High Dose Aprotinin Reduces Prothrombin and Fibrinogen Conversion in Patients Undergoing Extracorporeal Circulation for Myocardial Revascularization

An Evaluation of the Effects of a Standard Heparin Dose on Thrombin Inhibition During Cardiopulmonary Bypass in Neonates

We compared the adequacy of heparinization in neonates and older children undergoing cardiopulmonary bypass (CPB) by measuring heparin activity, thrombin formation, and thrombin activity. Ten neonates and 10 older children were administered 400 U/kg of heparin before CPB. Heparin anti-Xa activity, prothrombin fragment 1.2 (F1.2), and fibrinopeptide A (FPA) were measured at baseline, after 30 min on CPB, immediately post-CPB, and 3 and 24 h post-CPB. Heparin anti-Xa activity was significantly decreased during and immediately post-CPB in the neonatal group. F1.2 and FPA levels in neonates were significantly higher at baseline, decreased with the commencement of CPB, and increased to levels higher than those in older children after CPB. Our data show that with standard heparin doses, neonates exhibit less heparin anti-Xa activity during CPB. Higher baseline levels of F1.2 and FPA present in neonates indicate preoperative activation of their coagulation systems as compared with older children. Although F1.2 and FPA levels initially decrease with the commencement of CPB, probably representing hemodilution, the subsequent increase in these markers indicates significantly more thrombin formation and activity during and after CPB. These results raise the concern that 400 U/kg of heparin may not adequately suppress thrombin formation and activity in neonates undergoing CPB.

Is reduced systemic heparinization justified with heparin-bonded bypass circuits in cardiac surgery?--Experience with and without aprotinin

The effects of aprotinin combined with heparin-bonded bypass circuits and reduced systemic heparinization on haemostasis and inflammatory reactions were measured in patients with elective CABG operation. Patients were randomized to be operated on either without aprotinin (NOAPRO, n=15) or with aprotinin (APRO, n=15) at a low dose of 2 Mio KIU in the priming volume. Activated clotting time was adjusted to 400 +/- 50 s during cardiopulmonary bypass (CPB). Haemostasis (fibrinopeptide A (FPA), thrombin-antithrombin complex (TAT), D-Dimer, plasmin-antiplasmin (PAP), plasminogen-activator inhibitor (PAI)), inflammatory reaction (lactoferrin, IL-6, sTNF-IIR, SC5b-9) and clinical data were evaluated perioperatively. Perioperative clinical and laboratory data including mediastinal drainage volume, postoperative morbidity and mortality were comparable for patients in both groups. FPA was elevated in the APRO group during CPB (P=0.001), D-Dimer in the NOAPRO group after CPB (P=0.002). No differences were seen for TAT, PAP or PAI between the groups. Lactoferrin was elevated in NOAPRO at the end of CPB (P=0.01) and after heparin reversal with protamine sulphate (P=0.02). No intergroup differences were seen for IL-6, sTNF-IIR or SC5b-9 between the groups. In association with reduced heparinization, pump prime aprotinin retains its antifibrinolytic effect in modified bypass equipment with a heparin surface besides an anti-inflammatory effect in terms of inhibition of leukocyte activation. However, thrombin activation may be increased with aprotinin. We therefore recommend sufficient systemic heparinization despite heparin surface modification of bypass equipment.

Influence of high- and low-dose aprotinin on activation of hemostasis in open heart operations

BACKGROUND

The protease inhibitor aprotinin reduces hemostatic activation and blood loss after cardiac operations. The aim of the present study was to investigate the influence of two different aprotinin doses on hemostatic activation and to identify the most effective dose to reduce the postoperative bleeding tendency.

METHODS

In a prospective, randomized, double-blind clinical trial, 230 patients scheduled for routine open heart operations received either high-dose (group H) or low-dose (group L) aprotinin. Primary outcome measures were the level of F(1+2) prothrombin fragments as a marker of thrombin generation, the level of D-dimers as an indicator of fibrinolysis, and the amount of postoperative blood loss. Allogeneic blood transfusion was recorded as a secondary outcome measure.

