Anesthesiology

Right-to-Left shunts

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What the Anesthesiologist Should Know before the Operative Procedure

What are right-to-left shunts?

A shunt is an abnormal communication between the right and left sides of the heart or between the systemic and pulmonary vessels, allowing blood to flow directly from one circulatory system to the other. A right-to-left shunt allows deoxygenated systemic venous blood to bypass the lungs and return to the body.

Factors influencing the direction and degree of shunting include (1) the size of the shunt orifice, (2) the pressure gradient between the chambers or vessels involved in the shunt, and (3) the "downstream" resistance to flow that is determined by the ratio of pulmonary vascular resistance (PVR) to systemic vascular resistance (SVR), the relative compliance of the right and left ventricles, and the blood viscosity (hematocrit). A simple shunt has no fixed obstruction, whereas a complex shunt has a fixed obstruction to outflow from the chambers or vessels involved in the shunt.

What are the physiologic implications of right-to-left shunts

Right-to-left shunting results in decreased oxygen content of the systemic arterial blood, with the decrease in proportion to the volume of deoxygenated systemic venous blood mixing with the oxygenated pulmonary venous blood. Even with normal cardiac output, the decrease in tissue oxygen delivery limits exercise tolerance.

Chronic hypoxemia leads to compensatory polycythemiawith rheologic, hemostatic, neurologic, renal, and metabolic consequences. As blood viscosity increases, SVR (including coronary) and PVR increase markedly. Sludging of blood cells increases the risk for thromboembolism and stroke, particularly when the hemoglobin approaches or exceeds 20 g/dL, and in conjunction with dehydration. Long-standing hypoxemia and polycythemia can cause persistent cardiac muscle blood flow abnormalities, leading to myocardial dysfunction. Hemostatic abnormalities include thrombocytopenia, platelet dysfunction, decreased production of coagulation factors, low-grade disseminated intravascular coagulation, and primary fibrinolysis. Chronic hypoxemia during infancy and early childhood is a significant risk factor for reduced cognitive performance. Renal and hepatic dysfunction can occur with long-standing decreases in tissue oxygen delivery, polycythemia, and high venous pressures.

Examples of right-to-left shunts

Tetralogy of Fallot

Pulmonary atresia

Tricuspid atresia

Pulmonary hypertension of the newborn (meconium aspiration syndrome)

Eisenmenger syndrome

Tetralogy of Fallot (TOF) as an example of right-to-left shunt

Tetralogy of Fallot (TOF) is the most common cyanotic lesion and accounts for 10% of all congenital heart disease (CHD). Underdevelopment of the right ventricular (RV) outflow tract and anterior malalignment of the infundibular septum results in the classical tetrad of:

  • – right ventricular outflow tract (RVOT) obstruction

  • – large, nonrestrictive ventricular septal defect

  • – overriding aorta

  • – right ventricular hypertrophy

There is a wide variation in anatomic morphology. The RV outflow obstruction can be subvalvular, valvular, and/or supravalvular and may range in various combinations from infundibular narrowing (fixed or dynamic), pulmonary valve or annulus stenosis (80%) or atresia (20%), and hypoplasia of the main or branch pulmonary arteries to absence of the central pulmonary arteries. The pathophysiology is determined by the degree of obstruction to pulmonary blood flow.

Different variations of tetrology of Fallot

Classic form: TOF with pulmonary stenosis (TOF/PS): ~80%

74%: combination of infundibular and valvular stenosis.

26%: isolated infundibular stenosis.

TOF with pulmonary atresia (TOF/PA): ~ 20%

Collateral circulation to lungs necessary: patent ductus arteriosus (PDA) and/or aortopulmonary collaterals.

"Pink TOF" ("Pink Tet")

TOF with only mild to moderate RVOT obstruction, with predominantly left-to-right shunt via the VSD and risk for pulmonary overcirculation and congestive heart failure.

TOF with absent pulmonary valve: rare

Respiratory distress with airway compression and bronchial obstruction by massively dilated pulmonary arteries.

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Surgical repair in early infancy: The optimal management of surgical repair in early infancy is controversial. Some centers perform a one-stage repair in the neonatal period or early infancy, whereas other centers perform a two-stage repair, comprising a systemic to pulmonary artery shunt in early infancy followed by primary repair later in infancy or childhood.

The timing of surgery usually depends on the degree of obstruction to pulmonary blood flow, the response to medical therapy, and the presence of coexisting anomalies. TOF is often associated with other congenital cardiac (right aortic arch, anomalous coronary distribution, multiple VSDs) and noncardiac anomalies (especially 22q11 deletion syndromes, e.g., DiGeorge and velocardiofacial syndromes). The presence and frequency of hypercyanotic spells, so called "Tet spells," can also influence the timing of surgery.

Associated cardiac anomalies

Right aortic arch: 25%

Coronary anomalies: 5%

Additional VSDs: 3%-15%

Pulmonary artery stenosis: 15%-30%

Discontinuous pulmonary arteries: 1%-3%

Atrial septal defect: 5%-15%

Patent foramen ovale: 50%-60%

Persistent left SVC: 10%-15%

PDA: 5%-10%

Associated noncardiac anomalies

11.9%: Chromosomal anomalies: trisomy 21 (Down syndrome), 18 (Edwards syndrome), 13 (Patau syndrome), etc.

7.2%: Syndromes: DiGeorge syndrome, velocardiofacial syndrome, Alagille syndrome, CHARGE (coloboma, heart defects, choanal atresia, retardation, genital and ear anomalies), VACTERL (vertebral anomalies, anal atresia, cardiac malformation, tracheoesophageal fistula, esophageal atresia, renal and limb anomalies).

2.1%: Multiple anomalies.

11.4%: Other single-organ defects.

Only 67.8% of TOFs are isolated cardiac defects.

DiGeorge syndrome (DGS)

  • – Patients with TOF: 8%-25%

  • – Microdeletion of chromosome 22 (22q11) in >90%.

  • – Abnormalities of neural crest cell migration via 3rd, 4th, and 6th pharyngeal arches to the outflow tract of the developing heart.

  • – Resulting in aplastic or hypoplastic thymus and parathyroid glands as well as malformations of the outflow tract and great vessels.

  • – Associated with conotruncal heart defects in 75%: interrupted aortic arch, truncus arteriosus, tetralogy of Fallot.

  • – Distinct facial features, micrognathia and short trachea with possible difficult airway.

  • – T-cell mediated immune deficiency.

  • – Neonatal hypocalcemia.

  • – Diagnosed by FISH (fluorescence in-situ hybridization) testing.

Velocardiofacial syndrome (VCFS) or shprintzen syndrome

  • – Microdeletion of chromosome 22 (22q11).

  • – Significant clinical overlap with DiGeorge syndrome.

  • – Distinct facial features and palate anomalies, micro-and retrognathia with possible difficult airway.

  • – Speech and learning disabilities.

  • – Associated with congenital heart defects, especially conotruncal defects.

  • – Neonatal hypocalcemia, T-cell immunodeficiency, and hypothyroidism.

  • – Diagnosed by FISH (fluorescence in-situ hybridization) testing.

What is a "Tet Spell"?

Tet spells or hypercyanotic spells are episodes of intense cyanosis, abnormal respirations, and altered level of consciousness, seen in about 20% to 30% of patients with TOF.

These spells are not predicted by the degree of cyanosis; they can occur in acyanotic or only mildly cyanotic patients and are more common in the morning after awaking. Tet spells may be triggered by activity, crying, feeding or defecation; the onset is often signaled by irritability or agitation. The frequency peaks at about 2 to 3 months and decreases after the age of 2 to 3 years.

Infundibular spasms, increased contractility with catecholamine surges, paroxysmal hyperpnea with increased work of breathing, and/or hypovolemia may play a role. The spells are self-aggravating: hypoxia induces a decrease in SVR, which further worsens the cyanosis by increasing right-to-left shunting.

Treatment of "Tet spells

Directed toward improving pulmonary blood flow.

  1. Nonanesthetized children, with or without an intravenous catheter in situ, are treated initially with 100% oxygen, knee chest position, and morphine sulfate (0.05-0.1 mg/kg IM or IV) to relieve distress and air hunger. Ketamine is a suitable alternative (3-5 mg/kg IM; 1-2 mg/kg IV).

