A randomized trial of antithrombin concentrate for treatment of heparin resistance

Hereditary and acquired antithrombin deficiency: epidemiology, pathogenesis and treatment options

Antithrombin is a glycoprotein critical to the regulation of coagulation. Its primary action is the inhibition of the activated coagulation factors IIa (thrombin) and Xa. In addition there is growing evidence to suggest that antithrombin also plays a role in the inhibition of inflammation within the environment of the vascular endothelium. Reduced plasma antithrombin may result from congenital deficiency or arise secondarily from a range of disorders such as liver dysfunction, premature infancy and sepsis, or as a result of interventions such as major surgery or cardiopulmonary bypass. Congenital antithrombin deficiency is the most clinically important of the inherited thrombophilias resulting in thrombosis in the majority of those affected. The challenge in managing these patients is preventing potentially life-threatening thrombosis, while minimising the equally significant risk of haemorrhage associated with long-term anticoagulation. This is achieved in the first instance by identifying high-risk episodes such as surgery, immobility and pregnancy for which prophylactic anticoagulation can be used in the short term. Prophylaxis for such periods is best provided by the use of low molecular weight heparin (LMWH) with substitution by or addition of antithrombin concentrate in particularly high-risk circumstances. In the case of pregnancy, antithrombin concentrate is often used around the time of birth when LMWH may increase the risk of post-partum haemorrhage. As patients with congenital antithrombin deficiency get older so their thrombotic risk gradually increases and for many patients long-term anticoagulation becomes unavoidable because of recurrent episodes of venous thromboembolism. There has been much interest in the role of antithrombin deficiency in the setting of sepsis and the critically ill patient where there is a clear correlation between severity of illness and degree of antithrombin reduction. It is not clear yet, however, to what extent the depletion of antithrombin affects the clinical condition of such patients. A number of trials have investigated the use of antithrombin as a treatment in the intensive care setting with the overall conclusion being that there is some benefit to its use but only if large supra-physiological doses are used. It has also become clear that the concurrent use of any form of heparin removes whatever benefit may be derived from antithrombin treatment in this setting. Until recently, antithrombin replacement was only available as a pooled plasma-derived product, which despite effective viral inactivation still carries an uncertain risk of transfusion transmitted infection. A recombinant antithrombin product now under investigation, and recently licensed in Europe, may provide a useful alternative treatment option.

Preoperative low molecular weight heparin reduces heparin responsiveness during cardiac surgery

PURPOSE

Cardiac surgery with cardiopulmonary bypass requires systemic anticoagulation, defined by an activated clotting time (ACT) of 400-480 sec. Patients with altered heparin responsiveness require disproportionately higher doses of heparin to achieve this target ACT. A common risk factor for heparin resistance is preoperative heparin therapy. Recently, therapy with low molecular weight heparin (LMWH) has become an acceptable substitute for prolonged heparin therapy. The current study examines the effect of preoperative LMWH therapy on subsequent heparin responsiveness during cardiac surgery.

METHODS

Records of patients undergoing cardiac surgery with cardiopulmonary bypass over a period of four months were reviewed. We identified patients who, during the week preceding surgery, had received prolonged (>24 hr) therapy with either sc LMWH (LMWH group) or continuous iv unfractionated heparin (Heparin group). A Control group consisted of patients who received neither heparin nor LMWH preoperatively. The heparin sensitivity index (calculated as the first change in ACT from baseline divided by the first intraoperative heparin dose, normalized to body weight), was compared among groups using ANOVA.

RESULTS

One hundred and thirty-nine patients were included in the analysis. The heparin sensitivity index was 33-45% higher in the Control group (1.6+/-0.7 sec.IU-1.kg-1; P<0.0001) compared to the LMWH (1.2+/-0.4 sec.IU-1.kg-1) and Heparin (1.1+/-0.5 sec.IU-1.kg-1) groups. In a multivariable model, the use of preoperative LMWH remained a significant predictor of reduced intraoperative heparin responsiveness (P=0.002).

