I. What is pulmonary embolism? Pulmonary embolism, referred to as pulmonary embolism, is a clinical and pathophysiological syndrome in which endogenous or exogenous emboli block the pulmonary artery causing pulmonary circulation disorders. 75% of the thrombi originate from the deep venous system of the lower limbs or pelvis. The incidence of pulmonary embolism in western countries is about 1 per 1,000 and 0.5 per 1,000, and it is the most common fatal emergency in developed countries such as Europe and the United States. Autopsy studies in the United States have shown that about 60% of unexplained inpatient deaths are due to pulmonary embolism, and the misdiagnosis rate is as high as 70%. In China, 900 consecutive autopsies in Fu Wai Hospital confirmed that pulmonary embolism above the lung segment accounted for 11.0% of cardiovascular diseases, and pulmonary embolism accounted for the first place of pulmonary vascular diseases, suggesting that clinicians did not pay enough attention to it. The mortality rate of untreated pulmonary embolism is about 30%, but after adequate treatment, the mortality rate can be reduced to 2%-8%, which shows that pulmonary embolism is a kind of disease with high morbidity and mortality rate. Second, what are the risk factors of pulmonary embolism? The risk factors of pulmonary embolism include lower extremity deep vein thrombosis (DVT), recent surgery, trauma, long-term bed rest, tumor, obesity, childbirth, advanced age and chronic cardiopulmonary disease, deep phlebitis (such as intravenous drug injection), history of embolism, etc. Among them, DVT is the main cause of pulmonary embolism, while hyperlipidemia and obesity are considered as risk factors of DVT. Patients with acute pulmonary embolism are classified into acute and chronic pulmonary embolism according to the time of embolism. What are the manifestations of patients with acute pulmonary embolism? The typical symptoms of acute pulmonary embolism are dyspnea, chest pain and hemoptysis, which are called the triad of pulmonary infarction. The incidence of dyspnea is as high as 60%, mostly manifested as exertional dyspnea. The incidence of chest pain is also high, mostly pleuritic pain, which is caused by the involvement of the pulmonary infarction to the pleura. When a large pulmonary embolism or severe pulmonary hypertension is present, it can cause transient cerebral ischemia and manifest as syncope, which can be the first symptom of pulmonary infarction. In addition, it can also manifest as tachycardia and blood pressure drop, and sudden death can occur in critical cases. Pulmonary embolism, acute myocardial infarction and coarcted aortic aneurysm can be manifested as severe chest pain and called the triad of chest pain, which should be distinguished in the diagnosis and avoid missed diagnosis and misdiagnosis. 4.How to determine whether it is pulmonary embolism? Autopsy study shows that the misdiagnosis rate of pulmonary embolism is as high as 70%. In order to improve the diagnosis rate of acute pulmonary embolism, facilitate early treatment and reduce the mortality rate, the new concept and new thinking of international acute pulmonary embolism diagnosis and treatment procedure: for any patient with dyspnea, chest pain, cough and hemoptysis should be considered as possible acute pulmonary embolism, only in this way can we reduce the leakage and misdiagnosis. 1.CT pulmonary arteriography (CTA): It is the “gold standard” for the diagnosis of pulmonary embolism, with sensitivity and specificity above 95%, and is currently preferred for suspected cases of acute pulmonary embolism and completed within 24h of consultation. 2.Lower extremity vascular ultrasonography: The emboli of pulmonary embolism mainly originate from the lower extremity veins of patients with acute thrombophlebitis. Therefore, deep vein thrombosis of the lower limbs is important for the diagnosis of pulmonary embolism. 3.For plasma D-dimer (D-Dimer): The diagnosis of acute pulmonary embolism can be excluded if D-Dimer is lower than 500 μg/L. D-Dimer is a cross-linked fibrin metabolite, and the plasma level increases in acute pulmonary embolism, which is highly sensitive but not very specific. 4.Echocardiography: Transthoracic or esophageal two-dimensional echocardiography can indirectly or directly suggest the existence of pulmonary embolism, and is a valuable examination method. V. How to treat pulmonary embolism? The principle of pulmonary embolism treatment: to save life, stabilize the condition, and reopen the pulmonary vessels. 1.Thrombolytic therapy (1) is mainly applied to the early stage of acute pulmonary embolism within 1 week, the earlier the better. Thrombolytic therapy can quickly dissolve the embolus, rapidly improve pulmonary perfusion, restore the ratio of blood flow ventilation, increase effective gas exchange, and ultimately reduce the death rate of pulmonary embolism. Currently, the thrombolytic drugs approved by the U.S. Food and Drug Administration (FDA) for the treatment of pulmonary embolism include streptokinase (SK), urokinase (UK) and recombinant tissue-type fibrinogen activator (rt-PA). However, an important complication of thrombolytic therapy is intracranial hemorrhage, which is life-threatening. (2) Absolute contraindications to thrombolytic therapy: active internal bleeding and recent spontaneous intracranial hemorrhage. Relative contraindications include: major surgery, delivery, organ biopsy or vascular puncture that cannot be compressed to stop bleeding within 2 weeks; ischemic stroke within 2 months; gastrointestinal bleeding within 10 days; severe trauma within 15 days; neurosurgery and ophthalmology within 1 month; difficult to control hypertension (>180/110 mmHg); recent history of cardiopulmonary