  2. During anesthesia, ensure adequate airway control, depth of anesthesia, and provision of adequate analgesia.

  3. Ventilate to lower PVR with 100% oxygen and hypocapnia (respiratory alkalosis) with prolonged expiratory phase and avoidance of high airway pressures to allow for adequate venous return and pulmonary blood flow.

  4. Intravenous crystalloid (15-30 mL/kg) or colloid (5-10 mL/kg) to increase preload and decrease the dynamic component of the RV outflow tract obstruction.

  5. For ongoing cyanosis, a pure α-agonist is used to increase SVR: phenylephrine 0.5 to 2 mcg/kg.

  6. Judicious titration of ß-blocker (propranolol 0.1mg/kg or esmolol 0.5 mg/kg followed by an infusion of 50-300 mcg/kg/min) to slow the heart and relax the presumed infundibular spasm.

  7. Sodium bicarbonate (1-2 mEq/kg) is useful to lower PVR while correcting the metabolic acidosis and increasing the SVR.

1. What is the urgency of the surgery?

What is the risk of delay in order to obtain additional preoperative information?

Timing of cardiac surgery

Although there is still controversy regarding the optimal timing of cardiac surgery, timing usually depends on the degree of obstruction to pulmonary blood flow and level of cyanosis, the severity and frequency of hypercyanotic spells, and the presence of coexisting anomalies.

  1. Emergent: Occasionally, the RVOT obstruction is so severe that the neonate cannot be weaned off prostaglandin. If perinatal complications (e.g., intraventricular hemorrhage [IVH]), marked prematurity, sepsis, ARDS, or coexisting anomalies preclude a complete repair with cardiopulmonary bypass (CPB), a systemic to pulmonary arterial shunt can be performed via a sternotomy or lateral thoracotomy. Usually a modified Blalock-Taussig shunt is performed, whereby a small polytetrafluoroethylene (PTFE: Goretex or Impra) tube graft (3.5 mm in most cases) is placed between the subclavian or innominate artery and the pulmonary artery. Sometimes neonates may be brought to the cardiac catherization laboratory for balloon dilation of severe or atretic pulmonary valves.

  2. Urgent: Urgent surgery is indicated for patients with worsening cyanosis (decreasing from >90% at birth to <75-80%) or increased frequency/severity of hypercyanotic spells. A complete repair using CPB or a palliative shunt can be performed.

  3. Elective: For stable patients who are growing well, the optimal timing of elective surgery is still a topic for discussion: Many centers will schedule reparative surgery when the child is between 1 and 3 months of age.

2. Preoperative evaluation

  • Anatomical type of tetralogy of Fallot: TOF/PS versus TOF/PA

The degree and exact location of the RVOT obstruction are important to know, especially the differentiation into dynamic versus fixed obstruction. Dynamic obstruction tends to worsen with decreased preload, increased contractility, and tachycardia.

  • Previous palliative surgery or interventional cardiac catherization

A shunt-dependent circulation can influence the timing of reparative surgery and also has some anesthetic considerations. As modified Blalock-Taussig shunts do not grow and become calcified, the amount of pulmonary blood flow diminishes with age and growth. Consideration also needs to be given to whether there is subclavian artery narrowing and hence a lower measured blood pressure on the side of the shunt. Patients who have undergone pulmonary artery dilation for very severe PS or valvular atresia, with or without stent placement, may have recurrent RVOT obstruction and a variable degree of pulmonary regurgitation.

  • Associated cardiac anomalies

A right-sided aortic arch may alter the side of the surgical approach for shunt procedures (and also for the repair of tracheoesophageal fistula). In approximately 5% of patients, the coronaries are abnormal: anomalous origin of the anterior descending artery from the right coronary artery is the most frequent variation; occasionally, the right coronary artery may originate from the left coronary artery. Coronary branches that cross the RVOT can potentially be injured during the ventriculotomy or patch augmentation, and may necessitate an RV-PA conduit instead of an RVOT patch. Previously unrecognized additional VSDs can lead to ongoing shunting after the repair, sometimes causing difficulty with ventilator weaning.

  • Associated noncardiac anomalies

The presence of extracardiac anomalies or syndromes requires a focused airway examination and thorough assessment of all organ systems.

  • Severity and frequency of Tet spells

Increasing frequency and severity of Tet spells, unresponsive to medical therapy, can be an indication for an emergent or urgent surgical procedure.

  • Birth history

A history of prematurity or significant perinatal complications can influence the extent and timing of surgical repair, especially IVH or very immature lungs, which can lead to major complications with full anticoagulation and the post-CPB period.

  • Degree of polycythemia

Significant cyanosis usually results in polycythemia, the biological response to decreased tissue oxygen delivery and the attempt to maintain adequate tissue oxygenation. Increased tissue vascularity increases the risk. Long-standing chronic hyperviscosity can lead to poor rheology and microthrombus formation, resulting in organ vascular insufficiency. There is increased risk for bleeding abnormalities, endocarditis, stroke, brain abscess, and adverse neurodevelopmental outcome.

  • Coagulopathy

Cyanotic children tend to have thrombocytopenia, platelet dysfunction, decreased clotting factors, and increased tissue vascularity: factors which have to be evaluated and occasionally treated prior to surgical procedures.

  • NPO status

Critically high hemoglobin levels (>20 g/dL), especially when combined with dehydration, increase the risk for spontaneous thrombus formation and stroke. Adequate rehydration, sometimes requiring admission and overnight intravenous fluids, and short NPO times are important.

  1. Medical conditions warranting further evaluation include associated noncardiac anomalies such as the VACTERL association (vertebral anomalies, anal atresia, cardiac malformation, tracheoesophageal fistula, esophageal atresia, renal and limb anomalies) or significant perinatal complications associated with extreme prematurity.

  2. Delaying cardiac surgery may be indicated if the infant is hemodynamically stable without severe cyanosis, and associated anomalies or comorbidities require further evaluation and prior treatment.

3. What are the implications of co-existing disease on perioperative care?

b. Cardiovascular system

i. Perioperative evaluation

The following steps should be part of the cardiovascular evaluation:

History: Degree of cyanosis (blueness that is more apparent with crying) and hypoxemia (breathes quickly, sweats, feeds poorly, tired), frequency and severity of Tet spells, and previous cardiac interventions. Older "unrepaired" children might present with decreased exercise tolerance and frequent squatting (to increase SVR and decrease right to left shunting)

Physical exam: Cyanosis, right ventricular parasternal heave, single S2, murmur (harsh, long crescendo-decrescendo systolic ejection murmur along the left sternal border).

ECG: Right ventricular hypertrophy, right-axis deviation, right atrial enlargement, and precordial upright T-waves.

CXR: Decreased pulmonary vascularity, boot-shaped heart (coeur en sabot), possible right-sided aortic arch or absent thymus.

Transthoracic echo: The exam should be able to address the following questions:

  • – Exact location of RV outflow tract obstruction and gradient across RVOT

  • – Size of the pulmonary valve annulus

  • – Size and continuity of pulmonary arteries

  • – In case of pulmonary atresia, the source of pulmonary blood flow (PDA, aortopulmonary collaterals)

  • – Size of VSD, presence of additional VSDs

  • – Ventricular size and function

  • – Coronary artery anatomy, particularly important branch crossing the RVOT

  • – Associated defects such as PDA, ASD

  • – Evidence of a persistent left SVC to coronary sinus

Cardiac catherization: Not routinely performed and only indicated if the coronary artery anatomy and pulmonary artery anatomy cannot be obtained from echocardiography. Particularly with TOF/PA, aortopulmonary collaterals will be defined and sometimes coil-occluded to avoid a steal effect and flooding of the surgical field during cardiopulmonary bypass. Cardiac catherization is not without risk in these patients: guidewire or catheter manipulations often trigger hypercyanotic spells, requiring immediate treatment.

ii. Perioperative risk reduction strategies

  • – In neonates with duct-dependent pulmonary blood flow, a prostaglandin (PGE1) infusion will maintain ductal patency and should be continued until an alternative source of pulmonary blood flow has been established.

  • – Patients with frequent Tet spells or at risk for dynamic RVOT obstruction might be managed with prophylactic beta blocker therapy to slow heart rate and decrease contractility. To avoid any rebound effects, this therapy should not be interrupted in the preoperative period.

  • – Patients who have been palliated with a shunt are usually treated with various anticoagulation strategies to minimize the risk of shunt thrombosis and occlusion. Treatment can vary from aspirin only to aspirin plus clopidogrel to heparin infusion in an inpatient. In preparation for major surgery, especially cardiopulmonary bypass procedures, these medications have to be stopped in a timely fashion to reduce intraoperative bleeding.

