Adult Congenital Heart Disease in Noncardiac Surgery

Pulmonary

Any lesion that results in either increased pulmonary blood flow or pulmonary venous obstruction can cause increased pulmonary interstitial fluid with decreased pulmonary compliance and increased work of breathing. Patients with cyanotic heart disease have increased minute ventilation and maintain normocarbia. These patients have a normal ventilatory response to hypercapnia but a blunted response to hypoxemia that normalizes after corrective surgery and the establishment of normoxia. End-tidal CO ₂ underestimates arterial PaCO ₂ in cyanotic patients with decreased, normal, or even increased pulmonary blood flow.

Although enlarged hypertensive pulmonary arteries or an enlarged left atrium can impinge on bronchi in children, this is rare in adults. Late-stage Eisenmenger syndrome can result in hemoptysis, and patients with Eisenmenger physiology and erythrocytosis can develop thrombosis of upper lobe pulmonary arteries. Prior thoracic surgery could have injured the phrenic nerve with resultant diaphragmatic paresis or paralysis.

In an attempt to increase pulmonary blood flow, large collateral vessels originating from the aorta may have developed. These are sometimes embolized in the catheterization laboratory before thoracic surgery to prevent excessive intraoperative blood loss.

Hematologic

Hematologic manifestations of chronic CHD are primarily a consequence of long-standing cyanosis and incorporate abnormalities of both hemostasis and red blood cell (RBC) regulation. Long-standing hypoxemia causes increased erythropoietin production in the kidney and resultant increased RBC mass. Because solely RBC production is affected, these patients are correctly referred to as erythrocytotic rather than polycythemic. There is, however, a fairly poor relationship among oxygen saturation, RBC mass, and 2,3-diphosphoglycerate. The oxygen-hemoglobin dissociation curve is normal or minimally shifted to the right. Most patients have established an equilibrium state at which they have a stable hematocrit and are iron replete. Some patients, however, develop excessive hematocrits and are iron deficient, causing a hyperviscous state. Iron-deficient RBCs are less deformable and cause increased viscosity for the same hematocrit. This is a strong independent predictor of thrombosis in the setting of Eisenmenger syndrome. Symptoms of hyperviscosity are uncommon and typically develop only at hematocrits exceeding 65%, provided the patient is iron replete. Iron deficiency also shifts the oxygen-hemoglobin dissociation curve to the right, decreasing oxygen affinity in the lungs. Iron deficiency can be the result of misguided attempts to lower the hematocrit by means of repeated phlebotomies.

Symptomatic hyperviscosity is the indication for treatment to temporarily relieve symptoms. It is not indicated to treat otherwise asymptomatic elevated hematocrits (generally hemoglobin >20 g/dL and hematocrit >65%). Treatment is by means of a partial isovolumic exchange transfusion, and it is assumed that the increased hematocrit is not related to dehydration. Partial isovolumic exchange transfusion usually results in regression of symptoms within 24 hours. It is rare to require exchange of more than 1 unit of blood. Preoperatively, phlebotomized blood can be banked for autologous perioperative retransfusion if required. Elective preoperative isovolumic exchange transfusion has decreased the incidence of hemorrhagic complications of surgery. Hyperviscosity and erythrocytosis can cause cerebral venous thrombosis in younger children, but it is not a problem in adults, regardless of the hematocrit. Protracted preoperative fasts need to be avoided in erythrocytotic patients because they can be accompanied by rapid elevations in the hematocrit.

Bleeding dyscrasias have been described in up to 20% of patients. A variety of clotting abnormalities have been described in association with cyanotic CHD but none uniformly. Bleeding dyscrasias are uncommon until the hematocrit exceeds 65%, although excessive surgical bleeding can occur at lower hematocrits. Generally, higher hematocrits are associated with a greater bleeding diathesis. Abnormalities of a variety of factors in both the intrinsic and extrinsic coagulation pathways have been described. Fibrinolytic pathways are normal.