CONCLUSION

Prolonged preoperative LMWH therapy, similar to the known effect of prolonged unfractionated heparin infusion, reduces subsequent intraoperative response to heparin.

Antithrombin deficiency and its relationship to severe burns

Antithrombin (AT) is an important endogenous anticoagulant and exhibits marked anti-inflammatory properties. To evaluate the incidence of AT deficiency in severe burn and its correlation to the variables of the abbreviated burn severity index (ABSI), length of hospital stay (LOS) and mortality we collected data on the substitution of human plasma-derived AT concentrate in 201 consecutive patients suffering from severe burn. One hundred and eight patients (54%) developed AT deficiency during their hospitalisation and, according to our institutional practice, received substitution therapy by continuous infusion to maintain physiological plasma activity (70-120%). The mean administered dose served as a measure of AT deficiency. The percentage of patients in an AT deficient state was highest within the first 5 days after injury. It was 26% on day 1 and between 38% and 41% on days 2-5 and thereafter decreased constantly over time. A multiple regression analysis between the dependent variable mean administered dose of AT concentrate and the independent variables age, total body surface area burned (TBSA), gender, inhalation injury (INHAL), full thickness burn (FTB), LOS and mortality was performed. Age, gender and FTB showed no significant influence on the development of AT deficiency. Increasing TBSA and INHAL clearly increase the risk of developing AT deficiency (p-values 0.0001 and 0.037). The analysis also identified AT deficiency as an independent predictor of LOS and mortality (p-values 0.036 and 0.003). Development of AT deficiency is a frequent event after burn with significant correlation to TBSA and INHAL, increased mortality rates and longer hospital stays.

Antithrombin supplementation for anticoagulation during continuous hemofiltration in critically ill patients with septic shock: a case-control study

Introduction

Acquired antithrombin III (AT) deficiency may induce heparin resistance and premature membrane clotting during continuous renal replacement therapy (CRRT). The purpose of this study was to evaluate the effect of AT supplementation on filter lifespan in critically ill patients with septic shock requiring CRRT.

Methods

We conducted a retrospective case-control analysis based on a 4-year observational study with prospectively collected data in two medical intensive care units in a university hospital. In all, 106 patients with septic shock underwent CRRT during the study period (55 during 2001 to 2002 and 51 during 2003 to 2004). Of these, 78 had acquired AT deficiency (plasma level below 70%) at onset of renal supportive therapy, 40 in the first 2-year period and 38 in the last 2-year period. In the latter intervention period, patients received AT supplementation (50 IU/kg) during CRRT each time that plasma AT activity, measured once daily, fell below 70%.

Results

In a case-control analysis of the 78 patients with acquired AT deficiency, groups were similar for baseline characteristics, except in severity of illness as assessed by a higher Simplified Acute Physiology Score (SAPS) II after 2002. In comparison with controls, cases had a significantly greater AT level after AT supplementation, but not at baseline, and a smaller number of episodes of clots, without excess bleeding risk. The median hemofilter survival time was longer in the AT group than in the heparin group (44.5 versus 33.4 hours; p = 0.0045). The hemofiltration dose, assessed by the ratio of delivered to prescribed ultrafiltration, increased during intervention. AT supplementation was independently associated with a decrease in clotting rate, whereas femoral angioaccess and higher SAPS II were independent predictors of filter failure. However, mortality did not differ between periods, in the control period the observed mortality was significantly higher than predicted by the SAPS II score, unlike in the treatment period.

Conclusion

In sepsis patients requiring CRRT and with acquired AT deficiency, anticoagulation with unfractionated heparin plus AT supplementation prevent premature filter clotting and may contribute to improving outcome, but the cost-effectiveness of AT remains to be determined.

