Coagulofibrinolysis during heparin-coated cardiopulmonary bypass with reduced heparinization

Coagulofibrinolysis During Heparin-Coated Cardiopulmonary Bypass With Reduced Heparinization Hiroshi Kumano, MD, PhD, Shigefumi Suehiro, MD, PhD, Koji Hattori, MD, PhD, Toshihiko Shibata, MD, PhD, Yasuyuki Sasaki, MD, Mitsuharu Hosono, MD, and Hiroaki Kinoshita, MD, PhD Second Department of Surgery, Osaka City University Medical School, Osaka, Japan

Background. We examined the safety of reduced systemic heparinization during heparin-coated cardiopulmonary bypass by measuring coagulofibrinolitic indices, including fibrinopeptide A, which directly reflects fibrinogenesis. Methods. Twenty-four patients who had elective cardiac operations were perfused using a circuit coated with covalently bonded heparin. Twelve patients received 300 U/kg of heparin and the remaining 12 patients received 150 U/kg. Blood was obtained for the measurement of thrombin-antithrombin III complexes, fibrinopeptide A, plasmin-alpha 2 plasmin inhibitor complexes, and Ddimer preoperatively; after heparin administration; 10, 60, and 90 minutes after the start of bypass; after prota-

mine administration; and 1, 3, 6, 12, and 24 hours after the end of bypass. Results. Preoperative, intraoperative, and postoperative variables including postoperative bleeding were not significantly different between the two groups. Further, there were no complications in either group. No significant differences between the two groups were noted for any hematologic index at any time point. Conclusions. Reduced systemic heparinization combined with a heparin-coated cardiopulmonary bypass circuit is biochemically and clinically safe but does not reduce postoperative bleeding. (Ann Thorac Surg 1999;68:1252– 6) © 1999 by The Society of Thoracic Surgeons

C

the increase in the risk of thrombosis attributable to the use of a lower dose of heparin.

ardiopulmonary bypass (CPB) during cardiac operations causes coagulofibrinolytic disturbances when a large dose of heparin is used for anticoagulation and when blood comes into contact with artificial substances. These disturbances make postoperative hemostasis difficult [1]. Various methods have been used to decrease both perioperative and postoperative bleeding. Coating of the surface of a CPB circuit with heparin increases thromboresistance [2– 4]. As a result, the dose of heparin can be decreased [3–9]. Several studies found that postoperative bleeding can be decreased with the use of a lower dose of heparin [3–5, 7], but other studies suggested that a low dose of heparin increases the risk of thrombosis [6, 8, 10]. Thrombin-antithrombin III complex (TAT) was measured as an index of coagulation in some of those reports [4, 8]. However, measurements of TAT do not necessarily reflect fibrinogenesis, and might not be suitable as an index of coagulation. In this study, we measured indices of the coagulofibrinolytic system (including fibrinopeptide A, FPA) that directly reflect fibrinogenesis in patients who had heparin-coated CPB. In addition, we examined Accepted for publication March 26, 1999. Address reprint requests to Dr Kumano, Second Department of Surgery, Osaka City University Medical School, 1-5-7 Asahimachi, Abeno-ku, Osaka 545-0051, Japan.

© 1999 by The Society of Thoracic Surgeons Published by Elsevier Science Inc

Patients and Methods Twenty-four patients who had elective operations for coronary artery bypass grafting or aortic valve replacement were chosen for our study. Exclusion criteria included previous cardiac operation, renal dysfunction, liver dysfunction, or preoperative coagulopathy. Anticoagulation or antiplatelet therapy was discontinued 7 days before the operation in all patients. Informed consent was obtained from all patients the day before the operation. The protocol for this study was approved by the medical ethics committee of our institution.

Anesthesia All patients were medicated with morphine sulfate and scopolamine hydrobromide by intramuscular injection 1 hour before the induction of anesthesia. Anesthesia was induced and maintained with fentanyl and midazolam, and muscle relaxation was achieved with pancuronium bromide and vecuronium bromide. After endotracheal intubation, patients received mechanical ventilation with 100% oxygen. Standard monitoring methods (electrocardiography, radial arterial pressure monitoring, central venous-pulmonary arterial pressure monitoring, urinary 0003-4975/99/$20.00 PII S0003-4975(99)00697-9

Ann Thorac Surg 1999;68:1252– 6

KUMANO ET AL COAGULOFIBRINOLYSIS DURING HEPARIN-COATED CPB

output, and rectal and skin temperature monitoring) were used for all patients.

