Antithrombin Deficiency Increases Thrombin Activity After Prolonged Cardiopulmonary Bypass

Antithrombin supplementation attenuates heparin resistance in plasma spiked with Gla-domainless factor Xa S195A in vitro

BACKGROUND

Andexanet alfa is a Gla-domainless mutant (S195A) factor Xa (GDXa) approved for acute reversal of oral factor Xa inhibitors. Cardiac surgery patients exposed to andexanet before cardiopulmonary bypass often exhibit severe heparin resistance. There is a paucity of data on the effectiveness and optimal dosage of antithrombin use in this setting. The objective of this study was to evaluate the in vitro effect of increased heparin with antithrombin levels on attenuating heparin resistance induced by GDXa.

METHODS

Heparinised normal pooled plasma and cardiopulmonary bypass plasma were spiked with GDXa 4 μM. Tissue factor-activated thrombin generation was used to assess heparin reversal effects of GDXa and restoration of anticoagulation with additional heparin with and without antithrombin. Serum thrombin-antithrombin complex, antithrombin activity, and tissue factor pathway inhibitor were also measured in tissue factor-activated, recalcified cardiopulmonary bypass plasma spiked with GDXa.

RESULTS

In normal pooled plasma, GDXa-induced heparin reversal was mitigated by maintaining a high heparin concentration (12 U ml-1) and supplementing antithrombin (1.5-4.5 μM) based on peak and velocity of thrombin generation. Heparin reversal by GDXa was also demonstrated in cardiopulmonary bypass plasma, but supplementing both heparin (8 U ml-1) and antithrombin (3 μM) attenuated GDXa-induced changes in peak and velocity of thrombin generation by 72.5% and 72.2%, respectively. High heparin and antithrombin levels attenuated thrombin-antithrombin complex formation in tissue factor-activated, GDXa-spiked cardiopulmonary bypass plasma by 85.7%, but tissue factor pathway inhibitor remained depleted compared with control cardiopulmonary bypass plasma.

CONCLUSIONS

Simultaneous supplementation of heparin and antithrombin mitigate GDXa-induced heparin resistance by compensating for the loss of tissue factor pathway inhibitor.

Relationship between perioperative cardiopulmonary bypass time, platelet count, fibrinogen level, rotational thromboelastometry data, antithrombin level, and blood loss volume and the effects of deep hypothermic circulatory arrest: An observational study

INTRODUCTION

We hypothesized that perioperative fibrinogen level, platelet count, and rotational thromboelastometry (ROTEM) data values decrease in proportion to cardiopulmonary bypass (CPB) time, particularly in patients who underwent deep hypothermic circulatory arrest (DHCA).

METHODS

A total of 160 patients were enrolled and divided into the following three groups depending on CPB time: <2-h, 2- 3-h, and >3-h groups. Blood samples were obtained during CPB weaning. Platelet count, ROTEM data, fibrinogen level, and antithrombin level were determined. For propensity matching, we selected 15 patients who underwent DHCA and 15 patients who did not undergo DHCA and used propensity scores to match CPB time and other characteristics.

RESULTS

The <2-h, 2-3-h, and >3-h groups included 74, 63, and 23 patients, respectively. No significant differences in platelet count and fibrinogen level were observed between the groups. Antithrombin level and amplitude of clot firmness at 10 min in the EXTEM and FIBTEM tests were lowest in the >3-h group. Similarly, blood loss volume and transfusion volume were highest in the >3-h group. Significant differences in platelet count, ROTEM data, lowest esophageal and bladder temperatures, and transfusion volume were observed between patients who underwent DHCA and patients who did not undergo DHCA.

CONCLUSIONS

The longer the CPB time, the greater the perioperative blood loss volume and transfusion volume, particularly if CPB time is greater than 3 hours. Sub-group analysis revealed that DHCA affects perioperative platelet count and function as well as blood loss volume.

Effect of ultrafiltration on whole blood coagulation profile during cardiopulmonary bypass in cardiac surgery: a retrospective analysis

BACKGROUND

Ultrafiltration (UF) would enhance coagulation profiles by concentrating coagulation elements during cardiopulmonary bypass (CPB) for cardiac surgery.

