Preoperative hemostatic activity and excessive bleeding after cardiopulmonary bypass

Activated Partial Thromboplastin Time and Mortality in Coronary Artery Bypass Grafting Patients

Background. To evaluate the prognostic value of preoperative activated partial thromboplastin time (APTT) in patients who underwent coronary artery bypass grafting (CABG). Methods. All data were extracted from the Medical Information Mart for Intensive Care III (MIMIC-III) database. The study population was divided to two groups according to the optimal cut-off value of APTT calculated by X-tile software, and Cox proportional hazard model was used to define independent effect of APTT on 4-year mortality. Survival curves were estimated by the Kaplan-Meier method, and the area under the receiver-operating characteristic curve (AUC) was calculated to compare APTT with other severity scores. Propensity score matching (PSM) analysis were applied to ensure the robustness of this study. Results. A total of 2,706 patients were included. The optimal cut-off value of APTT for 4-year mortality was 44 seconds. The Cox proportional hazard model showed that patients with $\text{APTT}\ge 44$ had a significantly higher risk of all-cause death than those with $\text{APTT}<44$ both before (HR (95% CI), 1.42 (1.16-1.74), $P<0.001$ ) and after PSM (HR (95% CI), 1.47 (1.14-1.89), $P=0.003$ ). The survival curves showed that patients with longer APTT had a significantly lower 1-year and 4-year cumulative survival probability. The ROC of APTT combined with other severity scores significantly increased predictive ability for 1-year and 4-year mortality. Conclusions. A longer APTT (≥44) was associated with a higher risk of mortality and can serve as a prognostic predictor in CABG patients.

Factor XIII Deficiency and Thrombocytopenia Are Frequent Modulators of Postoperative Clot Firmness in a Surgical Intensive Care Unit

OBJECTIVE

Fibrinogen and factor XIII (FXIII) have been shown to critically influence clot firmness in the intraoperative setting and thus likely influence intraoperative bleeding. We were interested to identify potential modulators of postoperative clot firmness in a tertiary care hospital surgical intensive care unit setting, independent of their clinical course during surgery.

METHODS

272 day-shift consecutive patients were evaluated for whole blood clot firmness evaluated by the ROTEM® EXTEM thrombelastometric assay and various potential modulators of clot firmness upon arrival at the surgical intensive care unit (SICU).

RESULTS

Maximum clot firmness on the SICU was found to be independently influenced by the amount of colloids given during surgery as well as by platelet count, fibrinogen concentration, and FXIII activity at the time of SICU admission. In patients with lowest clot firmness, FXIII activity was the most important independent modulator of clot firmness; in patients with the highest clot firmness, platelet count and fibrinogen concentration were the most important modulators of clot firmness. Deficiencies (i.e., results below normal range) of these modulators of clot firmness were most prevalent for FXIII (activity < 70%: 45% of cases), which was significantly more frequent than thrombocytopenia (<150 × 10⁹/l: 32%) or fibrinogen deficiency (<1.5 g/l: 6%).

CONCLUSIONS

Postoperative clot firmness as evaluated by whole blood thrombelastometry (ROTEM EXTEM assay) is independently and frequently modulated though FXIII activity and the platelet count, while fibrinogen concentration is also an independent but much less frequent modulator. Different modulators show different influences, depending on the clot firmness being present. Colloids infused during surgery also independently modulate postoperative clot firmness. Based on our data, strategies can be developed to improving postoperative care of patients with bleedings or at risk for bleeding.

