Off-Pump coronary artery bypass operation does not increase procoagulant and fibrinolytic activity: preliminary results

PECAM-1/Thrombus Ratio Correlates with Blood Loss during Off-Pump Coronary Artery Bypass Grafting (OPCAB) Surgery: A Preliminary Study

Platelet endothelial cell adhesion molecule 1 (PECAM-1) is considered an antiplatelet molecule. Previously, we introduced a new parameter called the PECAM-1/thrombus ratio, which indicates the proportion of PECAM-1 in the thrombus and provides a precise description of human platelet activity (in vitro). The aim of this study was to determine whether the PECAM-1/thrombus ratio could serve as a predictive factor for bleeding events during off-pump coronary artery bypass grafting (OPCAB). To achieve this, we collected blood samples from 20 patients scheduled to undergo OPCAB surgery. We assessed the PECAM-1/thrombus ratio by evaluating thrombus formation on collagen fibers under flow conditions. Subsequently, we compared the ability of the PECAM-1/thrombus ratio in predicting bleeding risk with other methods that evaluate hemostasis activity. These methods included assessing platelet P-selectin secretion, platelet exposure of phosphatidylserine, plasma coagulation and fibrinolysis system activity, and thrombus formation using the T-TAS assay. Our findings revealed a positive correlation between the PECAM-1/thrombus ratio and the amount of blood component units transfused (BCUT) during the OPCAB surgery. Furthermore, BCUT did not show any significant correlation with other measured hemostasis parameters. This preliminary study suggests that the PECAM-1/thrombus ratio might be a good predictor of bleeding risk during the OPCAB procedure.

Off-pump cardiac surgery abolishes complement activation

Background. This prospective randomized study compared the inflammatory response in patients undergoing elective on-pump and off-pump coronary artery bypass grafting. Patients and methods. Forty-four patients undergoing elective coronary artery bypass grafting were recruited with 22 patients randomized to on-pump heart surgery and 22 patients to off-pump coronary bypass surgery. Plasma levels of C3bc, the terminal SC5b-9 complement complex, myeloperoxidase, β -thromboglobulin and prothrombin fragment F1 + 2 were measured before the operation, intraoperatively, at termination of the operation, and two hours post-operatively. Results. Complement was markedly activated in the on-pump group as indicated by a significant increase in C3bc and SC5b-9 (p < 0.001 for both), whereas no complement activation was seen in the off-pump group (p = 0.001 between the groups). In contrast, both groups showed significant activation of neutrophils, platelets and coagulation, as indicated by an early increase in myeloperoxidase and a post-operative increase in β-thromboglobulin and F1 + 2, respectively. Notably, there were no inter-group differences with regard to neutrophil and platelet activation, whereas coagulation activation was more pronounced in the off-pump group (p < 0.01). Conclusions. Off-pump surgery completely eliminated the heart-lung machine-induced complement activation. Neutrophils and platelets were equally activated in both groups, whereas coagulation was enhanced post-operatively in the off-pump group. Perfusion (2007) 22, 251—256.

Off-pump surgery: is it beneficial in patients with left ventricular dysfunction?

On-pump coronary artery bypass surgery remains the gold standard for complex multivessel disease. Off-pump revascularization has matured as a technique over the last twenty years, but is used in less than 20% of cases worldwide. The poor uptake has been attributed to the significant learning curve in learning the procedure and conflicting evidence reports, together with concerns over mortality related conversion, graft patency and completeness of revascularization. Given these concerns, patient selection continues to be paramount and the subgroups that benefit most are hotly debated. Patients with left ventricular dysfunction constitute a high-risk subgroup which is enlarging in size. There is some evidence to suggest that avoidance of cardiopulmonary bypass in this group may lead to superior results in terms of early mortality, non-cardiac complications and organ dysfunction. Even with the theoretical risk of incomplete revascularization, the technique may be an attractive option in managing high-risk patients.