Antithrombin reduces monocyte and neutrophil CD11b up regulation in addition to blocking platelet activation during extracorporeal circulation

BACKGROUND

Patients undergoing cardiac surgery requiring cardiopulmonary bypass develop a systemic inflammatory reaction. Antithrombin III (AT) has anticoagulant effects but also shows evidence of anti-inflammatory activity. The aim of this study was to examine whether exogenous AT could reduce white blood cell activation (CD11b up regulation or elastase release), in addition to inhibiting platelet (PLT) activation and fibrin generation, during simulated cardiopulmonary bypass (sCPB), undertaken in the absence of endothelium.

STUDY DESIGN AND METHODS

sCPB was carried out with minimally heparinized (2 U/mL) human blood for 90 minutes in controls and with supplementation by low-dose (1 U/mL) and high-dose (5 U/mL) AT.

RESULTS

High-dose AT blunted thrombin generation during sCPB (prothrombin fragment 1.2); both doses significantly inhibited thrombin activity (fibrinopeptide A). Complement activation (C3a and C5b-9) was unaffected by AT. High-dose AT inhibited PLT activation (P-selectin expression and P-selectin-dependent monocyte-PLT conjugate formation). AT supplementation at the higher dose significantly abrogated monocyte and neutrophil CD11b up regulation and neutrophil elastase release.

CONCLUSION

In addition to anticoagulant and anti-PLT effects, pharmacologic AT doses significantly blunted monocyte and neutrophil CD11b up regulation and neutrophil elastase release during sCPB, independent of endothelial effects. These data provide evidence for the direct anti-inflammatory activity of AT that has clinical relevance for CPB complications.

Formal heparin anticoagulation protocol improves safety of charcoal-based liver-assist treatments

Extracorporeal devices have had limited effectiveness in liver failure due to consequences of inadequate anticoagulation. The purpose of this study was to evaluate an anticoagulation protocol developed for Liver Dialysis Unit (LDU) treatments. Twelve patients underwent 19 LDU treatments for acetaminophen overdose (n = 1), subacute liver failure (n = 1), and refractory encephalopathy in cirrhosis (n = 10). The initial 6 patients (group 1) were treated according to the manufacturer's recommendations. The subsequent 6 patients (group 2) were treated using a formal heparin anticoagulation protocol that included 2000 units in prime solution and 30 units/kg induction, activated clotting time (ACT) measurements, and heparin administered by dose-response curve to maintain 300-second ACT. Protamine reversal was used. Treatments were well tolerated and equally effective in both groups. Adequate (ACT > or = 250 seconds) and therapeutic (ACT 250-350 seconds) anticoagulation was maintained more consistently in group 2 (90.9% vs 50.0%, p < 0.0001; and 77.4% vs 45.8%, p < 0.001). There was less consumption of fibrinogen (12.1% vs 43.3%, p < 0.005) and platelets (13.8% vs 29.9%, p < 0.05) and a trend for less blood product used (8.3 vs 15.8 units/patient, p = 0.13) and fewer complications (16.7% vs 66.7%, p = 0.15) in group 2. Anticoagulation using ACT monitoring, heparin dose-response curves, and a target ACT of 300 seconds improves the safety of LDU treatments.

Antithrombotic therapy in cardiac surgery

PURPOSE

To review the perioperative management of antithrombotic therapy in cardiac surgery, including the management of cardiopulmonary bypass (CPB) and off-pump surgery.

METHODS

A review of the relevant English literature over the period 1975-2005 was undertaken, in addition to a review of international practices in antithrombotic therapy in cardiac surgery.

PRINCIPAL FINDINGS

Cardiopulmonary bypass is required in most procedures and makes anticoagulation mandatory. Anticoagulation is, usually, achieved with unfractionnated heparin (UFH). Unfractionated heparin is monitored by point-of-care (POC) testing, such as the activated clotting time or the determination of heparin concentration. The target values of both tests remain empirical, with no clearly validated thresholds. The target value needs to be adjusted according to the POC test, given significant variations between devices and activators. After CABG, the need for antiplatelet therapy is well demonstrated, in order to limit the risk of postoperative death or ischemic events, and improve venous graft patency. Immediately after valvular surgery, antithrombotic therapy should take into account the specific risk carried by each patient and by each prosthetic device. The risk of venous thromboembolism, though poorly defined, is also present in the postoperative period and may require additional attention. Given the frequent exposure to UFH, occurrence of heparin-induced thrombocytopenia is not infrequent in these patients and requires careful individual management.

