Postoperative aprotinin: Effect on blood loss and transfusion requirements in cardiac operations

Postoperative Aprotinin: Effect on Blood Loss and Transfusion Requirements in Cardiac Operations Serta~ (~i~ek, MD, Ufuk Demirkili~, MD, Erkan Kuralay, MD, Ertugrul Ozal, MD, and Harun Tatar, MD Department of Cardiovascular Surgery, GATA Giilhane School of Medicine, Ankara, Turkey

Background. Aprotinin has been used increasingly to reduce postoperative blood loss in open heart operations. Although it was reported as safe in earlier studies, the overall safety of prophylactic use has been questioned recently. Because of the potential for complications and the high cost, it will be reasonable to use aprotinin more selectively in the postoperative period. Methods. We prospectively studied the effect of postoperative low-dose aprotinin (2 million kallikrein inactivator units [280 mg]) on blood loss and transfusion requirements in patients undergoing cardiopulmonary bypass. Seventy-five patients were randomly assigned to three groups: prophylactic high-dose aprotinin (group 1), postoperative aprotinin (group 2), or a nonmedicated control group (group 3). Results. The three groups were comparable in all

demographic and operative variables. Postoperative chest tube drainage was significantly decreased in both aprotinin groups compared with that in the control group (295 mL in group 1 and 325 mL in group 2 versus 411 mL in group 3; p < 0.05). No significant difference was seen between the two aprotinin groups. The use of homologous blood products was significantly less in group I and group 2 than in group 3 (1.15 + 1.13 U and 1.35 ± 1.30 U versus 2.55 ± 1.09 U; p < 0.05). Conclusions. Our results suggest that postoperative aprotinin reduces blood loss and transfusion requirements comparably with prophylactic high-dose aprotinin. Thus, one can restrict its use to patients with excessive postoperative bleeding.

he control and modification of the adverse effects of cardiopulmonary bypass (CPB) on the hemostatic system continue to be an area of major interest. Of the pharmacologic agents used to preserve hemostasis during CPB, the serine protease inhibitor aprotinin appears to be the most promising. Prophylactic use of aprotinin has been shown to decrease postoperative blood loss and transfusion requirements in patients undergoing cardiac operations with extracorporeal circulation [1, 2]. Since the first description of high-dose aprotinin for prophylaxis against excessive postoperative bleeding, numerous studies with different dose protocols have been conducted, with impressive results [2-6]. One point in common in these studies has been the application of aprotinin before and during CPB to prevent platelet activation and fibrinolysis. Although earlier studies reported few side effects related to the use of the drug, more recent studies have questioned its overall safety for prophylactic systemic therapy. With increasing systemic use have come higher incidences of adverse effects on aorta-coronary bypass graft patency, anaphylactic reactions during subsequent exposures, renal impairment, and disseminated intravascular coagulation after profound hypothermia [7-9]. Furthermore, the high cost of aprotinin restricts routine

prophylactic use in many centers, especially in the United States because of potential limitations in reimbursement to all health care providers [10]. It has been reported that excessive postoperative bleeding is seen in 5% to 25% of patients undergoing CPB, but in only 3% to 5% of all patients requiring reoperation for bleeding [11, 12]. This supports our contention that the majority of patients who are treated with aprotinin are unnecessarily exposed to the side effects of the drug. This problem has already led investigators to research alternative means of applying aprotinin on a selective basis. We developed the concept of topical aprotinin use in the pericardial cavity to prevent the adverse reactions to systemic aprotinin and to eliminate the need for prophylactic use [13]. Another effective strategy to achieve these goals would be to restrict the use of aprotinin exclusively to patients with established postoperative bleeding. Angelini and colleagues [14[ reported that aprotinin given postoperatively in 6 cases reduced bleeding that had failed to respond to conventional treatment. More recently, Kallis and associates [15] demonstrated that postoperative use of aprotinin in patients with established bleeding reduced blood loss. However, the effect of aprotinin once the fibrinolysis is in progress and platelets are activated is not well clarified and remains to be determined. This prospective, randomized clinical study was performed to investigate the effect of aprotinin given after CPB on postoperative blood loss.

