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Ann Thorac Surg 1995;59:438-442
© 1995 The Society of Thoracic Surgeons

Hemostatic Efficacy of Dipyridamole, Tranexamic Acid, and Aprotinin in Coronary Bypass Grafting

Department of Thoracic Surgery, Onze Lieve Vrouwe Gasthuis, Amsterdam, the Netherlands

Accepted for publication October 7, 1994.

	Abstract

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Sixty patients (four groups of 15 patients) were entered in a randomized, controlled study to compare the efficacy of prophylactic treatment with dipyridamole, tranexamic acid, and aprotinin to reduce bleeding after elective coronary artery bypass grafting. Only patients with a preoperative platelet count of less than 246 x 10⁹/L were selected because a previous study showed that these individuals are at risk for increased postoperative bleeding. Compared to control subjects, postoperative blood loss 6 hours after operation was significantly reduced by tranexamic acid (674 ± 411 versus 352 ± 150 mL; p < 0.05) and by aprotinin (270 ± 174 mL; p < 0.01). Dipyridamole did not reduce postoperative blood loss and was associated with complications in 3 patients. We conclude that hemostasis after cardiac operations can be improved with tranexamic acid and aprotinin. Dipyridamole appeared to be ineffective.

	Introduction

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Postoperative hemorrhage as a result of disturbed hemostasis is common in cardiac operations and leads to increased morbidity, exposure to the risk of homologous blood products, and consequently, heavily burdens hospital resources. Various authors reported structural and functional defects in platelets after extracorporeal circulation as a cause of disturbed hemostasis [1, 2]. Particularly, patients with low preoperative platelet counts might be at risk for increased postoperative bleeding [3]. In a prospective study we found a significantly higher blood loss in patients with preoperative platelet counts below the median value of 246 x 10⁹/L [4]. The low platelet counts in this group were not attributable to specific causes such as heparin treatment, infections, or cancer, but reflected the normal variation in platelet numbers.

Improved hemostasis by prophylactic pharmacologic treatment has been reported. Most promising were the results with dipyridamole [5, 6], tranexamic acid [7, 8], and aprotinin [9, 10]. Of the three treatments, the efficacy of high- and low-dose aprotinin has been confirmed by several controlled studies [9–12]. With aprotinin, significant results were obtained in relatively small groups of patients, and independent of preoperative aspirin treatment [13–15]. To screen whether the other reported hemostatic drugs are equally effective as aprotinin this randomized, controlled study of 60 patients in four groups included coronary bypass patients independent of preoperative treatment with aspirin. The administered doses of dipyridamole and tranexamic acid were similar to doses that were reported to be effective [5, 7]. Aprotinin was administered as a single dose of 2 million kallikrein inhibiting units (KIU) to the prime of the extracorporeal circuit. Previously we have demonstrated that this low-dose schedule is as equally effective as the high-dose schedule [10].

To obtain the maximum effect of pharmacologic treatment on postoperative hemorrhage we selected only patients from the high-risk group with a preoperative platelet count of less than 246 x 10⁹/L.

	Patients and Methods

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
A total of 60 patients scheduled for elective primary coronary artery bypass grafting entered the study. As is common in studies in our hospital patients aged more than 75 years were not included. Patients with a body weight of more than 100 kg were excluded to prevent large variations in the plasma levels of aprotinin. Because of possible renal damage after aprotinin treatment [11] patients with already impaired renal function (creatinine level more than 200 µmol/L) were not included. Also patients with intravenous heparin treatment or a history of coagulopathy were excluded. Routinely aspirin intake (80 mg acetylsalicylic acid or 100 mg carbasalate calcium daily) was discontinued 2 to 4 days before operation. Earlier discontinuation was not possible because we summon the patients only a few days before the operation. Bleeding time, partial thromboplastin time, and activated partial thromboplastin time were within normal ranges in all patients. The patients were randomly assigned to four groups: aprotinin (n = 15), tranexamic acid (n = 15), dipyridamole (n = 15), or the control (n = 15) group.