Data Collection and Measurements

Cardiopulmonary Bypass All components of the CPB circuit were coated with covalently bonded heparin (Carmeda Bioactive Surface; Medtronic Inc, Anaheim, CA). The CPB circuit consisted of a hollow-fiber membrane oxygenator (Maxima model CB 1380), a soft-shell venous reservoir (Maxima model CB 1386), a cardiotomy reservoir (model CB 1351), a 40-␮m arterial filter (model CBM-40) (all four components were produced by Medtronic), and a centrifugal pump (Bio-Pump model BP-80; Medtronic BioMedicus, Minneapolis, MN). The circuits were primed with a mixture of 1300 mL of lactated Ringer’s solution, 250 mL of human serum albumin (250 mg/mL), 200 mL of mannitol (200 mg/mL), and 100 mL of sodium bicarbonate (84 mg/mL). Standard ascending aortic cannulation (6.5-mm High Flow Aortic Arch Cannula model 12325; Sarns 3M Health Care, Ann Arbor, MI) and right atrial cannulation (DLP 34/48 F two-stage venous cannula; DLP Inc, Grand Rapids, MI) were done. Before aortic cannulation, 12 patients were randomly assigned to receive a 300 U/kg dose of bovine heparin (high-dose group), and the remaining 12 patients were assigned to receive a 150 U/kg dose of bovine heparin (low-dose group). During systemic heparinization, the activated clotting time (ACT) was measured using a Hemochron 801 (International Technidyne, Edison, NJ). The ACT was kept at 400 seconds or above in the high-dose group and 300 to 400 seconds in the low-dose group by the administration of more heparin during CPB as required. While the patient was fully heparinized and on CPB, a cardiotomy suction device was used to return pericardial blood. At all other times during the operation, a cell-saving device (Haemonetics Cell Saver 5 model 2005, Haemonetics Inc, Braintree, MA) was used. During CPB, a nonpulsatile flow of 2.4 L/m2 per minute was maintained, and moderate systemic hypothermia (rectal temperature, 32°C) was initiated. The mean arterial pressure was maintained between 50 and 80 mm Hg during CPB. The hematocrit value was maintained at more than 16% during CPB, with blood transfusions as necessary. The left ventricle was vented by cannulation via the right superior pulmonary vein. After the aorta was cross-clamped, cold crystalloid cardioplegic solution was administered in an antegrade fashion and then retrograde to arrest the heart. Topical cooling with ice slush was used during the infusion of the cardioplegic solution to maintain myocardial hypothermia. Patients were weaned from CPB with inotropic support. After termination of CPB, heparin was neutralized with an equivalent dose of protamine sulfate. If necessary, additional protamine was administered to reestablish the preoperative ACT. Blood lost postoperatively that was collected by mediastinal and pleural chest tubes was not autotransfused. Aprotinin was not used during this study.

1253

Intraoperative variables including the duration of aortic cross-clamping, the duration of CPB, initial heparin dose, and total protamine dose were recorded. The amount of blood lost postoperatively during the first 24 hours through mediastinal and pleural chest tubes was recorded. Blood samples were obtained from a radial arterial catheter or the arterial side of the extracorporeal circulation circuit at the following 11 times: before the induction of anesthesia; 5 minutes after heparin administration but before the initiation of CPB; 10, 60, and 90 minutes after the start of CPB; 5 minutes after protamine administration (10 minutes after the end of CPB); and 1, 3, 6, 12, and 24 hours after the end of CPB. The hematocrit was measured with an automatic cell counter (Coulter MicroDiff 18; Coulter Inc, Miami, FL). Plasma was separated from blood cells by centrifugation at 3,000 ⫻ g for 10 minutes, and stored at ⫺70°C until analysis. Fibrinopeptide A [11] and plasmin-alpha 2 plasmin inhibitor complex (PIC) [12] were measured by enzyme immunoassays. Thrombin-antithrombin III complex [13] and d-dimer [14] were measured by enzymelinked immunosorbent assays. Values obtained during CPB and 5 minutes after protamine administration were corrected for hemodilution and normalized to the hematocrit before the operation.

