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J Thorac Cardiovasc Surg 1994;108:437-445
© 1994 Mosby, Inc.
CARDIOPULMONARY BYPASS, |
Cleveland, Ohio
Supported in part by grant HL-16361 from the National Heart, Lung, and Blood Institute, National Institutes of Health.
Received for publication Aug. 10, 1993. Accepted for publication Feb. 14, 1994. Address for reprints: John R. Shainoff, PhD, Research Institute NC3, Cleveland Clinic, 9500 Euclid Ave., Cleveland, OH 44195.
Abstract
Current hematologic approaches to minimize postoperative bleeding have focused principally on antifibrinolytic agents. To explore whether a need might exist to promote clot stabilization independent of steps that might be taken to prevent lysis, we followed levels of the functional A-chain of factor XIII (fibrin stabilizing factor) immunologically in 19 patients undergoing coronary artery bypass grafting. The levels of factor XIIIA together with alterations in fibrinogen were followed at five stages of operation: (1) initial catheter placement (control), (2) heparinization, (3) initiation of cardiopulmonary bypass, (4) discontinuation of cardiopulmonary bypass, and (5) heparin neutralization with protamine sulfate. Significant (p < 0.05) inverse correlations were observed between postoperative chest-tube drainage volumes and levels of XIIIA at stages 1 through 3, and borderline associations (p < 0.1) were observed for stages 4 and 5. Pronounced losses of factor XIIIA accompanied initiation of cardiopulmonary bypass, when levels fell to 43%±12% (standard deviation) of the control value, significantly below the 59%±9% of the control value expected from hemodilution. By comparison, fibrinogen concentrations fell only to the extent attributable to hemodilution, unaccompanied by substantial degradation as indicated by electrophoretic, functional, and immunologic assays. There was a reversible heparin-induced precipitation of fibrin complexes and fibrinogen dimers from the blood on initiation of hypothermia, but these components returned to the circulation on restoration of normothermia. This precipitation was unrelated to losses of factor XIIIA. The findings warrant inference that XIIIA supplementation in deficient states should be considered as an adjunct to other therapies for postoperative bleeding. (J THORAC CARDIOVASC SURG1994;108:437-45)
Because of risks associated with transfused blood, strong attention is being directed to minimizing blood loss during and after cardiothoracic surgical procedures.
1 It is well known that cardiopulmonary bypass (CPB) can affect coagulation factors and platelets to predispose bleeding.
2 Recent studies have demonstrated improved hemostasis and reduced blood requirements in patients who received antifibrinolytic agents
3-6 and especially marked improvement with high doses of aprotinin before CPB.
7-11 Yet, postoperative bleeding persists along with formation of "soft clots" in some patients despite the minimization of clot lysis. We sought to determine whether a need might exist to promote the stabilization of clots independent of the steps that can be taken to prevent their lysis. To that end, we followed changes in immunologic levels of the functional A-chain of factor XIII (fibrin stabilizing factor) and made an assessment of the alterations in the condition and concentration of fibrinogen that accompany coronary artery bypass grafting (CABG).
METHODS
Human subjects
The study group included 19 randomly selected adult patients (15 men, 4 women) scheduled to undergo elective primary CABG. Patients on a long-term regimen of ß-adrenergic or calcium entry blockers continued to receive these medications until the morning of the operation. Selection and dosage of the drugs used for anesthetic premedication, induction, and maintenance were determined by the anesthesiologist according to patient condition and were not affected by participation in the study. Anesthetic management was done according to the usual practice in our institution and included electrocardiographic and hemodynamic monitoring. Induction and maintenance of anesthesia were obtained with a combination of narcotics, benzodiazepines, and neuromuscular blockers with supplemental administration of low concentrations of a potent inhalational agent (enflurane or isoflurane) when appropriate. At the election of the surgeon, CPB was done with the use of hypothermia (28° C) in 14 patients and normothermia (35° C) in 5 patients with no consideration for interests of this study. There were no deviations from the usual standards of care during the entire perioperative period.
Laboratory analyses done for this study required only fractional milliliter quantities of blood, which were derived from portions that would ordinarily be discarded from samples taken as part of routine monitoring of the hematocrit value, blood gases, and coagulation status of the patients during the operation. The analyses were made on blood samples taken (1) at the initial catheter placement before heparinization, (2) after the heparinization (initially 300 U/kg, followed by titration to produce an approximately 480-second activated whole blood clotting time), (3) after initiation of CPB, (4) at completion of operation and discontinuation of CPB, and (5) after heparin neutralization with protamine sulfate. Because no special or additional blood samples were taken, and because the study involved no deviations from standard protocols for CABG regularly used by the departments of cardiothoracic surgery and anesthesia at the institution, it qualified for exemption No. 5 under National Institutes of Health guide lines.
