The American College of Chest Physicians (ACCP) has recommended the guidelines for the diagnosis and prevention of VTE since 1995. A total of 9 issues have been published by the end of 2012 (4) , and the contents have also been continuously renewed. ACCP proposed that Trauma, surgery, old age, malignancies, pregnancy, heart failure and oral administration of contraceptives are the main risk factors of VTE and ACCP also proposed the concept of risk stratification for prophylaxis of VTE by which differ-Ivyspring International Publisher ent managements were used for prevention from VTE in different risk patients (5, 6) . The incidence of symptomatic VTE is not reduced but gradually increased, the reason of which may be related to the unclear pathogenesis of VTE (7) .