Direct Thrombin Inhibitor Resistance and Possible Mechanisms

Unresponsiveness of Activated Partial Thromboplastin Time to Bivalirudin in Adults Receiving Extracorporeal Membrane Oxygenation

Activated partial thromboplastin time (aPTT) is the standard for monitoring bivalirudin but demonstrates a nonlinear response at higher drug concentrations. The objective of this study was to assess the relationship between bivalirudin dose and aPTT in patients receiving extracorporeal membrane oxygenation (ECMO) to determine a threshold where aPTT unresponsiveness occurs. Two hundred fourteen adults receiving bivalirudin during ECMO between 2018 and 2022 were included. Piecewise regression in a linear mixed effects model was used to determine a bivalirudin dose threshold of 0.21 mg/kg/hr for aPTT unresponsiveness. For doses of less than 0.21 mg/kg/hr (n = 135), every 0.1 mg/kg/hr dose increase led to an aPTT increase of 11.53 (95% confidence interval [CI] = 9.85-13.20) seconds compared to only a 3.81 (95% CI = 1.55-6.06) seconds increase when dose was greater than or equal to 0.21 mg/kg/hr (n = 79) (pinteraction < 0.001). In multivariable logistic regression, venovenous configuration (odds ratio [OR] = 2.83, 95% CI = 1.38-5.77) and higher fibrinogen concentration (OR = 1.22, 95% CI = 1.05-1.42) were associated with greater odds of unresponsiveness, whereas older age (OR = 0.79, 95% CI = 0.63-0.98), kidney dysfunction (OR = 0.48, 95% CI = 0.25-0.92), and a higher baseline aPTT (OR = 0.89, 95% CI = 0.82-0.97) were associated with lower odds. Alternative methods are necessary to ascertain bivalirudin's hemostatic impact when doses exceed 0.21 mg/kg/hr during ECMO.

Anticoagulation Management in V-V ECMO Patients: A Multidisciplinary Pragmatic Protocol

(1) Background: Extracorporeal membrane oxygenation (ECMO) is a complex procedure affecting both the risk of thrombosis and bleeding. High-quality data to personalize anticoagulation management in ECMO are lacking, resulting in a high variability in practice among centers. For this reason, we review coagulation methods and monitoring and share a pragmatic proposal of coagulation management, as performed in our high-volume ECMO Referral Centre; (2) Methods: We revised the anticoagulation options and monitoring methods available for coagulation management in ECMO through PubMed search based on words including "anticoagulation," "coagulation assays," "ECMO," "ELSO," and "ISTH"; (3) Results: Actual revision of the literature was described as our routine practice regarding ECMO anticoagulation and monitoring; (4) Conclusions: No coagulation test is exclusively predictive of bleeding or thrombotic risk in patients undergoing ECMO support. An approach that allows for a tailored regimen of anticoagulation (regardless of agent used) and monitoring is mandatory. To accomplish this, we propose that the titration of anticoagulation therapies should include multiple laboratory tests, including anti-Xa, aPTT, ACT, viscoelastic tests, AT levels, platelet count, fibrinogen, and FXIII levels. Anticoagulation regimens should be tailored to a specific patient and personalized based on this complex array of essays.

Current and future strategies to monitor and manage coagulation in ECMO patients

Extracorporeal membrane oxygenation (ECMO) can provide life-saving support for critically ill patients suffering severe respiratory and/or cardiac failure. However, thrombosis and bleeding remain common and complex problems to manage. Key causes of thrombosis in ECMO patients include blood contact to pro-thrombotic and non-physiological surfaces, as well as high shearing forces in the pump and membrane oxygenator. On the other hand, adverse effects of anticoagulant, thrombocytopenia, platelet dysfunction, acquired von Willebrand syndrome, and hyperfibrinolysis are all established as causes of bleeding. Finding safe and effective anticoagulants that balance thrombosis and bleeding risk remains challenging. This review highlights commonly used anticoagulants in ECMO, including their mechanism of action, monitoring methods, strengths and limitations. It further elaborates on existing anticoagulant monitoring strategies, indicating their target range, benefits and drawbacks. Finally, it introduces several highly novel approaches to real-time anticoagulation monitoring methods including sound, optical, fluorescent, and electrical measurement as well as their working principles and future directions for research.

