Lower extremity deep vein thrombosis, known as DVT (deepvenousthrombosis), is the formation of a blood clot in the lumen of a vein for various reasons. The typical clinical presentation of DVT in the lower extremity is often swelling and pain in the unilateral lower extremity (left lower extremity is more common). However, early thrombosis can have no obvious symptoms, which is one of the reasons why venous thrombosis is easily overlooked. The main causes of DVT are damage to the vein wall, slow blood flow and a hypercoagulable state of the blood. External compression: physiological compression of arteries and spine, masses DVT mainly manifests as sudden swelling, pain, and increased soft tissue tension in the affected limb; it is aggravated by activity and can be reduced by elevating the affected limb, and there is often pressure pain at the site of venous thrombosis. DVT mainly manifests as sudden swelling, pain and increased soft tissue tone of the affected limb; it is aggravated by activity and can be relieved by elevating the affected limb, and there is often pressure pain at the site of venous thrombosis. One to two weeks after the onset of the disease, superficial veins may appear or dilate in the affected limb. When the thrombus is located in the muscular plexus of the lower leg, it can cause local pain, and patients with severe DVT of the lower extremity can develop white swelling of the femur or even bruising of the femur. Femoral leukomalacia is marked swelling and severe pain in the entire lower extremity, with pressure pain in the femoral triangle, N-fossa, and posterior calf, and pale skin, accompanied by elevated body temperature and increased heart rate. Femoral bruise is the most serious case of DVT in the lower extremity, because the iliofemoral vein and its side branches are all blocked by thrombus, the venous return is severely obstructed, the tissue tension is extremely high, resulting in arterial spasm in the lower extremity and limb ischemia; the clinical manifestations are severe pain in the affected extremity, the skin is shiny and blue-purple, the skin temperature is low with blisters, the dorsalis pedis artery pulsation disappears, the systemic reaction is strong, the body temperature is elevated; if not treated in time, shock and venous gangrene may occur If left untreated, shock and venous gangrene may occur. Once the venous thrombus is dislodged, it can enter and block the pulmonary artery with the blood flow, causing the clinical manifestations of PE. deep vein thrombosis sequelae (PTS) can occur in the chronic stage of DVT. The main symptoms are swelling and pain in the lower extremities (the severity of which varies with time), and signs include lower extremity edema, hyperpigmentation, eczema, varicose veins, and in severe cases, lipodermatous scleroderma and ulcers in the foot and boot area. the incidence of PTS is 20% to 50%. Treatment: Placement of inferior vena cava filter and placement of a tube for thrombolysis. The greatest complication of lower extremity DVT is pulmonary embolism. Patients with pulmonary embolism will experience: common symptoms of pulmonary embolism include dyspnea, chest pain, coughing up blood, panic, tachycardia, coughing, vertigo, and even sudden death. Currently, the annual incidence of pulmonary embolism in the United States is about 600,000 people or more, and deaths from pulmonary embolism amount to 200,000, ranking third among the clinical causes of death. It is noteworthy that only 7% of patients with PE who are diagnosed and treated promptly die, while 60% of patients who are not considered for the diagnosis of PE die, 33% of whom die rapidly within the first hour.