As a thromboembolic disease of the venous system, pulmonary embolism is becoming increasingly important to physicians and patients. Clinically, there seems to be an increasing trend in its incidence. In fact, this increase may be more due to the increased detection rate brought about by the widespread awareness of the disease. Two extremes may occur in many patients but both miss the diagnosis of pulmonary embolism until the dangers are fully recognized. In one case, the critically ill patient, the diagnosis of pulmonary embolism may not be made in time for sudden death or the opportunity for resuscitation may be missed and death may occur because there is no effective treatment for severe pulmonary embolism. Patients with moderate risk, on the other hand, may have more chances to be clinically diagnosed with pulmonary embolism and treated effectively. In terms of the degree of risk of the disease, the most important, of course, is the rapid diagnosis and immediate and effective treatment of the critically ill patient to save lives. How dangerous is severe pulmonary embolism? In patients with severe pulmonary embolism, the mortality rate can be as high as 15%, which is a very alarming figure. First of all, how to quickly determine a severe pulmonary embolism? What are the first indicators that should be concerned in determining whether a pulmonary embolism is severe or not? According to the general habit of thinking, from the name of the disease, it is natural that we will think of focusing on the lung and the thrombus; we will think of the imaging examination to find the thrombus and the destination of the thrombus. But for severe pulmonary embolism, the first concern should not be these, but some very easy to observe indicators that may be obtained even without. These are the patient’s vital signs, including blood pressure, pulse, and respiratory status. The diagnosis of severe pulmonary embolism can be made without doubt in a patient suspected of having pulmonary embolism who presents with shock manifestations, meaning persistent hypotension, or has had a decrease in blood pressure greater than 40 mmHg that lasts more than 15 minutes. If the patient is in the hospital, let’s say postoperative pulmonary embolism, abnormalities related to myocardial damage and right heart insufficiency related indicators can be examined at the same time. How can I help myself in case of a severe pulmonary embolism? What should be done especially when it occurs outside the hospital? There is no doubt that the first time to notify the emergency center is easy to be ignored. It is easy to ignore that the patient is immediately put into sedation to avoid the continued dislodgement of the embolus and aggravation of the disease. Loosen the upper garment to reduce breathing resistance, and if possible, immediately administer oxygen. After the emergency vehicle arrives, the patient should be transported flat. If self-transfer, you should also try to transfer as flat as possible. Absolutely avoid unnecessary lifting to reduce the risk of continued dislodgement of the venous thrombus. The majority of emboli in patients with pulmonary embolism come from the veins of the lower extremities, and there may be swelling in the lower extremities at the same time. Serious pulmonary embolism occurs in the hospital, mainly in postoperative patients. They often have a history of lower extremity braking, and when they first get out of bed, they suddenly collapse with severe respiratory distress and extremely unstable vital signs. While emergency cardiopulmonary resuscitation is performed, bedside anticoagulation and thrombolytic drugs can be tried to temporarily stabilize vital signs and strive for further treatment opportunities. For severe pulmonary embolism, intracavitary intervention is a rapid and effective treatment. In critically ill patients, after the initial stabilization of vital signs, the patient is quickly transferred to the catheterization laboratory for pulmonary angiography, which can rapidly clarify the diagnosis; after the diagnosis is confirmed, the inferior vena cava filter is quickly placed, and mechanical extraction and drug thrombolysis are performed through the pulmonary artery, which can rapidly reduce the pulmonary artery pressure, stabilize the vital signs and save lives. Pulmonary embolism, especially severe pulmonary embolism, can seriously endanger patients’ lives once it occurs. Emphasis is placed on prevention and rapid diagnosis and treatment after occurrence. However, outside the hospital and the primary hospital, the objective conditions are limited, and the resuscitation conditions are difficult to be in place, so prevention is very important.