  • – "Pink tetralogy" patients with a relatively unobstructed RVOT may present with pulmonary overcirculation and congestive heart failure, requiring treatment with diuretics, angiotensin-converting enzyme (ACE) inhibitors, and digoxin.

  • – Severely cyanotic patients or patients with frequent severe Tet spells, unresponsive to medical therapy, may require emergency ECMO cannulation or shunt insertion in the operating room

iii. Hemodynamic goals of management

With a large nonrestrictive VSD, the pressures in the right and left ventricle are equal, and the degree of shunting and, consequently, pulmonary blood flow and cyanosis is dependent on the degree of RVOT obstruction and the ratio of SVR and PVR. Any decrease in SVR (fever, vasodilation from medications), increases in PVR (hypoxia, hypercapnia, acidosis), or increase in the degree of dynamic RV outflow tract obstruction (infundibular spasm, hypovolemia) can worsen the right-to-left shunt and should be avoided. Thus, hemodynamic goals are to avoid excessive tachycardia (decreased diastolic filling time), maintain normal to increased preload, lower PVR, and avoid decreasing SVR; contractility is usually well preserved.

Factors influencing systemic vascular resistance (SVR)

a. Factors increasing SVR

  • – Vasoconstrictors or inotropic agents with alpha agonist effects

  • – Hypothermia

  • – Surgical manipulations

b. Factors decreasing SVR

  • – Potent inhalational agents

  • – Vasodilators

  • – Fever, sepsis

Factors influencing pulmonary vascular resistance (PVR)

a. Factors increasing PVR

  • – Low FiO2

  • – Hypoxia

  • – Hypercabia (effect mediated via pH)

  • – Acidosis

  • – High airway pressure (including excessive PEEP)

  • – Atelectasis

  • – Sympathetic stimulation (inadequate anesthesia, inadequate analgesia)

  • – Increased hematocrit (poor rheology)

  • – Surgical manipulation of RVOT

b. Factors decreasing PVR

  • – High FiO2

  • – Hyperoxia

  • – Hypocapnia

  • – Alkalosis

  • – Low airway pressure

  • – Lung volume at functional residual capacity (FRC)

  • – Blunted sympathetic response

  • – Pulmonary vasodilators (nitric oxide)

  • – Low hematocrit (but does decrease O2-carrying capacity)

Factors influencing the dynamic component of RVOTO

a. Factors increasing RVOTO

  • – Positive inotropic and chronotropic agents (epinephrine, dopamine, ephedrine)

  • – Tachycardia

  • – Decreased preload: hypovolemia, increased intrathoracic pressure, venodilation, surgical manipulation

b. Factors decreasing RVOTO

  • – Negative inotrope agents: beta-blockers, potent inhalation agents

  • – Slower heart rates

  • – Increased preload: fluid bolus, low mean intrathoracic pressure with longer expiratory time, vasoconstriction

HEMATOLOGIC

i. Perioperative evaluation

Polycythemia: Complete blood cell count (CBC) with mean cell volume (MCV) and mean cell hemoglobin (MCH) to assess the current hemoglobin/hematocrit level and exclude microcytic, hypochromic anemia. Polycythemia is necessary to maintain adequate tissue oxygenation, but excessive levels of hemoglobin lead to increased blood viscosity and poor rheology. Cyanotic patients are at risk for iron deficiency anemia, with a normal hemoglobin level often the first sign. Anemia not only decreases oxygen delivery but microcytosis worsens the effects of increased viscosity and can exacerbate vascular insufficiency and microthrombosis.

Coagulopathy: Cyanosis and polycythemia are associated with significant changes in the hemostatic system: thrombocytopenia, platelet dysfunction, decreased production of coagulation factors, low-grade disseminated intravascular coagulation, and primary fibrinolysis. The PT and PTT may be prolonged, as well as lower levels of fibrinogen, factor V, and factor VIII. Adequate treatment of excessive polycythemia and poor blood viscosity tends to improve the coagulopathy.

T–cell-mediated immunodeficiency associated with DiGeorge or velocardiofacial syndrome: Even without a full immunological workup, distinct facial features and an absent thymus on CXR or during surgical exploration should raise the suspicion of a 22q11 deletion syndrome. These patients are at risk for infection and require strict aseptic techniques as well as irradiated blood products to reduce graft-versus-host reactions after blood transfusions.

Hypocalcemia associated with DiGeorge or velocardiofacial syndrome: A history of neonatal hypocalcemic seizures or hemodynamic instability should trigger a genetic workup for 22q11 deletion syndrome (FISH test) and close monitoring of the ionized calcium levels, especially in the perioperative period (rapid changes in acid-base status, electrolyte disturbances, citrate containing blood products).

Endocarditis risk: Unrepaired cyanotic CHD, including palliative shunts and conduits, increases the risk for infective endocarditis.

ii. Perioperative risk reduction strategies

  • – Adequate hydration and avoidance of prolonged NPO periods.

  • – Hospital admission and overnight hydration with intravenous maintenance fluids if prolonged NPO period expected, patient already dehydrated, or hematocrit very high.

  • – Low dose heparin infusion (10 IU/kg/hr) to prevent thrombus formation in important intravascular lines (central venous access, umbilical lines, etc.).

  • – Treatment of iron deficiency anemia with iron supplements or even blood transfusion prior to urgent or emergent procedures.

  • – Identification and correction of coagulopathy as indicated: different for complete repair on cardiopulmonary bypass or palliative shunt procedures with risk of postoperative shunt thrombosis.

  • – Strict adherence to sterile techniques (e.g., for line placement and access to reduce the risk of infection, particularly in DiGeorge patients with immunodeficiency).

  • – Irradiated blood products for patients with absent thymus and T-cell mediated immunodeficiency.

  • – Close monitoring of ionized calcium levels and calcium administration as necessary to maintain normal levels.

  • – Endocarditis prophylaxis according to American Heart Association Guidelines.

  • – Polycythemia with hemoglobin >20 g/dL or hematocrit >60% to 65%: increased risk for spontaneous thrombus formation, vascular insufficiency, cerebrovascular accidents, and strokes. These patients require immediate rehydration or even phlebotomy, depending on the clinical presentation.

  • – Infective endocarditis, brain abscess, etc.: multiple blood cultures to identify organisms, imaging studies (head CT, echo), and initiation of appropriate antibiotic therapy prior to any surgical intervention.

iii. Goals of management

  • – Adequate levels of hemoglobin and hematocrit: <20 g/dL and <55% to 60%. Actual desired level will depend on the degree of hypoxemia and adequacy of cardiac output.

  • – Adequate hydration to avoid spontaneous thrombosis and stroke.

  • – Iron deficiency anemia corrected: treatment with iron supplements initiated if indicated.

  • – Coagulopathy diagnosed and treated appropriately.

  • – Infection prophylaxis.

  • – Normocalcemia.

c. Pulmonary

i. Perioperative evaluation

History and physical exam: Recent upper respiratory infection (URI), including RSV bronchiolitis, and presence of reactive airways disease (RAD) should be determined. Triggering factors for RAD (allergies, infections, exercise, cold air, etc.), current treatment, interval since last exacerbation, frequency of ER visits or hospitalizations/admissions to intensive care unit (ICU), and last treatment with steroids (inhaled vs systemic) need to be established. Respiratory distress with prolonged expiration and wheezing on ascultation.

CXR: Air trapping, hyperinflation, and evidence of infectious process should be sought.

Pulmonary function tests: Except for monitoring of peripheral oxygen saturation and clinical response to bronchodilator therapy, not really practical in infants and toddlers.

ii. Perioperative risk reduction strategies

  • – Continuation of current bronchodilator and anti-inflammatory therapy throughout the perioperative period.

  • – Consider preoperative course of steroids for patients with frequent exacerbations.

  • – Postponing elective surgery for 4 to 6 weeks (ideally) if there is evidence of current or recent URI or acute exacerbation of RAD. Increasing cyanosis requires admission to the hospital and adequate treatment prior to the cardiothoracic procedure.

iii. Goals of management

Suppression of airway reactivity to induction of anesthesia, airway manipulation, postoperative ventilation, and drug administration. Continue adequate bronchodilator and anti-inflammatory therapy perioperatively. Avoid known triggers of RAD.

d. Renal-GI:

i. Perioperative evaluation

Coexisting renal and gastrointestinal anomalies are usually detected during the appropriate work-up: DiGeorge syndrome, velocardiofacial syndrome, Alagille syndrome, CHARGE association (coloboma, heart defects, choanal atresia, mental retardation, genital and ear anomalies), and VACTERL association (vertebral anomalies, anal atresia, cardiac malformation, tracheoesophageal fistula, esophageal atresia, renal and limb anomalies).

