DIC: Simultaneous Thrombosis and Hemorrhage Pathogenesis

Disseminated intravascular coagulation (DIC) is a consumptive coagulopathy characterized by pathological activation of the coagulation cascade, leading to widespread microvascular thrombosis (causing organ ischemia) AND simultaneous hemorrhage (from consumption of clotting factors and platelets). The paradox of simultaneous clotting and bleeding is the hallmark of DIC. The pathogenesis involves: (1) Tissue factor (TF) exposure from damaged endothelium, tumor cells, or amniotic fluid activates the extrinsic coagulation pathway, generating massive thrombin; (2) Excessive thrombin converts fibrinogen to fibrin, forming widespread microthrombi in small vessels, causing organ ischemia (renal cortical necrosis, hepatic ischemia, acral gangrene, ARDS); (3) Consumption of clotting factors (fibrinogen, V, VIII) and platelets by the ongoing coagulation process depletes hemostatic reserves, causing hemorrhage; (4) Secondary fibrinolysis: plasmin activation breaks down the widespread fibrin clots, producing fibrin degradation products (FDPs) and D-dimers, which themselves have anticoagulant properties, further impairing hemostasis. Common triggers: sepsis (most common cause — endotoxin/LPS activates TF on monocytes), obstetric emergencies (placental abruption, amniotic fluid embolism, eclampsia), trauma (massive tissue injury), malignancy (acute promyelocytic leukemia, mucin-secreting adenocarcinomas), and transfusion reactions. Lab diagnosis: thrombocytopenia, prolonged PT/aPTT, decreased fibrinogen...