Vena cava filters are small metal devices that are implanted into the vena cava, the large vein that passes through the abdomen and returns blood from the lower half of the body to the heart.

These filters are designed to prevent potentially dangerous blood clots from traveling from the deep veins in the legs to the lungs, a life-threatening condition called pulmonary embolism.

Filter placement is recommended when other methods to combat deep vein clots prove inadequate or dangerous. In recent years, the use of vena cava filters has expanded to include situations where the formation of deep vein clots is highly likely but not confirmed.

A vena cava filter is a device that is implanted into the inferior vena cava, the large vein that passes through the abdomen and returns blood from the lower half of the body to the heart. The filter is designed to trap any blood clots that dislodge from deep veins, usually in the legs or pelvis, and prevent them from reaching the lungs, where they can cause an embolism. Pulmonary embolism is a life-threatening condition that affects an estimated 300,000 Americans each year.

Blood-thinning drugs called anticoagulants are ordinarily used to keep deep vein clots in check. However, in certain patients they are ineffective or can cause problems. Roughly one-fifth of patients who take anticoagulants still experience pulmonary embolisms, and patients who have bleeding problems or who have recently undergone surgery cannot receive anticoagulants. In cases like these, vena cava filters are an alternative treatment.

Several filter designs are currently in use. The filters all work according to the same principle but they vary somewhat in shape and size. Many take an umbrella-like shape, with a number of struts attached at the top to form a cone. The struts allow blood to flow through while any blood clots are caught at the point where the struts meet. An alternate design is the bird’s nest filter, a free-form mesh that is attached to the vena cava wall with four hooked struts. The filters are made of biocompatible metals such as titanium, nickel, and molybdenum.

The filter is usually inserted in the part of the vena cava below the kidneys and above the common iliac veins in the legs. The insertion is commonly performed in the special procedures room of a hospital radiology department by an interventional radiologist, a doctor who uses imaging techniques to guide minimally invasive procedures. It may also be performed by physicians in other specialties, including vascular surgery. The physician doesn't open the vena cava directly but reaches it through other blood vessels, starting from the right internal jugular vein in the neck, the right or left common femoral vein in the groin, or the brachial vein in the arm.

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