METHODS

We retrospectively reviewed electronic medical records of 75 patients who had undergone cardiac surgery with rotational thromboelastometry-based coagulation management in a university hospital and analyzed the UF-induced changes in the maximum clot firmness (MCF) of extrinsically activated test with tissue factor (EXTEM) during CPB in 30 patients.

RESULTS

The median volume of filtered-free water was 1,350 ml, and median hematocrit was significantly increased from 22.5% to 25.5%. As the primary measure, UF significantly increased the median MCF-EXTEM from 48.0 mm to 50.5 mm (P = 0.015, effect size r = 0.44). The area under the receiver operating characteristic curve pre-UF MCF-EXTEM for discrimination of any increase of MCF-EXTEM after applying UF was 0.89 (95% CI [0.77, 1.00], P < 0.001), and its cut-off value was 50.5 mm (specificity of 81.8% and sensitivity of 84.2% in Youden's J statistic). In the secondary analyses using the cut-off value, UF significantly increased the median MCF-EXTEM from 40.5 mm to 42.5 mm in 18 patients with pre-UF MCF-EXTEM ≤ 50.5 mm. However, it did not increase MCF-EXTEM in 12 patients with pre-UF MCF-EXTEM > 50.5 mm. There was a significant interaction between pre-UF MCF-EXTEM values and applying UF (P < 0.001 for the subgroup, P = 0.046 for UF, P = 0.003 for interaction).

CONCLUSIONS

Applying UF improved clot firmness, and the improvement was more pronounced when pre-UF MCF-EXTEM had been reduced during CPB.

Hemostatic capability of ultrafiltrated fresh frozen plasma compared to cryoprecipitate

This in vitro study evaluated the potential hemostatic effect of fresh frozen plasma (FFP) ultrafiltration on clotting factors, coagulation parameters, and plasma properties. ABO-specific units of FFP (n = 40) were prepared for the concentrated FFP and cryoprecipitate. Plasma water was removed from FFP by ultrafiltration using a dialyzer with a pump running at a 300 mL/min. The aliquot of each concentrated FFP after 50, 100, 200, and 250 mL of fluid removal were measured the standard coagulation assay, clotting activity, and plasma properties to compare those parameters of cryoprecipitate. Concentrated FFP contained 36.5% of fibrinogen in FFP with a mean concentration of 7.2 g/L, lower than the cryoprecipitate level. The levels of factor VIII (FVIII), von Willebrand factor (VWF):antigen (Ag), and VWF:ristocetin cofactor (RCo) were also lower in concentrated FFP, whereas the levels of factor V, factor IX, factor XIII, antithrombin and albumin was higher in concentrated FFP. Maximum clot firmness (MCF) in thromboelastometry was approximately one-half of that in cryoprecipitate. Although the levels of VWF:Ag, VWF:RCo, and FVIII differed depending on the ABO blood types, fibrinogen levels, and MCF were not significantly different among the ABO blood groups in FFP and concentrated FFP.

ClotPro Viscoelastometry Evaluation in Cardiac Surgery With Cardiopulmonary Bypass

OBJECTIVE

The aim of this study was to assess the reproducibility of the new viscoelastic analyzer ClotPro, and compare the parameters this system produces with the ROTEM delta system in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB).

DESIGN

A prospective and observational study.

SETTING

At a university hospital.

PARTICIPANTS

Forty adult patients undergoing cardiac surgery with CPB.

INTERVENTIONS

Correlations were calculated between ClotPro and ROTEM delta parameters.

MEASUREMENTS AND MAIN RESULTS

The ClotPro showed a high reproducibility in most of the parameters of each test; whereas ROTEM delta, although showing a low coefficient of variation in the parameters related to clot firmness, showed a high variability in the coagulation times. Excellent correlations were observed in most of the parameters of each test between ROTEM delta and ClotPro (≥0.93). However, a moderate correlation was obtained between the clotting time of the EXTEM and the EX-test (0.54). The concordance of amplitudes at different times within each test was almost 100% on both thromboelastometers. Regarding absolute differences in the test results, most of the measurements showed significant differences (p < 0.0001) between both devices.

