research objective

1. Optimize VTE prevention management after CRC surgery.
2. Improve the prevention and treatment level of VTE in current perioperative patients.
3. Reduce the social burden of VTE related diseases.

Participants will:

1. start low molecular weight heparin prophylaxis within 24 hours post-surgery.
2. The prophylactic regimen for the experimental group lasted 14 days, while the control group received it for 28 days. Low molecular weight heparin is given subcutaneously at a dose of 0.3ml once daily.
3. atients underwent lower limb color Doppler ultrasound on postoperative days 7 ± 2, 14 ± 3, and 28 ± 5, which included screening for thrombosis in the proximal deep veins (femoral, popliteal), distal deep veins (posterior tibial, fibular, and muscular veins), and their perforating branches.

Inclusion Criteria:

• Age>18 years old; Diagnosed with colorectal cancer and undergoing curative, palliative, or other limited surgeries (laparoscopic or open surgery), with an estimated surgery time of>45 minutes; Expected postoperative survival>6 months; Expected Caprini score of ≥ 5 on the first day after surgery; The patient agrees to the research plan and signs an informed consent form.

Exclusion Criteria:

• Renal dysfunction (CrCl<30 mL/min) or liver dysfunction (ALT>3 times the upper limit of normal); Known allergies to LMWH, anesthetics, or contrast agents; There is a systemic bleeding disorder or bleeding tendency, such as active peptic ulcer, uncontrolled hypertension, cerebral thrombosis within 6 months, cerebral hemorrhage, or a history of neurosurgical surgery; Known brain metastases, endocarditis, or previous heparin induced thrombocytopenia; VTE occurred within 3 months before surgery; Use heparin or oral anticoagulant therapy within 5 days before surgery; Pregnant or lactating women; Pregnant or lactating women; Any conditions that researcher determines the subject not suitable for anticoagulant therapy.