Statistical Analysis Data were analyzed using standard computer software (Statview 4.11 and Super ANOVA 1.11; Abacus Concepts, Berkeley, CA). All results are reported as the mean ⫾ standard deviation. The Mann-Whitney U test was used for the comparison of preoperative, intraoperative, and postoperative values between groups. A two-factor repeated-measures analysis of variance was done to evaluate differences between the groups. If significant differences were found, the Wilcoxon rank-sum test was applied to comparisons within groups and the MannWhitney U test was used for comparisons between groups. A p value of less than 0.05 was considered statistically significant.

Results The clinical data are summarized in Table 1. No statistically significant differences were noted between the groups with respect to mean age, gender, type of operation, or mean durations of the operation, aortic crossclamping, or CPB. Statistically significant differences in the mean initial heparin dose, total heparin dose, and total protamine dose were observed between the two groups ( p ⬍ 0.001). The mean volume of postoperative blood loss within the first 24 postoperative hours in the two groups (494 ⫾ 160 mL in the high-dose group and 519 ⫾ 454 mL in the low-dose group) was not significantly different ( p ⫽ 0.248). Perioperative myocardial infarction, cerebral infarction, thromboembolism, or other complications were not observed in any patients in either group.

1254

KUMANO ET AL COAGULOFIBRINOLYSIS DURING HEPARIN-COATED CPB

Ann Thorac Surg 1999;68:1252– 6

Table 1. Preoperative, Intraoperative, and Postoperative Patient Dataa

Variable Age (y) Male/Female CABG/AVR Duration of surgery (min) Duration of cardiopulmonary bypass (min) Aortic cross-clamp time (min) Initial heparin dose (units/kg) Total heparin dose (units/kg) Total protamine dose (mg/kg) Chest tube drainage (mL in 24 h)

High-Dose Group (n ⫽ 12)

Low-Dose Group (n ⫽ 12)

p Valueb

58.2 ⫾ 13.7 12/0 9/3 338 ⫾ 73.3

56.3 ⫾ 11.1 9/3 6/6 316 ⫾ 99.3

0.708 0.299 0.299 0.471

127 ⫾ 36.4

133 ⫾ 37.7

0.708

80.3 ⫾ 27.5

93.6 ⫾ 32.0

0.356

290 ⫾ 13.6

135 ⫾ 25.4

⬍ 0.001

292 ⫾ 15.5

168 ⫾ 56.0

⬍ 0.001

3.4 ⫾ 0.73

1.7 ⫾ 0.37

⬍ 0.001

494 ⫾ 160

519 ⫾ 454

0.248

Data are shown as mean ⫾ standard deviation. test.

a

AVR ⫽ aortic valve replacement; grafting.

b

Mann-Whitney U

CABG ⫽ coronary artery bypass

Activated Clotting Time In both groups, the ACT was significantly higher 5 minutes after heparin administration and remained high until 90 minutes after the start of CPB compared with the preoperative ACT (Fig 1). At each of these time points, the values for ACT in the high-dose group were significantly higher than those in the low-dose group ( p ⬍ 0.01).

Fig 1. Activated clotting time (ACT, mean ⫾ standard deviation). Closed circles indicate the high-dose (H) group and open circles the low-dose (L) group. Samples were obtained at the following time points: before induction of anesthesia (Bef); 5 minutes after heparin administration (Hep); 10, 60, and 90 minutes after the initiation of cardiopulmonary bypass (10m, 60m, and 90m); 5 minutes after protamine administration (Pro); and 1, 3, 6, 12, and 24 hours after the termination of cardiopulmonary bypass (1h, 3h, 6h, 12h, and 24h). Significant differences between the two groups were observed during systemic heparinization (*p ⬍ 0.01 versus the low-dose group.)