Activation of coagulation and fibrinolysis during coronary artery bypass grafting: a comparison between on-pump and off-pump techniques

Coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) is associated with intense activation of hemostatic mechanisms. But the precise knowledge of the effects of eliminating CPB in patients undergoing off-pump coronary artery bypass grafting (CABG) are not well established. The present study was carried out to compare and document the changes in selected coagulation and fibrinolysis variables in patients undergoing on-pump and off-pump CABG (OPCAB). A total of 42 patients of on-pump and 31 patients of off-pump CABG were selected for the study. Platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), Fibrinogen and D-dimer levels were measured immediately, 24 h and 7 days after operation and compared with the baseline preoperative values. Statistical analysis was done by mixed ANOVA for repeated measures and Post-hoc tests using the Bonferroni correction, Chi square and unpaired t test. All the parameters were significantly changed (P < 0.05) with the time. Platelet counts, fibrinogen and D-dimer levels were significantly different between on-pump and off-pump CABG patients on immediate and 24 h postoperative period and attained almost same level after 7 days of operation. Fibrinogen level and platelet counts were increased after a sharp fall in the immediate post-operative period whereas D-dimer levels were persistently increased with a sharp peak of rise in the immediate post-operative period in on-pump group. On-pump surgery was associated with excessive fibrinolytic activity immediately after operation. The off-pump group demonstrated less activation of coagulation and fibrinolysis and delayed postoperative response that became almost equal to the on-pump group in the later postoperative period.

Correlations between global clotting function tests, duration of operation, and postoperative chest tube drainage in pediatric cardiac surgery

BACKGROUND

Systemic coagulation disorders after cardiac surgery represent serious postoperative complications. There have been few reports, however, identifying preoperative coagulation tests that predict postoperative bleeding. The aim of the present study was to investigate the relationship between postoperative hemorrhage and coagulation parameters determined by global coagulation assays, to define potential predictive markers.

METHODS

Twenty-one pediatric patients were enrolled. Blood samples were collected before and 24 h after cardiac surgery. Laboratory investigations included platelet count, hematocrit, classical coagulation tests [prothrombin time, activated partial thromboplastin time, thrombin-antithrombin complex (TAT)], rotation thromboelastometry (ROTEM), and the thrombin generation test (TGT). The duration of the surgical procedure was recorded. Chest tube drainage was monitored for 24 h after operation as an index of postoperative hemorrhage.

RESULTS

Comparisons between preoperative and postoperative results indicated that TAT increased significantly after operation, whereas ROTEM parameters did not show a hypercoagulable pattern. Preoperative endogenous thrombin potential (ETP) measured in the TGT and clot formation time (CFT) in the ROTEM correlated with chest tube drainage. The classical coagulation tests were not informative. Postoperatively, peak height and ETP in TGT, all ROTEM parameters, and duration of surgery were correlated with chest tube drainage. Duration of surgery was correlated with postoperative ROTEM parameters but not with TGT. Postoperative maximum clot firmness and AUC were correlated with platelet count decrease ratio.

CONCLUSIONS

The preoperative CFT and ETP provide useful indices for predicting postoperative chest tube drainage volume. In addition, the duration of surgery also correlated with chest tube drainage and affected ROTEM parameters.

Current Status of Off-Pump Coronary Artery Bypass Surgery

The expanding indications for angioplasty coupled with the successful short and mid-term results of randomized controlled trials of drug-eluting stents have already had an unquestionable impact on the practice of coronary revascularization operations. However, coronary artery bypass grafting remains a major mode of therapy for coronary artery disease. It is likely that surgery will continue to be preferred for more complex subsets and that surgeons will have to continue to maintain good results in patients with more complex problems. Concerns regarding morbidity associated with conventional surgical myocardial revascularization on cardiopulmonary bypass have led to a resurgence of interest in off-pump bypass surgery during the last decade, with the expectation that it would be safer if cardiopulmonary bypass could be avoided. This review summarizes the impact of off-pump bypass surgery in reducing the morbidity and mortality associated with conventional coronary artery bypass on cardiopulmonary bypass by evaluating the current best-available evidence from randomized controlled trials and meta-analyses comparing off-pump surgery with conventional bypass grafting.

Heparin anticoagulation in patients undergoing off-pump and on-pump coronary bypass surgery

PURPOSE

The authors analyzed the coagulation data of patients who underwent on-pump coronary artery bypass graft (CABG) or off-pump coronary artery bypass surgery (OPCAB) in a randomized prospective trial.

METHODS

CABG and OPCAB patients received heparin anticoagulation at 400 U x kg(-1), and 180 U x kg(-1) plus 3000 U every 30 min, respectively. In addition, OPCAB patients received a rectal aspirin, 650 mg, during the procedure. Perioperative coagulation test results (platelet count, fibrinogen, prothrombin time, partial thromboplastin time [PTT], activated clotting time [ACT], and thromboelastography [TEG; Haemoscope] were collected from CABG (n = 99) and OPCAB (n = 98) patients. Residual heparin activity after protamine was measured, using an anti-activated factor X (Xa) assay, in 10 patients from each group.

