Use of bivalirudin, a direct thrombin inhibitor, and its reversal with modified ultrafiltration during heart transplantation in a patient with heparin-induced thrombocytopenia

A Historical Perspective on the Reversal of Anticoagulants

There has been a landmark shift in the last several decades in the management and prevention of thromboembolic events. From the discovery of parenteral and oral agents requiring frequent monitoring as early as 1914, to the development of direct oral anticoagulants (DOACs) that do not require monitoring or dose adjustment in the late 20th century, great advances have been achieved. Despite the advent of these newer agents, bleeding continues to be a key complication, affecting 2 to 4% of DOAC-treated patients per year. Bleeding is associated with substantial morbidity and mortality. Although specific reversal agents for DOACs have lagged the release of these agents, idarucizumab and andexanet alfa are now available as antagonists. However, the efficacy of these reversal agents is uncertain, and complications, including thrombosis, have not been adequately explored. As such, guidelines continue to advise the use of nonspecific prohemostatic agents for patients requiring reversal of the anticoagulant effect of these drugs. As the indications for DOACs and the overall prevalence of their use expand, there is an unmet need for further studies to determine the efficacy of specific compared with nonspecific pro-hemostatic reversal agents. In this review, we will discuss the evidence behind specific and nonspecific reversal agents for both parenteral and oral anticoagulants.

Acute Kidney Injury and Extracorporeal Membrane Oxygenation: Review on Multiple Organ Support Options

Extracorporeal membrane oxygenation (ECMO) is a temporary life support system used to assist patients with life-threatening severe cardiac and/or respiratory insufficiency. Patients requiring ECMO can be considered the sickest patients admitted to the intensive care unit (ICU). Acute kidney injury (AKI) represents a frequent complication during ECMO, affecting up to 70% of patients, with multifactorial pathophysiology and an independent risk factor for mortality. Severe AKI requiring Continuous Renal Replacement Therapy (CRRT) occurs in 20% of ECMO patients, but multiple indications and different timing may imply a significantly higher application rate in different centers. CRRT can be run in parallel to ECMO through different vascular access, or it can be conducted in series by connecting the circuits. Anticoagulation of ECMO is typically managed with systemic heparin, but several approaches can be applied for the CRRT circuit, from no anticoagulation to the addition of intra-filter heparin or regional citrate anticoagulation. The combination of CRRT and ECMO can be considered a form of multiple organ support therapy, but this approach still requires optimization in timing, set-up, anticoagulation, prescription and delivery. The aim of this report is to review the pathophysiology of AKI, the CRRT delivery, anticoagulation strategies and outcomes of patients with AKI treated with ECMO.

How would we treat our own heparin-induced thrombocytopenia during cardiac surgery?

The aim of this article is to provide a comprehensive review of the current state of knowledge on heparin-induced thrombocytopenia (HIT) in cardiac surgery. The management of HIT patients undergoing cardiac surgery with cardiopulmonary bypass is complex and requires an interdisciplinary and patient-tailored approach because available evidence is limited and current anticoagulation strategies have potential risks. An index case is used to discuss both the established and new perioperative therapeutic options in HIT patients undergoing urgent cardiac surgery with cardiopulmonary bypass.

Description of Bivalirudin Use for Anticoagulation in Pediatric Patients on Mechanical Circulatory Support

BACKGROUND

Although heparin has previously been the anticoagulant of choice during mechanical circulatory support (MCS), there is a lack of consistency in dose-response in pediatric patients. Bivalirudin offers more consistent dose-response in adults; however, there are limited data for pediatrics use.

OBJECTIVE

The purpose was to characterize the usage, dosage, and safety profile of bivalirudin when used for pediatric MCS in a tertiary care pediatric hospital.

METHODS

A retrospective review of pediatric patients receiving bivalirudin for extracorporeal membrane oxygenation/ventricular assist device (ECMO/VAD) anticoagulation was conducted. The primary outcome was the average dose of bivalirudin. Additional outcomes included initial and maximum bivalirudin dose, time to first therapeutic activated partial thromboplastin time (aPTT), time within goal aPTT range, bleeding and clotting complications, and cost. Data were compared between ECMO and VAD patients.

