cardiac procedures)
6. Cerebral embolism or thrombosis—risk greater with polycythemia, anemia, or sepsis
7. Complications specific to Blalock-Taussig shunts: congestive heart failure (CHF) if the shunt is too large, persistent cyanosis if the shunt is too small; shunt occlusion
LABORATORY AND DIAGNOSTIC TESTS
1. Chest radiograph—indicates increase or decrease in pulmonary flow, size of heart, and borders
2. Electrocardiogram (ECG)—to monitor right ventricular hypertrophy due to the pressure overload of the right ventricle; may also find left ventricular hypertrophy in patients with increased pulmonary blood flow due to collaterals or large shunts
3. Oxygen saturation by pulse oximetry—to monitor cyanosis as a clinical indication of the degree of pulmonic stenosis
4. Hematocrit or hemoglobin level—to monitor oxygen-carrying capacity and viscosity of blood, and for the development of iron deficiency anemia
5. Echocardiogram—to evaluate anatomy, pressure gradient across the obstruction
6. Cardiac catheterization; most patients with TOF do not require cardiac catheterization unless there is concern regarding the pulmonary artery anatomy
Preoperative
Refer to Appendix D for normal values and ranges of laboratory and diagnostic tests.
MEDICAL AND SURGICAL MANAGEMENT
Several medications may be used to medically manage TOF. The specific medication or combination of medications used depends on the child’s phsyiology. Propranolol (Inderal) is a beta-blocker that may be used to prevent or treat hypercyanotic spells and to treat arrhythmias. Diuretics, such as furosemide, may be used to promote diuresis. Though most children with TOF do not develop CHF because the pulmonic stenosis limits pulmonary blood flow, diuretics may be particularly useful in children with large ventricular septal defects and minimal pulmonic stenosis. In these same children, digitalis may be prescribed to improve cardiac performance by improving contractility and decreasing venous pressures. Further, digitalis slows conduction through the atrioventricular node and can therefore be used to treat selected cardiac arrhythmias (rarely given before correction unless shunt is too large).
Hypercyanotic spells are a medical emergency. A child experiencing a hypercyanotic spell should be placed in a knee-chest position and be given 100% oxygen by face mask. The knee-chest position improves venous return to the heart and therefore improves pulmonary blood flow. Oxygen is a potent pulmonary vasodilator and will also improve pulmonary blood flow. There are several medications that may also be helpful. Morphine is a sedative that decreases irritability, suppresses the respiratory center, and abolishes hyperpnea. Children with hypercyanotic spells quickly become acidotic. Therefore sodium bicarbonate, a potent systemic alkalizer, may be used to treat acidosis.
Definitive Surgical Repair
Historically, complete repair of TOF was postponed until the preschool years. Advances in surgical technique and medical management now allow for earlier repair. Single-stage repair is performed in most centers before the age of 6 months while the pulmonary artery dimensions are favorable. There are numerous benefits to earlier repair, including normal growth and development of organs, elimination of cyanosis at an earlier age, decreased incidence of late arrhythmias, and better late ventricular function. Repair requires cardiopulmonary bypass and is accomplished through a median sternotomy incision. Deep hypothermia may be used for some infants. If a previous shunt is in place, it is removed. Ideally, the surgeon will repair the defect through a right atrial incision. A right ventriculotomy is avoided when possible because of the potential for impaired ventricular function. The right ventricular outflow obstruction is resected and widened, using Dacron with pericardial backing. Care is taken to avoid pulmonary insufficiency. In cases of severe right ventricular outflow tract obstruction, a conduit may be inserted. The ventricular septal defect is closed with a Dacron patch to complete the operation.
Palliative Surgical Procedures
Owing to the preference for earlier complete repair, the need for palliative procedures is diminishing. Historically, a Blalock-Taussig (BT) shunt was placed to increase the pulmonary blood flow until complete repair could be performed. A classic BT shunt is created when the subclavian artery opposite the side of the aortic arch is ligated, divided, and anastomosed to the contralateral pulmonary artery. The advantages of this shunt procedure are the ability to construct very small shunts that grow with the child and the ease of shunt removal during definitive repair. Collateral circulation will develop to ensure adequate arterial flow to the arm, although a blood pressure reading will not be obtainable in that arm.