CONCLUSIONS

ClotPro can be used as an alternative to ROTEM delta to evaluate coagulation function in cardiac surgery, but specific reference ranges need to be established first.

Roles of Four-Factor Prothrombin Complex Concentrate in the Management of Critical Bleeding

Four-factor prothrombin complex concentrate (4F-PCC) is the term used to describe a pathogen-reduced, lyophilized concentrate that contains therapeutic amounts of at least 4 coagulation factors: Factor II (FII), Factor VII (FVII), Factor IX (FIX), and Factor X (FX). 4F-PCC has proven to be an effective hemostatic agent compared to plasma transfusion in several prospective randomized trials in acute warfarin reversal. In recent years, 4F-PCC has been used in various acquired coagulopathies including post-cardiopulmonary bypass bleeding, trauma-induced coagulopathy, coagulopathy in liver failure, and major bleeding due to anti-FXa (anti-Xa) inhibitors (eg, rivaroxaban and apixaban). As transfusion of frozen plasma (FP) has not been found efficacious in the above critical bleeding scenarios, there is increasing interest in expanding the use of 4F-PCC. However, efficacy, safety, and clinical implications of expanded use of 4F-PCC have not been fully elucidated. Prothrombin time and international normalized ratio are commonly used to assess dose effects of 4F-PCC. Prothrombin time/international normalized ratio are standardly use for warfarin titration, but they are not suited for real-time monitoring of complex coagulopathies. Optimal dosing of 4F-PCC outside of the current approved use for vitamin K antagonist reversal is yet to be determined. In this review, we will discuss the use of 4F-PCC in four critical bleeding settings: cardiac surgery, major trauma, end-stage liver disease, and oral anti-Xa reversal. We will discuss recent studies in each area to explore the dosing, efficacy, and safety of 4F-PCC.

Controversies in the Clinical Practice of Patient Blood Management

Patient blood management (PBM) has been proposed as a standard of care in modern perioperative medicine. PBM-related interventions usually are implemented as bundles, but randomized controlled trials on the implementation of PBM as a bundle are missing. This special article focuses on the current evidence and controversies in the clinical practice of PBM and on emerging data related to specific PBM-related interventions in patients undergoing cardiac surgery. Strong evidence for many PBM-related interventions is limited because of missing studies or the poor quality of published findings and study endpoints. Restrictive blood transfusion and timely interventions to maintain hemoglobin concentration and to reduce blood loss potentially might result in improved patient outcome, although the latter has yet to be proven.

Catastrophic Intracardiac Thrombosis During Emergency Repair of an Expanding Aortic Pseudoaneurysm: A Case Report

Catastrophic thrombosis is a rare but frequently fatal event following complex cardiac surgery. It is most often encountered following separation from cardiopulmonary bypass (CPB) and reversal of heparin anticoagulation, and somewhat paradoxically, at the time when bleeding from post-CPB coagulopathy is being treated. We report the case of a 41-year-old female taken to the operating room for repair of an expanding ascending aortic pseudoaneurysm. Following a prolonged operation, she developed intracardiac thrombus during transfusion of hemostatic blood products and procoagulant agents. Potential contributing factors are discussed.

Coagulation Factor Levels and Underlying Thrombin Generation Patterns in Adult Extracorporeal Membrane Oxygenation Patients

BACKGROUND

There is a paucity of data on the underlying procoagulant-anticoagulant balance during extracorporeal membrane oxygenation (ECMO). We hypothesized that adult ECMO patients would have an imbalance between procoagulant and anticoagulant factors, leading to an abnormal underlying thrombin generation (TG) pattern.

METHODS

Twenty adult venoarterial (VA) ECMO patients had procoagulant and anticoagulant factor levels measured temporally on ECMO day 1 or 2, day 3, and day 5. In heparin-neutralized plasma, underlying TG patterns, and sensitivity to activated protein C were assessed using calibrated automated thrombogram. TG parameters including lag time, peak TG, and endogenous thrombin potential (ETP) were compared against 5 normal plasma controls (3 males and 2 females) obtained from a commercial supplier. Thrombomodulin (TM) was added to some samples to evaluate for activated protein C resistance.