Choanal atresia, velopharyngeal incompetence, cleft palate: Often associated with 22q11 deletion.

Gastroesophageal reflux and dysphagia: Often diagnosed on clinical suspicion and confirmed with swallow study. Treatment includes reducing gastric acid secretion (omeprazole, pantoprazole, ranitidine), increasing motility (metoclopramide), positioning (30° head elevation), and modifying feeding techniques (jejunal feeding, G-tube, fortification of formulas).

ii. Perioperative risk reduction strategies

  • – Meticulous airway evaluation and particular attention to placement of oral/nasal airways and endotracheal tubes, removal of feeding tubes.

  • – Consultation with otolaryngology and plastic surgery regarding treatment plan for choanal atresia and cleft lip/ palate.

  • – Continue antiacid and antireflux medications throughout the perioperative period.

  • – Adequate NPO periods to minimize risk of aspiration.

  • – Elevation of head of bed/crib.

  • – Some anomalies (e.g., tracheoesophageal fistula) require surgical repair prior to cardiac surgery.

For patients with complex syndromes involving multiple organ systems, good communication between all involved surgical and nonsurgical specialties is very important in establishing a clear treatment plan and coordinating diagnostic and surgical procedures.

e. Neurologic:

i. Perioperative evaluation

History and physical exam

Acute issues: Cyanotic patients with right-to-left shunts are at increased risk for cerebrovascular complications, including stroke and brain abscess. Poor rheology with increased sludging (polycythemia, iron-deficient erythrocytes), embolization of microthombi from cardiac chambers, tissue hypoxia and microinfarction, and lack of normal phagocyte filtering in the pulmonary vasculature are possible contributory factors. Brain abscess usually presents with fever, headache, and focal neurological deficit.

Chronic disease: Genetic factors, the intrauterine environment, perioperative cerebral hypoxia-ischemia, cardiopulmonary bypass, and cardiac catheterization increase the risk for adverse neurodevelopmental outcome.

A thorough neurological examination should be performed to document preexisting neurologic abnormalities. Neurology consultation and imaging studies (CT scan, MRI), as indicated, should be done.

ii. Perioperative risk reduction strategies

  • – Neurology consultation regarding the risk of cerebral hemorrhage with anticoagulation for cardiopulmonary bypass in the setting of recent cerebral abscess or stroke.

  • – Review of neurologic imaging studies.

f. Endocrine:

Risk of neonatal hypocalcemia exists in patients with DiGeorge syndrome and parathyroid hypoplasia.

g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)

  • – Potential for difficult airway with DiGeorge or velocardiofacial syndrome: micrognathia, retrognathia, short trachea.

  • – Avoidance of nasal airways and intubations with choanal atresia.

  • – Previous thoracotomy for shunt placement increases the risk for scoliosis.

4. What are the patient's medications and how should they be managed in the perioperative period?

Prostaglandin E1

A prostaglandin (PGE1) infusion will maintain ductal patency in neonates with duct-dependent pulmonary blood flow and should be continued until an alternative source of pulmonary blood flow has been established. Side effects include apnea, hypotension, thrombocytopenia, fever, seizures, vascular irritation, and gastric outlet obstruction. Because of the risk of apnea, patients should be closely monitored in an ICU setting.

ß-blocker: propranolol

Patients with frequent Tet spells or at risk for dynamic RVOT obstruction might be managed with ß-blocker therapy to control heart rate and decrease contractility. To avoid any rebound effects, this therapy should not be interrupted in the preoperative period.

Anticoagulation: aspirin, clopidogrel, heparin

Patients who have been palliated with a shunt are usually treated with various anticoagulation strategies to minimize the risk of shunt thrombosis and occlusion. Treatment can vary from aspirin only to aspirin plus clopidogrel to heparin infusion (inpatient). In preparation for major surgery, especially cardiopulmonary bypass procedures, these medications have to be stopped in a timely manner to reduce intraoperative bleeding. Aspirin and clopidogrel are usually stopped 7 to 10 days prior to surgery, while heparin is usually stopped approximately 1 to 2 hours prior (anticoagulation effect half life, 1.5 hour).

Anticoagulation management should be discussed with the cardiologist and cardiovascular surgeon and individually adjusted to the specific situation and inherent risk for a potentially fatal shunt thrombosis. Occasionally, preoperative admission for hydration and intravenous heparin therapy is necessary.

Diuretic: furosemide

"Pink tetralogy" patients with a relatively unobstructed RVOT may present with pulmonary overcirculation and congestive heart failure, requiring treatment with diuretics, angiotensin-converting enzyme inhibitors, and digoxin. Generally, diuretics and ACE inhibitors are held on the morning of surgery to reduce the risk of hypotension during induction and maintenance of anesthesia.

Digoxin

Digoxin is occasionally prescribed as part of the anticongestive therapy for pink or acyanotic TOF. Due to its long elimination time and significant side effects, especially during periods of hypoxia, hypokalemia, and other electrolyte disturbances, digoxin is usually discontinued in the perioperative phase.

h. Are there medications commonly seen in patients undergoing this procedure and for which should there be greater concern?

Prostaglandin E1

A prostaglandin (PGE1) infusion will maintain ductal patency in neonates with duct-dependent pulmonary blood flow and should be continued until an alternative source of pulmonary blood flow has been established. Side effects include apnea, hypotension, thrombocytopenia, fever, seizures, vascular irritation, and gastric outlet obstruction. Because of the risk of apnea, patients should be closely monitored in an ICU setting.

ß-blocker: propranolol

Patients with frequent Tet spells or at risk for dynamic RVOT obstruction might be managed with ß-blocker therapy to control heart rate and decrease contractility. To avoid any rebound effects, this therapy should not be interrupted in the preoperative period.

Anticoagulation: aspirin, clopidogrel, heparin

Patients who have been palliated with a shunt are usually treated with various anticoagulation strategies to minimize the risk of shunt thrombosis and occlusion. Treatment can vary from aspirin only to aspirin plus clopidogrel to heparin infusion (inpatient). In preparation for major surgery, especially cardiopulmonary bypass procedures, these medications have to be stopped in a timely manner to reduce intraoperative bleeding. Aspirin and clopidogrel are usually stopped 7 to 10 days prior to surgery, while heparin is usually stopped approximately 1 to 2 hours prior (anticoagulation effect half life, 1.5 hour).

Anticoagulation management should be discussed with the cardiologist and cardiovascular surgeon and individually adjusted to the specific situation and inherent risk for a potentially fatal shunt thrombosis. Occasionally, preoperative admission for hydration and intravenous heparin therapy is necessary.

Diuretic: furosemide

"Pink tetralogy" patients with a relatively unobstructed RVOT may present with pulmonary overcirculation and congestive heart failure, requiring treatment with diuretics, angiotensin-converting enzyme inhibitors, and digoxin. Generally, diuretics and ACE inhibitors are held on the morning of surgery to reduce the risk of hypotension during induction and maintenance of anesthesia.

Digoxin

Digoxin is occasionally prescribed as part of the anticongestive therapy for pink or acyanotic TOF. Due to its long elimination time and significant side effects, especially during periods of hypoxia, hypokalemia, and other electrolyte disturbances, digoxin is usually discontinued in the perioperative phase.

i. What should be recommended with regard to continuation of medications taken chronically?

  1. Cardiac

    1. Propranolol: Continue throughout preoperative period.

    2. Prostaglandin E1: Continue until alternative source of pulmonary blood flow is established (arteriopulmonary shunt, RV-PA conduit, balloon dilation of pulmonary valve).

    3. Diuretics (furosemide, spironolactone, hydrochlorthiazide): Discontinue on day of surgery to avoid dehydration and hypotension during induction and maintenance of anesthesia.

    4. Digoxin: Discontinue to avoid toxic side-effects during periods of hypoxia or hypokalemia and other electrolyte abnormalities.

  2. Pulmonary

    1. Albuterol and inhaled steroids for reactive airway disease: Continue throughout the perioperative period.

    2. Nitric Oxide for pulmonary hypertension: Continue throughout the perioperative period to avoid rebound pulmonary hypertension.

