A Study of Initiation Timing of VTE Prevention After Colorectal Cancer Surgery

Inclusion Criteria: * ① Age \> 18 years old; ② The patient was diagnosed with colorectal cancer, and the cTMN stage was cT1-2, N0 or cT3, N0 or any cT, N1-2; (3) The patient was diagnosed with colorectal cancer and was able to receive radical surgery (laparoscopic or open surgery). The expected operation time was \>45 minutes, and the expected postoperative survival time was \>6 months. ④ The patient or guardian agrees to the study plan and signs the informed consent. Exclusion Criteria: * ① Renal insufficiency (CrCl\<30 mL/min) or hepatic insufficiency (ALT\> 3 times the upper limit of normal); * The patient was diagnosed with colorectal cancer with a cTMN stage of cT4 and/or local unresectable lesions. Unresectable local recurrent lesions included: (1) extensive lateral pelvic wall invasion, (2) external iliac vascular involvement, (3) tumor invasion into the great sciatic notch, sciatic nerve invasion, and (4) invasion of the second sacrum level and above. Known allergy to low molecular weight heparin (LWMH), narcotic drugs or radiocontrast agents; The presence of systemic hemorrhagic disease or bleeding tendency, such as active peptic ulcer, uncontrolled hypertension, cerebral thrombosis, cerebral hemorrhage or neurosurgical history within 6 months; * known brain metastases, endocarditis, or history of heparin-induced thrombocytopenia; * VTE occurred within 3 months before surgery; * Use heparin or oral anticoagulant therapy within 5 days before surgery; Women who are pregnant or breastfeeding; * Any situation in which the investigator determines that the subject is not suitable for anticoagulant therapy.