RESULTS

Our study showed that the current anticoagulation regimen in the OPCAB patients achieved a peak ACT of 445 +/- 73 s, and it preserved platelet counts and fibrinogen levels. A residual heparin effect was detected, with residual anti-Xa heparin activity of 0.2 U x ml(-1) up to 2 h after surgery in the OPCAB group. Despite the residual anticoagulation, the OPCAB group had a similar TEG index of native blood, postoperative chest tube drainage, and non-erythrocyte transfusion rate as compared with the CABG group.

CONCLUSION

We have shown that the heparin anticoagulation regimen in OPCAB patients does not lead to an immediate hypercoagulable state. Total doses of heparin and protamine were lower in the OPCAB group compared with the CABG group, and there was a residual heparin effect on TEG and PTT in the early postoperative period in the OPCAB group.

Comparison of early platelet activation in patients undergoing on-pump versus off-pump coronary artery bypass surgery

OBJECTIVE

Cardiopulmonary bypass has been shown to be associated with platelet dysfunction, which has a potential for increasing the risk of perioperative bleeding. Off-pump coronary artery bypass surgery is thought to avoid this deleterious effect of pump use on platelets. However, the influence of off-pump coronary artery bypass surgery on platelets has not been thoroughly studied.

METHODS

Accordingly, we evaluated 60 patients undergoing coronary artery bypass grafting prospectively using cardiopulmonary bypass and warm cardioplegic arrest (n = 30) or an off-pump technique (n = 30). Platelet function was evaluated before and 2 hours after coronary artery bypass grafting.

RESULTS

Among patients undergoing on-pump coronary artery bypass surgery, all studies of platelet function were significantly abnormal after surgical intervention compared with results before surgical intervention. Similarly, among patients undergoing off-pump coronary artery bypass surgery, evidence of platelet dysfunction after surgical intervention was noted, with a lower platelet count and a higher proportion of P-selectin- and Annexin V-positive platelets. However, compared with the preprocedural value, the postprocedural decrease in platelet count (78,200 x 10(3)/microL vs 103,000 x 10(3)/microL) and platelet aggregation (0.8% vs 10.9%) and increase in bleeding time (0 minutes vs +1.3 minutes), P-selectin-positive platelets (6.0% vs 9.1%), and Annexin V-positive platelets (1.7% vs 3.7%) were significantly lower in the off-pump coronary artery bypass surgery group compared with those in the on-pump coronary artery bypass surgery group, respectively.

CONCLUSIONS

Early postoperative decrease in platelet count and increase in platelet activation occurs to a much lesser extent and does not alter bleeding time or adenosine diphosphate-induced platelet aggregation in patients undergoing off-pump coronary artery bypass surgery. This lack of significant effects on platelets might in part account for the potential decreased risk in bleeding and for the preserved hemostasis seen in patients undergoing off-pump coronary artery bypass surgery compared with those undergoing on-pump coronary artery bypass grafting surgery.

Does off-pump coronary artery bypass surgery reduce secretion of plasminogen activator inhibitor-1?

Prior studies showed that postoperative increase in plasminogen activator inhibitor-1 (PAI-1) levels is associated with an increased risk of graft occlusion after coronary artery bypass surgery (CABG). This prospective study aimed to compare the changes of PAI-1 antigen levels after off-pump and on-pump CABG. Forty-four patients admitted for elective CABG were randomised to on-pump (n=22) or off-pump (n=22) surgery. Serum samples were collected for estimation of PAI-1 and tissue plasminogen activator (t-PA) antigen levels preoperatively and 2 h after the operation. The groups were similar in terms of age, weight, gender ratio and extent of coronary disease, left ventricular function and number of grafts per patient. Fibrinogen and t-PA levels increased postoperatively in both the groups when compared with baseline values. After operation, statistical analysis revealed that increase of PAI-1 values was higher in off-pump group (44.1+/-9.1 vs. 25.3+/-6.9) than on-pump group (37.2+/-5.5 vs. 27.3+/-7.8, p=0.002). This study shows that increase in PAI-1 antigen values in patients who undergo off-pump (beating heart) CABG is significantly higher than in those who undergo conventional CABG with cardiopulmonary bypass.

