Transfusion-Free Cardiac Reoperation in an 11-kg Jehovah’s Witness Child by Use of a Minimized Cardiopulmonary Bypass Circuit
Abstract: Herein, we describe the design of a perfusion system for a complex cardiovascular reoperation in an 11-kg Jehovah’s Witness patient. The goal of safe, transfusion-free surgery was achieved chiefly by minimizing the priming volume of the cardiopulmonary bypass circuit to 200 mL while providing adequate flow and standard safety features.
Cardiac surgery involving cardiopulmonary bypass (CPB) in Jehovah’s Witness patients presents a challenge to the surgical team. Particularly in pediatric cardiac surgery, the goal of safe, transfusion-free surgery is often defeated by the extreme hemodilution caused by the relatively large priming volume of the CPB system and by the potential blood loss during complex surgical procedures.
Herein, we describe the successful performance of complex cardiac reoperation in an 11-kg Jehovah’s Witness patient. Safe, transfusion-free surgery was enabled by extreme minimization of the CPB system through the use of a modified small-volume neonatal circuit.
Case Report: A 2-year-old girl, a child of Jehovah’s Witness parents, was admitted to our institution in February 2006 with corrected tetralogy of Fallot and absent pulmonary valve syndrome. When the child was 7 days old and weighed 3.55 kg,1 we had closed the ventricular septal defect, implanted a 12-mm valved Contegra conduit (Medtronic, Inc.; Minneapolis, Minn), and resected a left pulmonary artery (PA) aneurysm—all without blood transfusion. After 2 years and a tripling of body weight, the child now had a grown-out stenosis with a gradient of 60 mmHg between the right ventricle and the main PA, pulmonary valve regurgitation, and dilation of the right PA to 35 mm. We replaced the 12-mm Contegra conduit with a 16-mm conduit, and we further reduced the aneurysmal right PA.
The patient weighed 11 kg, and her height was 88 cm. Her calculated body surface area was 0.5 m2, and her calculated blood volume was 850 mL. Her preoperative hemoglobin value (Hb) was 12.8 g/dL (hematocrit [Hct], 38.4%). Accordingly, the use of our standard CPB circuit for an infant who weighed more than 7 kg would have required a priming volume of approximately 450 mL (Table I), resulting in a maximum Hb value of 7.5 mg/dL (Hct, 22.5%) during CPB (Fig. 1). Because this was a reoperation, and because of the likelihood of increased blood loss during reoperation and of subsequent hemodilution before CPB, we believed that the safety margin for use of this CPB circuit would be too small. Therefore, we decided to modify our neonatal CPB system so that it would require a priming volume of only 200 mL, to allow for the higher flow needed for this child.
The CPB circuit was redesigned as follows. Cannulation was performed with a 12F aortic cannula, and bicaval cannulation was done with 16F and 18F metal-tipped cannulas. We then modified a Stöckert SIII mast-mounted console (Stöckert Instrumente GmbH; Munich, Germany), which we usually use for neonates and infants. We made short tubing connections from the venous reservoir outlet to the arterial pump head and to the oxygenator/heat-exchanger inlet, and from the sucker-pumps to the cardiotomy reservoir inlet. We used polyvinylchloride tubing of 3/16-inch internal diameter (ID) in the entire extracorporeal circuit except for the arterial pump runway, where we used 1/4-inch-ID silicone tubing. In the 1st operation on the child, we had used the Polystan Safe Micro oxygenator (Polystan A/S, a Maquet Inc. company; Vaerløse, Denmark), which requires a priming volume of 52 mL. The maximal blood flow rate of this oxygenator is 0.8 L/min, which, if used in this reoperation, would have resulted in a maximal blood flow of only 1.6 L/m2. We therefore replaced this system by using the Capiox Baby RX05 oxygenator (Terumo Cardiovascular Systems; Ann Arbor, Mich), which requires a priming volume of 43 mL but allows a higher maximum blood flow of 1.5 L/min, resulting in a maximal blood flow of 3 L/m2 in our patient. In addition, we implemented vacuum-assisted venous drainage with a maximum negative pressure of 40 to 50 mmHg in order to achieve a venous return of 3 L/min per m2, and an arterial filter (Dideco D 736, Sorin Group Italia S.r.l.; Mirandola Modena, Italy) with a priming volume of 40 mL, resulting in a total priming volume of 200 mL. For this system, the calculated Hb value on CPB was calculated to be 10 g/dL (Hct, 30%).2,3
The patient was taken to surgery. To provide maximal protection of her coagulation system during CPB, we managed heparin and protamine dosages by use of the Hepcon HMS™ system (Medtronic), and administered aprotinin (Trasylol®, Bayer; Frankfurt, Germany) in accordance with a high-dose regimen (500,000 KIU) in the pump and a continuous infusion of 75,000 KIU/hr during perfusion.
