Preoperative therapy of low-dose aspirin in internal mammary artery bypass operations with and without low-dose aprotinin

Does the Use of Preoperative Aspirin Increase the Risk of Bleeding in Patients Undergoing Coronary Artery Bypass Grafting Surgery? Systematic Review and Meta-Analysis

BACKGROUND

The traditional recommendation has been to stop Aspirin seven to 10 days prior to coronary artery bypass surgery to reduce the potential risk of bleeding. A few reports have shown that Aspirin did not increase the risk of bleeding and may be beneficial to be continued until the time of surgery. The objective of this review was to evaluate the effect of preoperative Aspirin on bleeding in patients undergoing elective bypass surgery.

METHODS

A meta-analysis of 10 randomized and nonrandomized studies reporting comparisons between Aspirin and control was undertaken. The primary outcome was the total amount of postoperative chest tube drainage. Secondary outcomes were the number of units of packed red blood cell transfusion, platelet transfusion, fresh frozen plasma transfusion, and number of patients reexplored for bleeding.

RESULTS

Ten studies, involving 1748 patients, met the inclusion criteria for this review of whom 913 were in the Aspirin group and 835 were in the control group. Pooling the results of all studies showed a significant increase in blood loss and transfusion of red blood cells and fresh frozen plasma in the Aspirin group (p < 0.05). There was no significant difference between the two groups in the rate of platelet transfusion, or the incidence of reexploration (p > 0.05). Included studies were heterogeneous and of low methodological quality.

CONCLUSION

Aspirin is associated with increased chest tube drainage and may be associated with a greater requirement for blood products. High-quality prospective studies are warranted to reassess the effect of Aspirin on important postoperative outcomes.

Duration of increased bleeding tendency after cessation of aspirin therapy

BACKGROUND

Aspirin has a significant effect on hemostasis, so it is often recommended that patients taking aspirin discontinue treatment before elective surgery. While off aspirin, these patients may be at risk of thrombosis. The optimum period of time that aspirin should be withheld is controversial. The aim of this study was to establish the duration of the antihemostatic effect of prolonged aspirin therapy.

STUDY DESIGN

In a prospective study, 51 healthy volunteers were randomly assigned into 3 groups, each receiving an identical tablet for 14 days. One group received a placebo tablet; individuals in the other two groups received either 75 mg or 300 mg of aspirin once a day. Template bleeding times and specific platelet function testing (using the PFA-100; Dade Behring) were carried out on subjects before therapy and again after its completion until they returned to baseline.

RESULTS

Thirty-eight volunteers complied sufficiently with the protocol to provide useful results. All bleeding times normalized within 96 hours and all platelet function tests within 144 hours after stopping aspirin. There was no demonstrable hemostatic defect in any volunteer persisting by or beyond the sixth day after treatment cessation. There was no apparent difference in duration of effect between those taking either 75 mg or 300 mg of aspirin.

CONCLUSIONS

This study uses sensitive measures of platelet function to demonstrate the duration of increased bleeding tendency after withdrawal of aspirin therapy. It supports discontinuation of aspirin therapy 5 days before elective surgery (with the operation being performed on the sixth day).

Effect of preoperative aspirin use on mortality in coronary artery bypass grafting patients

BACKGROUND

Discontinuing aspirin use in patients before coronary artery bypass grafting (CABG) has focused on bleeding risks. The effect of aspirin use on overall mortality with this procedure has not been studied.

METHODS

We performed a case patient-control patient study of the 8,641 consecutive isolated CABG procedures performed between July 1987 and May 1991 in Maine, New Hampshire, and Vermont. Patients included all 368 deaths. Each case patient was paired with approximately two matched survivors (control patients). Aspirin use was defined by identification of ingestion within 7 days before the operation.

RESULTS

CABG patients using preoperative aspirin were less likely to experience in-hospital mortality in univariate (odds ratio [OR] = 0.73, 95% confidence interval [0.54, 0.97]) and multivariate [OR = 0.55, (0.31, 0.98)] analysis compared to nonusers. No significant difference was seen in the amount of chest tube drainage, transfusion of blood products, or need for reexploration for hemorrhage between patients who did and did not receive aspirin.

CONCLUSIONS

Preoperative aspirin use appears to be associated with a decreased risk of mortality in CABG patients without significant increase in hemorrhage, blood product requirements, or related morbidities.

Activation of the protein C system during cardiopulmonary bypass with and without aprotinin

BACKGROUND

The protein C system is important in the regulation of hemostasis. We studied its behavior during coronary artery bypass grafting procedures with and without aprotinin treatment using assays sensitive for activation of the protein C system.

METHODS

In a prospective, double-blind, randomized study of 48 patients we investigated the levels of antigen to proteins C and S and of the complexes between activated protein C with its two major plasma inhibitors, protein C inhibitor and alpha1-antitrypsin in patients treated with placebo (n = 17), low-dose (n = 15), and high-dose (n = 16) aprotinin during elective coronary artery bypass grafting.