Blood loss
The extent of postoperative bleeding was estimated from the recorded volumes of chest-tube drainage collected over a 24-hour period in the intensive care unit after operation. Measurements of intraoperative blood loss, from accounts of aspirated blood and sponge weights,
12 would have imposed significant changes inprotocol.
13 The blood conservation techniques currently used at our institution allow the return of all the blood collected intraoperatively in the extracorporeal circuit and suction bottles, and these conservation techniques were applied without deviation, as described.
14
Calculations of the theoretic dilutions of fibrinogen that would be expected from hemodilution during CPB were based in part on (1) the calculated change in plasma protein concentrations (PD/PU, diluted/undiluted) as a function of change in hematocrit (HD and HU, percent blood volume) that would accompany a simple dilution of the blood without any reequilibration (PD/PU = [HD(100 - HU)]/[HU(100 - HD)]) and (2) an adjustment based on consideration that approximately 20% of the total fibrinogen is extravascular and would reequilibrate with the diluted plasma.
15,16 Thus the expected percentage of initial concentration (%Co) would be given by %Co = 20% + 80%(PD/PU). The percentage extravascular exchangeable factor XIIIA has not been determined, but may be the same as that of fibrinogen because of indications that it circulates in association with fibrinogen.
17
Laboratory materials
Purchased media for electrophoretic characterizations of fibrin(ogen) were as described in previous studies,
18,19 as were the substances used as preservatives of the blood samples (aprotinin, heparin, glycylprolylarginine [GPR]). Purified recombinant factor XIIIA (rXIIIA) from yeast was a gift from Dr. Paul Bishop (Zymogenetics, Seattle, Wash.). Proteins prepared in-house were fibrinogen and antibodies to it and its component polypeptide chains, as described.
18
Assays
Blood samples were taken into Vacutainer tubes (Becton Dickinson Inc., Oxnard, Calif.) that contained ethylenediaminetetraacetic acid (EDTA), except for samples for determination of fibrinogen by the Clauss
20 method, for which citrate was used as the anticoagulant. The samples were centrifuged within 2 hours after the operation, and a portion (0.2 ml) of each EDTA/plasma sample was diluted with an equal volume of preservative cocktail that contained 10 U/ml heparin, 0.24 TIU/ml aprotinin, and 5 mmol/L GPR for the electrophoretic and immunologic analyses. For sodium dodecylsulfate (SDS) electrophoresis, 50 µl portions of the diluted samples were diluted further in half (
overall) with 4% SDS that contained 2% mercaptoethanol, and another portion was diluted with SDS without mercaptoethanol.
Factor XIIIA levels were determined by enzyme-linked immunosorbent assay with commercial goat antihuman factor XIII (A-chain and B-chain) antibodies (American Diagnostica Inc., Greenwich, Conn.) applied (18 hours, 4° C) at a level of 5 µg/ml (0.1 ml, 0.05 mol/L Tris buffer in 0.15 mol/L NaCl at pH 9.2) to coat as the "capture antibody" on 96-well flexible assay dishes (Falcon MicroTest III, Becton Dickinson Inc.), which were subsequently blocked (3 hours, 37° C) with 3% bovine serum albumin in phosphate-buffered saline containing 0.05% Tween 20 (PBS-Tween). Samples at four dilutions (1, 0.75, 0.5, and 0.25 x 1:1000) and standard plasma (CTS standard plasma, Behring Diagnostics, Inc., Somerville, N.J.) and rXIIIA (2 ng/ml to 1 µg/ml) in PBS-Tween with 4 mmol/L EDTA were applied (0.1 ml) and then washed after 18 hours at 4° C. The captured antigen was then measured by incubation with polyclonal rabbit antihuman factor XIIIA antibody (Calbiochem Corp., San Diego, Calif.) for 2 hours at 20° C, followed by a rinse and a 2-hour incubation with 0.1 ml of a 1:1000 dilution of horseradish peroxidaseswine antirabbit immunoglobulin G antibodies (DAKO Corp., Cartinteria, Calif.) in PBS-Tween. After washing, the retained horseradish peroxidase was measured from colored peroxidase reaction product formed in 10 minutes from 3.3 µmol/L o-phenylenediamine (Sigma Chemical Co., St. Louis, Mo.) in 0.1 mol/L NA2HPO4/0.05 mol/L citric acid/0.02% H2O2 in the dark at 20° C. Product formation was stopped with 50 µl of 10 N H2SO4 and was measured on a Bio-Tek EL 310 EIA Autoreader (Bio-Tek Instruments Inc., Burlington, Vt.) using dual wavelength settings of 490 and 600 nm. Readings were converted to XIIIA concentrations by calculation from fourth-order polynomial curve fitting (r = 0.99) of concurrently analyzed dilutions of plasma standards, the curve fitting being done by SlideWrite version 5.0 software (Advanced Graphics Software, Carlsbad, Calif.). Because this enzyme-linked immunosorbent assay method has not been described previously, a typical calibration curve relating factor XIIIA concentrations to absorbance is shown (Fig. 1). The factor XIIIA levels in the normal plasma standard (Berichrom normal plasma, Behring Diagnostics) corresponded to 9.3 ± 0.9 µg/ml, determined with the use of rXIIIA as a primary standard.