RESULTS

Procoagulant factors (factor [F] II, FV, and FX) were mostly in normal reference ranges and gradually increased during the first 5 ECMO days (P = .022, <.001, <.001). FVIII levels were elevated at all time points and did not change (P = .766). In contrast, FXI was in the low-normal range but did not increase during ECMO (P = .093). Antithrombin (AT) and protein C levels were below normal but increased during the first 5 ECMO days (P = .002 and P = .014). Heparinase-treated samples showed prolonged lag time, increased peak TG, and increased ETP compared to controls; mean difference in lag time on ECMO day 1 or 2 = 6.0 minutes (99% confidence interval [CI], 2.8-9.2), peak TG = 193.4 (99% CI, 122.5-264.3), and ETP = 1170.4 (99% CI, 723.2-1617.6). After in vitro TM treatment, differences in TG parameters were accentuated and ECMO samples appeared insensitive to TM treatment; mean difference in lag time on ECMO day 1 or 2 = 9.3 minutes (99% CI, 6.2-12.4), peak TG = 233.0 (99% CI, 140.9-325.1), and ETP = 1322.5 (99% CI, 764.8-1880.2). Similar differences in TG parameters were observed on ECMO days 3 and 5.

CONCLUSIONS

Contact activation occurs during ECMO, but procoagulant factor levels are generally preserved. Although heparin-neutralized TG is delayed, peak TG and ETP are supranormal in the setting of high FVIII and low AT and protein C levels. Resistance to TM is also apparent. These changes demonstrate a possible mechanism for hypercoagulability during adult VA ECMO.

Prothrombin Complex Concentrate in Cardiac Surgery: A Systematic Review and Meta-Analysis

BACKGROUND

Prothrombin complex concentrate (PCC) has recently emerged as an effective alternative to fresh frozen plasma (FFP) in treating excessive perioperative bleeding. This systematic review and meta-analysis evaluated the safety and efficacy of PCC administration as first-line treatment for coagulopathy after adult cardiac surgery.

METHODS

PubMed/MEDLINE, EMBASE, and the Cochrane Library were searched from inception to the end of March 2018 to identify eligible articles. Adult patients undergoing cardiac surgery and receiving perioperative PCC were compared with patients receiving FFP.

RESULTS

A total of 861 adult patients from four studies were retrieved. No randomized studies were identified. Pooled odds ratios (ORs) showed that the PCC cohort was associated with a significant reduction in the risk of RBC transfusion (OR, 2.22; 95% confidence interval [CI], 1.45 to 3.40) and units of RBC received (OR, 1.34; 95% CI, 0.78 to 1.90). No differences were observed between the groups for reexploration for bleeding (OR, 1.09; 95% CI, 0.66 to 1.82), chest drain output at 24 hours (OR, 66.36; 95% CI, -82.40 to 216.11), hospital mortality (OR, 0.94; 95% CI, 0.59 to 1.49), stroke (OR, 0.80; 95% CI, 0.41 to 1.56), and occurrence of acute kidney injury (OR, 0.80; 95% CI, 0.58 to 1.12). A trend toward increased risk of renal replacement therapy was observed in the PCC group (OR, 0.41; 95% CI, 0.16 to 1.02).

CONCLUSIONS

In patients with significant bleeding after cardiac surgery, PCC administration seems to be more effective than FFP in reducing perioperative blood transfusions. No additional risks of thromboembolic events or other adverse reactions were observed. Randomized controlled trials are needed to establish the safety of PCC in cardiac surgery definitively.

Novel therapeutics for hemophilia and other bleeding disorders

Hemophilia and von Willebrand disease are the most common congenital bleeding disorders. Treatment of these disorders has focused on replacement of the missing coagulation factor to prevent or treat bleeding. New technologies and insights into hemostasis have driven the development of many promising new therapies for hemophilia and von Willebrand disease. Emerging bypass agents including zymogen-like factor IXa and Xa molecules are in development and a bispecific antibody, emicizumab, demonstrated efficacy in a phase 3 trial in people with hemophilia A and inhibitors. Tissue factor pathway inhibitor, the protein C/S system, and antithrombin are targets of novel compounds in development to alter the hemostatic balance and new approaches using modified factor VIII molecules are being tested for prevention and eradication of inhibitor antibodies in hemophilia A. The first recombinant von Willebrand factor (VWF) product has been approved and has unique VWF multimer content and does not contain factor VIII. These new approaches may offer better routes of administration, improved dosing regimens, and better efficacy for prevention and treatment of bleeding in congenital bleeding disorders.

