Deep vein thrombosis is the abnormal clotting of blood in the deep veins, resulting in partial or complete blockage of the deep vein lumen. It occurs in the lower extremities and can cause a range of symptoms such as pain and swelling in the lower extremities. The disease can be followed by lower limb edema, secondary varicose veins, dermatitis, hyperpigmentation, stasis ulcers, venous gangrene, etc., which seriously impairs the health of working people. Moreover it is a disease with high recurrence and risk of death. The three major recognized causative factors of venous thrombosis are: blood stasis, venous wall damage and hypercoagulability, with “blood stasis” playing a key role in the process of venous thrombosis. Deep vein thrombosis occurs in the lower extremities, mainly because the human blood starts from the heart, is transported to the lower extremities through the arterial system, and then back to the heart through the venous system, the blood flows through the longest distance, and the pumping power of the heart becomes relatively weak to this part. And due to the effect of gravity, the blood is prone to slow flow in the lower extremities and stagnation in the veins. If the calf muscles, which are known as the “second heart”, are at rest at this time, the veins of the lower extremities are relatively prone to thrombosis in the same state as all parts of the body. Among the bilateral lower limbs, the left lower limb is more likely to form deep vein thrombosis than the right, which is related to its anatomical position. The left common iliac vein is sandwiched between the right common iliac artery and the sacral isthmus, which makes it easy for the left common iliac vein to be in contact with the anterior and posterior walls for a long time, which not only obstructs the reflux of the left common iliac vein, but also forms intraventricular adhesions. People with high incidence of DVT are: bedridden or inactive for a long time after surgery; trauma, obesity, hyperlipidemia or age over 40; patients with myocardial infarction, heart failure, stroke, nephrotic syndrome; patients with malignant tumor; patients with oral contraceptives, pregnancy, varicose veins or previous history of thrombosis, etc. Patients with surgery and trauma are especially prone to lower extremity deep vein thrombosis. Patients with acute thoracic and abdominal surgery, hip or knee replacement surgery, hip fracture, severe trauma and acute spinal injury are at very high risk for thromboembolism. During pregnancy, the enlarged uterus compresses the blood vessels in the abdominal cavity, obstructing the blood flow back to the lower extremities and aggravating the blood stasis in the lower extremities. At the same time, the blood in the body during pregnancy is secondary to hypercoagulation. The incidence of DVT in the lower extremities is greatly increased by the synergistic effect of both factors. What is the risk of DVT? About 80% of patients with DVT have no clinical symptoms, but sudden death is often the first and only clinical manifestation of the disease, and the cause of sudden death is “pulmonary embolism”: in 70-90% of patients with pulmonary embolism, DVT is detected. In the United States, the mortality rate of pulmonary embolism is the third highest after cancer and coronary heart disease. Therefore, deep vein thrombosis is called the “silent killer”. In China, with the change of people’s dietary structure and living habits, the incidence of lower limb deep vein thrombosis is increasing every year. However, the medical community is still far from understanding this disease, about 70% of the patients with pulmonary embolism are missed or misdiagnosed as myocardial infarction, coronary heart disease and pulmonary disease, and about 30% of the patients die due to untimely diagnosis and treatment. What are the symptoms of lower extremity DVT? Swelling, pain and superficial varicose veins are the three main symptoms of lower extremity DVT, pain is mostly cramping or dull pain, and superficial varicose veins are mostly the manifestation of the establishment of collateral circulation in the chronic stage. DVT of lower extremity can be divided into three types: peripheral type, central type and mixed type. There are also two special types: femoral cyanosis and femoral leukomalacia, both of which are emergency cases of DVT in the lower extremities and require emergency surgery to remove the embolus in order to save the affected limb. Treatment of lower extremity DVT Current treatment modalities include anticoagulation, thrombolysis and surgery. No matter which type of anticoagulant is applied, there is a risk that the anticoagulant effect will not be achieved with a small dose, and the bleeding complications will be greatly increased with a large dose. Therefore, during the application process, the blood coagulation function changes must be monitored to adjust the drug dose. Because the biggest danger of DVT in lower extremity is: embolus dislodgement leading to pulmonary embolism, which can cause sudden death, and the inferior vena cava filter is like a protective umbrella to capture and intercept part of the dislodged embolus. Especially for patients who have already had a pulmonary embolism or