The patient’s Hb value immediately before CPB was 11.6 g/dL (Hct, 34.8%). During the 84 minutes of CPB, the highest Hb value was 11.4 g/dL (Hct, 34.2%), and the lowest was 9.4 g/dL (Hct, 28.2%). The rate of blood flow ranged from 2.6 to 3 L/m2, and the blood lactate levels were within the normal range of less than 2 mg/dL. Venous oxygen saturation, which ranged from 67% to 85% in intermittently drawn samples, correlated well with near-infrared spectroscopic measurements (NIRO-200, Hamamatsu Photonics K.K.; Hamamatsu City, Japan) taken at the child’s head. Despite the relatively small diameter of the tubing of the venous line, the negative pressure required to augment the venous return was consistent with the values reported by others.2,3 With respect to hemolysis, the very small diameter of the arterial line was at the limit of acceptability, but arterial line pressures, measured before the line entered the oxygenator, remained between 350 and 450 mmHg (departmental standard range, 350–470 mmHg). The intensive use of cardiotomy suction in this special reoperation was potentially a major cause of hemolysis; however, no macrohematuria was noted. The replacement of the 12-mm Contegra conduit with a 16-mm conduit and the reduction of the aneurysmatic right PA to 12 mm from the pulmonary hilus to the bifurcation were performed with the patient on normothermic, beating-heart CPB. After venous decannulation, we infused the volume of the venous line, reservoir, and oxygenator into the patient, then directly reinfused the residual volume from the arterial filter and the arterial line.
After the administration of protamine, desmopressin (0.04 μg/kg) was given to stimulate tissue-factor release and improve coagulation. Modified ultrafiltration was not performed, because priming of the filter system would have caused additional hemodilution. After the completion of CPB and the complete re-transfusion of the CPB blood, the circuit was flushed with 1,000 mL of saline solution, which was then processed with a cell saver (Autolog; Medtronic). The 135-mL product, which had a Hb value of 5.5 g/mL (Hct, 16.5%), was returned to the patient after the stimulation of diuresis.
The patient was transferred to the intensive care unit with a Hb level of 10.1 g/dL (Hct, 30.3%). The postoperative activated clotting time was 125 sec, and the postoperative 24-hr blood loss was 20 mL. The patient was weaned from mechanical ventilation on the same day. The postoperative course was uneventful, and the patient was discharged from the hospital after 10 days. Therapy with supplemental iron and recombinant erythropoietin, which had been started 4 weeks before surgery, was continued postoperatively for 4 weeks.
Discussion: Reducing the hemodilution of the CPB circuit is the key to safe cardiac surgery in pediatric Jehovah’s Witness patients. Our patient’s case was complicated by a low preoperative Hb value, so the dilution imposed by a larger system would have created the need for transfusion. In a selected group of patients with cyanotic malformations, a high preoperative Hb value often facilitates safe, transfusion-free cardiac surgery.4 However, in patients with non-cyanotic malformations, the composition of the CPB circuit and the resultant priming volume becomes the central determinant for such surgery.
At our institution, we use CPB systems with a priming volume of 180 to 200 mL for neonates and small children with body weight of 2 to 6 kg. In children who weigh 7 to 20 kg, we usually apply an oxygenator with a higher capacity in combination with extracorporeal tubing of larger diameter, which increases the priming volume to approximately 450 mL. Consequently, a patient’s higher preoperative weight can be associated with a higher degree of hemodilution and a subsequent reduction of intraoperative Hb values (Fig. 1). In 2003, Jonas and colleagues5 found impaired neurocognitive development in infants whose intraoperative Hct levels had fallen below a critical value of 20% to 25% during hypothermic CPB.
These data and the Hb values expected in our patient if a conventional circuit were used prompted our decision to modify the system used for neonates. We considered our modified system safe, because the maximal blood flow rate in our patient was increased to 3 L/m2 (1.5 L/min) by replacing the standard oxygenator and using vacuum-assisted venous return—and, in contrast with systems described by other groups, ours incorporated safety features such as an arterial filter. Despite a reduction of the priming volume to 200 mL, the calculated Hb value was 10 g/dL (Hct, 30%).6
As evidenced by the baseline blood lactate levels, venous oxygen saturation, and near-infrared spectroscopic data, use of this circuit maintained homeostasis in the patient during the entire course of extracorporeal circulation. Blood flow was in the range of 2.5 to 3 L/m2, and Hb levels stayed within a safe range—between 9.5 and 11 g/dL (Hct, 28.5%–33%).
We believe that our modified CPB system and a priming volume of 200 mL allows the safe performance of normothermic CPB in patients who weigh approximately 11 kg and have a body surface area of 1 m2 or less, corresponding to a maximum calculated blood flow of 1.5 L/min. On the basis of our earlier experience with pediatric Jehovah’s Witness patients7 and with our current patient, we conclude that optimized, low-prime CPB circuits enable safe, transfusion-free, complex cardiac surgery regardless of the patient’s weight. Therefore, particular emphasis should be placed on the development of such specially designed circuits for pediatric patients of all weights.
References:
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