PE usually results from DVT, and DVT occurs because of predisposing risk. Thus, patients at risk for DVT are at risk for PE. Venous stasis, hypercoagulability, and endothelial damage—Virchow's triad—are well-recognized factors favoring the development of DVT. Tab!.e 5.2.-!. lists the commonly recognized risk factors for DVT and PE. The majority of patients with PE will have at least one risk factor, with immobilization being the most prevalent.6 While a minority of patients may not have clinically evident risk factors at presentation, they will generally be found to have abnormalities of coagulation or occult cancer on further evaluation. IDU may cause septic or aseptic thrombophlebitis by extension from superficial phlebitis, external compression by and septic extension from a perivascular abscess, or direct injection into the deep venous system. In addition, agents contaminating illicit drugs, such as talc and bacteria, have direct thrombogenic properties.
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