Patients with the following conditions are contraindications to vena cava filter implantation: chronic vena cava occlusion, vena cava malformation, lack of access to the vena cava, compression of the vena cava and absence of a place for the filter in the vena cava. Currently, there are four types of vena cava filters in clinical use: permanent filters, temporary filters, retrievable filters, and convertible filters (the last of which is not yet in clinical use in China). Permanent filters cannot be removed after implantation and are permanently implanted in the body; temporary filters must be removed within a certain period of time after implantation; and retrievable filters should be removed depending on the situation, but if there is no contraindication, it is recommended that they should be removed after the risk of PE to prevent complications of the filters. Currently, no studies have confirmed that implantation of an inferior vena cava filter improves patient survival, but it does prevent PE. but it needs to be clear: the only role of a vena cava filter implantation is to prevent PE, and it has no role in improving swelling of the affected limb, and may even lead to swelling of the healthy limb (e.g., formation of thrombus in the healthy limb punctured by the filter implantation after local compression, capture of thrombus within the filter, or in chronic occlusion of the inferior vena cava due to spontaneous formation of thrombus in the filter, which eventually leads to the formation of DVT in the healthy limb as well) or worsen the swelling of the affected limb. There are certain complications associated with filter implantation, except for puncture site complications and complications faced during filter implantation, which cannot completely prevent PE, but only reduce the incidence of PE. Other complications include filter displacement, hemorrhage due to filter puncture of the vena cava, filter disintegration and intra-filter thrombosis, and some complications are even fatal. Therefore, unless there is an absolute indication for filter implantation, other patients with VTE should be carefully evaluated and the benefits and risks of filter implantation should be carefully weighed before implanting a filter, so that the patient can benefit the most. Some off-topic remarks: if the thrombus is dislodged after DVT in the lower extremities, it will follow the venous blood flow through the inferior vena cava and the right heart and enter the pulmonary artery, and finally block the pulmonary artery, but not enter the left heart through the pulmonary capillary bed and then enter the systemic artery and cause arterial embolism. Therefore, it must be clear that except for a very small number of patients (this is because of the presence of atrial and ventricular septal defects in the heart and the pressure in the right heart is greater than that in the left heart, the embolus present in or entering the right heart will enter the left heart through the defect, causing systemic arterial embolism such as cerebral infarction, etc.), the vast majority of lower extremity deep vein thrombosis will not cause arterial embolism after dislodging. This point is confused by a part of medical personnel, who will mention that DVT thrombus dislodged from lower limbs will form arterial embolism such as cerebral infarction and heart infarction in addition to PE, and implantation of vena cava filter can prevent cerebral infarction and heart infarction in addition to PE, which is wrong. (PE: pulmonary artery embolism; DVT: deep vein thrombosis; VTE: venous thromboembolism) Various filter patterns diagram: Temporary type filter: Retrievable filter.