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Ann Thorac Surg 1995;59:384-388
© 1995 The Society of Thoracic Surgeons
The Albert Starr Academic Center for Cardiac Surgery, St. Vincent Hospital and Medical Center, and Emanuel Hospital, Portland, Oregon
Accepted for publication September 20, 1994.
| Abstract |
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| Introduction |
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| Material and Methods |
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After induction of anesthesia and insertion of monitoring lines, a median sternotomy was performed. Total correction of congenital heart defects with CPB was performed only if the Hct of the patient on CPB was predicted to be higher than 15%. If the predicted Hct was less than 16%, initial palliative procedures such as aortopulmonary shunt or pulmonary artery banding were performed. Predicted Hct was calculated according to an empiric formula:
![]() | (1) |
where EBV is the patient's estimated blood volume, and PV is the priming volume.
In 9 patients, CPB was instituted in routine fashion with aortic cannulation and dual venous cannulation. In the 6 largest patients, Medtronic Minimax oxygenators (Minneapolis, MN) with heparin-bonded tubing (Carmeda BioActive Surface; Carmeda AB, Stockholm, Sweden) were used to allow reduction of the initial systemic heparin sodium dose to 1 mg/kg. In the other 3 patients, Capiox oxygenators (Terumo Corp, Tokyo, Japan) with nonheparin-bonded tubing (Gish Biomedical, Irvine, CA) were used because the heparin-bonded circuits require a larger priming volume, and this could have led to an unacceptable decrease in Hct. The initial heparin dose in these 3 patients was 3 mg/kg, and heparin was added to the priming solution. Additional heparin was administered for maintenance of anticoagulation and was neutralized with protamine sulfate after CPB to restore the preoperative activated clotting time. To minimize the CPB circuit volume, the length and the diameter of the CPB tubing were reduced, and arterial filters were not used. The priming solution comprised the following: Plasmalyte, 247 ± 67 mL; 25% albumin, 103 ± 26 mL; 10% mannitol, 43 ± 17 mL; and NaHCO3, 16 ± 5 mEq. All procedures were performed with moderate hypothermia (20° to 28°C). The flow on CPB was expressed as a percentage of predicted full flow, which was 150 mL kg-1 min-1. The degree of hemodilution on CPB was calculated as 100 x (preoperative Hct - lowest measured Hct/preoperative Hct).
In all nine procedures, myocardial protection was achieved by the administration of blood cardioplegia through the aortic root. Cardioplegic solution was allowed to return to the CPB circuit if the Hct and potassium level were in acceptable ranges. Topical heart cooling was achieved with slushed ice. Blood samples were taken before CPB and every 20 minutes thereafter to check arterial and venous blood gases, Hct, and electrolyte levels. Arterial and venous pressures and urinary output were continuously monitored. At the end of CPB, 1 mg/kg of furosemide was administered if urinary output was inadequate. Intotropic support and sodium nitroprusside were used when indicated.
Cardiopulmonary bypass was not employed in 2 patients. An 11-day-old neonate (patient 10, Table 1
) with critical aortic stenosis underwent aortic valvotomy using moderate hypothermia (28°C). Both venae cavae were snared with tapes after placement of a single cannula in the ascending aorta and placement of a purse-string suture in the right atrium. The heart continued to beat and empty itself. After induced ventricular fibrillation, the aorta was cross-clamped. During a period of 3.5 minutes of circulatory arrest, a commissurotomy was performed on the rudimentary commissures between the right and left aortic valve leaflets and between the right and noncoronary leaflets. After closure of the aortotomy, the caval tapes were released, air was evacuated from the heart, and the aortic clamp was removed with spontaneous recovery of heart action and resulting excellent hemodynamics. The other patient, a 12-month-old-boy (patient 11), underwent a bidirectional cavopulmonary shunt procedure for tricuspid and pulmonary atresia and transposition of the great arteries. This patient also had a persistent left superior vena cava. The right and left superior venae cavae were anastomosed to the corresponding pulmonary arteries in a sequential fashion without the use of a temporary superior vena cavaright atrial shunt. Subsequently bilateral Blalock-Taussig shunts were clipped.
Postoperatively, the patients were continuously monitored in the intensive care unit (ICU). Blood tests were done on specific clinical indications to save blood. Patients received crystalloid solution at one fourth to one half the usual maintenance rates. Mechanical ventilation was continued until adequate spontaneous ventilation resumed. Patients were then extubated if in hemodynamically stable condition. Loss of red blood cells was calculated as the product of chest drainage and the lowest Hct after operation and was corrected for body weight. Patients who had an uncomplicated postoperative course were generally transferred to their room on the second postoperative day. Oral iron supplementation was begun before discharge if indicated.