21 The immunologic levels of XIIIA in dilutions of the plasma standards (Behring Diagnostics) correlated with activity assays performed on them (r = 0.97, n = 12).
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RESULTS
As illustrated (Fig. 2), subjects with high concentrations of plasma factor XIIIA tended to have less than average postoperative bleeding, determined from chest-tube drainage. This inverse relationship was statistically significant (p < 0.05) for the levels of XIIIA measured at stages 1 through 3 (preoperatively through the initiation of CPB), but only bordered on significance (p < 0.1) for stages 4 and 5 (after termination of CPB and administration of protamine). The significant correlations (r = 0.52 and 0.50 at stages 1 and 3) became blunted by a substantial 50% rise in the levels of XIIIA in two subjects who had low values at stage 3.
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A question arose as to whether the fall in levels of factor XIIIA might have been due to a coprecipitation with the macromolecular fibrinogen derivatives, but little coprecipitation was observed in laboratory studies. When fibrin monomer was added to normal heparinized plasma the fibrin remained soluble at concentrations up to 10% of the total fibrinogen while it was held at 37° C, but formed precipitates at levels higher than 0.5% of the fibrinogen when chilled to 25° C. This precipitation of added fibrin monomer, which was verified electrophoretically by the GPR technique,
19 was not accompanied by more than a 10% reduction in plasma concentrations of factor XIIIA, as determined by immunoassay.
DISCUSSION
The findings of this study that we believe to be important were that (1) significant inverse correlations exist between levels of factor XIIIA and postoperative blood loss, (2) losses of factor XIIIA occur during initiation of CPB and result in further reductions in concentrations beyond the effects of hemodilution, and (3) heparin combined with hypothermia mediates a partially reversible precipitation of the elevated concentrations of macromolecular fibrinogen derivatives that occur in blood of patients with coronary artery disease. The correlations between levels of factor XIIIA and amounts of chest-tube drainage were significant only for periods 1 through 3, but we believe that an extended study would demonstrate significance for the finishing stages (4 and 5) as well. The correlations established thus far, though hovering near the p = 0.05 level for rejection of the statistical null hypothesis, can be considered impressive in view of the large number of variables apart from levels of factor XIIIA, particularly fibrinolysis, platelet activation and consumption, and leukocyte activation, which contribute to hemostasis during and after CPB.
7,28-31
Factor XIII is frequently overlooked as a factor for wound healing and control of bleeding, except in cases of inherited deficiencies in which its activity is lacking. That is because supplementation through transfusion of plasma or cryoprecipitate in congenital deficiencies provides a long-lasting benefit for month-long periods until plasma levels fall to within a small percentage of normal. However, needs for wound healing after major operations are not analogous to normal needs. Indeed, recent studies on subjects with heterozygotic congenital deficiencies who had levels of factor XIIIA on the order of 50% of normal indicated that these subjects are prone to bleed excessively after both simple and extensive surgical procedures.
32,33 A large multicenter trial in Japan to assess the effects of supplementation of plasma factor XIII in 71 patients with impaired wound healing indicated that there was significant benefit as determined by an independent committee on review of photographs, radiographs of fistulas, drainage volumes, and wound areas of treated versus untreated subjects.
34
The reason for the fall in factor XIIIA concentrations beyond dilutional decline during initiation of CPB is not known. A possibility that it was coprecipitating with the macromolecular fibrin (ogen) derivatives could not be supported from laboratory studies, but those studies were based on measurements under conditions in which there was negligible proteolytic activation of the XIIIA. Factor XIIIA becomes activated by thrombin in the course of blood coagulation.