Anticoagulation Management during Extracorporeal Membrane Oxygenation-A Mini-Review

Extracorporeal membrane oxygenation (ECMO) has been established as a life-saving technique for patients with the most severe forms of respiratory or cardiac failure. It can, however, be associated with severe complications. Anticoagulation therapy is required to prevent ECMO circuit thrombosis. It is, however, associated with an increased risk of hemocoagulation disorders. Thus, safe anticoagulation is a cornerstone of ECMO therapy. The most frequently used anticoagulant is unfractionated heparin, which can, however, cause significant adverse effects. Novel drugs (e.g., argatroban and bivalirudin) may be superior to heparin in the better predictability of their effects, functioning independently of antithrombin, inhibiting thrombin bound to fibrin, and eliminating heparin-induced thrombocytopenia. It is also necessary to keep in mind that hemocoagulation tests are not specific, and their results, used for setting up the dosage, can be biased by many factors. The knowledge of the advantages and disadvantages of particular drugs, limitations of particular tests, and individualization are cornerstones of prevention against critical events, such as life-threatening bleeding or acute oxygenator failure followed by life-threatening hypoxemia and hemodynamic deterioration. This paper describes the effects of anticoagulant drugs used in ECMO and their monitoring, highlighting specific conditions and factors that might influence coagulation and anticoagulation measurements.

Bivalirudin in pediatric extracorporeal membrane oxygenation

PURPOSE OF REVIEW

This review summarizes the current literature surrounding the use of bivalirudin as an alternative anticoagulant for pediatric extracorporeal membrane oxygenation (ECMO) patients.

RECENT FINDINGS

Recent single center studies describe that bivalirudin may be associated with decreased blood product transfusion, decreased cost and similar clinical outcomes for pediatric ECMO patients who have failed unfractionated heparin (UFH) anticoagulation. aPTT is the most common test to monitor bivalirudin but has several limitations. Other tests including dilute thrombin time (dTT) and viscoelastic assays are promising but more study is needed. Current evidence suggests that bivalirudin is a well tolerated and effective alternative anticoagulant for pediatric ECMO patients who have failed UFH anticoagulation but prospective studies are needed to confirm these results.

SUMMARY

Bivalirudin is a promising alternative anticoagulant for pediatric ECMO patients who have failed UFH. Large prospective, multicenter studies are needed to confirm safety and efficacy.

Efficacy of Bivalirudin for Therapeutic Anticoagulation in COVID-19 Patients Requiring ECMO Support

Objectives

The Coronavirus Disease 2019 (COVID-19) pandemic has been associated with cases of refractory acute respiratory distress syndrome (ARDS) sometimes requiring support with extracorporeal membrane oxygenation (ECMO). Bivalirudin can be used for anticoagulation in patients on ECMO support, but its efficacy and safety in patients with COVID-19 is unknown. The authors set out to compare the pharmacologic characteristics and dosing requirements of bivalirudin in patients requiring ECMO support for ARDS due to COVID-19 versus ARDS from other etiologies.

Design and Setting

This retrospective case-control study was performed at Indiana University Health Methodist Hospital in Indianapolis, Indiana.

Participants

Patients were included if they were on venovenous ECMO support between June 2019 and June 2020, and divided into two groups: ARDS secondary to COVID-19 and those with ARDS from another etiology (Non-COVID).

Interventions

Patient demographics, such as age, sex, weight, chronic comorbid conditions, baseline antiplatelet and anticoagulant use, antiplatelet use during ECMO, and need for renal replacement therapy were collected, and compared between groups. Time to activated partial thromboplastin time (aPTT) goal, percentage of time at aPTT goal, bivalirudin rates, total bivalirudin requirements, total duration on bivalirudin, total duration on ECMO, mortality, and complications associated with ECMO were collected and compared between groups.