RESULTS

Thirty-four patients were included. The median dose of bivalirudin was 0.37 mg/kg/h (interquartile range [IQR] = 0.21-0.56), with a maximum dose of 0.62 mg/kg/h (IQR = 0.33-0.91). VAD patients had a higher median and maximum dose as compared with ECMO patients. Patients achieved their therapeutic goal in a median of 6.1 hours and averaged 61.9% time within therapeutic aPTT. One patient had significant hemorrhage, whereas 3 patients had clotting requiring a circuit change. Bivalirudin acquisition cost was higher than heparin.

CONCLUSION AND RELEVANCE

Bivalirudin dosing in ECMO and VAD patients is consistent with dosing seen in previous reports but may be higher in VAD patients. Comparative studies between heparin and bivalirudin are necessary to compare cost-effective outcomes for pediatric patients.

Bivalirudin Dosing Requirements in Adult Patients on Extracorporeal Life Support With or Without Continuous Renal Replacement Therapy

Systemic anticoagulation with unfractionated heparin is standard of care for patients receiving extracorporeal life support (ECLS); however, an alternative anticoagulant may be necessary when challenges with heparin therapy arise. Evidence for alternative anticoagulation in ECLS patients is limited. This retrospective analysis evaluated the dosing and outcomes associated with bivalirudin use in 14 adult ECLS patients. Indications for bivalirudin included heparin-induced thrombocytopenia, heparin resistance, or persistent clotting or bleeding while on heparin. The median initial bivalirudin dose to achieve target activated partial thromboplastin time was 0.15 mg/kg/h (range 0.04-0.26 mg/kg/h). Dosing requirements increased by 75-125% when renal replacement was included. Median time on bivalirudin was 5.2 days (range 0.9-28 days). Five patients (36%) required a circuit change while on bivalirudin because of clotting or failing oxygenation, and four (28.6%) had bleeding significant enough to require either reduction in activated partial thromboplastin time goals or temporary holding of anticoagulation. Bivalirudin appears to be a potential option for adult patients on ECLS who are unable to receive or fail heparin therapy; however, the wide variation in dosing suggests the need for careful management.

Simultaneous Liver-Kidney Transplantation in Patient with a History of Heparin-Induced Thrombocytopenia: A Case Report and Literature Review

Patient: Male, 58

Final Diagnosis: Heparin-induced thrombocytopenia

Symptoms: Liver and kidney failure

Medication: —

Clinical Procedure: Simultaneous liver-kidney transplantation

Specialty: Transplantology

Bivalirudin Medication Use Evaluation and Cost Savings Initiative

Bivalirudin is a parenteral anticoagulant that elicits its effect through inhibition of both free and clot bound-thrombin. Inhibition of thrombin serves as a unique mechanism for anticoagulation when compared to heparin as thrombin serves as the final common pathway for the intrinsic and extrinsic coagulation cascades. Due to unclear benefit over heparin, concerns regarding reversibility, and most importantly cost its use as a parenteral anticoagulant varies by institution. A recent drug expenditure review within our institution noted a significant increase in the contribution bivalirudin had on the overall drug budget. In an effort to establish the rationale for the cost increase, a medication use evaluation was performed. While it was discovered that 625 out of 1364 days of bivalirudin therapy were potentially avoidable, an equally important discovery was the amount of waste that was associated with bivalirudin therapy. Calculating daily requirements for bivalirudin indicated that 60% of patients required less than 100 mg per day. Within this article, we describe a cost-savings initiative to reduce bivalirudin waste and the resulting cost-avoidance following implementation.

Heparin-induced thrombocytopenia in solid organ transplant recipients: The current scientific knowledge

Exposure to heparin is associated with a high incidence of immunization against platelet factor 4 (PF4)/heparin complexes. A subgroup of immunized patients is at risk of developing heparin-induced thrombocytopenia (HIT), an immune mediated prothrombotic adverse drug effect. Transplant recipients are frequently exposed to heparin either due to the underlying end-stage disease, which leads to listing and transplantation or during the transplant procedure and the perioperative period. To review the current scientific knowledge on anti-heparin/PF4 antibodies and HIT in transplant recipients a systematic PubMed literature search on articles in English language was performed. The definition of HIT is inconsistent amongst the publications. Overall, six studies and 15 case reports have been published on HIT before or after heart, liver, kidney, and lung transplantation, respectively. The frequency of seroconversion for anti-PF4/heparin antibodies ranged between 1.9% and 57.9%. However, different methods to detect anti-PF4/heparin antibodies were applied. In none of the studies HIT-associated thromboembolic events or fatalities were observed. More importantly, in patients with a history of HIT, reexposure to heparin during transplantation was not associated with thrombotic complications. Taken together, the overall incidence of HIT after solid organ transplantation seems to be very low. However, according to the current knowledge, cardiac transplant recipients may have the highest risk to develop HIT. Different alternative suggestions for heparin-free anticoagulation have been reported for recipients with suspected HIT albeit no official recommendations on management have been published for this special collective so far.