CONCLUSIONS

Antithrombotic therapy is an essential component of cardiac surgery. Yet, with the exception of antiplatelet agents in CABG patients, antithrombotic therapy is often based on the clinical experience of medical teams more than on an evidence-based assessment of the literature.

Effects of Hemodilution, Blood Loss, and Consumption on Hemostatic Factor Levels During Cardiopulmonary Bypass

OBJECTIVES

The purpose of this study was to determine quantitatively the effects of consumption, hemodilution, and blood loss on coagulation and fibrinolytic factor levels during cardiopulmonary bypass.

DESIGN

A combination of measured levels of prothrombin, antithrombin, fibrinogen, plasminogen, and antiplasmin along with their activation markers F1.2, thrombin-antithrombin complex, fibrinopeptide A, plasmin-antiplasmin complex, and D-dimer were used with a computer model of each patient's vascular and hemostatic systems to estimate the cardiopulmonary bypass-associated loss of each factor because of hemodilution, blood loss, and consumption.

SETTING

University hospital.

PARTICIPANTS

Nine patients undergoing coronary artery bypass graft surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

At baseline, it was estimated that on average 2%, 3%, and 25%, respectively, of the baseline liver secretion of plasminogen, prothrombin,and fibrinogen were consumed by activation of these proteins. During cardiopulmonary bypass, thrombin and plasmin generation were increased, whereas fibrin generation was decreased because of heparin. Compared with baseline, hemodilution during cardiopulmonary bypass resulted in an average 35% +/- 7% decrease in the concentration of coagulation and fibrinolytic proteins, whereas blood loss was responsible for an average 6% +/- 5% decrease in these proteins. Blood loss varied substantially among patients, resulting in <1% to 14% decreases in hemostatic protein levels. On average, consumption because of activation resulted in less than a 1% drop in the concentration of coagulation and fibrinolytic factors during cardiopulmonary bypass.

CONCLUSIONS

Hemodilution is the primary cause of the drop in coagulation and fibrinolytic proteins during routine cardiopulmonary bypass, followed by blood loss, whereas consumption accounts for less than a 1% drop in most patients.

Acute normovolemic hemodilution does not reduce antithrombin concentration for cardiac surgery

BACKGROUND

Acute normovolemic hemodilution (ANH) is used to reduce allogeneic blood transfusion with cardiac surgery. This procedure involves pre-operatively removing and storing a volume of whole blood and replacing the volume with crystalloid. The stored blood is then available for transfusion, if required. Hemodilution associated with ANH may reduce the effectiveness of heparin anticoagulation due to dilution of antithrombin. The aim of this study was to determine if antithrombin concentrations are reduced in patients who undergo one unit of ANH during cardiac surgery.

METHODS

Patients scheduled for cardiac surgery (n = 71) were grouped according to whether they did or did not undergo ANH pre-operatively. Antithrombin concentrations were measured before and after ANH. This study had 80% power to detect a difference in reduction of antithrombin concentration of 6% between groups following ANH with an alpha error of <0.05. The effect of one unit ANH was expected to cause a difference of 12% or greater.

RESULTS

No significant difference in the concentration of antithrombin between ANH patients and those that did not have ANH, nor was there a difference in the decrease in antithrombin between groups.

CONCLUSIONS

The results indicate that one unit of ANH does not significantly reduce the concentration of antithrombin prior to cardiac surgery. Thus patients who undergo one unit of ANH are not at increased risk due to dilution of antithrombin.