More commonly used is the modified Blalock-Taussig shunt, which is essentially the same but uses a prosthetic material to connect the pulmonary artery to the subclavian artery. With the modified BT shunt, the size can be better controlled, which is critical in preventing CHF while providing adequate pulmonary blood flow. The modified BT shunt allows for placement despite aortic arch anomalies; however, a right-sided shunt is most often performed to ensure ease of removal at the time of complete repair. The removal of either the classic or the modified BT shunt is generally uncomplicated.
Both the classic and the modified BT shunts increase pulmonary blood flow by providing a means for systemic blood to enter the pulmonary circulation through the subclavian artery. This increases pulmonary blood flow under low pressure and avoids pulmonary congestion. This stabilizes pulmonary blood flow and improves cardiac and respiratory status until conditions are more favorable for complete repair.
NURSING ASSESSMENT
1. See the Cardiovascular Assessment section in Appendix A.
2. Assess child’s level of activity and achieving of developmental milestones (preoperatively) (see Appendix B).
3. Assess for changes in cardiopulmonary status (specific attention to the development of hypercyanotic spells).
4. Important additional postoperative assessments include assessment for complications in addition to those previously mentioned: bleeding, CHF, arrhythmias, pulmonary insufficiency, low cardiac output, pulmonary hypertension, pleural effusion, electrolyte imbalances, fluid overload, hepatomegaly, and neurologic complications.
NURSING DIAGNOSES
NURSING INTERVENTIONS
Maintenance Care
1. Monitor for changes in cardiopulmonary status as described in the Nursing Assessment section in this chapter.
2. Monitor and maintain hydration status.
3. Monitor child’s response to medications (see the Medical Management section in this chapter).
4. Provide foods high in iron (to prevent iron deficiency anemia) and protein (to promote healing).
5. Protect child from potentially infectious contacts and promote preventive practices (to prevent subacute bacterial endocarditis).
6. Monitor for signs of complications and child’s response to treatment regimen.
7. Monitor growth and development to ensure timely achievement of developmental milestones.
Preoperative Care
1. Prepare child for surgery by obtaining assessment data. See Laboratory and Diagnostic Tests in this chapter for details of what tests are needed and why.
2. Use age-appropriate explanations for preparation of child and family (see the Preparation for Procedures or Surgery section in Appendix F).
3. Do not take blood pressure readings or make arterial punctures in potential shunt arm.
Postoperative Care
TOF corrective surgery—monitor child’s clinical status for postoperative complications.
1. Monitor child’s cardiac function frequently per institutional policy.
3. CHF or ventricular dysfunction (more likely if ventricular incision is required)
5. Low cardiac output as evidenced by irritability, fatigue, poor feeding, change in neurologic responsiveness, tachycardia, auscultation of a gallop, diaphoresis, oliguria, pallor, peripheral cyanosis, and decreased capillary refill
6. Neurologic complications (refer to section in this chapter on Complications)
7. Pulmonary insufficiency as evidenced by rales, wheezing, increased respiratory effort, use of accessory muscles for respiratory effort, and cyanosis
8. Residual ventricular septal defect as evidenced by ongoing failure and echographic findings
9. Monitor child’s response to medications.
10. Monitor and maintain child’s fluid and electrolyte balance.
11. Monitor and maintain child’s respiratory status.
12. Monitor for chylothorax as evidenced by persistent pleural effusions.
13. Provide for child’s and family’s emotional needs (see the Supportive Care section in Appendix F).
14. Monitor and alleviate child’s pain (see Appendix I).
15. Provide developmentally appropriate stimulation and/or activities (see Appendix B).
Surgical Palliation
1. Assess child’s clinical status.
2. Note pulse pressure since a wide pulse pressure may indicate a large shunt.
3. Monitor child for any postoperative complications.
4. Monitor child’s response to administered medications—digitalis and diuretics are administered if needed.
5. Monitor and maintain fluid and electrolyte balance.
Discharge Planning and Home Care
1. Instruct parents or caregivers on home care treatment regimen.
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