Theoretical Modeling of Coagulation Management With Therapeutic Plasma or Prothrombin Complex Concentrate

Supplemental Digital Content is available in the text.

Published ahead of print August 24, 2017.

Prothrombin complex concentrates (PCCs) have been associated with a possible risk of thromboembolic complications, potentially attributable to an increased ratio of the plasma concentration of factor II (FII) to antithrombin (AT). We developed a mathematical model to examine the relationship between amounts of PCC or therapeutic plasma administered, and plasma levels of FII and AT. The model showed that PCC produces substantial increases in plasma levels of FII but only small changes in AT, increasing the FII:AT ratio. Therapeutic plasma was shown to have only modest effects on levels of FII or AT, unless high doses are used.

Prothrombin Complex Concentrates in Pediatric Cardiac Surgery: The Current State and the Future

BACKGROUND

After decades of practice of pediatric cardiac surgery, postoperative bleeding due to the immaturity of hemostasis, hemodilution, and hypothermia remains a concern. Recently, a new approach for adult coagulopathy after bypass has emerged. Prothrombin complex concentrates (PCCs), designed to treat bleeding in hemophilia patients, are safely and efficiently used off label for hemorrhage after bypass. However, optimal dosing, indications and contraindications, and laboratory tests to assess the efficacy of PCC use in children have not yet been established. This literature review outlines the challenges of bypass-related coagulopathy, the pharmacology, and the experience in use of PCCs, with a focus on their potential in pediatric cardiac surgery.

METHODS

After a thorough literature search of MEDLINE, Scopus, and Ovid databases using the term "prothrombin complex concentrate AND pediatric," 23 relevant articles were selected.

RESULTS

The data supporting successful use of PCCs in acquired coagulopathy after cardiac surgery in adults have been increasing. Although small volume, low immunogenicity, efficiency, and speed in correcting coagulopathy are attractive qualities of PCCs for pediatric practice, current evidence is only anecdotal. The main concerns are unknown dosing regimens, the inability to closely monitor the effects of PCCs in real time, and a possibility of thrombotic complications, which can be particularly devastating in young congenital cardiac patients whose lives frequently depend upon the patency of artificial shunts.

CONCLUSIONS

Extensive, high-quality research is warranted to fill in the gaps of knowledge regarding using PCCs in pediatric cardiac practice.

Prothrombin Complex Concentrates for Bleeding in the Perioperative Setting

Prothrombin complex concentrates (PCCs) contain vitamin K-dependent clotting factors (II, VII, IX, and X) and are marketed as 3 or 4 factor-PCC formulations depending on the concentrations of factor VII. PCCs rapidly restore deficient coagulation factor concentrations to achieve hemostasis, but like with all procoagulants, the effect is balanced against thromboembolic risk. The latter is dependent on both the dose of PCCs and the individual patient prothrombotic predisposition. PCCs are approved by the US Food and Drug Administration for the reversal of vitamin K antagonists in the setting of coagulopathy or bleeding and, therefore, can be administered when urgent surgery is required in patients taking warfarin. However, there is growing experience with the off-label use of PCCs to treat patients with surgical coagulopathic bleeding. Despite their increasing use, there are limited prospective data related to the safety, efficacy, and dosing of PCCs for this indication. PCC administration in the perioperative setting may be tailored to the individual patient based on the laboratory and clinical variables, including point-of-care coagulation testing, to balance hemostatic benefits while minimizing the prothrombotic risk. Importantly, in patients with perioperative bleeding, other considerations should include treating additional sources of coagulopathy such as hypofibrinogenemia, thrombocytopenia, and platelet disorders or surgical sources of bleeding. Thromboembolic risk from excessive PCC dosing may be present well into the postoperative period after hemostasis is achieved owing to the relatively long half-life of prothrombin (factor II, 60-72 hours). The integration of PCCs into comprehensive perioperative coagulation treatment algorithms for refractory bleeding is increasingly reported, but further studies are needed to better evaluate the safe and effective administration of these factor concentrates.