Fig 2. Plasma concentration of thrombin-antithrombin complex (TAT, mean ⫾ standard deviation). Abbreviations and other legends are the same as in Figure 1. There were no significant differences between the two groups at any time point.

Thrombin-Antithrombin III Complex In both groups, the TAT was significantly greater 10 minutes after the start of CPB than preoperatively, it continued to increase during CPB, and it reached a maximum value 5 minutes after protamine administration (189.6 ⫾ 66.1 ng/mL in the high-dose group versus 164.8 ⫾ 102.3 ng/mL in the low-dose group; Fig 2). Thereafter, TAT decreased. However, the value for TAT was still significantly higher than preoperative values until 3 hours after the end of CPB in both groups. No significant differences in TAT were observed between the two groups at any time point.

Fibrinopeptide A Compared with the preoperative values, FPA also increased significantly 10 minutes after the start of CPB in both groups but did not increase further during CPB (9.9 ⫾ 7.0 to 14.2 ⫾ 8.8 ng/mL in the high-dose group versus 9.2 ⫾ 8.4 to 16.3 ⫾ 6.5 ng/mL in the low-dose

Fig 3. Plasma concentration of fibrinopeptide A (FPA, mean ⫾ standard deviation). Abbreviations and other legends are the same as in Figure 1. There were no significant differences between the two groups at any time point.

Ann Thorac Surg 1999;68:1252– 6

KUMANO ET AL COAGULOFIBRINOLYSIS DURING HEPARIN-COATED CPB

1255

the preoperative values, the d-dimer in both groups increased significantly 60 minutes after the start of CPB, continued to increase gradually, peaked 5 minutes after protamine administration (752.0 ⫾ 214.1 ng/mL in the high-dose group versus 839.8 ⫾ 372.1 ng/mL in the low-dose group), and decreased gradually thereafter. In contrast to TAT, FPA, and PIC, the d-dimer concentration did not return to the preoperative level, even 24 hours after the end of CPB (87.9 ⫾ 37.7 versus 308.2 ⫾ 45.5 ng/mL in the high-dose group; 88.9 ⫾ 46.5 versus 269.2 ⫾ 89.0 ng/mL in the low-dose group). There were no significant differences between the two groups at any time point. Fig 4. Plasma concentration of plasmin-alpha 2 plasmin inhibitor complex (PIC, mean ⫾ standard deviation). Abbreviations and other legends are the same as in Figure 1. There were no significant differences between the two groups at any time point.

group; Fig 3). The FPA reached a maximum value 5 minutes after protamine administration in both groups (42.6 ⫾ 10.8 ng/mL in the high-dose group versus 34.2 ⫾ 22.1 ng/mL in the low-dose group). The value for FPA then decreased, but it was still significantly higher than the preoperative value until 1 hour after the end of CPB. There were no significant differences between the two groups at any time point.

Plasmin-Alpha 2 Plasmin Inhibitor Complex The PIC increased significantly 90 minutes after the start of CPB and peaked 3 hours after the end of CPB (1.7 ⫾ 0.97 ng/mL in the high-dose group versus 1.6 ⫾ 0.91 ng/mL in the low-dose group) in both groups (Fig 4). The PIC remained elevated until 6 hours after the end of CPB in both groups and then decreased rapidly. There were no significant differences between the two groups at any time point.

d-Dimer The changes in the d-dimer concentration were similar to the changes in PIC in both groups (Fig 5). Compared with

Fig 5. Plasma concentration of d-dimer (mean ⫾ standard deviation). Abbreviations and other legends are the same as in Figure 1. There were no significant differences between the two groups at any time point.