Off-Pump Versus On-Pump Coronary Artery Surgery Identification of Fibrinolysis Using Rotation Thromboelastography; A Preliminary, Prospective, Randomized Study

The aim of this preliminary, prospective, randomized study was to compare rotation thromboelastography (roTEG) results and D-dimer levels in off-pump versus on-pump coronary surgery in order to identify the activation of fibrinolysis. Twenty patients scheduled for coronary bypass grafting were assessed (off-pump group A, n = 10; on-pump group B, n = 10). Blood samples for roTEG examination were taken preoperatively (t0), 15 minutes after sternotomy (t1), on the completion of peripheral bypass anastomoses (t2), and at the end of procedures (t3). The time points for D-dimer levels analyses were before operation, at the end of procedures, and 24 hours later. A certain degree of roTEG signs of fibrinolysis was noticed at time t2 in both groups and in group B these marks were quite widely, but not significantly expressed (P for intergroup differences for Lysis on Set Time at 60 and 150 minutes were P = 0.190 and P = 0.122, respectively), borderline differences were found for Maximum Clot Firmness (P = 0.082) with a lower mean value for group B (arithmetic means [95% confidence intervals]--57.7 [54.2; 61.2] mm). Completely expressed roTEG signs of hyperfibrinolysis were observed in 2 patients from group B. In group B also the highest geometric means of D-dimers (1326.0 [943.5; 1863.6] ng mL(-1)) and thus a dramatic intergroup difference (P < 0.001) were observed at the end of surgery; 24 hours later the significantly elevated D-dimer levels in both groups (A: 1070.0 [723.5; 1582.6] versus B: 1093.3 [732.0; 1632.9] ng mL(-1)) were equalized (P = 0.932). Our roTEG results display a slightly greater, but fairly subtle activation of fibrinolysis during the course of cardiopulmonary bypass, compared to off-pump cardiac surgery.

Early administration of clopidogrel is safe after off-pump coronary artery bypass surgery

BACKGROUND

Patients who undergo off-pump coronary artery bypass graft surgery (OPCAB) may be hypercoagulable with an increased risk of graft thrombosis due to the lack of platelet dysfunction that accompanies "on-pump" surgery. Clopidogrel may be indicated in these patients to prevent recurrent ischemic events. The purpose of this observational study was to determine the safety of early clopidogrel administration after OPCAB.

METHODS

Thirty-day follow-up of 364 consecutive OPCAB patients (January to June, 2002) was determined from a computerized database. One hundred ninety-three patients received clopidogrel 4 hours postoperatively if chest tube output was less than 100 cc/h for 4 hours, then daily for 4 weeks. Aspirin was administered preoperatively and postoperatively to all patients. Telephone follow-up was made 6 to 12 months after OPCAB.

RESULTS

None of the patients who received clopidogrel in the early postoperative period required reoperation for mediastinal hemorrhage. Mean chest tube drainage at 24 hours was 1,024 +/- 563 mL in patients who received clopidogrel and 942 +/- 501 mL in patients who did not receive clopidogrel. The total number of blood units transfused and the number of patients receiving blood transfusions were similar between groups. In-hospital mortality was 1.6% in patients who received clopidogrel and 3.5% in patients who did not receive clopidogrel. No group differences in mortality or adverse cardiac events were observed at 6 months. Gastrointestinal bleeding occurred in 2.2% clopidogrel patients versus 0.7% of patients who did not receive clopidogrel.

CONCLUSIONS

When administered according to our postoperative protocol, OPCAB patients can safely receive clopidogrel in the early postoperative period without increased risk for mediastinal hemorrhage.

Antithrombotic- and anticoagulation regimens in OPCAB surgery. A Nordic survey

OBJECTIVES

The aim of the survey was to determine current practices for antiplatelet- and heparin therapy in OPCAB surgery in the Nordic countries.

DESIGN

A postal survey questionnaire was sent to all 26 departments of Cardiothoracic Surgery in Norway, Sweden, Iceland, Finland, and Denmark.

RESULTS

The overall response rate was 100%. The respondents performed between 130 and 1000 CABG procedures per year. Between 0.3% and 42.0% of these procedures were performed as OPCAB. Preoperative antiplatelet therapy was administered by 48%, while 96% routinely administer postoperative antiplatelet therapy. In the postoperative antiplatelet therapy there was a trend toward a combination of aspirin and low molecular weight heparin. Perioperative anticoagulation practices with heparin varied among departments as well as reversal with protamine. Eighty percent of the respondents register postoperative complications.

CONCLUSION

In the Nordic countries there is no uniform practice regarding antiplatelet therapy pre- and postoperatively as well as heparin therapy perioperatively. Dose regimens are highly variable and standard protocols have not yet been developed.