The study protocol was approved by the hospital's ethical committee and written informed consent was obtained from all patients.

Aprotinin (Trasylol; Bayer AG, Leverkusen, Germany) was added as a single dose of 2 x 10⁶ KIU to the pump prime. After induction of anesthesia tranexamic acid (Cyclokapron; Kabi Vitrum, Sweden) was infused as a bolus of 10 mg/kg body weight in 20 minutes and continued at a rate of 1 mg/kg up to a total dose of 1,000 mg. Treatment with dipyridamole (Persantin; Boehringer Ingelheim, Germany) was started 36 hours before operation with oral dipyridamole (100 mg four times per day). After induction of anesthesia treatment was continued with intravenous dipyridamole at a rate of 0.24 mg •; kg^-1 •; h^-1 for 24 hours.

Anesthesia comprised premedication with lorazepam, induction with sufentanyl, pancuronium bromide, and etomidate or propofol, and was maintained with a continuous infusion of sufentanyl. Routinely an infusion of dopamine and nitroglycerin was started at the termination of cardiopulmonary bypass (CPB).

The extracorporeal circuit contained either a William-Harvey HF 5400 (Bard, Tustin, CA) or an Avecor Ultrox I (Avecor, Plymouth, MN) oxygenator primed with 2,000 mL of Ringer's lactate solution, 200 mL of human albumin, 100 mL of mannitol, 50 mL of 8% sodium bicarbonate, 50 mg of heparin, and 2 g of cefamandole. Before cannulation heparin (3 mg/kg) was given. Additional doses of heparin were given whenever the activated clotting time (ACT) dropped to less than 400 seconds. In patients receiving aprotinin or tranexamic acid an additional 50 mg of heparin was given every hour during CPB irrespective of the ACT. Heparin was neutralized with protamine sulfate in a 1:1 ratio with the initial heparin dose. Additional dosage of protamine was guided by repeat ACTs after the residual volume in the extracorporeal circuit was returned to the patient. Flow ranges were from 2.0 to 2.4 L •; m^-2 •; min^-1 during moderate hypothermia. Cardioplegia was achieved with ice-cold St. Thomas solution infused in the ascending aorta after clamping.

To calculate the hemoglobin loss all gauzes were weighed, washed, and sampled for hemoglobin concentration. The volume of wasted suction was measured and, after vigorous shaking, sampled for hemoglobin concentration. Using these data we calculated intraoperative hemoglobin loss. The volume of mediastinally shed blood was measured 6 and 24 hours after the operation. Intraoperative and postoperative transfusions of homologous blood products were recorded.

Continuous data were analyzed with analysis of variance. When data were not normally distributed a log transformation was performed. The Bonferroni–Holm procedure was used to correct for the multiple-comparisons artifact. The hemoglobin and platelet concentrations were analyzed with analysis of variance for repeated measures. Categoric data were analyzed with the ² statistic. Differences were considered significant at a p level of less than 0.05. All analyses were performed with SPSS software (SPSS Inc, Chicago, IL).

	Results

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
The study groups were comparable with respect to demographic and operative data (Table 1).

The mean intraoperative blood loss in the four groups varied from 4.5 to 6.6 mmol hemoglobin with large variation in each group (Fig 1). The differences between the groups were not significant.

View larger version (18K): [in this window] [in a new window]   Fig 1. . Intraoperative hemoglobin loss ± standard deviation. No significant differences between the groups.

View larger version (25K): [in this window] [in a new window]   Fig 2. . Postoperative blood loss through chest tubes 6 and 24 hours after operation (mean ± standard deviation). Compared with controls blood loss was significantly decreased in the tranexamic acid group at 6 hours (+ p = 0.019) and in the aprotinin group at 6 hours (*p = 0.001). Blood loss in the aprotinin group was also significantly decreased compared with the dipyridamole group at 6 hours (#p = 0.008). (APR = aprotinin; CON = controls; DIP = dipyridamole; TRX = tranexamic acid.)

