What is a Vena Cava Filter?

The vena cava filter is a medical filter. Pulmonary embolism is an emergency with high clinical morbidity and mortality. In the United States, the number of symptomatic pulmonary embolisms that occur in the United States each year is 570,000 to 630,000, and 200,000 of them cause death. Although systemic anticoagulation can achieve some effects, but Pulmonary embolism occurs again in 3-20%, and anticoagulation therapy itself has 26% complications, of which 5-12% are fatal complications; some patients cannot receive anticoagulation treatment, such as acute bleeding, peptic ulcer, Primary or metastatic tumors (especially intracranial tumors), pregnancy, before surgery, etc.

Vena cava filter

The vena cava filter is a medical filter. Pulmonary embolism is an emergency with high clinical morbidity and mortality. In the United States, the number of symptomatic pulmonary embolisms that occur in the United States each year is 570,000 to 630,000, and 200,000 of them cause death. Although systemic anticoagulation can achieve some effects, but Pulmonary embolism occurs again in 3-20%, and anticoagulation therapy itself has 26% complications, of which 5-12% are fatal complications; some patients cannot receive anticoagulation treatment, such as acute bleeding, peptic ulcer, Primary or metastatic tumors (especially intracranial tumors), pregnancy, before surgery, etc.

Chinese name

Vena cava filter

Time

1968

The purpose is to

Want to stop blood clots from entering the pulmonary artery

Missing point

Impedes venous blood flow to the heart and reduces cardiac output

The history of heparin therapy can be traced back to 1938. In 1968, inferior vena cava ligation was proposed to solve this problem (Trousseau). The purpose was to prevent blood clots from entering the pulmonary artery. It was not until 1943 that femoral vein ligation was used in clinical practice. Prevent pulmonary embolism. This technique still caused 10 to 26% of patients with pulmonary artery embolism due to lower limb and pelvic collateral circulation. Another reason for this technique being eliminated was severe congestion of the vein after ligation of the femoral vein.

In 1943, Homans used inferior vena cava ligation, which had a significant disadvantage: it blocked venous blood flow back to the heart and reduced cardiac output. In addition, 7-50% of patients had recurrent pulmonary embolism due to collateral circulation.

Special instruments for the inferior vena cava began to appear in the early 1960s to solve this problem, such as the Adams-De Wesse inferior vena cava clamp, which divides the inferior vena cava into small venous channels (4 channels with a diameter of 3 mm). Pulmonary embolism decreased to 2-4%, but the incidence of inferior vena cava embolism and congestion was high (53%), and the complications of surgical placement of this device were higher (9-27%).

The development of interventional radiology provides a better way. A non-surgical intubation technique with minimal trauma can be used to insert a filter (Filter), which not only significantly improves the clinical application effect, but also reduces the traumatic effect. .

In 1967, the extension of the Mobin-Uddin umbrella filter reduced the incidence of pulmonary embolism to 3%, and the complications caused by the operation of the filter were 0%. The main disadvantage is that the vena cava patency rate is only 36-47%, 10- 75% of patients develop edema, ulcers and dermatitis of the lower limbs, so people have begun to research and develop more ideal vena cava filters.

In summary, it is known that patients with pulmonary embolism and deep vein thrombotic lesions who are not suitable for anticoagulation therapy are indications for placing filters. Venous thrombotic lesions easily affect the femoral, popliteal, popliteal, or inferior vena cava. 25-77% of these patients cannot be treated with anticoagulation, mainly because anticoagulation can cause serious complications such as bleeding for some coexisting diseases. Such as gastrointestinal ulcers, positive occult blood test, recent history of surgery (especially eye, brain and spinal cord surgery), hemophilia and so on.

If pulmonary embolism has occurred, filters should be placed with or without anticoagulation. Indications for prophylactic vena cava filters are: 1) deep vein thrombosis before surgery (25% of pulmonary arterial embolism); 2) unstable thrombosis in the inferior vena cava; 3) chronic pulmonary hypertension; 4) critical cardiopulmonary Functional reserve. Complications of metastatic tumors with lower extremity venous embolism or anticoagulant therapy with pulmonary embolism are high, and Moore reports bleeding or death in 25%.

Pulmonary embolism will occur in 19% of patients even with adequate anticoagulant therapy. Cohen et al. Reported 41 cases of this type. None of the bleeding complications occurred after prophylactic filter placement, and only 1 (2.4%) had fatal pulmonary arteries. embolism.

Animal experiments show that bacterial emboli filtered by Greenfield filters can be killed by systemic antibacterial treatment, and its mortality and complications are significantly lower than those of inferior vena cava ligation alone. Bacterial infectious venous inflammation can easily lead to pulmonary infarction and is an indication for filter placement.

The vena cava filter technology has almost no contraindications. Checking the patient's coagulation function is the main indicator before operation. The use of a small-diameter release system (14F) does not necessarily stop heparinization completely. If the jugular vein approach is adopted, the patient can be placed in a semi-recumbent position after surgery to reduce the central pressure of the vein to help stop bleeding. Those who need magnetic resonance imaging examination should choose non-magnetic filters (such as Titanium Greenfield, Vena-Tech and Nitinol Filter).

Before the filter is placed, a complete vena cava angiogram must be done. This can not only understand the diameter of the inferior vena cava, but also obtain some important information that has not been known before the angiography.

The method of venipuncture is not special, but some patients are difficult to puncture due to vascular obstruction. Some foreign hospitals use ultrasound Doppler (pen probe) to guide puncture to increase the puncture hit rate. After successful puncture, the puncture needle sheath or vascular sheath should be used. Contrast injection showed iliac vein. If there are emboli (filling defect) in iliac and femoral vein, transjugular approach should be used instead.