Heparin induced thrombocytopenia in critically ill: Diagnostic dilemmas and management conundrums

Thrombocytopenia is often noted in critically ill patients. While there are many reasons for thrombocytopenia, the use of heparin and its derivatives is increasingly noted to be associated with thrombocytopenia. Heparin induced thrombocytopenia syndrome (HITS) is a distinct entity that is characterised by the occurrence of thrombocytopenia in conjunction with thrombotic manifestations after exposure to unfractionated heparin or low molecular weight heparin. HITS is an immunologic disorder mediated by antibodies to heparin-platelet factor 4 (PF4) complex. HITS is an uncommon cause of thrombocytopenia. Reported incidence of HITS in patients exposed to heparin varies from 0.2% to up to 5%. HITS is rare in ICU populations, with estimates varying from 0.39%-0.48%. It is a complex problem which may cause diagnostic dilemmas and management conundrum. The diagnosis of HITS centers around detection of antibodies against PF4-heparin complexes. Immunoassays performed by most pathology laboratories detect the presence of antibodies, but do not reveal whether the antibodies are pathological. Platelet activation assays demonstrate the presence of clinically relevant antibodies, but only a minority of laboratories conduct them. Several anticoagulants are used in management of HITS. In this review we discuss the incidence, pathogenesis, diagnosis and management of HITS.

Plasma Exchange on Venovenous Extracorporeal Membrane Oxygenation With Bivalirudin Anticoagulation

A pediatric patient requiring venovenous (VV) extracorporeal membrane oxygenation (ECMO) as a bridge to lung transplantation developed heparin-induced thrombocytopenia. Unfractionated heparin was discontinued, and a bivalirudin infusion was started. During the lung transplant evaluation, he was found to have allosensitization, requiring treatment with plasma exchange along with pulse methylprednisolone, rituximab, bortezomib, and pooled immunoglobulin infusion. We describe our experience with successful plasma exchange for allosensitization during bivalirudin anticoagulation on VV ECMO in a pediatric patient.

Pathology consultation on monitoring direct thrombin inhibitors and overcoming their effects in bleeding patients

OBJECTIVES

Direct thrombin inhibitors (DTIs), a relatively new class of anticoagulants, present several challenges regarding monitoring of their anticoagulant effects and overcoming bleeding associated with their use. The aim of this article is to (1) briefly present the pharmacologic properties of currently available DTIs, (2) discuss approaches to laboratory assessment of these drugs, and (3) review management of bleeding associated with their use.

METHODS

Published literature on DTIs, including clinical trials, case reports, and experimental animal models, was reviewed. The primary authors also reviewed their first-hand experiences with DTI anticoagulation.

RESULTS

Based on the literature review and the practical experiences of the authors, suggestions for the monitoring of DTIs and algorithmic approaches for the management of DTI-associated bleeding were developed.

CONCLUSIONS

Routine coagulation assays (eg, the prothrombin time) show a relatively poor correlation with the degree of anticoagulation and DTI drug concentrations. Newer assays, such as the ecarin clotting time and dilute thrombin time, may be more useful in assessing DTI anticoagulation, but these assays are not yet widely available. Low-grade DTI-associated bleeds are best managed with cessation of the drug and supportive care, while higher-grade and/or life-threatening bleeds may best be reversed by active drug removal (eg, via the administration of activated charcoal or hemodialysis). At present there is little evidence to suggest that transfusion products such as factor concentrates or thawed plasma are of any particular benefit in DTI reversal; however, these products may play a supportive role in the management of bleeding.

Bivalirudin versus heparin as an anticoagulant during extracorporeal membrane oxygenation: a case-control study

OBJECTIVE

Heparin-based anticoagulation for patients undergoing extracorporeal membrane oxygenation has many limitations, including a high risk of heparin-induced thrombocytopenia. However, little experience with other anticoagulants in these patients has been described. The aim of this study was to compare bivalirudin-based anticoagulation with heparin-based protocols in a population of patients treated with venovenous or venoarterial extracorporeal membrane oxygenation.