Measurements and Main Results

A total of 42 patients met inclusion criteria (n = 19 COVID-19, n = 23 non-COVID). However, percentages of aPTTs at goal were maintained more consistently in patients with COVID-19 versus non-COVID (86% v 74%: p < 0.01). Higher median (IQR) daily rates (3.1 μg/kg/min [2.3-5.2] v 2.4 μg/kg/min [1.7-3.3]: p = 0.05) and higher median (IQR) maximum rates of bivalirudin (5 μg/kg/min [3.7-7.5] v 3.8 μg/kg/min [2.5-5]: p = 0.03) were required in the COVID-19 group versus the non-COVID group. Time to goal aPTT was similar between groups. There were no differences in complications associated with anticoagulation, as demonstrated by similar rates of bleeding and thrombosis between both groups.

Conclusions

Patients on ECMO with ARDS from COVID-19 require more bivalirudin overall and higher rates of bivalirudin to maintain goal aPTTs compared with patients without COVID-19. However, COVID-19 patients more consistently maintain goal aPTT. Future randomized trials are needed to support efficacy and safety of bivalirudin for anticoagulation of COVID-19 patients on ECMO.

Anticoagulation in ECMO patients: an overview

Extracorporeal membrane oxygenation (ECMO) is a form of cardiorespiratory support, and is being increasingly used to support refractory heart and respiratory failure. It involves draining blood from the vascular system, which is then circulated outside the body by a mechanical pump and then later reinfused back into the circulation. The blood that is circulated outside the body comes in contact with a large surface area of non-endothelial biosurface. This exposure leads to a pro-thrombotic state, and hence anticoagulation is required. Unfractionated heparin is the most commonly used anticoagulation in most ECMO centers, but it does require close monitoring. Despite the advances made, hemostasis remains a challenge for physicians who manage patients on ECMO.

Prospective Exploratory Experience With Bivalirudin Anticoagulation in Pediatric Extracorporeal Membrane Oxygenation

OBJECTIVES

Objective of this study was to determine if bivalirudin resulted in less circuit interventions than unfractionated heparin. A secondary objective was to examine associations between bivalirudin dose and partial thromboplastin time, international normalized ratio, and activated clotting time.

DESIGN

Prospective observational.

SETTING

Medical-surgical and cardiac PICUs.

PATIENTS

Neonatal and pediatric extracorporeal membrane oxygenation patients who received bivalirudin anticoagulation.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twenty extracorporeal membrane oxygenation runs in 18 patients used bivalirudin; 90% were venoarterial. Median (interquartile range) age was 4.5 months (1.6-35 mo). Thirteen patients (72%) had an underlying cardiac diagnosis. Of the 20 runs using bivalirudin, 16 (80%) were initially started on unfractionated heparin and transitioned to bivalirudin due to ongoing circuit thrombosis despite therapeutic anti-Xa levels (n = 13), ongoing circuit thrombosis with unfractionated heparin greater than or equal to 40 U/kg/hr (n = 2), or absence of increase in ACT after bolus of 100 U/kg of unfractionated heparin and escalation of unfractionated heparin infusion (n = 1). Initial bivalirudin dose ranged from 0.2 to 0.5 mg/kg/hr; no bolus doses were used. Median (range) bivalirudin dose was 0.9 mg/kg/hr (0.15-1.6 mg/kg/hr). Median (interquartile range) time on extracorporeal membrane oxygenation was 226.5 hours (150.5-393.0 hr) including 84 hours (47-335 hr) on bivalirudin. Nonparametric results are as follows: the rate of circuit intervention was significantly lower in patients on bivalirudin than on unfractionated heparin (median [interquartile range]: 0 [0-1] and 1 [1-2], respectively; Wilcoxon p = 0.0126). Bivalirudin dose was correlated to PTT (rs = 0.4760; p < 0.0001), INR (rs = 0.6833; p < 0.0001), and ACT (rs = 0.6161; p < 0.0001). Four patients had a significant bleeding complication on bivalirudin. Survival to hospital discharge was 56%.

