 Researchers have defined a subgroup of pediatric patients with critical illness who have a specific coagulation profile associated with thrombocytopenia. This distinct entity, defined as thrombocytopenia-associated multiple organ failure TAMOF, has been demonstrated to predispose affected children to worsening organ failure and increased risk of death. A preliminary single-center study performed at Childrens Hospital of Pittsburgh CHP suggested significant improvement in organ system dysfunction in TAMOF patients using a plasma exchange protocol compared to standard therapy alone. The investigators desire to further evaluate plasma profiles and clinical outcomes in pediatric TAMOF in a broader geographic setting. The investigators propose to perform a prospective multi-center observational cohort study to evaluate plasma response and clinical outcomes in pediatric patients with TAMOF due to critical illness associated with systemic infection, sepsis, organ transplant, chemotherapy or cardiopulmonary bypass. Plasma samples will be obtained from all patients for measurement of markers of coagulation and inflammation. The primary clinical endpoints measured will be organ failure index scores, pediatric logistic organ dysfunction PELOD scores, and days until resolution of organ failures. Cohort outcome analysis will also be performed by pairing patients at different centers receiving standard therapy with those receiving plasma exchange as an additional therapy. 