Antithrombin: anti-inflammatory properties and clinical applications

Many humoral and cellular components participate in bidirectional communication between the coagulation and inflammation pathways. Natural anticoagulant proteins, including antithrombin (AT), tissue factor pathway inhibitor, and protein C, suppress proinflammatory mediators. Conversely, inflammation blunts anticoagulant activity and, when uncontrolled, promotes systemic inflammation-induced coagulation, such as those that occur in disseminated intravascular coagulation and severe sepsis. This review discusses the mechanisms of action and clinical use of AT concentrate in critically ill patients and in the settings of perioperative anticoagulation management for surgery and obstetrics. AT is a serine protease inhibitor with broad anticoagulant activity and potent anti-inflammatory properties. In clinical conditions associated with hereditary or acquired AT deficiency, administration of AT concentrate has been shown to restore proper haemostasis and attenuate inflammation. Of note, AT modulates inflammatory responses not only by inhibiting thrombin and other clotting factors that induce cytokine activity and leukocyte-endothelial cell interaction, but also by coagulation-independent effects, including direct interaction with cellular mediators of inflammation. An increasing body of evidence suggests that AT concentrate may be a potential therapeutic agent in certain clinical settings associated with inflammation. In addition to the well-known anticoagulation properties of AT for the treatment of hereditary AT deficiency, AT also possesses noteworthy anti-inflammatory properties that could be valuable in treating acquired AT deficiency, which often result in thrombotic states associated with an inflammatory component.

The balance of pro- and anticoagulant processes underlying thrombin generation

BACKGROUND

The generation of thrombin in time is the combined effect of the processes of prothrombin conversion and thrombin inactivation. Measurement of prothrombin consumption used to provide valuable information on hemostatic disorders, but is no longer used, due to its elaborate nature.

OBJECTIVES

Because thrombin generation (TG) curves are easily obtained with modern techniques, we developed a method to extract the prothrombin conversion curve from the TG curve, using a computational model for thrombin inactivation.

METHODS

Thrombin inactivation was modelled computationally by a reaction scheme with antithrombin, α(2) Macroglobulin and fibrinogen, taking into account the presence of the thrombin substrate ZGGR-AMC used to obtain the experimental data. The model was validated by comparison with data obtained from plasma as well as from a reaction mixture containing the same reactants as plasma.

RESULTS

The computational model fitted experimental data within the limits of experimental error. Thrombin inactivation curves were predicted within 2 SD in 96% of healthy subjects. Prothrombin conversion was calculated in 24 healthy subjects and validated by comparison with the experimental consumption of prothrombin during TG. The endogenous thrombin potential (ETP) mainly depends on the total amount of prothrombin converted and the thrombin decay capacity, and the peak height is determined by the maximum prothrombin conversion rate and the thrombin decay capacity.

CONCLUSIONS

Thrombin inactivation can be accurately predicted by the proposed computational model and prothrombin conversion can be extracted from a TG curve using this computational prediction. This additional computational analysis of TG facilitates the analysis of the process of disturbed TG.

Role of prothrombin complex concentrate in perioperative coagulation therapy

Prothrombin complex concentrate (PCC) is a term to describe pharmacological products that contain lyophilized, human plasma-derived vitamin K-dependent factors (F), FII, FVII, FIX, FX, and various amounts of proteins C and S. PCCs can be rapidly reconstituted in a small volume (20 ml for about 500 international units (IU)) at bedside and administered regardless of the patient's blood type. PCCs are categorized as 4-factor PCC if they contain therapeutic amounts of FVII, and 3-factor PCC when FVII content is low. In addition, activated PCC which contains activated FVII and FX with prothrombin is available for factor VIII bypassing therapy in hemophilia patients with inhibitors. Currently, 4-factor PCC is approved for the management of bleeding in patients taking warfarin, but there has been increasing use of various PCCs in the treatment of acquired perioperative coagulopathy unrelated to warfarin therapy and in the management of bleeding due to novel oral anticoagulants. There is also an ongoing controversy about plasma transfusion and its potential hazards including transfusion-related lung injury (TRALI). Early fixed ratio plasma transfusion has been implemented in many trauma centers in the USA, whereas fibrinogen concentrate and PCC are preferred over plasma transfusion in some European centers. In this review, the rationales for including PCCs in the perioperative hemostatic management will be discussed in conjunction with plasma transfusion.