DESIGN

In this case-control study, 10 patients received bivalirudin (cases) and 10 heparin (controls). The target activated partial thromboplastin time (aPTT) was 45 to 60 seconds.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

aPTT variations >20% of the previous value were much more frequent in patients treated with heparin than in patients receiving bivalirudin (52 v 24, p < 0.001). The number of corrections of the anticoagulant dose was higher in the heparin group compared with the bivalirudin group (58 v 51), although it did not reach statistical significance. Bleeding, thromboembolic complications, extracorporeal membrane oxygenation (ECMO) support duration, mortality, and the number of episodes of aPTT >80 seconds were not different between the 2 groups. A further analysis was performed in the bivalirudin group according to the presence of acute renal failure requiring continuous venovenous hemofiltration. The median bivalirudin dose in patients with or without hemofiltration was 0.041 (0.028-0.05) mg/kg/h and 0.028 (0-0.041) mg/kg/h, respectively (p = 0.2).

CONCLUSIONS

Bivalirudin-based anticoagulation may represent a new method of anticoagulation for reducing thromboembolic and bleeding complications, which still jeopardize the application of extracorporeal membrane oxygenation. Moreover, bivalirudin is free from the risk of heparin-induced thrombocytopenia. Higher doses of bivalirudin may be needed in patients undergoing hemofiltration.

Antiphospholipid syndrome; its implication in cardiovascular diseases: a review

Antiphospholipid syndrome (APLS) is a rare syndrome mainly characterized by several hyper-coagulable complications and therefore, implicated in the operated cardiac surgery patient. APLS comprises clinical features such as arterial or venous thromboses, valve disease, coronary artery disease, intracardiac thrombus formation, pulmonary hypertension and dilated cardiomyopathy. The most commonly affected valve is the mitral, followed by the aortic and tricuspid valve. For APLS diagnosis essential is the detection of so-called antiphospholipid antibodies (aPL) as anticardiolipin antibodies (aCL) or lupus anticoagulant (LA). Minor alterations in the anticoagulation, infection, and surgical stress may trigger widespread thrombosis. The incidence of thrombosis is highest during the following perioperative periods: preoperatively during the withdrawal of warfarin, postoperatively during the period of hypercoagulability despite warfarin or heparin therapy, or postoperatively before adequate anticoagulation achievement. Cardiac valvular pathology includes irregular thickening of the valve leaflets due to deposition of immune complexes that may lead to vegetations and valve dysfunction; a significant risk factor for stroke. Patients with APLS are at increased risk for thrombosis and adequate anticoagulation is of vital importance during cardiopulmonary bypass (CPB). A successful outcome requires multidisciplinary management in order to prevent thrombotic or bleeding complications and to manage perioperative anticoagulation. More work and reporting on anticoagulation management and adjuvant therapy in patients with APLS during extracorporeal circulation are necessary.

Direct thrombin inhibitors: pharmacology and application in intensive care medicine

PURPOSE

Anticoagulation is part of the daily routine of intensive care physicians. As the possibilities of pharmacological anticoagulation are becoming more numerous and diverse, intensive care physicians have to be familiar with indications, contraindications, dosing, and reversal of many different substances. This paper presents an overview of the substance group of direct thrombin inhibitors (DTI) indicated for alternative anticoagulation in intensive care medicine.

METHODS

The review is a synopsis of scientific evidence, expert opinion, open forum commentary, and clinical feasibility data.

RESULTS AND CONCLUSIONS

Due to their antithrombotic potential without direct activation of platelets, DTI could offer potential advantages over heparins and vitamin K antagonists in critically ill patients, especially regarding heparin-induced thrombocytopenia. Because of multiple organ dysfunction, organ failure, and comedications, simple extrapolation of results of medical to critically ill patients is not permissible. The fine line between thrombosis and bleeding in intensive care patients requires cautious dosing and close drug monitoring. Studies dealing with DTI in the intensive care setting are of utmost clinical interest.

Prefilter Bivalirudin for Preventing Hemofilter Occlusion in Continuous Renal Replacement Therapy

Objective:

To describe a case of successful bivalirudin use as a prefilter anticoagulant in continuous venovenous hemofiltration (CVVH).

