Pulmonary embolism (PE) is a syndrome of respiratory and circulatory dysfunction caused by thrombotic or (and) non-thrombotic emboli that dislodge and block the pulmonary arteries or branches. The emboli causing PE can be divided into thrombotic and non-thrombotic according to their nature. The former is born in the blood vessels and accounts for about 90% of the cases. In addition to thrombotic emboli, fat embolism caused by adipose tissue damage due to multiple fractures of long bones or pelvis, cancer embolism caused by cancer infiltration of veins, amniotic fluid embolism during obstructed labor or cesarean delivery, air embolism caused by trauma and operation errors that cause rapid air entry into the circulation or other medical emboli can also obstruct the pulmonary circulation and cause pulmonary embolism (PE). Because of the different emboli, their respective clinical manifestations and treatment are different from pulmonary thromboembolism (PTE). Pulmonary thromboembolism is a potentially fatal and health-threatening disorder that is gradually gaining attention. Recent studies have confirmed that PTE is not uncommon in the national population and should be given high priority in certain populations with predisposing factors, especially in ICU inpatients. I. Relationship between DVT and PTE DVT is related to PTE There are two types of veins in the body circulation, deep and superficial, those located in the deep surface of deep fascia or body cavity are called deep veins, while superficial veins are located in the superficial subcutaneous fascia, which are eventually injected into deep veins. Deep vein thrombosis (DVT) is the abnormal clotting of blood in the deep venous system, which is a venous reflux disorder and is most common in the lower extremities. DVT and PTE are closely related and share common characteristics in etiology, treatment and prognosis. DVT and PTE are extremely correlated and share common characteristics in many aspects such as etiology, treatment and prognosis. The integrity of vascular endothelial cells and the production of a variety of anti-thrombotic bioactive substances regulate the coagulation and fibrinolytic system under normal conditions, which can prevent the formation of thrombus. However, under the conditions of the presence of certain pathological factors, this balance and stability is disrupted, leading to the formation of thrombus.2. Blood hypercoagulable state, which includes congenital factors: deficiency of anticoagulant substances – AT-III, protein C, S deficiency, etc.; and acquired factors: malignancy, diabetes, hyperlipidemia, pregnancy, oral contraceptive drugs, chronic myeloproliferative diseases.3. Slow blood flow. Long-term bed rest, local venous reflux disorders, tumor and other compressions. (ii) Risk factor classification: Among the acquired susceptibility factors, surgery is the most important aspect. The risk of postoperative VTE can be classified as low, moderate or high according to the type of surgery and whether other predisposing factors are combined. For smaller elective surgeries, the incidence of fatal PTE is only 1 in 10,000, while for larger orthopedic lower extremity surgery, total abdominal or pelvic tumor surgery, the incidence of proximal venous thrombosis can be 10% to 30%, and the incidence of fatal PTE can be as high as 5%. Among the non-surgical patients, patients with acute and chronic diseases of the three systems of heart, lung and brain as well as patients with malignant tumors belong to the high-risk group. (C) The incidence of PTE-DVT in ICU I CU patients are typically a high-risk group with more than 4 risk factors per capita. The incidence of VTE (venous thromboembolism) is high in ICU patients, but the diagnosis of VTE is low.