who need thrombolytic therapy, the risk of embolus dislodgement is higher and inferior vena cava filter placement is feasible. Placement of an inferior vena cava filter can significantly reduce the incidence of pulmonary embolism. During treatment, attention should also be paid to bed rest, elevation of the affected limb, and local wet and hot compresses for patients with DVT of the lower extremities. The duration of bed rest is usually 10-14 days, and light activities can be performed when the systemic symptoms and local pressure pain are relieved. When you get up and move around, you need to wear gradient decompression elastic stockings or elastic bandage. The main complications of DVT are as follows 1. Pulmonary embolism Pulmonary embolism is a pathological process caused by the obstruction of the pulmonary artery or its branches by emboli. It has a low diagnosis rate, high misdiagnosis rate and high morbidity and mortality rate. According to the literature, there are 650,000 pulmonary embolisms and 240,000 people die from pulmonary embolism in the United States every year. In the UK, there are 40,000 non-fatal pulmonary embolisms and 20,000 inpatients who die from pulmonary embolism every year. It is believed that 80% to 90% of pulmonary embolism emboli originate from lower extremity deep vein thrombosis, especially during thrombolytic therapy, and large emboli can lead to death within minutes. The mortality rate of pulmonary embolism due to iliofemoral vein thrombosis has been reported to be as high as 20-30%. The typical symptoms of pulmonary embolism are dyspnea, chest pain, cough, and hemoptysis. The three major signs of pulmonary embolism are the pulmonary wormwood and the iliac femoral vein. At present, the prevention of pulmonary embolism mostly uses vena cava filter placement in clinical practice. The inferior vena cava filter is a device made of metal wire that is placed into the inferior vena cava through a special delivery device to intercept larger thrombi in the blood flow and avoid entering the pulmonary artery with the blood flow, which can cause a fatal pulmonary embolism. However, placement of the filter can lead to complications such as filter displacement, obstruction, bleeding, etc., and is more expensive. The cost of an inferior vena cava filter is expensive (about 15,000), and the reimbursement rate is not high, usually 50%, depending on the patient’s family’s financial situation. A small number of patients may experience filter occlusion after placement of an inferior vena cava filter for one of two reasons: in most cases, a thrombus (mostly newly formed) is dislodged from a lower extremity vein and captured by the filter (indicating that the filter is working), or a new thrombus is formed in the filter. In either case, it is associated with the formation of a new thrombus. Therefore, oral warfarin anticoagulation is important. Therefore, long-term anticoagulation is required for patients with filter placement. 2. Bleeding The most important complication in thrombolytic therapy is bleeding. Especially, we should be alert to gastrointestinal and intracranial bleeding. Therefore, the blood type, hemoglobin, platelets and coagulation function should be checked before thrombolytic therapy; the adjustment of drug dosage is usually appropriate to maintain the prothrombin time (PT) and partial thromboplastin time (APTT) at 2~2.5 times of the normal value. The patient should be closely observed for bleeding tendency during and after thrombolysis, such as vascular puncture sites, skin, gums, etc. Observe whether there is hematuria and microscopic hematuria, abdominal pain, black stool, etc.; if there is bleeding at the puncture site, compress to stop the bleeding. In case of severe hemorrhage, thrombolysis should be terminated and symptomatic treatment with blood or plasma transfusion should be given. For bleeding complications, patients should be instructed to observe and prevent themselves. For example, gum bleeding, nasal bleeding, skin and mucous membrane bleeding, black stool, etc. Ask the patient not to pick teeth with hard or sharp objects, dig nostrils and ear canals, do not cough hard to avoid hemoptysis; use soft-haired toothbrush to brush teeth and move gently to avoid unnecessary trauma; eat a light and digestible diet to avoid food damage to the digestive tract, and keep the stool open with fiber-rich food many times. 3.Post-thrombosis syndrome is the most common and important complication, in the process of thrombosis, the venous valve is damaged or even disappears or adheres to the wall, resulting in secondary deep venous valve insufficiency, that is, post-thrombosis syndrome. The post-thrombotic syndrome occurs several months to years after the formation of deep vein thrombosis in the lower limbs, mainly manifested as chronic edema, pain, muscle fatigue (venous claudication), varicose veins, pigmentation, subcutaneous tissue fiber changes, and in severe cases, local ulcers, which affects the quality of life of patients. After discharge from the hospital, wearing elastic stockings, taking oral anticoagulant drugs to avoid prolonged standing and sitting, and elevating the affected limb at rest, the post-thrombotic syndrome usually rarely occurs.