The decreased plasma volume in erythrocytotic blood can result in spuriously elevated measures of the prothrombin and partial thromboplastin times, and the fixed amount of anticoagulant in the collection tube will be excessive because it presumes a normal plasma volume in the blood sample. Erythrocytotic blood has more RBCs and less plasma in the same volume. If informed in advance of a patient's hematocrit, the clinical laboratory can provide an appropriate sample tube.

Platelet counts are typically normal or occasionally low, but bleeding is not due to thrombocytopenia. Platelets are reported per milliliter of blood, not per milliliter of plasma. When corrected for the decreased plasma fraction in erythrocytotic blood, the total plasma platelet count is closer to normal. That said, abnormalities in platelet function and life span have on occasion been reported. Patients with low-pressure conduits (Fontan pathway) or synthetic vascular anastomoses are often maintained on antiplatelet drugs.

Cyanotic erythrocytotic patients have excessive hemoglobin turnover, and adults have an increased incidence of calcium bilirubinate gallstones. Biliary colic can develop years after cyanosis has been resolved by cardiac surgery.

A variety of mechanical factors can also affect excessive surgical bleeding in patients with cyanotic CHD. These factors include increased tissue capillary density, elevated systemic venous pressure, aortopulmonary and transpleural collaterals that have developed to increase pulmonary blood flow, and prior thoracic surgery. Aprotinin and ε-aminocaproic acid improve postoperative hemostasis in patients with cyanotic CHD. The results with tranexamic acid have been mixed.

Renal

Some degree of renal insufficiency is common in adults with CHD, and the severity is a predictor of death. Moderate or severe renal dysfunction (estimated glomerular filtration rate [GFR] of <60 mL/min per m ² ) carries a fivefold increased risk of death at 6-year follow-up compared with patients with normal GFR and a threefold increase over those with mild elevations in GFR. Renal dysfunction is particularly prevalent in cyanotic patients and those with poor cardiac function. Adult patients with cyanotic CHD can develop abnormal renal histology with hypercellular glomeruli and basement membrane thickening, focal interstitial fibrosis, tubular atrophy, and hyalinized afferent and efferent arterioles. Cyanotic CHD is often accompanied by elevations in plasma uric acid levels that are caused by inappropriately low fractional uric acid excretion. Decreased urate reabsorption is thought to result from renal hypoperfusion with a high filtration fraction. Despite the elevated uric acid levels, urate stones and urate nephropathy are rare. Although arthralgias are common, true gouty arthritis is less frequent than would be expected from the degree of hyperuricemia.

Neurologic

Adults with persistent or potential intracardiac shunts remain at risk for paradoxical embolism. Paradoxical emboli can occur even through shunts that are predominantly left-to-right because during the cardiac cycle, there can be small transient reversals of the shunt direction. It has been said that, unlike in children, adults with cyanotic CHD are not at risk for the development of cerebral thrombosis despite the hematocrit. However, this assertion has been challenged with the suggestion that an association of stroke occurs, not with RBC mass but with iron deficiency and repeated phlebotomy. Adults do, however, remain at risk for the development of brain abscess. A healed childhood brain abscess can provide the nidus for the development of seizures throughout life.

Prior thoracic surgery can result in permanent peripheral nerve damage. Surgery at the apices of the lungs is particularly associated with the risk of nerve damage. These operations would include Blalock-Taussig shunts, ligation of patent ductus arteriosus (PDA), banding of the pulmonary artery, and repair of aortic coarctation. Nerves that are susceptible to injury include the recurrent laryngeal nerve, the phrenic nerve, and the sympathetic chain. The incidence of migraine headaches is higher in adults with CHD compared with a control group with acquired heart disease (45% vs. 11%) and is increased in left-to-right, right-to-left, and no-shunt groups.

Vasculature

Vessel abnormalities can be congenital or iatrogenic. They can affect the suitability of vessels for cannulation by the anesthesiologist or measurement of correct pressures. These abnormalities are described in Table 8.1 .

Pregnancy

The physiologic changes of pregnancy, labor, and delivery can significantly alter the physiologic status of women with CHD, and mortality and morbidity are increased in mothers with CHD. Several texts are available that specifically discuss issues of pregnant women with CHD in more detail than is possible here. Management and clinical outcomes during pregnancy and delivery for several cardiac lesions are included under the later discussions of these lesions.