View larger version (17K): [in this window] [in a new window]   Fig 3. . Perioperative hemoglobin (Hb) levels (mean values ± standard deviation). Not all standard deviations are shown to improve legibility. There is a significant difference between the dipyridamole and aprotinin groups at 6 hours postoperatively (po) (*p = 0.007). ( = controls; = dipyridamole; = tranexamic acid; = aprotinin.)

View larger version (17K): [in this window] [in a new window]   Fig 4. . Perioperative platelet counts (mean values ± standard deviation). Not all standard deviations are shown to improve legibility. Same symbols as in Figure 3. No significant differences between the groups.

	Comment

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
In our comparative study hemostasis after elective coronary operations improved by administration of aprotinin and tranexamic acid but not by dipyridamole.

Dipyridamole acts directly on platelets and inhibits platelet phosphodiesterase, which leads to decreased cyclic adenosine monophosphate formation and reduced Ca²⁺ mobilization, essential for platelet activation [16]. As a result platelets become more resistant to activation and aggregation stimuli but platelet adhesive function is not affected [17]. Dipyridamole was used perioperatively by Teoh and colleagues [5] to prevent platelet activation and consumption by nonphysiologic stimuli during CPB for cardiac operation in the hope of preserving hemostatic potential. They found that platelet numbers were preserved and postoperative bleeding was decreased. We could not confirm these results in our patients. Compared with controls postoperative bleeding was not different and platelet numbers were not preserved. An explanation could be that we used membrane oxygenators in all patients, whereas in the initial study by Teoh and colleagues [5] only bubble oxygenators were used. Membrane oxygenators have been shown to preserve platelets better than bubble oxygenators [18]. In a second study by Teoh and co-workers [6], using membrane and bubble oxygenators, the effectiveness of dipyridamole on postoperative blood loss was only present when the untreated bubble oxygenator group was compared with the dipyridamole-treated membrane oxygenator group. This indicates that the positive effect of dipyridamole could be obscured by the use of membrane oxygenators in our patients.

Three patients in the dipyridamole group were excluded from the analysis because the infusion was stopped at the ICU after serious complications occurred. Insufficient data are available to attribute the complications directly to the drug. However, the hemodynamic instability we observed in 1 patient might be an extreme form of postural hypotension often observed in patients taking oral dipyridamole. Two patients were excluded because of excessive bleeding. In these patients there is the theoretical possibility that clotting disorders developed due to excessive inhibition of platelet activation by dipyridamole. Moreover, one of the patients was on aspirin treatment before operation. The combination of aspirin and dipyridamole, when used to improve graft patency, has been shown to result in an increased rate of bleeding complications [19]. In our opinion, although our experience with dipyridamole comprises only few patients, the use of dipyridamole as a hemostatic agent in cardiac operations should be reconsidered.

Tranexamic acid is an antifibrinolytic agent that prevents binding of plasminogen to fibrin, thus making it inaccessible for plasminogen activators. As a result plasmin formation is decreased and fibrinolysis is inhibited [20]. The antiprotease aprotinin inactivates several serine proteases, such as plasmin, kallikrein, and trypsin, by formation of stoichiometric complexes. Inactivation of plasmin is responsible for the antifibrinolytic effect [20]. By inactivating kallikrein, aprotinin is an inhibitor of the contact activation system and thus inhibits activation of the intrinsic clotting cascade and formation of thrombin [21]. With the doses used in our study both tranexamic acid and aprotinin improved hemostasis but treatment with aprotinin resulted in the greatest reduction of postoperative blood loss. This could be explained by observations of van Oeveren and colleagues [10], who found that aprotinin can preserve the expression of the adhesive GpIb receptor on platelets during CPB. The expression of GpIb is decreased after exposure of platelets to both plasmin and thrombin [22–24]. With aprotinin treatment both these proteases are inhibited. The latter could result in more optimally preserved hemostasis than with only tranexamic acid's inhibition of plasmin. Nevertheless, tranexamic acid is an effective hemostatic drug significantly reducing blood loss after CPB, even in small populations and irrespective of preoperative use of aspirin. Further biochemical studies are warranted to clarify the role of thrombin and plasmin generation in postoperative bleeding.