[Inflammatory response and haematological disorders in cardiac surgery: toward a more physiological cardiopulmonary bypass]

The systemic inflammatory response in cardiac surgery is closely related to the haemostasis disturbances. It is responsible of a significant morbidity and mortality that was previously suspected to be caused by cardiopulmonary bypass alone. However, it is time now to clearly identify the factors that are material-dependent from that material-independent. From this point of view, off-pump surgery allowed for better comprehension of the multiple sources of the inflammatory response. Numerous pathways are activated, involving complement, platelets, neutrophiles and monocytes. The tissue pathway of the coagulation system, through tissue factor, is of major importance and has to be surgically considered in order to reduce the whole body inflammatory response postoperatively. The quality of the extracorporeal perfusion through its consequences on organ perfusion, particularly in the splanchnic area, also participates to this pathophysiological process. Beyond the progress of technology provided by the industry, particularly the minimally extracorporeal circulation derived from off-pump surgery evolution, the surgical approach is of major importance in the control of the systemic inflammatory response and must not be ignored yet.

Activation of the coagulation system during coronary artery bypass grafting: Comparison between on-pump and off-pump techniques

OBJECTIVE

The activation of the coagulation and fibrinolytic systems and platelet function in patients undergoing coronary artery bypass surgery on-pump or off-pump techniques was compared.

METHODS

Thirty-two patients were randomly assigned to on-pump or off-pump coronary artery bypass grafting. Heparin was given at the same dose. Activation of the coagulation and fibrinolytic systems was evaluated by measurement of several markers. Platelet function was evaluated by in vitro bleeding time test. Blood samples were collected at 7 different times, up to postoperative day 6.

RESULTS

Overall tissue factor production was similar in the two groups. Thrombin formation was more elevated in the on-pump group (P < .001), particularly during the operation; prothrombin fragment 1.2 discharge values were higher than the preoperative ones (P = .002). Levels of tissue-plasminogen activator showed no difference between the groups (P = .1). D-dimers release was higher in the on-pump group (P = .0002). In vitro bleeding time was longer in the on-pump group (P < .0001), particularly in the first 24 hours; it was not prolonged in the off-pump group. In both groups, regardless of aspirin treatment, discharge in vitro bleeding times were lower than the preoperative ones (P < .01).

CONCLUSION

Although the extrinsic coagulation pathway is similarly activated, thrombin formation is more pronounced in patients having on-pump bypass grafting. Patients subjected to off-pump bypass grafting have normally functioning platelets and a weak activation of the fibrinolytic system. At discharge, both groups have preserved platelet function and increased thrombin formation. Further studies with angiographic evaluation are needed to establish a correlation between coagulation parameters, platelet function, and graft patency.

Impact of off-pump coronary artery bypass surgery on postoperative bleeding: current best available evidence

Cardiopulmonary bypass (CPB) is a prerequisite for open-heart surgery, and is a procedure routinely used. CPB exposes blood to artificial surfaces, to mechanical trauma from the pump, to alterations in temperature, and to dilution with fluids, whole blood, plasma products, and drugs, and leads to the activation of platelets, coagulation, and fibrinolysis. Coagulopathy during cardiac surgery with CPB results in impairment in hemostasis and subsequently higher morbidity and mortality. Recent advances in surgical techniques and postoperative management have aimed at reducing postoperative morbidity and mortality. Off-pump coronary artery bypass (OPCAB) surgery is one such advance that attempts to avoid the deleterious effects of extracorporeal circulation by performing myocardial revascularization without CPB. Emerging evidence from several randomized controlled trials (RCTs) as well as large registries such as the Society of Thoracic Surgeons (STS) database suggests that OPCAB reduces the postoperative morbidity and mortality. This review article attempts to evaluate the current best available evidence from RCTs on the impact of OPCAB on postoperative bleeding and transfusion requirements.

Hemostasis in Off-Pump Compared to On-Pump Coronary Artery Bypass Grafting: A Prospective, Randomized Study

BACKGROUND

We hypothesized that off-pump coronary artery bypass grafting has less impact on the hemostatic systems than on-pump surgery.

METHODS

Thirty-one patients were randomized to on-pump or off-pump coronary artery bypass grafting. Factors of hemostasis as well as markers of endothelial activation were measured up to 24 hours after the operation: Fibrin D dimer, prothrombin fragment 1+2, alpha2-macroglobulin, protein C1 esterase inhibitor, fibronectin, and von Willebrand factor. Overall hemostasis potential, overall coagulation potential, and overall fibrinolysis potential were determined with a previously developed assay. We also measured platelet count before and after surgery.

