Age-dependent Heterogeneity in the Efficacy of Prophylaxis With Enoxaparin Against Catheter-associated 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.