The efficacy of hemostatic drugs might be underestimated when only postoperative drainage volume is measured and not postoperative hemoglobin loss. It has been demonstrated that with aprotinin treatment hemoglobin loss is more reduced than drainage volume, probably because aprotinin does not reduce the loss of exudate and transudate from the wound [9]. We did not calculate postoperative hemoglobin loss because the collection device we use prevents easy mixing of the contained blood and thus reliable sampling. It is likely that improved hemostasis is better reflected in reduced drainage volume 6 hours postoperative than 24 hours postoperative because of the larger share of blood loss in the total drainage volume shortly after the operation.

Thromboembolic complications were not observed in this series. Theoretically, however, the use of antifibrinolytic agents could lead to thromboembolic complications because the balance between clotting and thrombolysis is disturbed. Therefore, we prefer the low-dose aprotinin regimen because it is administered only during CPB when the patient is protected from thrombus formation by full heparization. For the same reason tranexamic acid should not be administered after heparin neutralization.

The main goal of the hemostatic agents is reduction of transfusion requirements and exposure of the patient to the risk associated with blood products. Although the use of blood products was reduced in the pharmacologically treated groups, the reductions were not significant. The fact that the postoperative hemoglobin levels were lower in the dipyridamole group (and the blood use lowest) indicate that the indications for transfusion in our patients were not strictly standardized. This confirms that next to improved hemostasis a strict blood salvage protocol is required for a significant reduction of the need for blood products and minimize the number of patients exposed to any blood product [25].

In conclusion, aprotinin and tranexamic acid can effectively improve hemostasis after coronary artery bypass operations in patients with low preoperative platelet counts and independent of preoperative aspirin use. Aprotinin may be more effective as a result of a different pharmacologic mechanism. Dipyridamole appeared not to be effective and was associated with a high complication rate.

	Acknowledgments

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
We thank the staff of the Departments of Anesthesiology and Hematology for their technical assistance and Jos J. P. Nauta, MSc, for his statistical advice.

	Footnotes

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 
Address reprint requests to Dr Wildevuur, Department of Thoracic Surgery, Onze Lieve Vrouwe Gasthuis, PO Box 95500, 1090 HM Amsterdam, the Netherlands.

	References

Top Footnotes Abstract Introduction Patients and Methods Results Comment Acknowledgments References

 