  3. Renal

  4. Neurologic

    1. Antiseizure medications: Continue throughout perioperative period if possible; in the immediate postoperative phase, oral medications might have to be changed to intravenous formulations.

    2. Calcium: Neonatal seizures due to hypocalcemia should be managed with calcium replacement, and ionized calcium levels should be monitored closely.

    3. Benzodiazepine and opioid tolerance: Patients who have undergone complex neonatal surgery and/or prolonged sedation in the neonatal ICU may demonstrate tolerance to these classes of drugs. If lorazepam and methadone are being used to prevent withdrawal, these should be continued up to the time of surgery. Sustained tolerance frequently necessitates higher than normal doses for sedation and analgesia.

  5. Antiplatelet agents

    1. Low-dose ASA or combination of low-dose ASA and clopidogrel in patients with palliative shunts: Discuss risk for shunt thrombosis with cardiologist and cardiovascular surgeon; stop 7 to 10 days prior to procedure if low risk.

  6. Psychiatric

    1. Older children and adolescents who have undergone infant cardiac surgery are at increased risk for attention-deficit hyperactivity disorder and may be on a methylphenidate, which is generally continued preoperatively.

j. How To modify care for patients with known allergies -

Antibiotic allergies are rarely seen in neonates and young infants but can be a problem in older children with staged repair. The standard antibiotic prophylaxis for surgical site infection is cefazolin. If a patient is allergic to cephalosorins, vancomycin is administered as a slow infusion over 60 minutes to avoid significant hypotension or red man syndrome.

k. Latex allergy- If the patient has a sensitivity to latex (eg. rash from gloves, underwear, etc.) versus anaphylactic reaction, prepare the operating room with latex-free products.

Currently, most Children's hospitals attempt to do away with latex-containing products to reduce or avoid sensitization of frequently hospitalized infants and children as well as health care workers. Latex allergy in an infant presenting for primary repair of tetralogy of Fallot is highly unlikely but may occur in older children presenting for staged repair. Careful preoperative evaluation and meticulous attention to a latex-free environment are essential.

l. Does the patient have any antibiotic allergies- [Tier 2- Common antibiotic allergies and alternative antibiotics]

Antibiotic allergies are rarely seen in neonates and young infants but can be a problem in older children with staged repair. The standard antibiotic prophylaxis for surgical site infection is cefazolin. If a patient is allergic to cephalosorins, vancomycin is administered as a slow infusion over 60 minutes to avoid significant hypotension or red man syndrome.

m. Does the patient have a history of allergy to anesthesia?

Malignant hyperthermia

Standard precautions and management are taken with respect to documented or familial history of malignant hyperthermia, risk of hyperkalemic response to succinylcholine, pseudocholinesterase deficiency, other pharmacogenetic diseases, allergies to local anesthetics, and mitochondrial disorders.

Although myocardial function is generally well preserved with TOF, the unrepaired patient is very preload-dependent such that considerable caution needs to be exercised if propofol is used as part of a nontriggering anesthetic.

5. What laboratory tests should be obtained and has everything been reviewed?

  1. Complete blood count: Hemoglobin/hematocrit, white blood cells, platelets, MCV, MCH.

  2. Chemistry: Na, K, Cl, bicarbonate, BUN, creatinine, Ca, Mg.

  3. Coagulation panel: PT/INR, PTT, fibrinogen, platelets.

  4. Electrocardiogram.

  5. Imaging: Routine – chest X-ray, echocardiogram. Cardiac catherization if performed. Depending on age and coexisting disease: head ultrasound, abdominal imaging (upper gastrointestinal series, plain X-ray, ultrasound), CT scans, MRI, skeletal films.

  6. Blood type and crossmatch: Each institution usually has a surgical blood-ordering protocol. Will also need to order platelets and cryoprecipitate to correct preexisting and CPB-induced coagulopathy.

  7. Review other tests performed: Newborn screen, FISH test for 22q11 deletion, and chromosomal and other genetic testing.

Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?

Patients with tetralogy of Fallot are usually repaired or palliated under opioid-based general anesthesia, supplemented with midazolam and isoflurane as tolerated. Consider the potential for a difficult airway in patients with associated syndromes (DiGeorge, velocardiofacial, CHARGE). Although regional anesthesia as the sole anesthetic is unsuitable for cardiothoracic procedures in this age group, it is possible (but very rare) to place catheters as an adjunct for postoperative pain management. A careful risk/benefit assessment is important in considering the preexisting coagulopathy in cyanotic patients, the need for full anticoagulation during cardiopulmonary bypass, and the postoperative antithrombotic therapy for palliative shunts.

Patients are positioned supine with the arms tucked at the sides. Ensure functioning of peripheral intravenous and arterial lines with patient positioning. Meticulous attention should be given to padding of pressure points. The head is usually turned slightly to the side to prevent compression and/or kinking of the endotracheal tube; avoid excessive head rotation to maintain good cerebral venous drainage. A forced-air warming device can be placed beneath the patient to maintain temperature post-bypass.

6. What is the author's preferred method of anesthesia technique and why?

I. Anesthesia for palliative shunt procedures without cardiopulmonary bypass

We prefer an opioid based (fentanyl 25-50 mcg/kg) general anesthesia technique supplemented with midazolam and isoflurane, as tolerated, and postoperative ventilation in a critical care unit. In addition to standard monitoring and a urinary catheter, invasive monitoring with an arterial catheter and a central venous line (usually right internal jugular vein) is necessary for optimal hemodynamic and ventilatory management and inotrope and fluid administration. Postoperative ventilation is used to allow time for assessment of shunt and pulmonary function.

Prophylactic antibiotics: Cefazolin 25mg/kg IV within 60 minutes of surgical incision. Alternatively vancomycin 10 mg/kg IV over 60 minutes (SCIP 10/2010).

What do I need to know about the surgical technique to optimize my anesthetic care?

(i) Modified Blalock-Taussig shunt via midline sternotomy

A midline sternotomy offers the advantage of prompt institution of CPB if the clinical condition deteriorates, less distortion of the lobar pulmonary arteries as dissection is more proximal, a better cosmetic result as a single incision is used for all stages, a lower risk of scoliosis, and a lower incidence of Horner's syndrome.

After subtotal resection of the thymus, the pericardium is opened and the right pulmonary, innominate and right subclavian arteries are dissected free, carefully avoiding the right recurrent laryngeal nerve, which loops around the right subclavian artery. The subclavian or innominate artery is controlled with a vascular clamp, and an end-to-side anastamosis is performed between a polytetrafluoroethylene (PTFE: Goretex, Impra) graft (usually 3.5 mm) and the subclavian or innominate artery. The tube graft is closed with a bulldog clamp, cut to the appropriate length, and the distal end is then anastomosed to the superior surface of the pulmonary artery, controlling pulmonary artery flow with a vascular clamp or silastic vessel loops. Many surgeons request 0.5 to 1 mg/kg heparin during shunt placement.

After release of the clamps, the oxygen saturation should increase as pulmonary blood flow rises, and the surgeon should be able to feel a thrill in the newly created shunt. The blood pressure can decrease with opening of the shunt due to an increase in pulmonary blood flow and a decrease in diastolic pressure from runoff into the lungs, necessitating fluid/blood administration. Anesthetic management is then geared to balancing the systemic-to-pulmonary blood flow ratio (Qp:Qs). The heparin is usually not reversed unless excessive bleeding is present. A chest tube is placed and the chest closed in the usual fashion.

(ii) Modified Blalock-Taussig shunt via thoracotomy

Although thoracotomy is used much less frequently in the current era, the chest is entered in the 4th intercostal space on the side opposite the ductus arteriosus. After retracting the lung, the mediastinal pleura is opened and the aortic arch vessels are identified and dissected free, carefully avoiding the laryngeal nerve on the right side, which loops around the right subclavian artery. The subclavian or innominate artery is controlled with a vascular clamp and an end-to-side anastamosis is performed between a polytetrafluoroethylene (PTFE: Goretex, Impra) graft (usually 3.5 mm) and the subclavian or innominate artery.

The tube graft is closed with a bulldog clamp, cut to the appropriate length, and the distal end is then anastomosed to the superior surface of the pulmonary artery, controlling pulmonary artery flow with a vascular clamp or silastic vessel loops. Many surgeons request 0.5 to 1mg/kg heparin during shunt placement.