RESULTS

The levels of proteins C and S showed a rapid decrease after heparinization, decreased greatly after start of cardiopulmonary bypass, and remained stable during cardiopulmonary bypass. Activated protein C inhibitor complexes were markedly elevated at the start of the procedure. Activated protein C-alpha1-antitrypsin decreased greatly after the start of cardiopulmonary bypass and remained stable during cardiopulmonary bypass. A significant peak was observed at the intensive care unit. Activated protein C-protein C inhibitor levels showed a peak after heparinization in accordance with the accelerating effect of heparin on the complex formation but decreased thereafter. Treatment with aprotinin did not notably alter any of the measured patterns.

CONCLUSIONS

In this study no evidence was found for increased activation of the protein C system during coronary artery bypass grafting. Administration of aprotinin did not result in different patterns of activation of the protein C system.

Aprotinin counterbalances an increased risk of peri-operative hemorrhage in CABG patients pre-treated with Aspirin

OBJECTIVE

As Aspirin (ASA) has proven efficacy in preventing patients with CAD from complications related to cardiovascular diseases, most patients scheduled for CABG are treated with ASA therapy. Consequently, impaired hemostasis is a problem in the management of CABG patients. Clinical studies have shown that Aprotinin can reduce bleeding and the use of blood products by 50% in patients both with and without pre-operative ASA therapy. Concerning the combined effect of peri-operative low-dose ASA therapy and intra-operative high-dose Aprotinin therapy, the gathering of additional and prospective data seemed to be necessary.

METHODS

We conducted a double-blind two-centre randomised three-arm study in patients with elective primary CABG surgery. Three groups have been tested, comprising 119 patients in total (group A: ASA + Aprotinin, group B: placebo + Aprotinin, group C: placebo + placebo) to investigate a possible reduction of bleeding in Aprotinin treated patients. For all patients, thromboxane levels were used to identify ASA or placebo treatment.

RESULTS

The post-operative blood loss is significantly reduced by 21% after Trasylol administration (B vs. C; P = 0.009). The unexpected result of this study has been that the pre-treatment with ASA led to a further reduction of 18% (A vs. C; P < 0.0001). The difference between the two Aprotinin groups (A and B) is significant (P = 0. 01) in favour of ASA pre-treatment. Myocardial infarction (MI) had been diagnosed at levels of 1.8% in total (2/113), 2.6% (1/38) in group B and 3.2% (1/31 ) in group C. An additional blinded evaluation of ECG, enzyme levels and clinical status revealed 'definite, probable and possible' MIs of 5% in group A, compared to 16% in group B and 13% in group C, thus providing no evidence for a higher risk of infarction by Aprotinin treatment. When comparing the ASA group to non-ASA pre-treatment, a strong trend towards a reduction in MI rate becomes obvious, from 15% to 5% in favour of the ASA pre-treatment (P = 0.08). Concerning other peri-operative complications, no statistical difference between the groups could be detected.

CONCLUSIONS

A reduction in post-operative blood loss in primary elective CABG surgery with intra-operative Aprotinin treatment could be confirmed. A low-dose ASA treatment combined with a high-dose aprotinin administration during surgery not only neutralized a potentially higher risk of bleeding, but did in fact reduce the post-operative blood loss. The protective effect of ASA on peri-operative MI has been evident through a reduction of MI rate in ASA treated patients.

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.

Pharmacological prophylaxis of bleeding in surgical patients treated with aspirin

A Medline search and subsequent meta-analysis shows that pre-operative aspirin increases blood loss and transfusion requirements in patients undergoing coronary artery bypass grafting. Both aprotinin and desmopressin are effective in counteracting this. There are almost no data on the effects of bleeding of aspirin, aprotinin and desmopressin in other procedures.

Reduction in requirements for allogeneic blood products: pharmacologic methods

BACKGROUND

Numerous articles describe the reduction of perioperative bleeding by the therapeutic or prophylactic administration of drugs such as prostacyclin, desmopressin, and natural or synthetic antifibrinolytics.

METHODS

A review of the literature was carried out to help the reader define the indications of these drugs during cardiopulmonary bypass operations, highlight the questions that remain concerning their indications and modes of action, and suggest future studies to answer these remaining questions.

RESULTS

Prostacyclin reduces platelet trauma induced by extracorporeal circulation but does not effectively reduce postoperative bleeding and transfusion requirements. Desmopressin acts as a "glue," improving platelet adhesion, and may be effective when postoperative bleeding is excessive, but its routine use in cardiac operations cannot be recommended. Natural and synthetic antifibrinolytics inhibit plasmin and plasmin-induced platelet dysfunction. These agents have been shown to decrease bleeding and the need for allogeneic transfusions after open heart operations. However, with antifibrinolytic drugs, the risk of thromboembolic phenomena cannot be neglected. With aprotinin, this risk appears to be minimal when the drug is used at concentrations high enough to inhibit plasma kallikrein also.

CONCLUSIONS

Prophylactic antifibrinolytics are efficacious, but their routine use remains controversial, both for economic reasons and for fear of thromboembolic complications.

Hemostatic efficacy of dipyridamole, tranexamic acid, and aprotinin in coronary bypass grafting

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 10(9)/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.