Attenuation of leukocyte beta 2-integrin expression by antithrombin-III

Antithrombin-III exerts antiinflammatory effects via ligation of heparan sulfate proteoglycans. Here we show in vitro that recombinant human antithrombin-III attenuates CD11b/CD18 expression of activated neutrophils and monocytes in whole blood ex vivo. As leukocyte integrin expression is triggered by extracorporeal circulation, this observation may be of relevance for pharmacological treatment during cardiopulmonary bypass.

Anticoagulation in Hypercoagulable Conditions: Special Considerations in the Treatment and Prevention of Venous Thromboembolism

Patients with hypercoagulable conditions, including malignancy, are at increased risk of recurrent venous thromboembolic events (VTE). The general approach to treatment and prevention of VTE in patients with thrombophilia is similar to that of patients who present with VTE associated with transient risk factors, including immobility, trauma, and surgery. However, several important issues must be considered in the initial management of acute VTE, in the long-term prevention of VTE following an initial event, and in VTE prophylaxis in patients with hypercoagulable conditions. Patients with antithrombin deficiency are prone to heparin resistance and may require concurrent antithrombin concentrates or anticoagulation with direct thrombin inhibitors for adequate treatment of acute VTE. In patients with malignancy, low-molecular-weight heparins have been found to be more effective than unfractionated heparin for the initial treatment of VTE. Long-term prevention is preferred for most patients with hypercoagulable conditions, and the latest trials show that low-intensity warfarin is not as effective as typical moderate-intensity therapy for chronic therapy. Primary prophylaxis of asymptomatic carriers is not warranted unless they are exposed to additional risk factors, including surgery, trauma, immobilization, and pregnancy. Prolonged prophylaxis may be appropriate in patients with malignancy who undergo surgical procedures.

Surveillance de l'anticoagulation des circulations extracorporelles par l'héparine non fractionnée : quels sont les problèmes non résolus ?

Cardiac surgery with extracorporeal circulation induces major alterations of haemostasis and requires high level of anticoagulation, usually achieved by unfractionated heparin infusion. Optimization of anticoagulant regimen, through adapted biological monitoring, can probably improve postoperative course, at least for postoperative haemostatic status. Despite increasing knowledge on extracorporeal circulation-induced haemostatic abnormalities and the development of new biological devices for heparin monitoring, the optimal level of anticoagulation remains matter of debate, as well as the monitoring procedures. This critical review presents the current available data on heparin anticoagulation and monitoring in this specific context, and underlines the pending issues about anticoagulation management during extracorporeal bypass.

Decreased concentration of antithrombin after preoperative therapeutic heparin does not cause heparin resistance during cardiopulmonary bypass

OBJECTIVE

To determine if preoperative heparin therapy causes an increase in the incidence of intraoperative heparin resistance by reducing the concentration of antithrombin in plasma.

DESIGN

Prospective laboratory investigation of clinical samples.

SETTING

Public tertiary care hospital and public pathology service.

PARTICIPANTS

Forty-six patients undergoing cardiac surgery involving cardiopulmonary bypass.

INTERVENTIONS

Fourteen patients received preoperative heparin therapy (POHI group) and 32 patients were controls (CONT group).

MEASUREMENTS AND MAIN RESULTS

The concentration of antithrombin, activated coagulation time (ACT), and clinical parameters were measured at intervals. More POHI patients had on-bypass heparin resistance than CONT (43% and 3%, respectively, p < 0.01). The POHI group had a lower concentration of antithrombin than the CONT group before (80.9% and 92.6%, respectively, p < 0.01) and while on cardiopulmonary bypass (51.6% and 57.5%, respectively, p = 0.04). Comparison of heparin-resistant and heparin-responsive POHI patients showed that the concentration of antithrombin did not differ before bypass (82.4% and 79.8%, respectively, p = 0.53) or during bypass (51.8% and 51.4%, respectively, p = 0.91). In fact, antithrombin concentrations were slightly higher in the heparin-resistant POHI patients (not significant). POHI patients received more heparin than CONT patients (medians 787 U/kg and 600 U/kg, respectively, p = 0.01) and were transfused with more fresh frozen plasma on bypass (p = 0.03).