Endogenous thrombin potential following hemostatic therapy with 4-factor prothrombin complex concentrate: a 7-day observational study of trauma patients

Introduction

Purified prothrombin complex concentrate (PCC) is increasingly used as hemostatic therapy for trauma-induced coagulopathy (TIC). However, the impact of PCC administration on coagulation status among patients with TIC has not been adequately investigated.

Methods

In this observational, descriptive study, data relating to thrombin generation were obtained from plasma samples gathered prospectively from trauma patients upon emergency room (ER) admission and over the following 7 days. Standard coagulation tests, including measurement of antithrombin (AT) and fibrinogen, were performed. Three groups were investigated: patients receiving no coagulation therapy (NCT group), patients receiving fibrinogen concentrate only (FC group), and patients treated with PCC and fibrinogen concentrate (FC-PCC group).

Results

The study population (77 patients) was predominantly male (84.4%); mean age was 40 ± 15 years and mean injury severity score was 25.6 ± 12.7. There were no significant differences between the three study groups in thrombin-related parameters upon ER admission. Endogenous thrombin potential (ETP) was significantly higher in the FC-PCC group compared with the NCT group on days 1 to 4 and the FC group on days 1 to 3. AT levels were significantly lower in the FC-PCC group from admission until day 3 (versus FC group) or day 4 (versus NCT group). Fibrinogen increased over time, with no significant between-group differences after ER admission. Despite ETP being higher, prothrombin time and activated partial thromboplastin time were significantly prolonged in the FC-PCC group from admission until day 3 to 4.

Conclusions

Treatment with PCC increased ETP for several days, and patients receiving PCC therapy had low AT concentrations. These findings imply a potential pro-thrombotic state not reflected by standard coagulation tests. This is probably important given the postoperative acute phase increase in fibrinogen levels, although studies with clinical endpoints are needed to ascertain the implications for patient outcomes. We recommend careful use of PCC among trauma patients, with monitoring and potentially supplementation of AT.

The occurrence of antibodies to heparin-platelet factor 4 in cardiac and thoracic surgical patients receiving desirudin or heparin for postoperative venous thrombosis prophylaxis

INTRODUCTION

This randomized, exploratory study compared the incidence of heparin-dependent antibodies associated with subcutaneous (SC) desirudin or heparin given for deep-vein thrombosis prophylaxis following cardiac and thoracic surgery.

MATERIALS AND METHODS

Adult patients scheduled for elective cardiac or thoracic surgery received desirudin 15 mg SC twice daily or unfractionated heparin 5000 units SC thrice daily. Duration of thrombosis prophylaxis was determined by the treating physician. Primary outcome measure was the incidence of new antibody formation directed against platelet factor 4 (PF4)/heparin complex. Secondary outcomes included bleeding and thrombotic complications. Blood was tested for anti-PF4/heparin antibodies at baseline, after surgery prior to study drug administration, postdrug day (PDD) 2, PDD 7, and at 1 month. Doppler studies were done before discharge.

RESULTS

Of 120 patients, 61 received desirudin, 59 received heparin. New PF4/heparin antibodies occurred in 10.2% and 13.6% of desirudin- and heparin-treated patients, respectively. Among desirudin patients with no heparin exposure, none (0/36) developed PF4/heparin antibodies versus 17.1% with heparin exposure. Incidence of deep venous thrombosis was 4.9% and 3.4% in the desirudin and heparin groups, respectively. Two heparin-group patients developed pulmonary embolism. Two patients per group had bleeding events; no patients required re-exploration for bleeding complications. Median chest tube output was similar with desirudin (900 mL) and heparin (692 mL) as was blood transfusion requirements of more than 2 units (5/61, desirudin; 2/59 heparin).

CONCLUSIONS

The incidence of thrombotic events was low in both groups. There were no safety concerns, and desirudin was not associated with anti-PF4/heparin antibodies.