After release of the clamps, the oxygen saturation should increase as pulmonary blood flow rises, and the surgeon should be able to feel a thrill in the newly created shunt. The blood pressure can decrease with opening of the shunt due to an increase in pulmonary blood flow and a decrease in diastolic pressure from runoff into the lungs, necessitating fluid/blood administration. Anesthetic management is then geared to balancing the systemic-to-pulmonary blood flow ratio (Qp:Qs). The heparin is typically not reversed unless excessive bleeding is present. A chest tube is placed and the chest closed in the usual fashion.

(iii) Historical shunts

Classic Blalock-Taussig shunt: Via a right thoracotomy with connection of the proximal portion of the right subclavian artery, directly to the right pulmonary artery. The distal subclavian artery is oversewn, resulting in decreased or absent pulses in the corresponding arm.

Waterston shunt: Anastomosis between ascending aorta and right pulmonary artery.

Potts shunt: Anastomosis between descending aorta and left pulmonary artery.

What can I do intraoperatively to assist the surgeon and optimize patient care?

Support cardiac output and pulmonary blood flow: Adjust ventilation to facilitate surgical exposure without compromising oxygenation; manual ventilation is sometimes necessary. Prevent (sometimes possible) and treat hypercyanotic spells during manipulation of the pulmonary arteries. Discuss strategy with the surgeon to prevent early shunt thrombosis.

What are the most common intraoperative complications and how can they be avoided/treated?

Hypercyanotic spell: Tet spells can occur during induction and maintenance of anesthesia, particularly in the Trendelenberg position for central venous line insertion, during positioning in the lateral decubitus position, or surgical manipulations. Tet spells can possibly be prevented by close monitoring and attention to oxygenation and ventilation, hemodynamics, depth of anesthesia, analgesia, and the operative field. A very early indication is an increase in duskiness of the right atrial wall.

Prevention and treatment comprise of (i) good airway control and high FiO2. Ventilate to lower PVR with 100% oxygen and mild hypocapnia (respiratory alkalosis) with low mean airway pressure and longer expiratory phase to allow for venous return and pulmonary blood flow; (ii) fluid administration (crystalloid [15-30 ml/kg] or colloid [5-10 ml/kg]) prior to induction of anesthesia and initiation of positive pressure ventilation, as well as during the spell; (iii) reduced sympathetic stimulation with adequate depth of anesthesia and adequate analgesia. Caution is advised with high concentration of inhalational agent and the associated vasodilation; ketamine and fentanyl are good options; (iv) increases in SVR with a pure α-agonist – phenylephrine 0.5 to 2 mcg/kg; (v) treatment of acidosis with sodium bicarbonate (1-2 mEq/kg) to lower PVR; (vi) avoidance of excessive tachycardia and dynamic RV outflow tract obstruction by judicious administration of a b-blocker such as esmolol (0.5 mg/kg followed by an infusion of 50-300 mcg/kg/min); (vii) immediate institution of cardiopulmonary bypass if hypercyanotic spell is persistent, severe, and unresponsive to treatment.

Hypoxemia during thoracotomy, vessel manipulation, and shunt insertion: Careful adjustment of ventilation, FiO21.0, and fluid administration if hypovolemic. Use of cardiopulmonary bypass if hypoxemia is unacceptable or associated with significant hemodynamic compromise.

Hypoxemia after release of clamps: The differential diagnosis includes shunt obstruction either due to mechanical factors (kinking, torsion external compression, too small a shunt) or early shunt thrombosis, inadequate perfusion pressure (low cardiac output, bleeding), or lung disease (atelectasis, pulmonary hemorrhage, or inadequate ventilation settings). Treatment is directed toward the most likely cause.

Pulmonary overcirculation and hypotension with low diastolic pressures: Requires reassessment of the shunt size and adjustment in ventilation and oxygenation strategy to more favorably balance the PVR/SVR ratio. Occasionally, flow through the shunt needs to be restricted by placing small clips on the tube graft.

Pulmonary hemorrhage: Caused by manipulation of the pulmonary artery, pulmonary overcirculation, or coagulopathy. Treated with frequent suctioning, lavage, and adequate ventilation with PEEP.

Shunt thrombosis: Prophylactic heparin (50-100 IU/kg) during shunt insertion, avoidance of antifibrinolytic agents, adequate fluid administration, avoidance of excessive blood transfusions, and very high hematocrit levels.

II. Anesthesia for complete repair of tetralogy of Fallot

We prefer an opioid-based general anesthesia technique, generally fentanyl 50 to 100 mcg/kg, supplemented with isoflurane and midazolam as tolerated. In addition to standard monitoring and a urinary catheter, invasive monitoring with an arterial catheter and a central venous line (usually right internal jugular vein) is necessary for optimal hemodynamic and ventilatory management and inotrope and fluid administration during a cardiothoracic procedure with cardiopulmonary bypass in a small infant. Cerebral oximetry with near infrared spectroscopy (NIRS) has become routine.

a. What prophylactic antibiotics should be administered?

Cefazolin 25mg/kg within 60 minutes of skin incision, 25mg/kg added to the bypass prime and 25mg/kg after successful separation from cardiopulmonary bypass. Alternatively, ancomycin 10 mg/kg IV over 60 minutes and another 10 mg/kg added to the bypass circuit. (SCIP 10/2010)

b. What do I need to know about the surgical technique to optimize anesthetic care?

Repair of tetralogy of Fallot with pulmonary stenosis and infundibular obstruction: After midline sternotomy, subtotal resection of the thymus and opening of the pericardium, cardiopulmonary bypass is initiated in the standard fashion, with either bicaval or single atrial venous cannulation, depending on the size of the patient and competence of the tricuspid valve.

Moderate hypothermia at 25°C or above is typical, and the left ventricle is vented via the right upper pulmonary vein. For infants, less than 2 to 2.5 kg deep hypothermic circulatory arrest at 18°C might be necessary. Immediately after commencing bypass, the PDA or previous shunt is ligated (with a concomitant increase in the mean arterial pressure). During the cooling phase, the pulmonary arteries are dissected free and the size of the pulmonary valve annulus inspected to determine the need for a transannular patch. The coronary artery distribution over the RV outflow tract is examined to find the best location for the ventriculotomy if the ventricular approach rather than atrial approach is chosen. Once the aortic cross-clamp is placed and cardioplegia given, resection of infundibular muscle bundles and VSD closure is performed via the ventriculotomy (or via an atrial approach).

If the pulmonary valve annulus is severely hypoplastic, a transannular pericardial patch is placed. If there is mild-moderate annular hypoplasia, a hybrid approach with balloon dilation of the pulmonary valve in the operating room is increasingly being performed in an attempt to preserve as much function of the pulmonary valve as possible. If the annulus is of adequate size, a valve-sparing technique with 2 separate patches is preferred to avoid free pulmonary regurgitation and RV volume overload: one patch is placed over the main pulmonary artery for supravalvular stenosis and one over the infundibular area.

In young infants at high risk for postoperative RV dysfunction, a PFO or small ASD is often left or even created to allow for a "pop-off" right-to-left shunt during the early postoperative period characterized by RV dysfunction and high PVR. A left atrial line may be placed prior to separation from bypass, and, occasionally, a PA or RV line to monitor PA or RV pressures in the postoperative period. Residual VSDs, RV outflow tract obstructions, pulmonary valve function, and ventricular performance can be assessed by transesophageal or epicardial echocardiography, depending on the size of the patient.

The surgeon may perform direct measurements of RV and PA pressures to determine the residual RVOT gradient (20 mmHg is acceptable) and measure RA and PA oxygen saturation, looking for a step-up in the oxygen saturation, which suggests a residual VSD. Atrial and ventricular epicardial pacing wires and chest tubes are placed, and the chest closed in the usual fashion.

In very small babies with significant myocardial edema and RV dysfunction, the chest may be left open and covered with part of an Esmarch bandage. After 3 to 4 days, once RV function has improved, adequate diuresis is established and the tissue swelling has subsided, the chest can be closed.

c. What can I do intraoperatively to assist the surgeon and optimize patient care?

Adjust ventilation to facilitate and optimize surgical exposure without compromising oxygenation, using manual ventilation as necessary. Treat hypercyanotic spells during surgical manipulations. Initiate vasoactive support with dopamine, phenylephrine, or epinephrine to treat low output syndrome and maintain adequate perfusion pressures as necessary. Ensure that functional temporary pacemaker and antiarrhythmic drugs for treatment of complete heart block or JET are immediately available.

d. What are the most common intraoperative complications and how can they be avoided/treated?