35 Because of heparinization, little activation by thrombin would be expected. However, other potential activators released or potentiated by surface phenomena may contribute to the fall. Activated XIIIA could undergo greater coprecipitation with the macromolecular fibrin(ogen) derivatives than that observed with nonactivated XIIIA, because of strengthening of binding to fibrin subsequent to activation.
36
The disappearance of fibrin complexes and fibrinogen dimers from plasma during CPB in patients undergoing hypothermia and the partial reappearance of these derivatives on restoration of normothermia were attributed to incorporation of the derivatives into complexes with heparin, fibronectin, and calcium. We did not measure fibronectin levels in the plasma during CPB, but others have shown that it undergoes large heparin-induced reductions in association with hypothermia.
37 The studies on fibronectin were done with heparin dosages ten times greater than those used in the present study, but laboratory studies by Stathakis and associates
26 showed that fibronectin is an essential component in the heparin-induced precipitation. We suspect that the precipitation occurred within the patients' circulation and was not restricted to the oxygenator, because much of the return of the derivatives occurred after the bypass was discontinued. Recent studies have shown that patients who undergo normothermic systemic perfusion tend to bleed less.
13 Except for the pronounced disappearance of macromolecular fibrin (ogen) under hypothermic conditions, we did not uncover other differences between normothermic perfusion in this study, but suspect that differences would be found in an expanded study, which we believe would be justified in light of the present findings.
The need for homologous blood transfusion associated with CABG has fallen dramatically from the 20 to 30 units required in the early 1950s to about 10 units in the 1960s and early 1970s to only an occasional unit in the early 1980s largely because of improved extracorporeal pumps and oxygenators
38 and improved blood conservation techniques implemented at our institution. However, several factors have evolved in the past decade that have led to a continuing increase in perioperative bleeding in association with cardiac operations. These were accompanied by an increase in frequency of surgical exploration for hemostasis.
Factors independent of bleeding, including advanced age, reduced red cell mass, small body surface area, female gender, and preexisting anemia, have been shown to be associated with an increased need for homologous blood transfusions.
39 Also, complex surgical procedures, reoperations, emergency operations, and preoperative therapy with aspirin or fibrinolytic drugs are associated with increased bleeding.
40-42 They exacerbate the coagulation and platelet abnormalities that accompany the performance of CPB, including activation of complement, fibrinolysis, inadequate reversal of heparin, and heparin rebound. Because more patients undergoing CABG have increased risk factors for bleeding and need homologous blood transfusions, there has been an increased awareness of the potential complications associated with transfused blood, in particular transmission of hepatitis and human immunodeficiency virus infection. Currently used methods to decrease the need for homologous blood supplementation include meticulous hemostasis and intraoperative blood salvage, as well as preoperative autodonation of red blood cells and platelet-rich plasmapheresis. Therapy with deamino-8-D-arginine vasopressin,
-aminocaproic acid, and aprotinin has been used extensively to improve platelet function and inhibit fibrinolysis and serine proteases.
In view of the present findings, low levels of factor XIIIA should be included among the list of risk factors for postoperative blood loss. None of the patients we studied had excessive bleeding, and none received whole blood, plasma, or platelets. We anticipate from case studies already cited that low levels of factor XIIIA will have an additive effect on other causes of bleeding associated with cardiac operations. We found that in 6 of 19 patients XIIIA levels decreased to 30% of normal during CPB. Soft clots and oozing of wounds remain major concerns in postoperative care. It would be of benefit if those concerns could be minimized. When the need for blood supplementation arises, the preventive measures that might have been taken are too late.
The principal goal of the present study was to determine whether levels of postoperative bleeding might be related to levels of factor XIIIA. We view the observed correlations as warranting expanded study. A critical test of the importance of factor XIIIA would be to assess whether supplementation can be of benefit in patients with low levels. The availability of recombinant factor XIIIA now makes it feasible to examine that question
21 and also warrants consideration that supplementation might offer therapeutic or prophylactic advantages for subjects who have low preoperative levels of factor XIIIA or who have excessive postoperative bleeding or poor wound healing. Laboratory studies with preactivated XIIIA indicate that high levels of factor XIII activity do not promote fibrin deposition, but serve to fix fibrin in the form in which it is found.
43,44 It can prevent coagulation of soluble fibrin complexes circulating in the blood by fixing the complexes in soluble form and functioning to stabilize the fibrin that undergoes self-aggregation into a clot.
45,46 In a sense factor XIIIA functions as a molecular surgeon, sewing the molecules together in the form in which they are assembled.
Acknowledgments
David A. Urbanic and Veronica Valenzuela assisted in these studies. Ms. Valenzuela was the recipient of a Summer Student Stipend from the American Heart Association Northeast Ohio Affiliate, Inc.
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