Case Summary:

A 30-year-old male was brought to the hospital by ambulance with an anterior communicating artery subarachnoid hemorrhage, signs of intraparenchymal hemorrhage, and hydrocephalus. During the patient's complicated hospital course, he developed acute renal failure requiring CVVH, as well as hepatic insufficiency (Child-Pugh class B). Unfractionated heparin was used as a prefilter anticoagulant. After he had a positive heparin-induced thrombocytopenia (HIT) antibody test, prefilter heparin was discontinued in favor of bivalirudin. Filter survival and systemic activated partial thromboplastin time (aPTT) values were compared between prefilter heparin (n = 5) and bivalirudin (n = 4). Filter survival was similar (median 26 h with heparin vs 37 h with bivalirudin; p = 0.52). Prefilter bivalirudin 1–2.5 mg/hour (0.009–0.023 mg/kg/h) was effective in maintaining systemic aPTTs that were 1–1.4 times the reference range. Serotonin release assay and subsequent HIT antibodies were negative. The patient's renal function improved and CVVH was discontinued.

Discussion:

Critically ill patients requiring CVVH often need regional or systemic anticoagulation to prevent filter occlusion. In some patient populations, such as those with HIT or liver failure, prefilter heparin and regional citrate, respectively, may not be options. Alternative anticoagulants may be needed to avoid complications of frequent filter occlusions. The direct thrombin inhibitors (DTIs) lepirudin and argatroban have been used to maintain hemofilter patency, in small studies. Bivalirudin may have pharmacokinetic advantages over other DTIs when used in patients with hepatic and renal impairment. In our patient, bivalirudin provided a safe alternative to heparin therapy and was effective in maintaining hemofilter patency during CVVH.

Conclusions:

Prefilter bivalirudin may be an option to prevent filter occlusion in patients requiring continuous renal replacement therapy. Future studies are needed to validate the safety and efficacy of bivalirudin as a prefilter anticoagulant.

[Direct thrombin inhibitors: pharmacology and application in cardiovascular anesthesia]

The options for drug-controlled anticoagulation are becoming noticeably more manifold. In the area of anaesthesiology and intensive care, there are furthermore special disease patterns, such as heparin-induced thrombocytopenia (HIT) to be known, diagnosed and treated. This article gives a review of the substance groups of the direct thrombin inhibitors (DTI) as alternative anticoagulants for HIT in combination with cardiovascular diseases. For the administration of DTIs, experience and the correct dose are the keys to success and are the deciding factors for the two sides of haemostasis: thrombosis and haemorrhage.

Bivalirudin for patients with heparin-induced thrombocytopenia undergoing cardiovascular surgery

OBJECTIVE

To evaluate the use of bivalirudin in patients with heparin-induced thrombocytopenia (HIT) undergoing cardiovascular surgery.

DATA SOURCES

Relevant information was identified through a search of MEDLINE (1966-April 2008), International Pharmaceutical Abstracts (1960-April 2008), and Cochrane Databases (publications archived until April 2008) using the terms bivalirudin, heparin-induced thrombocytopenia, and cardiovascular surgery.

STUDY SELECTION AND DATA EXTRACTION

Prospective and retrospective studies, case reports, and case series in adults were eligible for inclusion if bivalirudin had been used in a patient with known HIT undergoing any cardiovascular surgical procedure other than percutaneous coronary intervention.

DATA SYNTHESIS

Two small, open-label, multicenter clinical trials were identified that evaluated treatment with bivalirudin in patients with HIT undergoing coronary artery bypass graft surgery. One looked at on-pump cardiopulmonary bypass (CPB), while the other looked at off-pump CPB. Procedural success was achieved at day 7 in 94% (n = 46) of patients in the on-pump CPB study and in 92% (n = 47) of patients in the off-pump CPB study. Dosing strategies varied between the 2 trials, with the on-pump study using a 1-mg/kg bivalirudin bolus followed by a 2.5-mg/kg/h infusion; the off-pump study used a 0.75-mg/kg bolus followed by a 1.75-mg/kg/h infusion. In addition, 10 case reports met the criteria to be included in the review and are summarized. In these cases, procedural success was reported using various bivalirudin doses in valve repair and replacement, right ventricular assist device implantation, and heart transplantation.