RESULTS

Aprotinin plasma concentrations 5 minutes after the onset of cardiopulmonary bypass were 166 +/- 45 kallikrein inactivator units per milliliter in group H and 118 +/- 30 kallikrein inactivator units per milliliter in group L (p < 0.05). Fibrinolytic activation was reduced significantly in group H compared with group L: the level of D-dimers at the end of CPB was 1,027 +/- 781 ng/mL and 1,977 +/- 1,001 ng/mL, respectively, in the two groups (p < 0.05). However, thrombin generation (F(1+2) fragments) did not differ between the two groups (7.4 +/- 3.5 nmol/L in group H and 8.6 +/- 4.3 nmol/L in group L). Twenty-four-hour postoperative blood loss was 663 +/- 461 mL in group H compared with 877 +/- 513 mL in group L (p < 0.05), and the corresponding allogeneic blood requirement was 1.3 +/- 1.9 U in group H and 1.9 +/- 2.3 U in group L (p < 0.05).

CONCLUSIONS

A high-dose aprotinin regimen was significantly more effective than a low-dose regimen in attenuating fibrinolysis and reducing the bleeding tendency and allogeneic blood requirements, but not in reducing F(1+2) prothrombin fragments. High-dose aprotinin therapy appears to be superior to low-dose therapy.

Monitoring thrombin generation with prothrombin fragment 1.2 assay during cardiopulmonary bypass surgery

Despite high plasma levels of heparin during cardiopulmonary bypass surgery, activation of the coagulation system has been reported. We hypothesize that the coagulation system activity most appropriately could be assessed by molecular markers of thrombin generation. The aim of the present study was to describe the changes in thrombin generation during CPB, using prothrombin fragment F1 + 2 (F1.2) as an indicator and evaluate different blood sampling regimens for interpretation of the F1.2 measurements. Twenty patients, operated under extracorporeal circulation with coronary artery bypass grafting (CABG), comprised the study material. The heparin levels were maintained above 2.5 IU/ml throughout the bypass procedure and the functional AT-III level was kept above 0.5 U/ml. Despite of this anticipated inactivation of the coagulation system, the concentrations of F1.2 and FpA increased throughout CPB, particularly after release of the aortic crossclamp. F1.2 and FpA correlated significantly (R = 0.69). No statistically significant correlation was found between F1.2 formation rate and age, bodyweight, baseline ACT, ACT after 200 IU heparin/kg, average heparin concentration during CPB or average AT-III level during CPB.

CONCLUSIONS

Thrombin formation seems to be a continuous process during CPB despite adequate heparinization. The pattern of thrombin generation can be assessed most appropriately in terms of F1.2 generation rate. Extraordinary high levels of F1.2 were seen after release of the aortic crossclamp, indicating that the periods before and after aortic crossclamping should be evaluated separately.

Low-dose and high-dose aprotinin improve hemostasis in coronary operations

Prophylactic aprotinin therapy has become a popular method to reduce bleeding associated with cardiac operations. Today essentially two dose regimens are used, a high-dose regimen with administration throughout the complete operative procedure and a low-dose regimen with administration only during bypass. In unblinded studies both regimens were found to be equally effective. This double-blind placebo-controlled study in 115 patients undergoing elective coronary artery bypass grafting was done to confirm these results without potential investigator bias. Intraoperative hemoglobin loss was significantly reduced (p < 0.01) by 42% in the high-dose group and by 17% in the low-dose group compared with loss in control subjects. Blood loss 6 hours after operation was 377 ml in the low-dose and 266 ml in the high-dose group compared with 630 ml in the placebo group (p < 0.05 and p < 0.001, respectively). The average number of transfusions with packed red blood cells was reduced 31% in the low-dose group and 45% in the high-dose group, but the reductions were not significant. In a subgroup of patients, markers for coagulation and fibrinolysis were studied to investigate whether a different extent of activation existed. Fibrinolysis as measured by D-dimer levels was completely inhibited by the high-dose regimen, but was only partly suppressed in the low-dose group as compared with findings in the placebo group. Thrombin generation during cardiopulmonary bypass as reflected by F1 + 2 levels was lower in patients treated with aprotinin, but the difference was not significant. Concentrations of thrombin inactivated by antithrombin III were not different between the groups. The observation that low-dose aprotinin significantly improved hemostasis but did not inhibit hyperfibrinolysis supports our previous finding that low-dose aprotinin mainly protects platelet adhesive function. The better result obtained with high-dose aprotinin may indicate the contribution of hyperfibrinolysis to bleeding after cardiopulmonary bypass. Because high-dose aprotinin is administered outside the period of full heparinization and might therefore increase the risk of thromboembolic complications, we propose a modification of the low-dose schedule to increase aprotinin levels sufficient for plasmin inhibition before release of the aortic crossclamp.