T

Accepted for publication Jan 10, 1996. Address reprint requests to Dr ~iffek, Sectionof CardiovascularSurgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905. © 1996 by The Society of Thoracic Surgeons Published by Elsevier Science Inc

(Ann Thorac Surg 1996;61:1372-6)

0003-4975/96/$15.00 PlI S0003-4975(96)00058-6

Ann Thorac Surg 1996;61:1372-6

Patients and Methods This study was performed on patients scheduled for elective cardiac operations with CPB at the GATA Department of Cardiovascular Surgery. Informed consent was obtained from all patients. Patients who received platelet-active drugs within 7 days of operation, who were taking anticoagulant agents, or who had any kind of bleeding diathesis were excluded from the study. Seventy-five patients (62 male and 13 female) were randomly assigned to three groups intended to comprise 25 patients each: Group 1 was the high-dose aprotinin group. The patients received a bolus of 2 × 106 kallikrein inhibiting units (KIU) of aprotinin (280 mg) (Trasylol; Bayer AG, Leverkusen, Germany) after the Swan-Ganz catheter was introduced, plus a maintenance dose of 0.5 × 106 K I U / h (70 mg/h) until the end of the operation. In addition, 2 × 106 KIU (280 mg) was added to the oxygenator priming fluid. Group 2 was the postoperative aprotinin group. The patients received a bolus of 2 × 106 KIU aprotinin (280 mg) at the end of the procedure before transfer to the intensive care unit. Group 3 was a nonmedicated control group. Operative procedures performed in groups 1, 2, and 3 were as follows: coronary artery bypass grafting in 16, 21, and 17; aortic valve/mitral valve replacement in 6, 2, and 6; and adult congenital operations in 3, 2, and 2, respectively. All patients were operated on and cared for by the same team. The anesthetic management and conduct of CPB were standardized. The extracorporeal circuit consisted of a hollow-fiber membrane oxygenator (Terumo Copiox E; Terumo Co., Tokyo, Japan). Polyvinyl chloride tubing was used throughout the circuit except for the roller pump tubing, which was silicone rubber. Before CPB, the patients were given 300 U/kg bovine lung heparin; whenever the activated clotting time (ACT) was shorter than 480 seconds, additional doses of heparin were given. All measurements were performed using a Hemochron 400 (International Technidyne Co, Edison, NJ). The ACT was measured using standard ACT tubes (CA 510; International Technidyne Co) with 2 mL of blood. Mild to moderate hypothermia, cold crystalloid cardioplegia (Plegisol; Abbott Laboratories, Chicago, IL) for induction, and cold blood cardioplegia for maintenance every 20 minutes were infused for myocardial protection. Before declamping the aorta, we administered warm blood cardioplegia (500 mL at 37°C). The cardioplegic solution (either crystalloid or blood cardioplegic solution) was returned to the circuit. Left internal m a m m a r y artery grafts were used routinely in patients undergoing coronary artery bypass grafting. The saphenous vein was harvested as needed. The left pleural space was opened during internal m a m m a r y artery harvesting and was emptied as far as possible by suction before chest closure. During systemic heparin administration, blood was routinely returned to the pump-oxygenator and reinfused. Finally, all blood remaining in the venous tubing and in the oxygenator after CPB was collected and reinfused when necessary, intraoperatively or in the intensive care

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unit. At the end of CPB, heparin was reversed with protamine sulfate at a 1:1 ratio. Hemoglobin, hematocrit, platelet count, prothrombin time, activated partial thromboplastin time, fibrinogen level and D-dimers were measured in all patients preoperatively and when they arrived in the intensive care unit. D-dimers were measured by enzyme-linked immunosorbent assay (Asserachom D-dimer; Diagnostico stago, Asni~res, France). Intraoperative blood loss was measured by adding the volume of the blood in the suction and the weight of the sponges. The shed mediastinal blood was collected in a commercially available volumetric collection system, and the amount was measured every half hour for the first day and hourly thereafter. The mediastinal and thoracic drains were removed when the total drainage was less than 100 mL over the previous 8 hours. Homologous packed red blood cells were administered only when the hematocrit value fell to less than 24%. Patients received fresh frozen plasma when excessive blood loss was accompanied by a prolonged (greater than 1.5 times the normal value) prothrombin time; additional protamine was administered if the ACT/control ratio was more than 1.5. Platelet transfusions were not used. Autotransfusion of shed blood was not used in any of the patients during this study. Reoperation for bleeding was undertaken if the blood loss exceeded 500 mL for 2 consecutive hours without signs of decrease despite appropriate therapy. Cardiopulmonary bypass time, total operation time, amount of total chest tube drainage, incidence of reoperation for bleeding, cause of bleeding, and need for donor blood transfusion or fresh frozen plasma were recorded for all patients. The course of the blood hemoglobin content during hospitalization was analyzed in each patient. For diagnosis of perioperative myocardial infarction, we used postoperative electrocardiograms and serial measurements of creatine kinase myocardial band isoenzymes. All results are expressed as the mean and standard deviation. Results were compared by analysis of variance with subsequent pairwise comparisons according to Duncan's multiple range test. A p value less than 0.05 was considered statistically significant. Statistical analyses were done using the Nwastatpak (Northwest Analytical, Inc, Portland, OR) statistical software package.