CONCLUSIONS

Growing data demonstrate procedural success with bivalirudin in patients with HIT undergoing cardiovascular surgery. However, bivalirudin dosing and goal-activated clotting times varied between the studies and case reports. Bivalirudin represents a viable alternative to heparin in patients with HIT undergoing cardiovascular surgery; however, further trials are warranted to identify optimal dosing and monitoring parameters.

Heparin-Induced Thrombocytopenia in Left Ventricular Assist Device Bridge-to-Transplant Patients

BACKGROUND

The presence of heparin-induced thrombocytopenia (HIT) increases the risk for thromboembolic events in ventricular assist device (VAD) patients undergoing transplantation. However, cardiopulmonary bypass with alternative anticoagulants is often complicated by bleeding. Owing to this concern, we compared outcomes of HIT-positive versus control bridge-to-transplantation VAD patients; both groups were reexposed to heparin for cardiopulmonary bypass during transplant.

METHODS

From February 2000 to January 2006, data were reviewed on 92 consecutive adult patients who underwent VAD placement as a bridge to transplantation. Patients in whom thrombocytopenia developed after heparin exposure were tested for HIT with an enzyme-linked immunosorbent assay for antiheparin/platelet factor-4 (HPF4) antibody (GTI Diagnostics, Waukesha, Wisconsin). During VAD support, heparin was avoided in HIT-positive patients, but all patients were reexposed to heparin during transplantation. Comparisons between HIT-positive and control patients for survival and freedom from thromboembolic events were determined using the Kaplan-Meier method and log-rank test. Continuous and categorical variables were compared using the Wilcoxon rank-sum and Student t test.

RESULTS

Twenty-four of the 92 patients (26.1%) were determined to be HIT positive by enzyme-linked immunosorbent assay. Survival to transplant was not different between the two groups. When compared with control patients, HIT-positive patients who were reexposed to heparin had a greater decrease in platelet counts immediately after transplant (postoperative days 1 to 4, p < 0.05). Despite this transient thrombocytopenia, there was no difference in posttransplant mortality or thromboembolism.

CONCLUSIONS

Heparin-induced thrombocytopenia-positive VAD patients did not experience increased thromboembolism or mortality after heparin reexposure. In light of the risks of using heparin alternatives, heparin reexposure is a safe management strategy for HIT-positive VAD patients.

Perioperative blood transfusion and blood conservation in cardiac surgery: the Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline

BACKGROUND

A minority of patients having cardiac procedures (15% to 20%) consume more than 80% of the blood products transfused at operation. Blood must be viewed as a scarce resource that carries risks and benefits. A careful review of available evidence can provide guidelines to allocate this valuable resource and improve patient outcomes.

METHODS

We reviewed all available published evidence related to blood conservation during cardiac operations, including randomized controlled trials, published observational information, and case reports. Conventional methods identified the level of evidence available for each of the blood conservation interventions. After considering the level of evidence, recommendations were made regarding each intervention using the American Heart Association/American College of Cardiology classification scheme.

RESULTS

Review of published reports identified a high-risk profile associated with increased postoperative blood transfusion. Six variables stand out as important indicators of risk: (1) advanced age, (2) low preoperative red blood cell volume (preoperative anemia or small body size), (3) preoperative antiplatelet or antithrombotic drugs, (4) reoperative or complex procedures, (5) emergency operations, and (6) noncardiac patient comorbidities. Careful review revealed preoperative and perioperative interventions that are likely to reduce bleeding and postoperative blood transfusion. Preoperative interventions that are likely to reduce blood transfusion include identification of high-risk patients who should receive all available preoperative and perioperative blood conservation interventions and limitation of antithrombotic drugs. Perioperative blood conservation interventions include use of antifibrinolytic drugs, selective use of off-pump coronary artery bypass graft surgery, routine use of a cell-saving device, and implementation of appropriate transfusion indications. An important intervention is application of a multimodality blood conservation program that is institution based, accepted by all health care providers, and that involves well thought out transfusion algorithms to guide transfusion decisions.