CONCLUSIONS

Bivalirudin appears to be a viable option for systemic anticoagulation in pediatric extracorporeal membrane oxygenation patients who have failed unfractionated heparin, but questions remain namely its optimal monitoring strategy. This pilot study supports the need for larger prospective studies of bivalirudin in pediatric extracorporeal membrane oxygenation, particularly focusing on meaningful monitoring variables.

Evaluation of Bivalirudin As an Alternative to Heparin for Systemic Anticoagulation in Pediatric Extracorporeal Membrane Oxygenation

OBJECTIVES

Heparin is the universal anticoagulant for patients receiving extracorporeal membrane oxygenation support. However, heparin has many disadvantages, especially in young children, who develop heparin resistance. Recently our center has used bivalirudin, a direct thrombin inhibitor, for systemic anticoagulation in pediatric extracorporeal life support. Bivalirudin binds directly to thrombin with no need for antithrombin III and it inhibits both circulating and clot-bound thrombin. In this study, we sought to evaluate our experience with bivalirudin in pediatric extracorporeal life support.

DESIGN

Retrospective chart review study of patients receiving extracorporeal membrane oxygenation support between October 2014 and May 2018.

SETTING

Tertiary, academic PICU.

PATIENTS

Sixteen patients receiving heparin and 16 patients receiving bivalirudin on extracorporeal life support were included in the study.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients in the bivalirudin group had a median age of 31 months versus 59 months in the heparin group (p = 0.41). Recovery and extracorporeal membrane oxygenation decannulation were similar in both groups (56% in the heparin group and 62% in the bivalirudin group; p = 0.62). Time to reach goal therapeutic anticoagulation level was shorter in the bivalirudin group (11 vs 29 hr; p = 0.01). Bleeding events were fewer in the bivalirudin group, and there was no difference in the rate of thrombotic events between the two groups. Comprehensive cost analysis that includes anticoagulant, laboratories, and antithrombin III cost, showed that heparin anticoagulation therapy total cost was significantly higher than bivalirudin (1,184 dollars per day in heparin group vs 494 dollars per day in bivalirudin group; p = 0.03). Bivalirudin dose required to maintain target anticoagulation will increase over time, and this is associated with an increase in creatinine clearance and an increase in fibrinogen serum levels.

CONCLUSIONS

This study showed that the use of bivalirudin in pediatric extracorporeal membrane oxygenation support is feasible, safe, reliable, and cost-effective in comparison to heparin. Further prospective randomized clinical trials are necessary to confirm our observations.

Bivalirudin for Maintenance Anticoagulation During Venovenous Extracorporeal Membrane Oxygenation for COVID-19

In its severe manifestation, coronavirus disease 2019 (COVID-19) compromises oxygenation in a manner that is refractory to maximal conventional support and requires escalation to extracorporeal membrane oxygenation (ECMO). Maintaining ECMO support for extended durations requires a delicately balanced anticoagulation strategy to maintain circuit viability by preventing thrombus deposition while avoiding excessive anticoagulation yielding hemorrhage—a task that is complicated in COVID-19 secondary to an inherent hypercoagulable state.

Bivalirudin, a member of the direct thrombin inhibitor drug class, offers potential advantages during ECMO, including to its ability to exert its effect by directly attaching to and inhibiting freely circulating and fibrin-bound thrombin. Herein, the successful use of an anticoagulation strategy using the off-label use of a continuous infusion of bivalirudin in a case of severe hypoxemic and hypercarbic respiratory failure caused by COVID-19 requiring venovenous ECMO is reported. Importantly, therapeutic anticoagulation intensity was achieved rapidly with stable pharmacokinetics, and there was no need for any circuit interventions throughout the patient's 27-day ECMO course. In COVID-19, bivalirudin offers a potential option for maintaining systemic anticoagulation during ECMO in a manner that may mitigate the prothrombotic nature of the underlying pathophysiologic state.