Although cardiac complications, spontaneous abortions, premature delivery, thrombotic complications, peripartum endocarditis, and poor fetal outcomes can occur, successful pregnancy to term with vaginal delivery is possible for most patients with congenital defects. High-risk factors for mothers and fetuses include pulmonary hypertension, depressed ventricular function, Marfan syndrome with dilated aortic root, cyanosis, severe left heart obstructive lesions, and pressure (vs. volume) lesions. Eisenmenger physiology is a particular risk factor. Up to 47% of cyanotic women have worsening of functional capacity during pregnancy. Hematocrits greater than 44% are associated with birth weights less than 50th percentile, and fetal death is about 90% or more with hemoglobin levels greater than 18 g/dL or oxygen saturation less than 85%, with most losses in the first trimester. The increases in stroke volume and cardiac output during pregnancy can stress an already pressure-overloaded ventricle. The decrease in systemic vascular resistance that accompanies pregnancy is better tolerated by women with regurgitant lesions and typically offsets the added insult of pregnancy-related hypervolemia. The decrease in systemic vascular resistance can, however, increase right-to-left shunting. Hypervolemia can be problematic in patients with poor ventricular function. Maternal cyanosis is associated with increased incidences of prematurity and intrauterine growth retardation. Profound cyanosis is associated with a high rate of spontaneous abortion. Endocarditis prophylaxis is not currently recommended for vaginal deliveries. The recurrence risk of any congenital cardiac defect in a newborn is 2.3% with one affected older sibling (any defect), 7.3% with two affected older siblings, and 6.7% if the mother has a congenital cardiac defect but only 2.1% if the father is affected. However, it has become apparent that recurrence risk can be specific to the type of maternal defect and the underlying genetic basis. If possible, pregnancies in mothers with CHD should be managed in a high-risk obstetric center with cardiologists experienced with the care of ACHD and with early consultation with the obstetric anesthesia service. Women on long-term anticoagulation likely need peripartum modifications, and postpartum thromboembolism is a potential significant problem. Anesthesiologists generally encounter pregnant patients well into the last trimester. Most of the major physiologic changes associated with pregnancy occur before the third trimester, and if patients have maintained good functional status to this point, they will have demonstrated themselves to be in a relatively low-risk group. Pregnancy is a stress test, and if they have successfully arrived at the mid to late third trimester, it is more likely that they will successfully tolerate delivery. Also, many high-risk women will have been counseled to avoid pregnancy. There is no a priori reason to favor an instrumented or cesarean delivery over a vaginal one. This is an obstetric, not cardiologic, decision. That said, there is a common belief that women with ACHD will not tolerate the “stress” of labor, particularly bearing down in the second stage. However, a well-functioning epidural makes uterine contractions easy to tolerate. Furthermore, avoidance of second-stage pushing is an option as long as progress is being made and can be combined with a maneuver such as low-outlet vacuum or forceps to facilitate delivery. The third stage can be accompanied by an autotransfusion of placental blood or potentially with hypovolemia with uterine atony and hemorrhage. If oxytocic drugs are required, the hemodynamic effects must be kept in mind. Oxytocin will decrease systemic vascular resistance and increase heart rate and pulmonary vascular resistance (PVR). Methylergonovine will increase systemic vascular resistance. These rapid changes in loading conditions can be poorly tolerated in mothers with fixed cardiac output, and pulmonary edema or heart failure can develop.

Some mothers take medications for their cardiac condition, including antiarrhythmics. In general, these are safe for the infant. Exceptions include β-blockers, which can interfere with fetal growth and the response of the fetus to the stress of labor, and amiodarone, which can affect fetal thyroid function. Maternal cardioversion appears to be safe for fetuses at all stages because of the low intensity of the electrical field at the uterus. However, fetuses should be monitored throughout the procedure. Women with implanted internal defibrillators have carried successfully to term. If cardiopulmonary bypass (CPB) is required during pregnancy, it carries with it increased fetal risk, particularly if hypothermia is used.