CONCLUSIONS

Based on available evidence, institution-specific protocols should screen for high-risk patients, as blood conservation interventions are likely to be most productive for this high-risk subset. Available evidence-based blood conservation techniques include (1) drugs that increase preoperative blood volume (eg, erythropoietin) or decrease postoperative bleeding (eg, antifibrinolytics), (2) devices that conserve blood (eg, intraoperative blood salvage and blood sparing interventions), (3) interventions that protect the patient's own blood from the stress of operation (eg, autologous predonation and normovolemic hemodilution), (4) consensus, institution-specific blood transfusion algorithms supplemented with point-of-care testing, and most importantly, (5) a multimodality approach to blood conservation combining all of the above.

Heparin-Induced Thrombocytopenia: Treatment Options and Special Considerations

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse effect that typically manifests several days after the start of heparin therapy, although both rapid- and delayed-onset HIT have been described. Its most serious complication is thrombosis. Although not all patients develop thrombosis, it can be life threatening. The risk of developing HIT is related to many factors, including the type of heparin product administered, route of administration, duration of therapy, patient population, and previous exposure to heparin. The diagnosis of HIT is typically based on clinical presentation, exposure to heparin, and presence of thrombocytopenia with or without thrombosis. Antigen and activation laboratory assays are available to support the diagnosis of HIT. However, because of the limited sensitivity and specificity of these assays, bedside probability scales for HIT were developed. When HIT is suspected, prompt cessation of all heparin therapy is necessary, along with initiation of alternative anticoagulant therapy. Two direct thrombin inhibitors--argatroban and lepirudin--are approved for the management of HIT in the United States, and bivalirudin is approved for use in patients with HIT who are undergoing percutaneous coronary intervention. Other agents, although not approved to manage HIT, have also been used; however, their role in therapy requires further evaluation. A comprehensive HIT management strategy involves the evaluation of numerous factors. Many patients, including those undergoing coronary artery bypass surgery, those with acute coronary syndromes, those with hepatic or renal insufficiency, and children, require special attention. Clinicians must become familiar with the available information on this serious adverse effect and its treatment so that optimum patient management strategies may be formulated.

Deep Hypothermic Circulatory Arrest and Bivalirudin Use in a Patient With Heparin-Induced Thrombocytopenia and Antiphospholipid Syndrome

BACKGROUND

Patients with heparin-induced thrombocytopenia II (HIT II) need an alternative nonheparin-based method of anticoagulation for cardiopulmonary bypass (CPB) to prevent thrombosis and thrombosis related complications.

METHODS

Bivalirudin was used during CPB and deep hypothermic circulatory arrest (DHCA) for resection of multiple right atrial masses in a patient with HIT II and antiphospholipid antibodies syndrome (APS). Anticoagulation was monitored with the activated clotting time (ACT) and a target ACT of 450 seconds or greater was maintained.

RESULTS

Surgical removal of multiple right atrial masses was successful and there was no evidence of thromboembolic events. Clot was noticed in the cardiotomy and venous reservoir after CPB was discontinued and the system flushed. The postoperative course was uneventful.

CONCLUSIONS

Anticoagulation was successfully managed with bivalirudin, a new short-acting, and direct thrombin inhibitor. Further studies are necessary to evaluate the safety of bivalirudin during DHCA.

Hydroxyethyl starch enhances argatroban-mediated decreases in clot propagation and strength by diminishing thrombin–fibrinogen interactions

Direct thrombin inhibitors (DTIs) have been administered for anticoagulation during cardiopulmonary bypass for patients with heparin-induced thrombocytopenia. While DTIs prolonged clot initiation and decreased clot propagation, clot strength did not change. Hydroxyethyl starches (HES), however, significantly decreased clot propagation and strength. We hypothesized that DTI with HES could significantly decrease hemostasis more than DTI alone. Plasma was exposed to 0 or 5 microg/ml argatroban with 0 or 30% dilution with 0.9% NaCl, 10% pentastarch or 6% Voluven. Additional argatroban-exposed samples diluted with HES had addition of alpha-thrombin (0.25 U/ml) and fibrinogen (150 mg/ml). Clot kinetics were determined via thrombelastography. While dilution with 0.9% NaCl significantly (P < 0.05) decreased the clot strength by 17% compared with samples only exposed to argatroban, dilution with pentastarch and Voluven significantly (P < 0.05) markedly decreased clot strength (53 and 78%, respectively). Voluven dilution significantly increased the time to clot initiation and decreased the velocity of clot propagation compared with samples only exposed to argatroban. Addition of alpha-thrombin/fibrinogen restored clot strength. DTI/HES administration diminished hemostasis to a greater extent than DTI exposure alone. Further investigation is warranted to determine whether this therapeutic approach can improve the safety of anticoagulation during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia.