Early graft thrombosis due to antithrombin III deficiency following CABG

The serine protease inhibitor antithrombin III (AT-III), an α2-globulin synthesized in the liver and endothelial cells, is the principal in vivo inhibitor of blood coagulation inactivating mainly thrombin. AT-III deficiency presents a rare hereditary or acquired disorder that most often comes to light when a patient suffers recurrent venous thrombosis and pulmonary embolism. Triggers for the onset of the thrombosis include various mechanisms such as pregnancy, delivery, surgery, trauma, and contraceptive pill use. Decreased response to heparin may be the first sign of AT-III deficiency. Since heparin is a conditio sine qua non for cardiopulmonary bypass, rapid consumption of AT-III promoted by heparin may lead to systemic thrombosis. The effect of heparin on graft patency after CABG in patients with AT-III deficiency, particularly with respect to early graft thrombosis, has not been fully investigated. The early detection and timely treatment of this disorder may impact perioperative morbidity. We present a case of simultaneous thrombosis of three venous grafts after elective coronary artery bypass surgery in a patient with AT-III deficiency.

Finding the optimal concentration range for fibrinogen replacement after severe haemodilution: an in vitro model

BACKGROUND

Replacement of fibrinogen is presumably the key step in managing dilutional coagulopathy. We performed an in vitro study hypothesizing that there is a minimal fibrinogen concentration in diluted whole blood above which the rate of clot formation approaches normal.

METHODS

Blood samples from six healthy volunteers were diluted 1:5 v/v with saline keeping haematocrit at 24% using red cell concentrates. We measured coagulation factors and thrombin generation in plasma at baseline and after dilution. Thromboelastometry was used to evaluate (i) speed and quality of clot formation in diluted samples supplemented with fibrinogen 50-300 mg dl(-1) and (ii) clot resistance to fibrinolysis. Diluted and undiluted samples with no added fibrinogen served as controls.

RESULTS

Coagulation parameters and platelets were reduced by 74-85% after dilution. Peak thrombin generation was reduced by 56%. Adding fibrinogen led to a concentration-dependent improvement of all thromboelastometric parameters. The half maximal effective concentration (EC50) for fibrinogen replacement in haemodiluted blood was calculated to be 125 mg dl(-1). Adding tissue plasminogen activator, 0.15 microg ml(-1), led to a decrease of clot firmness and lysis time.

CONCLUSIONS

The target plasma concentration for fibrinogen replacement was predicted by these in vitro results to be greater than 200 mg dl(-1) as only these concentrations optimized the rate of clot formation. This concentration is twice the level suggested by the current transfusion guidelines. Although improved, clots were prone to fibrinolysis indicating that the efficacy of fibrinogen therapy may be influenced by co-existing fibrinolytic tendency occurring during dilutional coagulopathy.

Blood coagulation: hemostasis and thrombin regulation

Perioperative bleeding is a major challenge particularly because of increasing clinical use of potent antithrombotic drugs. Understanding current concepts of coagulation is important in determining the preoperative bleeding risk of patients, and in managing hemostatic therapy perioperatively. The serine protease thrombin plays pivotal roles in the activation of additional serine protease zymogens (inactive enzymatic precursors), cofactors, and cell-surface receptors. Thrombin generation is closely regulated to locally achieve rapid hemostasis after injury without causing uncontrolled systemic thrombosis. During surgery, there are major disturbances in coagulation and inflammatory systems because of hemorrhage/hemodilution, blood transfusion, and surgical stresses. Postoperative bleeding often requires allogeneic blood transfusions, which support thrombin generation and hemostasis. However, procoagulant activity and inflammation are increased postoperatively; thus, antithrombotic therapy may be required to prevent perioperative thrombotic complications. There have been significant advances in the management of perioperative hemostasis and thrombosis because of the introduction of novel hemostatic and antithrombotic drugs. However, a limitation of current treatment is that conventional clotting tests do not reflect the entire physiological processes of coagulation making optimal pharmacologic therapy difficult. Understanding the in vivo regulatory mechanisms and pharmacologic modulation of thrombin generation may help control bleeding without potentially increasing prothrombotic risks. In this review, we focus on the regulatory mechanisms of hemostasis and thrombin generation using multiple, simplified models of coagulation.