Catheter-Related Early Thromboprophylaxis With Enoxaparin Studies (CRETE)

Age-dependent Heterogeneity in the Efficacy of Prophylaxis With Enoxaparin Against Catheter-associated Thrombosis in Critically Ill Children

Children's Hospital Colorado, Children's Hospital of Philadelphia, Virginia Commonwealth University, BJC HealthCare, Medical College of Wisconsin, Children's of Alabama, Golisano Children's Hospital, Maria Fareri Children's Hospital, Nationwide Children's Hospital, New York Presbyterian Hospital, Penn State University, University of Iowa, Johns Hopkins All Children's Hospital, University of Oklahoma, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)

The goal of the CRETE Studies is to investigate the newly identified age-dependent heterogeneity in the efficacy of enoxaparin in reducing the risk of central venous catheter-associated deep venous thrombosis in critically ill children.

Pediatric venous thromboembolism (VTE), which is predominantly deep venous thrombosis (DVT), is a top contributor to harm in hospitalized children. Its incidence increased by >300% in the past 2 decades. Critical illness and central venous catheter (CVC) are the most important risk factors for VTE in children. Among critically ill children, the risk of CVC-associated DVT (CADVT) is as high as 54% with 72% of cases in infants <1-year old. Pharmacologic prophylaxis is the most effective strategy against VTE in adults. However, due to paucity of age-appropriate evidence on its efficacy against CADVT, pharmacologic prophylaxis is uncommon in children. Extrapolation of evidence from adults is not appropriate because the hemostatic system changes significantly with age. The investigators recently completed a Bayesian phase 2b randomized clinical trial. In this trial, the investigators randomized critically ill children to early administration of prophylactic dose of enoxaparin, the most commonly used anticoagulant for prophylaxis, or usual care. Prophylaxis with enoxaparin appeared to reduce the risk of CADVT by half. In post hoc analyses, reduction was limited to older children 1-17 years old. The goal of the CRETE Studies is to investigate this newly identified age-dependent heterogeneity in the efficacy of enoxaparin in reducing the risk of CADVT in critically ill children. To achieve this goal, the investigators aim (1) to confirm the efficacy and safety of early administration of prophylactic dose of enoxaparin in reducing the risk of CADVT in critically ill older children; (2) to determine the efficacy and safety of early administration of therapeutic dose of enoxaparin in reducing the risk of CADVT in critically ill infants; and, (3) to probe the mechanisms that underly the age-dependent heterogeneity in the efficacy of enoxaparin in reducing the risk of CADVT in critically ill children. The investigators will conduct 2 multicenter Bayesian explanatory randomized clinical trials in parallel to address Specific Aims 1 and 2. Depending on age, subjects will be randomized to different doses of enoxaparin vs usual care. Subjects will be systematically assessed for the development of CADVT using ultrasonography and clinically for bleeding. Using plasma obtained from subjects in the 2 trials, the investigators will conduct an exploratory mechanistic nested case-control study to address Specific Aim 3. Biomarkers of selected mechanisms underlying CVC-associated thrombus formation, particularly thrombin generation, will be compared between subjects with and without CADVT. The investigators will use Bayesian methods to improve the efficiency in the conduct and analyses of these studies. The CRETE Studies will provide high-quality age-appropriate evidence that will inform preventive strategies against CADVT and decrease harm in hospitalized children.

Older children 1-17 years old and infants <1 year old will be randomized separately. Older children will be randomized 2:1 to prophylactic dose of enoxaparin or control stratified by age. Infants will be randomized 1:1:1 to therapeutic dose of enoxaparin with high or low anti-Xa target or control stratified by age.

The CRETE Studies are open-label with blinded endpoint. Systematic ultrasonographic assessment will be performed with the images blindly and centrally adjudicated.

Enoxaparin is a LMWH produced from UFH that exerts its anticoagulant effects by binding to and inducing a conformational change in antithrombin to accelerate the inactivation of factor Xa and thrombin. Age-specified dose of enoxaparin will be administered within 24 hours after insertion of the CVC with the dose subsequently adjusted to pre-specified anti-Xa target.

Thrombus in the central vein where the CVC was inserted that is diagnosed with systematic ultrasonographic surveillance.

Bleeding that is fatal, with drop in hemoglobin by ≥2 g/dl in 24 hours, requires medical or surgical intervention to restore hemostasis, or in the retroperitoneum, pulmonary or central nervous system.

Unexplained drop in platelet count to <50 x 10^3/mcL or by 50 percent of baseline platelet count in the ICU within 21 days following exposure to heparin, and with a positive anti-platelet factor 4 antibody.

Inclusion criteria >36 weeks corrected gestational to <17 years old <24 hours after insertion of an untunneled CVC CVC inserted in the internal jugular or femoral vein Exclusion criteria Radiologic diagnosis of CADVT in the site of insertion in prior 6 weeks Currently receiving an antithrombotic agent, e.g., LMWH, UFH, warfarin and aspirin, but not UFH at dose to maintain patency of a vascular catheter Presence of clinically relevant bleeding, i.e., hemoglobin decreased ≥2 g/dl in 24 hours, required medical or surgical intervention to restore hemostasis, or in the retroperitoneum, pulmonary, intracranial or central nervous system, in the prior 60 days Surgery in the prior 7 days Major trauma in the prior 7 days Presence of coagulopathy, i.e., INR >2.0, aPTT >50 seconds or platelet count <50 x 10^3/mcL Presence of renal failure, i.e., creatinine clearance <30 mL/min/1.73 m2 Known hypersensitivity to heparin or pork products Laboratory confirmed HIT Current pregnancy or lactation Presence of an epidural catheter Limitation of care Previous enrollment in the CRETE Studies