Statistical Analysis
Analysis of variance and Scheffé's F test were used to determine associations between the preoperative and intraoperative Hct levels. A p value equal to or less than 0.05 was considered significant.
| Results |
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| Comment |
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We set a tentative limit for body weight of 5 kg for infants of Jehovah's Witnesses to undergo repair of congenital heart defects with CPB without the use of blood. In symptomatic patients with a lower body weight, initial palliative procedures circumvent the use of CPB and allow secondary correction of the defect at a later time; this was done in 6 patients in this series. Balloon valvuloplasty is a valuable treatment option for the neonate or infant with congenital aortic or pulmonary valve stenosis; alternatively, as was done in 1 neonate in this series with critical aortic stenosis, use of venous inflow occlusion with a short period of circulatory arrest allows performance of an aortic valvotomy. Use of CPB can also be avoided in infants and children with univentricular physiology who need a bidirectional cavopulmonary shunt by temporary insertion of a superior vena cavaright atrial shunt. Use of such a shunt may not be necessary in the occasional patient with bilateral superior venae cavae and a bridging vein in whom bilateral bidirectional cavopulmonary shunts are created in a sequential fashion.
Concern that hemodilution may lead to inadequate oxygenation in the infant on CPB and in the early postoperative period [7] prompted us to use moderate hypothermia and set a tentative limit of no less than 16% for the Hct on CPB in infants or children of Jehovah's Witnesses, although in older children and adolescents (body weight, 9.1 to 63 kg), others [3] have reported an Hct of 10.5% during CPB without untoward postoperative effects. Moderate hypothermia should decrease oxygen consumption to approximately 25% of normal [2]. Hypothermia, on the other hand, increases viscosity of blood, peripheral vascular resistance, and arteriovenous shunting, thereby impairing peripheral perfusion and oxygenation. However, hemodilution counteracts and offsets these effects of hypothermia [8, 9]. There was no evidence of impaired tissue perfusion or inadequate oxygen delivery in the patients in our study, as reflected by an adequate pH, arterial oxygen tension, venous oxygen tension, and urinary output. We did not experience any difficulty in weaning from CPB in terms of prolonged CPB or inotropic support.
We were concerned that crystalloid hemodilution might cause cardiac, cerebral, and pulmonary edema with its resulting untoward effects on the physiology of these organs [8]. Addition of plasma proteins may be effective in decreasing extravascular water [10]; therefore we added 25% albumin to the priming solution. None of the 9 patients who underwent CPB had development of cardiac edema to such an extent that it precluded chest closure. Also, crystalloid hemodilution did not grossly interfere with cerebral or pulmonary function, as manifested by absence of detrimental neurologic sequelae in all patients and early extubation (mean time, 27 ± 11 hours) in 8 of the 9 patients who underwent CPB, respectively. Hemodilution also facilitated postoperative diuresis and reduced the requirement of diuretic medication to maintain urinary output.
Clotting abnormalities after cardiac operations are most critical in the presence of polycythemia. In our patients, as in two other reports [2, 3], measured postoperative blood loss was greater in polycythemic than nonpolycythemic patients; this may have been caused mainly by the greater dilution by pump priming solution in the former group. None of the patients required reexploration for surgical bleeding. Early return of clotting factors and their rapid concentration with diuresis were probably the most important measures for preserving clotting capacity.
The moral and ethical concerns about repair of congenital heart defects in children of Jehovah's Witnesses are monumental because the child is undergoing the risk of an open heart operation without blood because of the parents' consciences and cognitive choices. Without ignoring this concern, we show great respect for the parents' religious belief and make a strong effort to avoid the use of blood products in their children. As a result of this intent not to use blood products, they have, in fact, not been required in this experience. This intent and the careful selection of patients in terms of body weight, some of whom require treatment with erythropoietin, have made it possible to test the limits of hemodilution without introducing additional mortality and morbidity.
We have expanded our policy to try to avoid the use of blood products in cardiac operations on infants and children with a body weight of 5 kg or more who need repair of congenital heart defects with CPB and whose parents are not of the Jehovah's Witness faith. In these patients, we use only blood to prime the CPB circuit when the predicted Hct on CPB is less than 20%. When the use of blood cannot be avoided, we strive for use of donor-directed blood. Employment of the techniques outlined and additional use of cell-saving techniques generally result in minimal homologous blood transfusion requirements in these patients.
In summary, it is gratifying that perfection of surgical techniques and continual improvements in perfusion and cell-saving technology have steadily lowered the risk of CPB and cardiac operations in infants and children. Although the patients in this series represent a select group, currently available technology generally allows correction of congenital heart defects with CPB and without the use of blood in patients with a body weight of 5 kg or more. In symptomatic neonates and infants with a lower body weight, initial palliative procedures circumvent the use of CPB and allow secondary correction of the defect at a later time.
| Footnotes |
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| References |
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