1. Harker LA, Malpass TW, Bronson HE, Hessel EA II, Slichter SJ. Mechanism of abnormal bleeding in patients undergoing cardiopulmonary bypass: acquired transient platelet dysfunction associated with selective alpha-granule release. Blood 1980;56:824–34.[Free Full Text]
2. Mohr R, Golan M, Martinowitz U, Rosner F. Effect of cardiac operation on platelets. J Thorac Cardiovasc Surg 1986;92:434–41.[Abstract]
3. Fassin W, Himpe D, Alexander JP, et al. Predictive value of coagulation testing in cardiopulmonary bypass surgery. Acta Anaesthesiol Belg 1991;42:191–8.[Medline]
4. Eijsman L. Cardiopulmonary bypass and haemostasis [Thesis]. University of Groningen, the Netherlands, 1992:76–83.
5. Teoh KH, Christakis GT, Weisel RD, et al. Dipyridamole preserved platelets and reduced blood loss after cardiopulmonary bypass. J Thorac Cardiovasc Surg 1988;96:332–41.[Abstract]
6. Teoh KH, Christakis GT, Weisel RD, et al. Blood conservation with membrane oxygenators and dipyridamole. Ann Thorac Surg 1987;44:40–7.[Abstract]
7. Horrow JC, Hlavacek J, Strong MD, et al. Prophylactic tranexamic acid decreases bleeding after cardiac operations. J Thorac Cardiovasc Surg 1990;99:70–4.[Abstract]
8. Horrow JC, Van Riper DF, Strong MD, Brodsky I, Parmet JL. Hemostatic effects of tranexamic acid and desmopressin during cardiac surgery. Circulation 1991;84:2063–70.[Abstract/Free Full Text]
9. Royston D, Taylor KM, Bidstrup BP, Sapsford RN. Effect of aprotinin on need for blood transfusion after repeat open-heart surgery. Lancet 1987;1:1289–91.
10. 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.[Abstract]
11. Blauhut B, Gross C, Necek S, Doran JE, Späth P, Lundsgaard-Hansen P. Effects of high-dose aprotinin on blood loss, platelet function, fibrinolysis, complement, and renal function after cardiopulmonary bypass. J Thorac Cardiovasc Surg 1991;101:958–67.[Abstract]
12. Havel M, Teufelsbauer H, Knöbl P, et al. Effect of intraoperative aprotinin administration on postoperative bleeding in patients undergoing cardiopulmonary bypass operation. J Thorac Cardiovasc Surg 1991;101:968–72.[Abstract]
13. Bidstrup BP, Royston D, McGuinness C, Sapsford RN. Aprotinin in aspirin pretreated patients. Perfusion 1990;5:S77–81.
14. Schönberger JPAM, Bredee JJ, van Oeveren W, et al. Preoperative therapy of low-dose aspirin in internal mammary artery bypass with and without low-dose aprotinin (2 million KIU). J Thorac Cardiovasc Surg 1993;106:262–7.[Abstract]
15. Tabuchi N, Gallandat Huet RGC, Sturk A, Eijsman L, Wildevuur CRH. Aprotinin preserves hemostasis in aspirin-treated patient undergoing cardiopulmonary bypass. Ann Thorac Surg 1994;58:1036–9.[Abstract]
16. Mills DCB, Smith JB. The influence on platelet aggregation of drugs that affect the accumulation of adenosine 3-5 cyclic monophosphate in platelets. Biochem J 1971;121:185–9.[Medline]
17. Emmons PR, Harrison MJG, Honour AJ, Mitchell JRA. Effect of dipyridamole on human platelet behaviour. Lancet 1965;2:603–6.[Medline]
18. Boers M, van den Dungen JJAM, Karliczek GF, Brenken U, Homan van der Heide JN, Wildevuur CRH. Two membrane oxygenators and a bubbler: a clinical comparison. Ann Thorac Surg 1983;35:455–62.[Abstract]
19. Van der Meer J, Hillege HL, Kootstra GJ, et al. Prevention of one-year vein-graft occlusion after aortocoronary bypass surgery: a comparison of low-dose aspirin, low-dose aspirin plus dipyridamole, and oral anticoagulants. Lancet 1993;342:257–64.[Medline]
20. Verstraete M. Clinical application of inhibitors of fibrinolysis. Drugs 1985;29:236–61.[Medline]
21. De Smet AAEA, Chang M, van Oeveren W, et al. Increased anticoagulation during cardiopulmonary bypass by aprotinin. J Thorac Cardiovasc Surg 1990;100:520–7.[Abstract]
22. Adelman B, Michelson AD, Loscalzo J, Greenberg J, Handin RI. Plasmin effect on platelet glycoprotein IB-von Willebrand factor interactions. Blood 1985;65:32–40.[Abstract/Free Full Text]
23. Cramer EM, Lu H, Caen JP, Soria C, Berndt MC, Tenza D. Differential redistribution of platelet glycoproteins Ib and IIb-IIIa after plasmin stimulation. Blood 1991;77:694–9.[Abstract/Free Full Text]
24. Hourdille P, Heilmann E, Combrie R, et al. Thrombin induces a rapid redistribution of glycoprotein Ib-IX complexes within the membrane systems of activated human platelets. Blood 1990;79:1503–13.
25. Cosgrove DM, Thurer RL, Lytle BW, Gill GC, Peter M, Loop FD. Blood conservation during myocardial revascularization. Ann Thorac Surg 1979;28:184–9.[Abstract]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Ron G. H. Speekenbrink Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Speekenbrink, R. G. H. Articles by Eijsman, L. Search for Related Content PubMed PubMed Citation Articles by Speekenbrink, R. G. H. Articles by Eijsman, L.