CONCLUSIONS

Preoperative heparin causes an increased incidence of heparin resistance and reduced antithrombin concentrations. However, heparin resistance was not causally related to reduced antithrombin because antithrombin concentrations were not different between heparin-resistant and heparin-responsive patients in the POHI group.

Management of heparin resistance during cardiopulmonary bypass: the effect of five different anticoagulation strategies on hemostatic activation

OBJECTIVE

Attenuation of hemostatic activation is a central goal during CPB. However, this poses a problem in patients insensitive to heparin. The present investigation was performed to assess different strategies of managing patients with heparin resistance during CPB.

DESIGN

A randomized, prospective clinical investigation.

SETTING

A major European heart center.

PARTICIPANTS

Five groups with 20 patients each were investigated.

INTERVENTIONS

The groups were handled as follows: (1). maintenance of a target ACT, (2). maintenance of the target unfractionated heparin (UFH) level and supplementation of a UFH level-based strategy with (3). AT III, (4). the direct thrombin inhibitor r-hirudin, or (5). the short-acting platelet glycoprotein (GP) IIb/IIIa antagonist tirofiban. Platelet count and generation of contact factor XIIa, thrombin, and soluble fibrin were assessed. Samples were obtained before CPB and after CPB before protamine infusion.

MEASUREMENTS AND MAIN RESULTS

There were no differences observed in the generation of factor XIIa. The UFH-based strategy and supplementation with AT III, r-hirudin, and tirofiban resulted in significantly reduced (p < 0.05) thrombin generation compared with ACT management. A significant reduction of fibrin formation was seen only in patients who received AT III, r-hirudin, or tirofiban supplementation to the UFH. The administration of tirofiban resulted in a significant preservation of the platelet count compared with the other groups. There were no significant differences in the postoperative blood loss.

CONCLUSIONS

Activation of hemostasis during CPB in heparin-resistant patients most likely has to be attributed to stimulation of the tissue factor pathway. Even the sole use of high concentrations of UFH does not effectively inhibit this activation. Therefore, in these patients anticoagulation during CPB with UFH should be supplemented with either AT III, a short-acting direct thrombin inhibitor, or a short-acting platelet glycoprotein IIb/IIIa antagonist.

Antithrombin III concentrate to treat heparin resistance in patients undergoing cardiac surgery

OBJECTIVE

The purpose of this report is to describe the clinical use of antithrombin III concentrate in 53 patients who were found, in the operating room before cardiopulmonary bypass, to be heparin resistant.

METHOD

Resistance to heparin was determined to be present when greater than 600 U/kg body weight of heparin failed to prolong the kaolin-activated clotting time to more than 600 seconds in 53 aprotinin-treated patients. Blood samples were obtained for subsequent antithrombin III activity determination. Patients were then administered 500 U of antithrombin III concentrate, and the activated clotting time was remeasured. If the activated clotting time remained less than 600 seconds, a second 500-U dose was given.

RESULTS

Of the 53 patients, 45 (85%) had subnormal measured antithrombin III activity, and the mean plasma antithrombin III activity level for the entire group was 67% (normal 80%-120%). Administration of antithrombin III concentrate (500 U in 45 patients and 1000 U in 8 patients) resulted in prolongation of the mean activated clotting time from 492 to 789 seconds without additional heparin. The mean heparin dose response increased from 36.5 to 69.3 s x U(-1) x mL(-1) with antithrombin III treatment. Only one patient did not achieve the target activated clotting time, despite administration of greater than 600 U/kg heparin and 1000 U of antithrombin III concentrate, and was treated with fresh-frozen plasma.

CONCLUSIONS

On the basis of the criterion used in this report, most of the patients defined as being heparin resistant had subnormal plasma antithrombin III activity. Treatment with antithrombin III concentrate resulted in potentiation of the heparin effect to meet predetermined activated clotting time thresholds and allow for cardiopulmonary bypass.