Collaborative Risk-stratified Investigation in Thrombosis-prone Inpatients With Critical Illness: Anticoagulation With LMWH in Teens for ThromboProphylaxis (CRITICAL-Teens-TP).

Inclusion Criteria: * Admission Age between 12- 18 years of age * Within 24 hours of pediatric intensive care unit (PICU) admission for enrollment * Presence of a Central Venous Catheter * Presumed or confirmed infection or systemic inflammatory condition Exclusion Criteria: * Active treatment for VTE or known VTE present prior to or on pediatric intensive care unit (PICU) admission * Current receipt of an antithrombotic agent excluding unfractionated heparin for vascular catheter patency * Active ISTH-defined clinically relevant bleeding * Surgery in the last 7-days * Major trauma within the last 7-days * Admission for management of congenital heart disease including perioperative management of critical congenital heart disease * Presence of coagulopathy including: * International normalized ratio (INR) 2.0 activated partial thromboplastin time (aPTT) 50 seconds Platelet count 50 x103/mL * Creatinine clearance 30 ml/min/1.73 m2 * Known hypersensitivity to heparin or pork products * Laboratory confirmed heparin induced thrombocytopenia * Current pregnancy or lactation, * Presence of an epidural catheter * Prior enrollment in the CRITICAL-Teens-TP Trial