Results There were no statistically significant differences among the three groups with regard to age, sex, CPB time, and duration of operation. In addition, the number of bypass grafts and the number of internal m a m m a r y arteries used per patient in coronary artery bypass graft operations were not statistically different among the groups (Table 1). The types of operative procedures performed were also similar in the three groups. There were no significant differences among the groups in postoperative hemodynamic indices, duration of intensive care, or postoperative hospital stay (data not shown). One patient was

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Ann Thorac Surg 1996;61:1372-6

Table 1. Patient Characteristics a

Variable n

Age (y) Male/female CPB time (min) Number of grafts Number of IMAs

Group 1

Group 2

Group 3

25 44.9 +_18.6 22/3 73.0 _+25.6 3.0 + 1.1 0.9 ± 0.3

25 52.8 ± 12.4 19/6 68.0 + 37.2 2.6 + 1.2 1.0 + 0.0

25 46.7 _+ 15.0 21/4 59.0 ± 34.2 2.4 ± 1.1 0.9 ± 0.2

a Values are mean ± standard deviation or n. No significant differences were observed in patient characteristics. CPB = cardiopulmonary bypass; IMAs= internal mammary arteries.

r e o p e r a t e d on for excessive b l e e d i n g in group 2. A n anastomotic site responsible for b l e e d i n g was identified. There were no cases of renal i m p a i r m e n t or allergic reactions to aprotinin. U p o n o p e n i n g the chest, we could not observe any difference visually a m o n g the three groups with r e g a r d to b l e e d i n g from the operative field. A l t h o u g h intraoperative b l o o d loss was lower in group 1 than in group 2 or group 3, this did not reach statistical significance (448 mL versus 595 mL versus 546 mL, respectively). The p o s t o p erative chest tube drainage for the first 24 hours a n d until r e m o v a l of the chest tubes is shown in Table 2. Significantly r e d u c e d postoperative chest tube drainage was found in b o t h the high-dose a n d postoperative aprotinin groups c o m p a r e d with that in the n o n m e d i c a t e d control group (p < 0.05) after the first 24 hours a n d at chest tube removal. No significant difference was seen b e t w e e n the aprotinin groups (295.0 + 161.9 mL versus 325.0 + 237.4 mL). The use of b a n k e d donor blood products intraoperatively was not significantly different a m o n g the groups. However, the transfusion r e q u i r e m e n t was significantly lower in the h i g h - d o s e a n d postoperative aprotinin groups than in the control group, again with no difference found b e t w e e n the aprotinin groups (see Table 2). O n l y 34% of a p r o t i n i n - t r e a t e d patients (32% in group 1 a n d 36% in group 2) r e q u i r e d d o n o r b l o o d or b l o o d products, c o m p a r e d with 60% of those in the control group. Significant increases in fibrin split p r o d u c t D - d i m e r levels were o b s e r v e d postoperatively in comparison with p r e o p e r a t i v e concentrations in all groups. However, postoperative D - d i m e r concentrations were significantly lower in the two aprotinin groups c o m p a r e d with the control group (0.7 ~ 0.1 ~ g / m L versus 1.0 + 0.3 /J,g/mL versus 2.6 + 0.7 /~g/mL; p < 0.01). Although D - d i m e r levels were lower in group I than in group 2, this d i d not reach statistical significance. There were no statistically significant differences a m o n g the three groups with reg a r d to platelet count, p r o t h r o m b i n time, activated partial t h r o m b o p l a s t i n time, a n d fibrinogen level p r e o p e r a tively a n d early after operation w h e n the patients arrived in the intensive care unit. After h e p a r i n administration a n d d u r i n g CPB, ACTs were significantly higher in group 1, with all patients having ACTs of more than 700 seconds. There was no