Patients should be allowed to perform Valsalva movements when imaging radiography, which is conducive to accurate measurement of the inferior vena cava. If the diameter of the blood vessel is larger than the filter diameter, the filter will be displaced after placement. After the filter is placed, the vena cava angiography should be repeated as a data retention to facilitate future comparisons and determine whether displacement occurs.

1. Repeated inferior vena cava: The incidence of repeated inferior vena cava (also known as double inferior vena cava) is 0.2% to 3%. The inferior vena cava on both sides can be the same thickness, but most appear as the right side is larger than the left and the left inferior vena cava The vein generally terminates in the left renal vein. In this variant case, if only one filter is placed on the "normal" side, the left venous blood flow will "bypass" the filter, so two filters must be placed. Some authors report embolization of the smaller left inferior vena cava (embedding steel rings, etc.) before placing the right vena cava filter.

2. Left inferior vena cava: The incidence of left inferior vena cava is 0.2 to 5%, and the left renal vein is drained across the midline to the contralateral side. In this case, it is not suitable to use a filter with low flexibility (such as Greenfield, Vena Tech) to release through the right internal jugular and right femoral veins. It is easier to use the left femoral artery approach, and the bird nest filter or Simon Nitinol filter is easier. Release from the right approach.

3 Epidural renal vein after orbiting the aorta: The incidence of the left accessory renal vein after walking around the aorta ranges from 1.5 to 8.7%. The venous drainage of the left kidney crosses the midline from the back of the aorta via the lower appendix renal vein. Often 2 to 3 vertebrae below the primitive renal vein. If this kind of mutation is encountered, the filter must be placed below the level of the left kidney and renal vein. If venography is not found, after the conventional method is inserted into the filter, the variant vein is equivalent to the collateral circulation, and the emboli will surround the filter.

A good filter should have the following characteristics: 1) the comprehensive projection area of the filter is small (low resistance to blood flow); 2) easy to release; 3) good biocompatibility; 4) good elasticity and good corrosion resistance; 5) no Procoagulant effects; 6) Non-ferromagnetic; 7) Recyclability (removed from the body by minimally invasive methods for a period of time after placement); 8) Maintaining the vena cava fully open; no pulmonary embolism after placement; 10) No damage to the inferior cavity The veins will not shift.

Recyclable filters are available on the market, but are not officially approved by the FDA. The current "recyclable" feature can only be achieved within a short time after the epithelialization of the connection between the filter and the venous wall, which needs to be placed clinically Longer time to help patients through difficult times (venous and pelvic surgery, etc.). Therefore, if the filter can be safely recovered in the vena cava for a longer period of time, it is a goal of current research.

There have been many reports on the results of clinical application of inferior vena cava filters. There is no significant difference in the efficacy of different types of filters. In general, the vena cava maintenance rate is about 90%, and the recurrence rate of pulmonary embolism is less than 10%. To date, no multicenter, randomized prospective study has been seen. Various filter applications have encountered complications such as displacement. Fortunately, the incidence is low and clinically acceptable.

Based on the above reasons, the choice of filters depends to a large extent on personal experience and training methods, but there are also several principles that must be adhered to: 1) Different filters have different placement paths and should be operated according to the manufacturer's requirements. 2) Determine the diameter of the inferior vena cava. So far, except for Bird's Nest IVC Filter, ordinary filters are only suitable for vena cava with a diameter of less than 28mm. In 3% of patients, the inferior vena cava is larger than 28mm, but less than 48mm. At this time, the bird's nest or bilateral iliac vein can be used to place a filter at the same time. Although this iliac vein double filter technology has clinical significance, its occlusion rate is higher than that of the iVC Be tall. From the point of view of operating technology and cost, Bird's Nest seems more preferable.

1. Hemorrhage and hematoma at the puncture site; 2. Inferior vena cava obstruction; 3. Thrombosis at the puncture site (10-41%). In severe cases, the jugular vein can expand to the intracranial sinus; Lateral displacement); 5. Inferior vena cava injury, and can involve related organs (aorta, duodenum, liver, portal vein, etc.).

Place the vena cava filter

In some cases, the filter needs to be placed in the vena cava above the renal vein opening, for example: 1) thrombosis of the renal vein; 2) thrombus expansion of the inferior vena cava beyond the level of the renal vein; 3) pregnant or impregnating women; 4) already Repeated pulmonary embolism occurred after placing the filter; 5) Thrombosis of genital vein caused pulmonary embolism.

Indications of superior vena cava filter

Pulmonary embolism caused by thrombosis of the veins of the upper extremities and the large thoracic veins, the patients with inferior anticoagulation treatment or those who are not suitable for anticoagulation can consider the placement of superior vena cava filters.

The use of clinical filters began in Europe and the southern United States, and is mainly targeted at high-risk patients within a limited time, such as: 1) post-natal hemagglutination and hypercoagulability; 3) preoperative prevention of venous thrombotic lesions; 4) those with pulmonary embolism High-risk patients, especially those who cannot undergo anticoagulation therapy or have complications after anticoagulation, and those who still have pulmonary embolism after anticoagulation. The above indications are actually indications for prophylactic filter placement.

In fact, so far, no temporary filter has been approved by the US FDA for clinical use. Preliminary experiments have not yet answered certain questions, and many aspects are still controversial. It is estimated that it will take some time.

Temporary filters can be divided into two categories: 1) restricted filters (referred to as Tethered Filters): with attached auxiliary catheters or guidewires, which are pulled out of the body at the time of recovery; 2) unrestricted filters: no attached- Restricted department, when re-inserting the instrument to cover the filter, and then recycle.