Comment In the present study of reduced systemic heparinization during the use of a heparin-coated CPB circuit, we found that (1) there were no differences in the changes in the coagulofibrinolytic indices when compared with the use of the standard heparin dose, (2) there were no differences in the changes in FPA between the two heparin doses, and (3) there was no difference in the amount of postoperative blood loss. We conclude that a heparincoated CPB circuit can be used safely with reduced systemic heparinization. However, this method does not necessarily decrease postoperative blood loss. To assess changes in the coagulation factors with reduced systemic heparinization during CPB, determination of FPA as well as TAT is necessary. In previous reports, TAT has been measured during CPB with reduced systemic heparinization, but FPA has not [4, 8]. Heparin does not have any inherent anticoagulant activity. Rather, it accelerates TAT formation by binding the serine protease inhibitor antithrombin III to thrombin. Consequently, heparin inhibits the effect of thrombin on fibrinogen, resulting in anticoagulation. In accord with this mechanism of action, TAT values reflect the generation of thrombin but not of fibrin. Therefore, it is impossible to evaluate the coagulation system based solely on the determination of TAT. In contrast, FPA is produced from the cleavage of fibrinogen by thrombin, and therefore reflects fibrinogenesis. In determining the risk of thrombosis, measuring the generation of fibrin is important, and changes in FPA must be quantified. In the present study, the concentration of FPA increased slightly with the initiation of CPB but did not increase further during CPB, in contrast to TAT. These changes suggest that fibrinogenesis remains in an acceptable range, even with reduced systemic heparinization. In agreement with other reports [2, 4, 8, 10], we found that TAT continued to increase after the initiation of CPB. This effect appears to result from thrombin’s rapid binding to the heparin-antithrombin III complex, thereby suppressing the effect on fibrinogen. The finding of no difference in the changes in TAT between the two groups suggests that this reaction is not affected by the level of systemic heparinization. Although FPA increased during CPB in both groups, the FPA concentration was much lower than after the administration of protamine.

1256

KUMANO ET AL COAGULOFIBRINOLYSIS DURING HEPARIN-COATED CPB

Ann Thorac Surg 1999;68:1252– 6

Therefore, it can be said that fibrinogenesis did not increase, even when the dose of systemic heparin was reduced. Clinically, no complications occurred. On the basis of those findings, we conclude that the use of a heparin-coated CPB circuit with reduced systemic heparinization is biochemically and clinically safe. Several reasons could account for why the amount of postoperative bleeding did not decrease with reduced heparinization in the present study. First, we studied a small number of patients. A significant decrease in blood loss was found only in previous studies that included a large number of patients [4, 5, 7]. In contrast, no significant decrease in blood loss has been observed in studies of small numbers of patients [6, 8 –10, 15]. An insufficient reduction in the heparin dose might also be responsible for the lack of a decrease in blood loss. However, a greater reduction in the heparin dose was not considered because of the aspiration of pericardial blood using a cardiotomy suction device during systemic heparinization. Specifically, it has been reported that there is a tenfold higher concentration of coagulating substances in pericardial blood compared with circuit blood [16], and an extreme reduction in the heparin dose could be dangerous. Increased bleeding after cardiac operations might also result from acceleration of fibrinolytic activity after CPB. It has been reported that postoperative bleeding is strongly affected by postoperative fibrinolytic activity [17]. In the present study, although TAT and FPA increased rapidly after protamine administration and then rapidly decreased, high concentrations of PIC and ddimer persisted for several hours after CPB. If we assume that the effect of increased fibrinolytic activity on postoperative bleeding is great, then decreased postoperative bleeding cannot be achieved with a reduction of the heparin dose unless postoperative fibrinolysis also is inhibited. It has been reported that heparin-coated CPB circuits not only improves thromboresistance but also increases biocompatibility and suppresses the activation of complement components and granulocytes [9, 15]. In addition, use of heparin-coated CPB circuits also inhibits the release of cytokines [18], prevents respiratory disorders [19], and improves the postoperative course [5, 20]. Adverse effects should decrease further with the reduction in the systemic heparin dose because of a reduction in the required protamine dose. Our conclusions are limited because our sample was small and we had unequal distributions of operative procedures and gender between groups. Moreover, our conclusions are all based on tests of the hypothesis with nonsignificant results. Therefore, larger prospective randomized studies will be necessary.