Evidence Based Coagulation Monitors: Heparin Monitoring, Thromboelastography, and Platelet Function

The hemostatic management of patients undergoing cardiac surgery is a unique challenge. Since its inception, cardiopulmonary bypass (CPB) has required meticulous attention to maintaining adequate anticoagulation. New anticoagulants and alternative monitoring techniques present an opportunity to investigate potential advances in the area of anticoagulation for CPB. Hemostasis after CPB is still a vexing problem, and the addition of antiplatelet medication to the platelet defect already incurred during CPB has led to hemorrhagic complications in cardiac surgery. The two opposing processes of anticoagulation and hemostasis must be managed carefully and modified with respect to the patient's hematologic status and desired hemostatic outcome. Cardiac surgical patients consume a much larger fraction of perioperative blood transfusions than the percentage of the surgical population they represent. Thus, during CPB, careful attention must be paid to optimal anticoagulation, platelet quiescence, biocompatible circuitry and interventions, and to monitoring hemostasis. The multifactorial etiology of the CPB-induced hemostatic defect requires a multimodal approach to blood conservation and hemostasis monitoring, including heparin maintenance and sophisticated point-of-care hemostasis monitoring. Each technology has its own attributes and each may be suitable for different populations based upon the expected defects being measured. This article reviews the evidence supporting the use of point-of-care monitors in coagulation and hemostasis management in cardiac surgical patients.

Simultaneous testing of the heparin effect on the soluble phase and platelet component of hemostasis

BACKGROUND

This study assessed the anticoagulant effect of heparin on both platelet activity and soluble phase coagulation.

METHODS AND RESULTS

Blood samples were collected from 32 patients undergoing cardiac catheterization before and 5 minutes after a heparin injection (2000 U). Activated clotting time (ACT), activated partial thromboplastin time (aPTT), and whole blood platelet aggregation [adenosine diphosphate (ADP) and collagen] were compared with the flow device variables platelet hemostasis time (PHT) and collagen-induced thrombus formation (CITF). Before heparin, all patients had a normal aPTT and all but 1 had a normal ACT. After heparin, all patients showed a prolonged aPTT and ACT. In contrast, the flow device showed considerable variability after heparin. Only 47% of patients increased both PHT and CITF above the upper limit of normal, and 13% did not prolong either. After heparin, enhanced platelet aggregation to ADP and collagen occurred in 53% and 63% of patients, respectively.

CONCLUSIONS

Although patients seem to have an anticoagulant effect after heparin based on ACT and aPTT results, the flow device identified a lack of any hemostatic impairment in 25 to 41% of patients. These findings probably reflect the variable effect of heparin on platelet function and may explain the poor heparin effect or, alternatively, the excessive bleeding after heparin administration that occurs in some patients.

Monitoring the Hematologic Complications of Cardiopulmonary Bypass

Patients undergoing cardiopulmonary bypass (CPB) procedures have a variety of hemostatic defects that lead to bleeding and the frequent need for transfusion of allogeneic blood products. Dilution of the patient's blood volume by the extracorporeal circuit priming so lution causes depletion of platelets and coagulation factor levels. Contact of blood with the extracorporeal circuit induces a hemorrhagic diathesis through a vari ety of mechanisms. Contact activation causes the for mation of kallikrein, bradykinin, and complement acti vation, leading to a whole-body inflammatory reaction. Intrinsic coagulation is stimulated, leading to subse quent activation of the fibrinolytic system. Platelet dys function caused by the effects of the extracorporeal circuit on platelet membrane integrity and the effects of circulating platelet inhibitors have also been described. The use of high-dose heparin for CPB mitigates these effects but does not completely eliminate them. Prota mine, administered to antagonize heparin's effects, has antiplatelet properties and anticoagulant effects when given in excess. Because of the numerous hemostatic insults incurred during and after CPB, complex moni toring techniques are necessary to ensure adequate anticoagulation, adequate heparin neutralization, and normal platelet function. Coagulation monitoring has allowed more specific identification of particular distur bances of hemostasis and has been linked with a reduc tion in hemorrhagic complications after CPB. Copyright © 2001 by W.B. Saunders Company.