resuscitation; platelet count <100×109/ L; pregnancy; bacterial endocarditis; severe hepatic and renal insufficiency; diabetic hemorrhagic retinopathy, etc. 2.Surgical treatment (1) The main surgical treatment for acute pulmonary embolism is pulmonary embolism removal. Indication for surgery: large pulmonary embolism with clear lung scan and pulmonary arteriogram. Lethal pulmonary embolism is very dangerous, especially large pulmonary embolism, the morbidity and mortality rate is up to 70% or more, but if the resuscitation is timely and active surgical treatment after clear surgical indication, the morbidity and mortality rate can be controlled to about 20%. (2) Pulmonary embolism can be followed by chronic thrombotic pulmonary hypertension (CTPH), which is closely related to the pathological process of pulmonary embolism. If pulmonary artery pressure exceeds 30 mmHg (1 mmHg = 0.133 kPa), the 5-year survival rate is 30%, and if pulmonary artery pressure exceeds 50 mmHg, the 5-year survival rate is only 10%. Pulmonary thromboendarterectomy (PTE) for proximal pulmonary artery endarterectomy can greatly reduce pulmonary artery pressure, reduce respiratory insufficiency, improve right heart status, and is the main measure for the treatment of chronic embolic pulmonary hypertension. 3. Anticoagulation therapy: Patients with pulmonary embolism usually have abnormal coagulation mechanism or function, so they need lifelong anticoagulation therapy, such as heparin, low molecular heparin or warfarin. VI. What is the effect of surgical treatment for pulmonary embolism? (1) Fatal pulmonary embolism is very dangerous, especially large pulmonary embolism, and the death rate is up to 70% or more. If acute pulmonary embolism embolism removal is performed in time, the death rate can be controlled to about 20%. (2) It can prevent the evolution of acute pulmonary embolism into chronic thrombotic pulmonary hypertension. (3) Pulmonary artery thromboendarterectomy is a more accurate and main treatment for chronic thrombotic pulmonary hypertension, which can reduce pulmonary artery pressure and respiratory insufficiency, and greatly change the prognosis of patients with chronic embolic pulmonary hypertension. VII. Misconceptions about the diagnosis of pulmonary embolism in China Misconception 1. The incidence of pulmonary embolism is very low: the signs and symptoms of pulmonary embolism lack specificity, and it is easy to misdiagnose other diseases such as coronary artery disease, pleural effusion and pulmonary infection. Foreign countries report that the prenatal diagnosis rate is only 10%-30%, and only 7% of patients with pulmonary embolism who can be diagnosed and treated in time die, while 60% of undiagnosed pulmonary embolism die, and 33% of them die rapidly within the sixth hour after the onset of the disease. Therefore, the early and correct diagnosis of pulmonary embolism is very important. Awareness of pulmonary embolism should be raised so that patients with pulmonary embolism can be diagnosed promptly and treated correctly at an early stage. Myth 2: Diagnosis of pulmonary embolism is very difficult: In China, with the improvement of doctors' awareness of this disease and the improvement of diagnostic tools, the number of confirmed cases has also increased significantly. It is the first choice for suspected cases of acute pulmonary embolism and should be done within 24 hours of consultation. At present, thrombolysis is an important and effective measure for the treatment of acute PE. The traditional indications for thrombolysis are: large pulmonary embolism or pulmonary embolism with circulatory failure. However, in recent years, many scholars have disputed this indication, believing that thrombolysis, compared with heparin anticoagulation, does not reduce the recurrence rate and death rate of patients with massive pulmonary embolism, and may increase the risk of bleeding. Also, thrombolytic therapy has absolute and relative contraindications. Myth 2: Surgical treatment has a high mortality rate. Traditionally, surgical thrombectomy is considered only for large pulmonary embolism with shock, when the patient is in an unstable state, when medical treatment fails, or when thrombolysis is contraindicated and medical treatment is not appropriate. This is the main reason for the high mortality rate of surgical procedures for acute pulmonary embolism. In fact, the technology of extracorporeal circulation is very mature, and surgical operation can remove the thrombus in the main trunk and large branches of the left and right pulmonary arteries in a timely and effective manner, and the removal rate can reach 80% or even 100%, and combined with assisted breathing, the success rate of surgery can reach 80% at present. Surgery can rapidly improve pulmonary perfusion, restore the ratio of blood flow ventilation and increase effective gas exchange; at the same time, it can prevent chronic obstruction of blood vessels and reduce the risk of pulmonary hypertension. For patients with acute pulmonary embolism with large thrombus in the main pulmonary artery or left or right pulmonary artery trunk, surgical thrombectomy under extracorporeal circulation is recommended as long as there is no contraindication for surgery. Myth 3: Patients with pulmonary embolism will be cured at once and will be fine in the future. First of all, whether after thrombolysis or surgical treatment, patients should be treated with lifelong anticoagulation. At the same time, the prevention of pulmonary embolism is more important than the treatment. Only by increasing the awareness of this disease and actively preventing it, the damage caused by this disease can be significantly reduced, among which, the necessary anticoagulation is the key to prevention.