Successful use of bivalirudin for cardiac transplantation in a child with heparin-induced thrombocytopenia

Bivalirudin, a direct thrombin inhibitor, has recently emerged as a promising option for anti-coagulation during cardiopulmonary bypass in patients who cannot receive heparin. There is limited experience with the use of bivalirudin in children. We present the case of a child with heparin-induced thrombocytopenia with thrombosis (HIT Type II) who underwent successful orthotopic cardiac transplantation using bivalirudin as the primary anti-coagulant for cardiopulmonary bypass.

Evaluation of Bivalirudin Treatment for Heparin-Induced Thrombocytopenia in Critically Ill Patients with Hepatic and/or Renal Dysfunction

STUDY OBJECTIVE

To evaluate the safety, effectiveness, and dosing of bivalirudin for treatment of heparin-induced thrombocytopenia (HIT) in critically ill patients with hepatic and/or renal dysfunction.

DESIGN

Retrospective cohort study.

SETTING

University-affiliated medical center

PATIENTS

Eighteen patients older than 18 years who were admitted to the intensive care unit (ICU), had hepatic and/or renal dysfunction, and were treated with bivalirudin for the diagnosis of HIT between January 1, 2004, and March 31, 2005.

MEASUREMENTS AND MAIN RESULTS

Patient records were reviewed for dosage and duration of bivalirudin therapy, occurrence of thrombosis, and clinically significant adverse effects. Of the 18 patients identified, 12 had both hepatic and renal dysfunction (group 1), four had hepatic dysfunction (group 2), and two had renal dysfunction (group 3). Demographics were similar among the groups. Mean +/- SD age was 54 +/- 15 years and weight was 82 +/- 14 kg, 67% were male, 83% were Caucasian, and 56% were receiving renal replacement therapy. Mean bivalirudin doses were 0.06 +/- 0.15 mg/kg/hour (median 0.03 mg/kg/hr), 0.14 +/- 0.05 mg/kg/hour (median 0.14 mg/kg/hr), and 0.05 +/- 0.01 mg/kg/hour (median 0.05 mg/kg/hr) for patients in groups 1, 2, and 3, respectively. Ten patients receiving continuous venovenous hemofiltration with or without dialysis received a mean dose of 0.04 +/- 0.03 mg/kg/hour (median 0.03 mg/kg/hr). In the 18 patients, mean bivalirudin duration was 15 +/- 17 days, activated partial thromboplastin time (aPTT) was 69 +/- 22 seconds, and international normalized ratio was 2.2 +/- 0.8. Supratherapeutic aPTTs were most common on days 1 (22%) and 2 (28%) when bivalirudin doses were highest. Clinically significant bleeding did not occur in any patient. Thrombosis occurred in one patient (6%) while receiving bivalirudin.

CONCLUSION

Patients in the ICU who have hepatic and/or renal dysfunction require low doses of bivalirudin to achieve aPTT values 1.5-2.5 times baseline. Bivalirudin can be safely started at 0.14 mg/kg/hour in patients with hepatic dysfunction, 0.03-0.05 mg/kg/hour in those with renal or combined hepatic and renal dysfunction, and 0.03-0.04 mg/kg/hour in patients receiving continuous renal replacement therapy.

Bivalirudin: a review

Bivalirudin (Angiomax) is a thrombin-inhibiting oligopeptide that was developed via rational drug design as a hirudin analogue ('hirulog'). Similar to hirudin, it is a bivalent thrombin inhibitor, as its 20-amino acid structure combines a carboxy-terminal region that recognises thrombin's fibrin(ogen)-binding site, and an amino-terminal tetrapeptide that inhibits the active site of thrombin, connected by a tetraglycine spacer. It has certain pharmacological advantages over hirudin, including enzymic metabolism (less dependence on renal clearance) and low immunogenicity (reduced potential for anaphylaxis). Bivalirudin is approved for use in percutaneous transluminal coronary angioplasty (PTCA), and is undergoing active investigation for anticoagulation during cardiac surgery, both 'off-pump' and with cardiopulmonary bypass ('on-pump'). Anecdotal 'off-label' experience for the treatment of heparin-induced thrombocytopenia shows promise.