Management approaches to platelet-related microvascular bleeding in cardiothoracic surgery

Patients undergoing cardiac surgery with cardiopulmonary bypass are at increased risk for microvascular bleeding that requires perioperative transfusion of blood components. Platelet-related defects have been shown to be the most important hemostatic abnormality in this setting. The exact association between preoperative use of potent platelet inhibitors and either bleeding or transfusion in patients undergoing cardiac surgical procedures is currently being defined. Laboratory evaluation of platelets and coagulation factors can facilitate the optimal administration of pharmacologic and transfusion-based therapy. However, their turnaround time makes laboratory-based methods impractical for concurrent management of surgical patients, which has led many investigators to study the role of point-of-care coagulation tests in this setting. Use of point-of-care tests of hemostatic function can optimize the management of excessive bleeding and reduce transfusion. Accordingly, point-of-care tests that assess platelet function may also identify patients at risk for acquired, platelet-related bleeding. The ability to reduce the unnecessary use of blood products and to decrease operative time or reexploration rates has important consequences for blood inventory, blood costs, and overall health care costs.

Optimal management of bleeding and transfusion in patients undergoing cardiac surgery

Patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) are at increased risk for excessive perioperative blood loss requiring transfusion of blood products. Point-of-care evaluation of platelets, coagulation factors, and fibrinogen can enable physicians to rapidly assess bleeding abnormalities, facilitate the optimal administration of pharmacological and transfusion-based therapy, and also identify patients with surgical bleeding. The ability to reduce the unnecessary use of blood products in this setting has important implications for emerging issues in blood inventory and blood costs. The ability to decrease surgical time, along with exploration rates, has important consequences for health care costs in an increasingly managed health care environment.

Platelets and soluble fibrin promote plasminogen activation causing downregulation of platelet glycoprotein Ib/IX complexes: protection by aprotinin

Blood loss during and after open-heart surgery with cardiopulmonary bypass (CPB) is largely caused by platelet dysfunction. Previous studies indicate that plasmin can induce platelet dysfunction and affect primary hemostasis by proteolytic degradation and/or redistribution of essential platelet membrane glycoprotein complexes such as the glycoprotein Ib/IX complex. In this study, we present a model for plasmin generation localized on the platelet surface. Platelets treated with soluble fibrin or platelets in a mixture with soluble fibrin, t-PA, and plasminogen caused a significantly increased plasmin generation (p<0.01), dependent on t-PA, soluble fibrin, and platelet concentration. The plasmin generation resulted in a downregulation of platelet membrane glycoprotein Ib/IX glycoprotein complexes. Finally, we demonstrated that inhibitors of fibrinolysis, such as %2-antiplasmin, tranexamic acid, and aprotinin, can inhibit plasmin activity in the fluid phase. The downregulation of platelet glycoprotein Ib/IX complexes, however, was only prevented by aprotinin and not by alpha2-antiplasmin and tranexamic acid. These in vitro observations suggest a platelet localized activation of plasminogen, dependent on t-PA, enhanced by the presence of soluble fibrin. Since high concentrations of soluble fibrin and elevated levels of t-PA during CPB are observed, plasmin activity on the platelet surface during this period is anticipated. This plasmin activity reduces platelet metabolic functions and can be directed towards membrane glycoproteins such as glycoprotein Ib/IX complexes, thereby affecting hemostasis during and after CPB.

Preoperative values of molecular coagulation markers identify patients at low risk for intraoperative haemostatic disorders and excessive blood loss

Conventional laboratory investigations of haemostasis like prothrombin time and activated partial thromboplastin time are not useful in predicting and managing intra-operative bleeding complications. In order to establish a possible "perioperative reference range" for thrombin generation prothrombin fragment F1+2 (F1+2) and fibrin degradation (D-dimer) markers, we measured F1+2 and D-dimer concentrations before surgery (but after induction of anaesthesia), 30 minutes into surgery, 10 minutes after the event expected to induce the maximal activation of the haemostatic systems, 90 minutes after surgery and on postoperative days 1 and 2 in 226 consecutive patients. Samples were collected from arterial lines. Twenty patients developed a clinically defined, intraoperative disorder of haemostasis, 206 did not. Patients with an intraoperative disorder of haemostasis had significantly higher preoperative F1+2 and D-dimer concentrations. Preoperative values for F1+2 and D-dimer concentrations above the 75th percentile of patients without an intraoperative disorder of haemostasis indicated a 2.70 to 2.88 fold risk of developing an intraoperative disorder of haemostasis (odds ratios were 3.04, 3.12 and 3.29 for D-dimer, ELISA, F1+2, and D-dimer latex tests, respectively with 95% confidence intervals from 1.20 to 8.46) with negative predictive values of 94%, but positive predictive values of only 16% to 26%. These data suggest that preoperative determination of molecular markers might be helpful in identifying a group of patients at high risk for intraoperative disorder of haemostasis by exclusion of low risk patients. Validation of such an approach requires a prospective trial.

