To investigate the incidence of lower limb deep vein thrombosis and related risk factors in high-risk patients after major surgery in China. Methods 233 consecutive patients with major surgery or small to medium surgery with high-risk factors were enrolled, and all of them underwent ultrasound examination of both lower extremities within 3~10 d after surgery, and 57 non-surgical outpatients underwent ultrasound of both lower extremities at the same time, and all of them recorded the venous blood flow velocity of both lower extremities and the site of thrombosis. Among the 233 patients enrolled, 111 patients were found to have deep vein thrombosis by ultrasound, and the overall thrombosis detection rate was 47.64%. Among them, 3 cases (1.29%) occurred in the femoral vein and 108 cases (46.35%) were in the peroneal vein. The difference in blood flow velocity in the deep veins of the lower extremities was not significant in the postoperative thrombosed group compared with the nonthrombosed group, but was significantly lower in both groups than in the nonoperative patients. The incidence of deep vein thrombosis increased with increasing age and weight and the number of risk factors, but it was not related to anesthesia, operating time and choice of anesthesia method. 58 cases (24.89%) had discomfort such as swelling, pain or numbness in both lower limbs. 1 patient died for unknown reasons after surgery and pulmonary embolism was highly suspected. Conclusion The incidence of deep vein thrombosis in patients undergoing major surgical procedures from 3 to 10 d postoperatively was 47.64%. Conventional antithrombotic measures such as low molecular weight heparin and intermittent pneumatic compression devices should be considered in the perioperative period. Venous thromboembolism includes deep vein thrombosis (DVT) and pulmonary embolism, and the high incidence of postoperative venous thromboembolism, which is the main cause of postoperative death and disability, has been reported abroad. More and more patients with venous thromboembolism have been diagnosed in China in recent years, but there are few systematic reports on the incidence of venous thromboembolism after surgery, and there is a lack of objective basis for postoperative drugs or devices for thrombosis prevention and treatment. In this study, we proposed to investigate the incidence of postoperative DVT in patients with high risk of thrombosis, to clarify the incidence of postoperative DVT and related risk factors, so that corresponding measures can be taken to effectively prevent the occurrence of venous thromboembolism. Data and methods Inclusion criteria : Patients undergoing major surgical procedures Orthopedics: pelvic and lower limb trauma, joint replacement, spinal surgery; general surgery: total pelvic organ resection, pancreatic, gastric, biliary, colon and rectal surgery; neurosurgery: all craniotomies; thoracic surgery: lung and esophageal surgery; urology: radical treatment of prostate cancer, resection of malignant tumors of bladder, ureter, kidney and adrenal gland. Exclusion criteria: small to medium-sized surgeries without high-risk factors; patients on preoperative heparin or oral warfarin anticoagulation therapy. Documented concomitant risk factors: advanced age (>60 years), hypertension, hyperlipidemia, diabetes mellitus, smoking, paralysis, history of venous thromboembolism, family history of thromboembolism, tumor, obesity, varicose veins, myocardial infarction, congestive heart failure, ischemic stroke, transient ischemic attack, heparin-induced thrombocytopenia, cancer chemotherapy, nephrotic syndrome, inflammatory bowel disease (ulcerative colitis, etc.) oral contraceptives and estrogen application. Vascular ultrasound examination of lower extremities All patients were examined by ultrasound of both lower extremities deep veins using American Esaote D u3 high-resolution bedside color Doppler ultrasound in 3~10 d after surgery, if the thrombosis occurred above the s vein (including s vein), it was proximal DVT, if the thrombosis occurred below the s vein (excluding s vein), it was distal DVT. longitudinal and transverse vessels were not compressible, blood flow and sound disappeared after color ultrasound pressure as ultrasound diagnostic criteria for venous thrombosis, along with recording of blood flow velocity and site of thrombus in both lower extremities. All enrolled patients were evaluated for risk factors, and the number of risk factors was recorded. Statistical analysis The measurement data were expressed as mean±standard deviation, and ANOVA was used for comparison between groups, group t-test was used for comparison within groups, and c2 test was used for incidence rate, with significant difference at P<0.05. Results Consecutive patients were enrolled in 233 cases, aged 40 to 86 years, 131 males and 102 females. Among them, 71 cases in general surgery were malignant tumors of intestine, biliary tract or liver; 42 cases in thoracic surgery were malignant tumors of lung and esophagus; 26 cases in brain surgery were cerebral hemorrhage, meningioma, glioma or pituitary tumor; 34 cases in urology were tumors of kidney, prostate and bladder; 60 cases in orthopedics were total knee and hip replacement or spine surgery. A total of 49 cases in general surgery and orthopedic surgery were postoperatively anticoagulated with low molecular heparin (Sapirin, Sanofi). general information on DVT according to surgical departmentalization is shown. DVT was detected by ultrasound in 111 patients from 3 to 10 d after surgery, with an overall thrombus detection rate of 47.64%, including proximal DVT in 3 patients with an incidence of 1.29% and distal DVT in 108 patients with an incidence of 46.35%. Analysis of risk factors possibly associated with DVT showed that there were significant differences in age and number of risk factors in the thrombosis group compared with the no-thrombosis group. The incidence of DVT in the lower extremities was not statistically significant (P>0.05) in patients with different anesthesia and duration of surgery, and the incidence of DVT in the lower extremities was not statistically significant when comparing age >45 years, and age <45 years. The incidence of DVT increased significantly with the increase in the number of risk factors (P<0.05); in addition, there was a relationship between body mass index and the incidence of DVT, and the larger the body mass index, the higher the incidence. There was no significant difference in the blood flow rate of the deep veins of the lower extremities, regardless of whether DVT occurred or not. The incidence of DVT was 42.86% (21/49) in 49 patients (mainly orthopedic and general surgery patients) who were anticoagulated with low molecular heparin. The age and number of risk factors were significantly higher in anticoagulated patients than in non-anticoagulated patients (P<0.05) see. Among the patients who underwent examination with ultrasound, 24 (10.3%) of them showed symptoms of swelling of one or both lower limbs, 42 (18.2%) showed pain, numbness and discomfort, and 58 (24.9%) showed one of the above clinical symptoms. 1 case of unexplained postoperative death was highly suspected to be caused by pulmonary embolism.