Bivalirudin resistance in a patient on veno-venous extracorporeal membrane oxygenation with a therapeutic response to argatroban

A 48-year-old male patient requiring extracorporeal membrane oxygenation (ECMO) support for hypoxaemic respiratory failure failed to achieve therapeutic anticoagulation with bivalirudin after continuous dose escalations, and continued to have recurrent fibrin stranding in the circuit over a 6-day course of treatment. Suspecting bivalirudin resistance, the patient was transitioned to argatroban and achieved a therapeutic response in less than 24 hours. The case describes the challenges of anticoagulation in ECMO supported patients. The interplay between bivalirudin metabolism, renal replacement therapy, and immunological effects leading to a heparin-like-effect, inflammatory mediators, and thrombotic burdens may all impact the clinical effect during bivalirudin therapy. The structural biochemistry of thrombin and bivalirudin likely plays a role in the presented patient's successful response to argatroban. Bivalirudin may fail at achieving therapeutic anticoagulation in patients with genetic thrombin mutations or structural defects that alter the binding pockets at the thrombin exosites.

Anticoagulation with direct thrombin inhibitors during extracorporeal membrane oxygenation

Use of extracorporeal membrane oxygenation to support patients with critical cardiorespiratory illness is increasing. Systemic anticoagulation is an essential element in the care of extracorporeal membrane oxygenation patients. While unfractionated heparin is the most commonly used agent, unfractionated heparin is associated with several unique complications that can be catastrophic in critically ill patients, including heparin-induced thrombocytopenia and acquired antithrombin deficiency. These complications can result in thrombotic events and subtherapeutic anticoagulation. Direct thrombin inhibitors (DTIs) are emerging as alternative anticoagulants in patients supported by extracorporeal membrane oxygenation. Increasing evidence supports DTIs use as safe and effective in extracorporeal membrane oxygenation patients with and without heparin-induced thrombocytopenia. This review outlines the pharmacology, dosing strategies and available protocols, monitoring parameters, and special use considerations for all available DTIs in extracorporeal membrane oxygenation patients. The advantages and disadvantages of DTIs in extracorporeal membrane oxygenation relative to unfractionated heparin will be described.

Antithrombotic Management during Percutaneous Mitral Valve Repair with the Mitraclip System in a Patient with Heparin-Induced Thrombocytopenia

Interventional cardiology procedures require full anticoagulation to prevent thrombus formation on catheters and devices with potential development of embolic complications. Bivalirudin, a short half-life direct thrombin inhibitor, has been largely used during percutaneous coronary interventions and represents the preferred alternative to heparin in patients with heparin-induced thrombocytopenia (HIT). However, few data are available about intraprocedural use of bivalirudin during transcatheter structural heart disease interventions. Activated clotting time (ACT) monitoring during bivalirudin infusion presents some limitations and it is not mandatory. We report a case of bivalirudin use in a patient with type-2 HIT during percutaneous mitral valve repair with the Mitraclip system (Abbott, Abbott Park, Illinois, United States). Despite use of standard bivalirudin dose (0.75 mg/kg bolus and 1.4 mg/kg/min infusion—reduced infusion rate was motivated by a glomerular filtration rate of 37 mL/min), the patient developed a large thrombus on the second clip during its orientation toward the mitral orifice. ACT was measured at that time and was suboptimal (240 seconds). The case was successfully managed with clip and thrombus retrieval, adjunctive 0.3 mg/kg bivalirudin bolus and increased infusion rate, and clip repositioning with ACT monitoring. This report makes the case for mandatory ACT checking and drug titration during high-risk catheter–based structural heart disease interventions, even when thromboprophylaxis is performed with bivalirudin. Additional coagulation tests may be useful to monitor bivalirudin response in similar cases.