Predictors of blood loss after coronary artery bypass grafting

OBJECTIVE

To assess the predictive value of variables possibly associated with blood loss after coronary artery bypass grafting (CABG).

DESIGN

A prospective study.

SETTING

A university hospital.

PARTICIPANTS

Eighty-nine patients scheduled for elective CABG.

INTERVENTIONS

Blood samples were drawn before and after surgery. Chest tube drainage was measured hourly until removal of drains.

MEASUREMENTS AND MAIN RESULTS

Activation of coagulation and fibrinolysis, routine clotting tests, and expression of platelet surface antigens were analyzed using flow cytometry. A significant correlation was found among blood loss and activated partial thromboplastin time, fibrinogen, prothrombin fragment 1 + 2, D-dimers, platelet count, GPIb and P-selectin expression on platelets, use of internal thoracic artery, cross-clamp time, and thrombin-antithrombin III complex. In a multiple regression model, glycoprotein (GP) Ib expression on platelets, platelet count, use of internal thoracic artery, and D-dimers were significantly associated with blood loss. Logistic regression analysis showed that GPIb and D-dimers predicted an increased blood loss with a positive predictive value of 73% and a negative predictive value of 91%.

CONCLUSIONS

Postoperative D-dimers and GPIb expression may be useful to exclude nonsurgical causes in bleeding patients after CABG.

Different anticoagulants and platelet reactivity in cardiac surgical patients

A technique for assessing platelet reactivity to shear stress from nonanticoagulated blood samples was employed to compare the relative effects of an unfractionated heparin, a low-molecular-weight heparin, and hirudin. The in vitro platelet effect of unfractionated heparin (5 U/mL) was measured in 290, the effect of a low-molecular-weight heparin (1 anti-Xa unit/mL) in 74, and the effect of hirudin (8 micrograms/mL) in 50 cardiac surgical patients. The relative proportions of patients exhibiting an enhanced platelet reactivity, a mild to moderate inhibition, and a severe inhibition were, respectively: 8.6%, 58.6%, and 32.8% for unfractionated heparin; 22%, 66%, and 12% for the low-molecular-weight heparin; and 6%, 66%, and 28% for hirudin. At the concentrations examined, a significantly greater proportion (p < 0.01) of the patients exhibited enhanced platelet reactivity and a significantly smaller proportion (p < 0.01) showed severely inhibited platelet reactivity associated with the low-molecular-weight heparin versus the unfractionated heparin, whereas there was no significant difference between the patients treated with hirudin and unfractionated heparin. Although the relevance of this study is limited because the clinically appropriate concentration of the alternative anticoagulants and comparative doses are unknown, it can be inferred that low-molecular-weight heparin may reduce the blood loss associated with cardiopulmonary bypass.

Reduction of heparin binding to and inhibition of platelets by aprotinin

The direct effect of aprotinin on in vitro platelet function was assessed by hemostatometry (n = 10). No significant enhancement was demonstrated. However, aprotinin reduced platelet inhibition secondary to heparin. Hemostatometry demonstrated a significant preservation of in vitro platelet function (n = 25) (p = 0.04), which was particularly marked (p = 0.003) in the subgroup (n = 7) demonstrating a severe inhibition of platelet function with heparin. Aprotinin significantly reduced the binding of tritium-labeled heparin to both nonactivated (n = 25) (p = 0.004) and activated platelets (n = 25) (p < 0.0001). We conclude that interference with heparin-induced inhibition of platelet function by aprotinin may be one of its hemostatic actions in cardiac surgery. This effect is probably secondary to aprotinin reducing binding of heparin to platelets.