2. Hattori K. Clinical effects of standard and heparin-coated circuits on coagulation and fibrinolysis during cardiopulmonary bypass. Jinko Zoki (Jpn J Artif Organs) 1996;25:649–54. 3. Von Segesser LK, Weiss BM, Garcia E, von Felten A, Turina MI. Reduction and elimination of systemic heparinization during cardiopulmonary bypass. J Thorac Cardiovasc Surg 1992;103:790–9. 4. Øvrum E, Holen EÅ, Tangen G, et al. Completely heparinized cardiopulmonary bypass and reduced systemic heparin: clinical and hemostatic effects. Ann Thorac Surg 1995;60: 365–71. 5. Aldea GS, Doursounian M, O’Gara P, et al. Heparin-bonded circuits with a reduced anticoagulation protocol in primary CABG: a prospective, randomized study. Ann Thorac Surg 1996;62:410– 8. 6. Kuitunen AH, Heikkila¨ LJ, Salmenpera¨ MT. Cardiopulmonary bypass with heparin-coated circuits and reduced systemic anticoagulation. Ann Thorac Surg 1997;63:438– 44. 7. Von Segesser LK, Weiss BM, Pasic M, Garcia E, Turina MI. Risk and benefit of low systemic heparinization during open heart operations. Ann Thorac Surg 1994;58:391– 8. 8. Øvrum E, Brosstad F, Holen EÅ, Tangen G, Abdelnoor M. Effects on coagulation and fibrinolysis with reduced versus full systemic heparinization and heparin-coated cardiopulmonary bypass. Circulation 1995;92:2579– 84. 9. Fosse E, Moen O, Johnson E, et al. Reduced complement and granulocyte activation with heparin-coated cardiopulmonary bypass. Ann Thorac Surg 1994;58:472–7. 10. Gorman RC, Ziats NP, Rao AK, et al. Surface-bound heparin fails to reduce thrombin formation during clinical cardiopulmonary bypass. J Thorac Cardiovasc Surg 1996;111:1–12. 11. Amiral J, Walenga JM, Fareed J. Development and performance characteristics of a competitive enzyme immunoassay for fibrinopeptide A. Semin Thromb Hemost 1984;10: 228– 42. 12. Aoki N, Takenaga T, Hasegawa H, et al. Evaluation of the assay for alpha 2 PI and alpha 2 PI-plasmin complex using one step sandwich method (EIA). RinsyoByori 1987;35: 1275– 81. 13. Pelzer H, Schwarz A, Heimburger N. Determination of human thrombin-antithrombin III complex in plasma with an enzyme-linked immunosorbent assay. Thromb Haemost 1988;59:101– 6. 14. Elms MJ, Bunce IH, Bundesen PG, et al. Measurement of crosslinked fibrin degradation products: an immunoassay using monoclonal antibodies. Thromb Haemost 1983;50: 591– 4. 15. Gu YJ, van Oeveren W, Akkerman C, Boonstra PW, Huyzen RJ, Wildevuur CRH. Heparin-coated circuits reduce the inflammatory response to cardiopulmonary bypass. Ann Thorac Surg 1993;55:917–22. 16. Tabuchi N, de Haan J, Boonstra PW, van Oeveren W. Activation of fibrinolysis in the pericardial cavity during cardiopulmonary bypass. J Thorac Cardiovasc Surg 1993;106: 828–33. 17. Minami K, Notohamiprodjo G, Buschler H, Prohaska W, Reichelt W, Ko¨rfer R. Alpha-2 plasmin inhibitor-plasmin complex and postoperative blood loss: double-blind study with aprotinin in reoperation for myocardial revascularization. J Thorac Cardiovasc Surg 1993;106:934– 6. 18. Steinberg BM, Grossi EA, Schwartz DS, et al. Heparin bonding of bypass circuits reduces cytokine release during cardiopulmonary bypass. Ann Thorac Surg 1995;60:525–9. 19. Redmond JM, Gillinov AM, Stuart RS, et al. Heparin-coated bypass circuits reduce pulmonary injury. Ann Thorac Surg 1993;56:474–9. 20. Øvrum E, Holen EÅ, Tangen G, Ringdal MAL. Heparinized cardiopulmonary bypass and full heparin dose marginally improve clinical performance. Ann Thorac Surg 1996;62: 1128–33.

References 1. Bagge L, Lilienberg G, Nystro¨m SO, Tyde´n H. Coagulation, fibrinolysis and bleeding after open-heart surgery. Scand J Thorac Cardiovasc Surg 1986;20:151– 60.