evidence of postoperative m y o c a r d i a l infarction as determ i n e d b y electrocardiogram a n d serial m e a s u r e m e n t s of creatine kinase myocardial b a n d i s o e n z y m e s in this s t u d y population. S e r u m creatine kinase m y o c a r d i a l b a n d isoenzyme levels were f o u n d to be elevated postoperatively in all groups. However, the three groups d i d not differ significantly in the p e a k levels (32.2 + 6.3 U/L versus 26.7 ___ 8.1 U/L versus 28.8 + 9.7 U/L).

Comment The efficacy of aprotinin as a hemostatic agent in the setting of cardiac o p e r a t i o n s is indisputable. It has p r o v e n m o r e effective t h a n tranexamic acid [16], c-aminocaproic acid, a n d d e s m o p r e s s i n [10]. Patient selection r e g a r d i n g the use of aprotinin in individuals u n d e r g o i n g CPB r e m a i n s a key question. Because of the potential for complications a n d the high cost of aprotinin, it will be logical to use aprotinin on a selective basis in patients with established bleeding. In the p r e s e n t study, n e i t h e r postoperative b l o o d loss nor transfusion r e q u i r e m e n t s differed significantly between the prophylactic high-dose aprotinin group a n d the post-CPB aprotinin group; b o t h were significantly lower than in the control group. The reduction of postoperative blood loss, to our surprise, is c o m p a r a b l e to that in other studies in which the aprotinin was a p p l i e d prophylactically [2-4]. It has b e e n suggested that aprotinin has a beneficial effect only w h e n given before extracorporeal circulation [1, 17]. However, G r a m a n d colleagues [18] d e m o n s t r a t e d the presence of an e n h a n c e d fibrinolytic state after the neutralization of h e p a r i n in patients u n d e r g o i n g open heart operations. They suggested that substantial a m o u n t s of tissue-type p l a s m i n ogen activator are i n c o r p o r a t e d into fibrin g e n e r a t e d after the neutralization of heparin, a n d t h e r e b y m a y cause d e g r a d a t i o n of cross-linked fibrin until at least 24 hours after operation even t h o u g h tissue-type p l a s m i n o gen activator returns to baseline levels m u c h earlier. It is also k n o w n that activation of fibrinolysis is accelerated 100-fold in the presence of fibrin or fibrin m o n o m e r s [19]. This creates a positive feedback cascade a n d increases the risk of postoperative bleeding. The d e c r e a s e d fibrin split p r o d u c t D - d i m e r levels o b s e r v e d in group 1 a n d

Table 2. Blood Loss and Transfusion Requirements a

Variable

Group 1

Group 2

Group 3

First 24-h chest 255 -+ 117 275 _+203 411 _+151 tube drainage (mL) 295±161 325-+237 b 502-+178 Total chest tube drainage (mL) Blood products 1.15 +- 1.13 1.35 +- 1.30 2.55 -+ 1.09 transfused (U) Percentage of 32 36 60 patients having transfusion Values are mean ± standard deviation or percent, reentry for operative bleeding.