RESULTS

Fibrin D dimer and prothrombin fragment 1+2 concentrations were lower during surgery in the off-pump group (p < 0.001). Four hours after admission to the intensive care unit, these differences were eliminated. alpha2-macroglobulin, protein C1 esterase inhibitor, fibronectin, and von Willebrand factor concentrations did not differ between groups (p = 0.59, p = 0.28, p = 0.22, and p = 0.69). Protein C1 esterase inhibitor and von Willebrand factor concentrations increased over time (p < 0.001) in both groups. Overall hemostasis potential and overall coagulation potential increased over time (p < 0.001), while overall fibrinolysis potential decreased (p < 0.001) with no difference between groups (p = 0.69, p = 0.91). Platelet count decreased on the first postoperative day (p < 0.001), but increased from the first to the third postoperative day (p = 0.004) in both groups without any inter group difference (p = 0.82).

CONCLUSIONS

There was a tendency toward less activation of coagulation and fibrinolysis in low-risk patients during elective off-pump coronary artery bypass surgery when compared with on-pump surgery.

Safety, efficacy, and cost of intraoperative cell salvage and autotransfusion after off-pump coronary artery bypass surgery: A randomized trial

OBJECTIVE

We evaluated, in a randomized controlled trial, the safety and effectiveness of intraoperative cell salvage and autotransfusion of washed salvaged red blood cells after first-time coronary artery bypass grafting performed on the beating heart.

METHODS

Sixty-one patients undergoing off-pump coronary artery bypass grafting surgery were prospectively randomized to autotransfusion (n = 30; receiving autotransfused washed blood from intraoperative cell salvage) or control (n = 31; receiving homologous blood only as blood-replacement therapy). Homologous blood was given according to unit protocols.

RESULTS

The groups were well matched with respect to demographic and comorbid characteristics. Patients in the autotransfusion group had a significantly higher 24-hour postoperative hemoglobin concentration (11.9 g/dL; SD, 1.41 g/dL) than those in the control group (10.5 g/dL; SD, 1.37 g/dL) (mean difference, 1.02 g/dL; 95% confidence interval, 1.60-0.44 g/dL; P = .0007), as well as a 20% reduction in the frequency of homologous blood product use (11/31 vs 5/30; P = .095). Autotransfusion of washed red blood cells was not associated with any derangement of thromboelastograph values or laboratory measures of clotting pathway function (prothrombin time, activated partial thromboplastin time, and fibrinogen levels), increased postoperative bleeding, fluid requirements, or adverse clinical events. There was no statistical difference between groups in the total operation, hospitalization, and management costs per patient (median difference, USD 1015.90; 95% confidence interval, -USD 2260 to USD 206; P = .11). Conclusions Intraoperative cell salvage and autotransfusion was associated with higher postoperative hemoglobin concentrations, a modest reduction in transfusion requirements, no adverse clinical or coagulopathic effects, and no significant increase in cost compared with controls. This study supports its routine use in off-pump coronary artery bypass grafting surgery.

Plasmin generation and D-dimer formation during cardiopulmonary bypass

The purpose of this study was to estimate the in vivo rates of plasmin and D-dimer generation for comparison with the rate of fibrin formation during cardiopulmonary bypass (CPB), a procedure known to induce a hyperfibrinolytic state. Plasmin and D-dimer generation rates were based on measured levels of antiplasmin, plasmin-antiplasmin complex and D-dimer obtained before, during and after CPB from nine males, combined with a computer model of each patient's vascular system that continuously accounted for secretion, clearance, hemodilution, blood loss and transfusion. At baseline the average plasmin and D-dimer generation rates were 0.27 +/- 0.07 and 0.18 +/- 0.07 pmol/s, respectively. Within 5 min of CPB initiation, plasmin generation increased over 100-fold to 36 +/- 40 pmol/s while D-dimer generation increased 200-fold to 37 +/- 39 pmol/s. For the remainder of the CPB, average plasmin and D-dimer generation remained 20-fold to 30-fold above baseline levels. During CPB, the rate of D-dimer generation was similar to the rate of total fibrin formation, indicating that, in the absence of fibrinolytic inhibitors, CPB induces plasmin-mediated removal of fibrin from the vascular system at a rate similar to the rate of fibrin formation.