Hypercyanotic spell: Tet spells can occur during induction and maintenance of anesthesia, particularly in the Trendelenberg position for central venous line insertion, during positioning in the lateral decubitus position, or surgical manipulations. Tet spells possibly can be prevented by close monitoring and attention to oxygenation and ventilation, hemodynamics, depth of anesthesia, analgesia, and the operative field. A very early indication is an increase in duskiness of the right atrial wall.

Prevention and treatment comprise of (i) good airway control and high FiO2. Ventilate to lower PVR with 100% oxygen and mild hypocapnia (respiratory alkalosis) with low mean airway pressure and longer expiratory phase to allow for venous return and pulmonary blood flow; (ii) fluid administration (crystalloid [15-30 ml/kg] or colloid [5-10 ml/kg]) prior to induction of anesthesia and initiation of positive pressure ventilation, as well as during the spell; (iii) reduction of sympathetic stimulation with adequate depth of anesthesia and provision of adequate analgesia. Caution is advised with high concentration of inhalational agent and the associated vasodilation; ketamine and fentanyl are good options; (iv) increase of SVR with a pure α-agonist - phenylephrine 0.5-2 mcg/kg; (v) treatment of acidosis with sodium bicarbonate (1-2 mEq/kg) to lower PVR; (vi) with excessive tachycardia and dynamic RV outflow tract obstruction, judicious administration of a ß-blocker such as esmolol (0.5 mg/kg followed by an infusion of 50-300 mcg/kg/min); (vii) performing cardiopulmonary bypass if persistent, severe, and unresponsive to treatment.

Coronary Ischemia: May occur if a coronary artery crossing the RVOT is inadvertently transected or the outflow tract patch results in coronary artery obstruction. This is evidenced by poor ventricular function, myocardial duskiness, ST segment changes, and arrhythmias during rewarming and separation from bypass. Careful evaluation of coronary artery distribution in infundibular area and limitation of ventricular incision can help to prevent this complication. Treatment depends on severity of injury and ranges from return to bypass with surgical revision to increased inotropic support, nitroglycerin administration, and other measures to maintain adequate coronary perfusion.

Residual RV outflow tract obstruction: This is easily detected with echocardiography and/or direct measurement of RV and PA pressure, and may necessitate return to bypass and surgical revision.

Conduction and rhythm abnormalities:

  • – Right bundle branch block is common.

  • – Complete heart block after VSD patch closure requires immediate pacing via the temporary epicardial pacing wires. It is often temporary due to traction or edema around the conduction system. If resolution of conduction occurs, it usually happens within 8 to 10 days postoperatively.

  • – Ventricular ectopy and fibrillation should raise suspicion for ischemia of the hypertrophied RV (hypotension, air in coronaries, or coronary injury), severe RV dysfunction and dilation, electrolyte abnormalities, or ventricular irritation from ventriculotomy. Treatment with defibrillation, antiarrhythmic medications, support of RV function, and correction of electrolyte abnormalities.

  • – Junctional ectopic tachycardia (JET) is a catecholamine sensitive arrhythmia with a rapid junctional focus and AV dissociation. Rates may be as high as 200 to 230 bpm and associated with significant hemodynamic compromise. Adequate anesthesia; analgesia and sedation (ICU); lower levels of inotropic support, if possible; and avoidance of hyperthermia might help to reduce the incidence. Treatment includes deepening anesthesia, reducing the inotropic support as tolerated, cooling to 34°C to 35°C, and administering antiarrhythmic agents such as procainamide or amiodarone. If the rate is relatively low, atrial pacing at a slightly higher rate may improve cardiac output. Dexmedetomidine has also been used to treat JET.

Bleeding: Usually causes of bleeding include leaking suture lines, bypass-induced coagulopathy, and preexisting clotting abnormalities in a cyanotic patient. Adequate rewarming, protamine reversal of heparin effects, exploration of the operative field for potential surgical causes, and transfusion of blood products (platelets, cryoprecipitate, and packed red blood cells to maintain adequate hematocrit) are important management steps.

Postoperative RV dysfunction and low cardiac output syndrome: Causative factors include poor RV function, high PVR, residual lesions, myocardial ischemia due to coronary artery injury, and cardiac tamponade. Poor RV function and high PVR are managed with increased inotropic support (dopamine, epinephrine) and ventilator strategies to lower PVR. Chest X-ray to determine and thereby treat atelectasis, hemothorax, pneumothorax, and right mainstem intubation. Echocardiography to determine if residual lesions or significant pericardial effusion. Bronchodilators if necessary.

  1. Cardiac complications: Residual VSD (patch leak/dehiscence, second VSD), residual RV outflow tract obstruction, free pulmonary valve regurgitation (transannular patch), RV dysfunction and low cardiac output syndrome, myocardial ischemia, rhythm and conduction abnormalities.

  2. Pulmonary: "Pump lung" – reperfusion injury and systemic inflammatory response with increased lung water after cardiopulmonary bypass.

  3. Neurologic: Embolic or hypoxic-ischemic injury in the early postoperative period can present as stroke (ischemic, hemorrhagic), seizures, or, rarely, choreoathetosis.

a. Neurologic

  1. Unique to procedure: Embolic stroke (air or thrombotic material), ischemic stroke, intracerebral hemorrhage, seizures, choreoathetosis.

b. If the patient is intubated, are there any special criteria for extubation?

Palliative shunt procedures without cardiopulmonary bypass

Patients are mechanically ventilated for at least 12 to 24 hours, particularly to assess shunt and pulmonary function. Excessive flow across the shunt with pulmonary overcirculation can result in pulmonary edema, pulmonary hemorrhage (can be unilateral), and systemic hypotension. Diastolic hypotension due to "run-off" into the pulmonary circulation, together with a volume loaded ventricle as a result of QP:QS>1, can lead to myocardial ischemia. Inadequate shunt flow (see below) can result in profound hypoxemia.

Repair of tetralogy of Fallot with pulmonary stenosis and infundibular obstruction

Patients are mechanically ventilated in the ICU, with most patients being eligible for extubation within the first 24 hours. Neonates and very sick young infants with RV dysfunction and high PVR may need a few days to a week or so of mechanical ventilation. In the typical patient, extubation is possible once stable hemodynamics with minimal inotropic requirement (dopamine 5 mcg/kg/min) are achieved, bleeding is controlled, respiratory effort and gas exchange are good with low FiO2, a small amount of PEEP or pressure support and no significant abnormality on chest X-ray, the patient is normothermic and only mildly sedated.

Cardiac factors contributing to inability to wean from mechanical ventilation include significant residual defects with ventricular volume and/or pressure overload, myocardial dysfunction and arrhythmias; complete heart block requiring epicardial pacing typically does not preclude extubation. Respiratory factors include atelectasis, large pleural effusions, hemothorax or pneumothorax, and phrenic nerve injury.

c. Postoperative management

What analgesic modalities can I implement?

Patients usually remain intubated and ventilated for at least several hours after the procedure. Pain is initially treated with intravenous opioids, either intermittent doses of morphine or continuous infusions of morphine or fentanyl, depending on hemodynamic stability and the expected time to extubation. Acetaminophen (rectal or intravenous) is a useful adjunct and is also used to reduce fever. Once any existing postoperative coagulopathy has resolved, bleeding has stopped, and there are no concerns regarding renal function, nonsteroidal anti-inflammatory agents such as ketorolac can be added to the analgesic regimen. Following extubation and establishment of oral intake, there is a transition to oral analgesics.

What level of bed acuity is appropriate?

Postoperative admission to a Pediatric Intensive Care Unit with expertise in the perioperative management of pediatric cardiac surgical patients. ICU admission is necessary to ensure close monitoring and immediate availability of staff and equipment to treat postoperative complications such as bleeding, cardiac tamponade, myocardial ischemia, low output syndrome, and arrhythmias.

What are common postoperative complications, and ways to prevent and treat them?

Surgical palliation

Hypoxemia: May be due to pulmonary, hemodynamic, or shunt factors. Pulmonary causes include high PVR; endotracheal tube obstruction; circuit disconnection; atelectasis; contusion following lung retraction; pulmonary hemorrhage; hemo-, pneumo-, or chylothorax (damage to thoracic duct); poor ventilator settings; and interstitial and alveolar edema following prolonged pulmonary overcirculation.