p Value <0.05 <0.05 <0.05 <0.01

b Including one

Ann Thorac Surg 1996;61:1372-6

group 2 indicate a lower level of fibrinolytic activity. Whether aprotinin influences hyperfibrinolysis in the early postoperative period can be elucidated by measurement of plasmin release in the plasma. Increased plasmin levels in the plasma reflect fibrinolytic activity, so that quantification of plasmin levels is essential to detect a current fibrinolytic state. Of great interest is a recent report by Kallis and associates [15], who demonstrated the efficacy of aprotinin for hemostasis when used postoperatively on patients with pronounced bleeding. Sixty patients were randomized to receive either aprotinin or placebo in addition to conventional treatment. The patients in the aprotinin group bled significantly less. The tissue plasminogen activator antigen decreased and the fibrinogen level increased in the aprotinin group. In addition, aprotinin increased the platelet surface expression of glycoprotein Ib (36% versus 5%; p < 0.01) and maintained the platelet von Willebrand factor activity. Kallis and associates suggested that aprotinin, by inhibiting excessive fibrinolysis and reducing plasmin levels, allows replenishment of the platelet surface glycoprotein Ib receptors from intraplatelet pools. Michelson and Barnard [20] also showed that platelets recover from plasmin as soon as it is neutralized by redistribution of the platelet glycoprotein Ib receptor. Thus, postoperative aprotinin m a y restore platelet function in addition to its direct antifibrinolytic effect. Endothelial cells play an important role in the regulation of hemostasis. Protein C is a major regulatory protein of thrombus formation; it also promotes fibrinolysis by inactivating the plasminogen activator inhibitors [21]. Aprotinin has been shown to inactivate protein C [22]. Boldt and associates [23] suggested that aprotinin contributes to preserve endothelial function during CPB. Postoperative aprotinin m a y also exert an antifibrinolytic action by modulating endothelial cell function. However, the complex interactions a m o n g the fibrinolytic system, platelets, and the endothelial aspects of coagulation, and the effect of aprotinin on these systems when applied postoperatively, require more comprehensive investigations. It has been shown that a much lower dosage is required to inhibit the enzyme activity of plasmin as compared with plasma kallikrein (50 versus 200 KIU/mL [7 versus 28 txg/mL]) [24]. In the present study, we used the low-dose regimen (2 million KIU [280 mg]) because low-dose aprotinin is sufficient to obtain the required antiplasmin effect and to preserve glycoprotein Ib receptors [24, 25]. Despite the small size of our patient population, our study shows that even when administered after activation of the hemostatic system, aprotinin is effective in reducing blood loss. The data from the current study, combined with those of Kallis and associates [15], suggest that its mode of action seems to be not only the inhibition of fibrin degradation, but also stabilization of the hemostatic plug through the enhancement of platelet surface receptors and preservation of von Willebrand factor levels. These results suggest that aprotinin could be used

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in patients with post-CPB bleeding refractory to conventional treatment. The comparable efficacy of postoperative infusion also allows us to minimize the overzealous use of prophylactic aprotinin and to restrict its use to patients with established postoperative bleeding. However, because our patient population is at the lower end of the bleeding-risk spectrum and the routine use of aprotinin in this group is not advocated, the results cannot simply be applied universally. Higher-risk patients need to be investigated regarding the comparative efficiency of postoperative aprotinin administration.

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end und nach Operation mit Hilfe der Herz-LungenMaschine. Thoraxchirurgie 1973;21:534-43. Gram J, Janetzko T, Jespersen J, Bruhn HD. Enhanced effective fibrinolysis following the neutralization of heparin in open heart surgery increases the risk of post-surgical bleeding. Thromb Haemost 1990;63:241-5. Lucas FV, Miller ML. The fibrinolytic system. Cleve Clin J Med 1988;55:531-41. Michelson AD, Barnard MR. Plasmin-induced redistribution of platelet glycoprotein lb. Blood 1990;76:2005-10. Dahlback B. The protein C anticoagulant system: inherited defects as basis for venous thrombosis. Thromb Res 1994;77: 1-43. Espana F, Estelles A, Griffin JH, Aznar J, Gilabert J. Aprotinin

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(Trasylol) is a competitive inhibitor of activated protein C. Thromb Res 1989;56:751-6. 23. Boldt J, Zickman B, Schindler E, Welters A, Dapper F, Hempelmann G. Influence of aprotinin on the thrombomodulin/protein C C system in pediatric cardiac operations. J Thorac Cardiovasc Surg 1994;107:1215-21. 24. Fritz H, Wunderer G. Biochemistry and applications of aprotinin, the kallikrein inhibitor from bovine organs. Arzneimittelforschung 1983;33:479-94. 25. Van Oeveren W, Harder MP, Roozendaal KJ, Eijsman L, Wildevuur CRH. Aprotinin protects platelets against the initial effect of cardiopulmonary bypass. J Thorac Cardiovasc Surg 1990;99:788-97.

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