Aprotinin in perspective

Aprotinin is a nonspecific serine protease inhibitor extracted from bovine lung. It was first used during cardiopulmonary bypass to inhibit plasmin-induced complement activation. By chance significant reductions of blood loss and blood requirements were noted in treated patients. Subsequent investigation showed improved hemostasis to result from protection of platelet adhesive receptors (Gp Ib) at the onset of cardiopulmonary bypass. Without aprotinin the contact system of plasma is massively activated on first passage through the cardiopulmonary bypass circuit. Activation of the intrinsic coagulation pathway causes thrombin formation, which impairs platelet adhesive function. Aprotinin blocks contact activation of the kallikrein system during cardiopulmonary bypass and in synergy with heparin prevents thrombin formation through inhibition of the intrinsic clotting cascade. It is likely that neither thrombin nor platelets become involved in the blood-foreign surface contact activation process in aprotinin-treated patients. The fact that the hemostatic process is affected from the very beginning of cardiopulmonary bypass is substantiated by the fact that low-dose aprotinin therapy (2 x 10(6) KIU aprotinin added to the pump prime) leads to the same preservative effect on Gp Ib receptors and blood loss as continuous high-dose infusion (6 x 10(6) KIU) throughout the whole surgical procedure. In the presence of heparin aprotinin prolongs the activated clotting time and the in vitro activated partial thromboplastin time. This has important implications for heparin dosage. An inhibitory effect on the endothelial cell anticoagulant function may also have consequences during hypothermic low flow and circulatory arrest states.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of warfarin on arterial thrombogenesis: problems of monitoring

Platelet reactivity to shear stress and collagen and dynamic overall coagulation were measured in vitro from nonanticoagulated blood of 137 patients on warfarin. One hundred five matched, healthy subjects served as controls. Platelet reactivity to both stimuli and contribution of platelets to plasmatic coagulation were significantly inhibited in patients on warfarin. No correlation was found between platelet reactivity and the coagulation status assessed by the international normalized prothrombin time ratio (INR). Despite similar INR, platelet reactivity showed great individual variation. In 98 patients who were followed up for 3 months, measurement of platelet reactivity to shear stress could discriminate between those who had either bleeding or thromboembolic episodes. These findings suggest that monitored platelet function would help in individualizing oral anticoagulant regimens and hence would increase the benefit of therapy without the risk of bleeding complications.

Effect of heparin on in vitro platelet reactivity in cardiac surgical patients--a comparative assessment by whole blood platelet aggregometry and haemostatometry

The in vitro effect of heparin on platelet reactivity was assessed simultaneously by haemostatometry (response to shear stress) and whole blood platelet aggregometry response to collagen (WBPA). From each blood sample a ratio (HR for haemostatometry and MR and IR for WBPA) showing platelet reactivity in the presence or absence of heparin (5 U/ml) was calculated. A value less than 1 represented a proaggregatory effect and greater than 1 an inhibitory effect. Non-anticoagulated blood samples obtained from 290 cardiac surgical patients were tested by haemostatometry and citrated whole blood samples from 100 patients with aggregometry. Haemostatometry demonstrated a proaggregatory effect of heparin in 8.6% (25) and an inhibitory effect in 91.4% (265). Assessed by WBPA, heparin was proaggregatory in 41-46% and inhibitory in 54-59%. In the 100 patients tested by both methods there was a significant correlation between the findings with the two techniques (r = 0.46, p less than 0.0001). A wide individual variation in the platelet effect of heparin was demonstrated. This variation appeared greater and a higher proportion showed inhibition when blood was tested by haemostatometry.