Hemodynamic factors are inadequate shunt perfusion as a result of low systemic pressure (and hence less pressure to drive blood across the shunt into the pulmonary circulation), low cardiac output, and low SVR; management includes fluid, often RBC to maintain hematocrit >40%, and intotropic administration.

Shunt factors, usually beyond the control of the anesthesiologist and intensivist, are associated with decreased shunt flow and include too small a shunt, thrombosis, compression, torsion and kinking; the chest may need to be opened emergently in the ICU and the shunt problem addressed.

Hypotension: Close monitoring and maintenance of cardiac output in the postoperative period by administration of fluid, often RBC to maintain hematocrit >40%, and support of myocardial contractility with an inotropic agent if necessary. Hypotension can also be due to excessive PBF or pulmonary overcirculation.

Pulmonary overcirculation with systemic hypotension: An increased QP:QS from too large a shunt or excessive lowering of PVR results in excessive PBF with run-off (steal) from the systemic circulation and pulmonary edema, initially manifesting as a high SaO2 (>85%) and low diastolic blood pressure. Diastolic hypotension with a volume-loaded ventricle and high heart rate can result in myocardial ischemia. Weaning from mechanical ventilation may be difficult. Treatment requires reassessment of the shunt size and adjustment in ventilation and oxygenation strategy to more favorably balance the QP:QS by manipulation of the PVR:SVR ratio. Occasionally, flow through the shunt needs to be restricted by placing small clips on the tube graft.

Pulmonary hemorrhage: Caused by manipulation of the pulmonary artery, pulmonary overcirculation, or coagulopathy. This is treated with frequent suctioning, adequate ventilation with PEEP, and correction of any coagulopathy.

Shunt narrowing or obstruction (thrombosis): Monitoring of shunt murmur and end-tidal CO2 and, if necessary, assessment of shunt flow with echocardiography or cardiac catheterization if echocardiography is inconclusive. Prophylaxis of shunt thrombosis with adequate fluid administration, heparin infusion (10 IU/kg/hr) once surgical bleeding has resolved, avoidance of antifibrinolytic agents, and avoidance of very high hematocrit levels. Thrombosis can be treated by surgical exploration and embolectomy with Fogarty catheter at the bedside or balloon dilation in the cardiac catheterization laboratory; successful thrombolysis with tPA has been described.

Bleeding: Major bleeding following surgical palliation is infrequent.

Complete repair

Postoperative bleeding and tamponade: Close monitoring of chest tube output, hemodynamic status, filling pressures, and frequent "stripping" of the chest tubes to prevent clot formation and obstruction are important preventive measures. Persistently high (>3-4 mL /kg/hr) or increasing chest tube output should trigger a coagulation work-up with clotting factor (platelets and/or cryoprecipitate) administration and surgical exploration as necessary.

Hematocrit should be maintained around 40%. Hypotension with elevated cardiac filling pressures and "loss" of chest tube output should raise a high index of suspicion for cardiac tamponade, necessitating urgent echocardiography and opening of the chest or pericardiocentesis.

Residual RV outflow tract obstruction: Results in RV pressure overload and is easily diagnosed by a persistently loud murmur and on echocardiography. Gradients up to 20 mmHg are acceptable. Higher gradients may necessitate surgical revision.

Residual VSD: Results in RV volume overload and dysfunction; if large, it may be poorly tolerated, especially if associated with pulmonary regurgitation, and delay weaning from mechanical ventilation. May result from patch leak, patch dehiscence, or undiagnosed second VSD. Surgical revision or device closure in the catheterization laboratory may be necessary.

Postoperative RV dysfunction and low cardiac output syndrome: Causative factors include poor RV function (long cross-clamp time, ventriculotomy), high PVR, residual lesions, myocardial ischemia due to coronary artery injury, and cardiac tamponade. Close monitoring for signs of low cardiac output (poor perfusion, increased lactate, low mixed venous oxygen saturation, low cerebral oxygen saturation), and elevated central venous pressures (edema, hepatomegaly, liver dysfunction).

Poor RV function and high PVR are managed with increased inotropic support (dopamine, epinephrine) and ventilator strategies to lower PVR. A chest X-ray is necessary to exclude and treat other causes of increased PVR – atelectasis, hemothorax, pneumothorax, and right mainstem intubation. Echocardiography to determine if residual lesions or significant pericardial effusion. Bronchodilators if necessary. Occasionally, if there is no atrial level communication, an atrial balloon septostomy can be performed in the catheterization laboratory to decompress the RV and improve cardiac output (LV filling improved with right-to-left shunt).

Coronary Ischemia: May occur if a coronary artery crossing the RVOT is inadvertently transected or the outflow tract patch results in coronary artery obstruction. Evidenced by poor ventricular function, low cardiac output, ST segment changes, and arrhythmias. Diagnosed by echocardiography and/or cardiac catheterization with coronary angiography. Treatment depends on severity of ischemia and ranges from surgical exploration to increased inotropic support, nitroglycerin administration, and other measures to maintain adequate coronary perfusion.

Conduction and rhythm abnormalities:

  • – Right bundle branch block is common.

  • – Complete heart block is a classic complication, usually resulting from traction or edema around the conduction system in this era, and requires pacing via the temporary epicardial pacing wires. Fortunately, it is usually transient, resolving in 8 to 10 days postoperatively. In the ICU, the ECG should be continuously monitored, the pacing thresholds of the temporary wires assessed, and a pacemaker box be immediately available.

  • – Ventricular ectopy is quite common after ventriculotomy and with RV dysfunction. Close monitoring of electrolytes and replacement is important, especially of potassium after onset of diuresis. Ventricular fibrillation should raise suspicion for ischemia of the hypertrophied RV (hypotension, coronary injury), severe RV dysfunction and dilation, electrolyte abnormalities, or ventricular irritation from ventriculotomy. Treatment with defibrillation, antiarrhythmic medications, support of RV function and correction of electrolyte abnormalities.

  • – Junctional ectopic tachycardia (JET) is a catecholamine-sensitive arrhythmia with a rapid junctional focus and AV dissociation. It usually has a sudden onset during the first postoperative night; rates can be as high as 200 to 230 bpm, and, although self-limiting, can be associated with significant hemodynamic compromise. Treatment includes adequate sedation, reduction of inotropic support as tolerated, cooling to 34°C to 35°C, paralysis, and with antiarrhythmic agents such as procainamide or amiodarone. If the rate is relatively low, atrial pacing at a slightly higher rate may improve cardiac output.

What's the Evidence?

Apitz, C, Webb, GD, Redington, AN. "Tetralogy of Fallot". Lancet. vol. 372. 2009. pp. 1462-71.

Starr, JP. "Tetralogy of Fallot: yesterday and today". World J Surg. vol. 34. 2010. pp. 658-68.

Park, MK, Park, MK. "Pathophysiology of Cynaotic Congenital Heart Defects". Pediatric Cardiology for Practioners. Mosby. 2002.

Park, MK, Park, MK. "Cyanotic Congenital Heart Defects". Pediatric Cardiology for Practioners. Mosby. 2002.

Breitbart, R, Fyler, D, Keane, JF, Lock, JE, Fyler, DC. "Tetralogy of Fallot". Nadas' Pediatric Cardiology. Saunders Elsevier. 2006.

Jonas, R, Jonas, R. "Tetralogy of Fallot with pulmonary stenosis". Comprehensive Surgical Management of Congenital Heart Disease. Hodder Arnold. 2004.

Mavroudis, C, Backer, CL, Mavroudis, C, Backer, CL. "Palliative Operations". Pediatric Cardiac Surgery. Mosby. 2003.

Hirsch, J, Bove, EL, Mavroudis, C, Backer, CL. "Tetralogy of Fallot". Pediatric Cardiac Surgery. Mosby. 2003.

Robinson, JD, Rathod, RH, Brown, DW. "The evolving role of intraoperative balloon pulmonary valvuloplasty in valve-sparing repair of tetralogy of Fallot". J Thorac Cardiovasc Surg. vol. 142. 2011. pp. 1367-73.

Ibsen, L, Shen, I, Ungerleider, RM, Nichols. "Perioperative management of patients with congenital heart disease: a multidisciplinary approach". Critical Heart Disease in Infants and Children. Mosby. 2006.

Laussen, PC, Roth, SJ, Andropoulos, DB. "Cardiac Intensive Care". "Anesthesia for Congenital Heart Disease". Wiley-Blackwell. 2010.

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