Inferior Vena Cava Filters
The inferior vena cava is the vein that drains deoxygenated blood from the lower part of the body into the heart. As such, every vein that serves the lower extremities and the organs of the lower body, including the kidneys, the liver, the lower abdominal wall, the adrenal glands, and the gonads. As a main tributary, the inferior vena cava, also known as the posterior vena cava, is an essential link in the circulatory system, carrying blood to the heart, and then the lungs, in order to replenish the body’s oxygen supply.
In patients susceptible to deep vein thrombosis (DVT), blood clots from in the deep veins of the legs, impeding circulation. The symptoms are pain, swelling and erythema of the effected extremity. Clots (thombi) often form behind the valves of veins, or where veins are weakened and blood pools. Many cases of DVT resolve spontaneously, but the most severe consequence of DVT is when a portion of the thrombus breaks off of the main body. This is called embolization, and the smaller fragment of the main clot travels through the circulatory system into the inferior vena cava, into the heart, and eventually into the pulmonary vein, which brings deoxygenated blood to the lungs for refreshment. A large clot that gets lodged into the smaller circulatory vessels of the lungs causes a pulmonary embolism, or PE.
PE is a potentially life-threatening condition. It causes shortness of breath, rapid and ineffectual breathing, and coughing up blood. When a patient is cyanotic, which means the patient’s skin, especially of the lips or lower extremities, turns blue, this is a sign of severe PE. It is estimated that 15% of all cases of sudden death are caused by pulmonary embolism.
The usually recommended treatment for DVT, and the associated reduction of risk of PE, is to prescribe anticoagulant drugs such as heparin. What anticoagulants do is reduce the blood’s ability to form clots. Following an optimal regimen of prescribed anticoagulants, thrombi dissolve on their own and pose no risk to the heart or lungs. There are cases, however, when anticoagulant therapy is contraindicated. In 2012 the American College of Chest Surgeons recommended that retrievable inferior vena cava filters be used when patients cannot be prescribed anticoagulants, when the patient is at acute risk of PE, or when the patient is diagnosed with acute proximal DVT, which is deep vein thrombosis occurring above the knee.
Retrievable inferior vena cava filters are officially considered Class II, or low-risk, devices by the U.S. Food and Drug Administration (FDA). By August 2010, the FDA had received over 900 reports of adverse effects due to the placement of retrievable inferior vena cava filters. In a statement released by the FDA, the agency noted that the devices had been implicated in increased risk of DVT, in filter embolization due to filter fracture, and in perforation of the inferior vena cava. The FDA’s official recommendation is that radiologists, surgeons and primary care providers who manage the care of patients with retrievable inferior vena cava filters weigh the risks versus the benefits of keeping the filters in place. Specifically, the FDA recommends that retrievable filters be removed as soon as the risk of PE is no longer clinically evident.