Vena caval filters: keeping big clots down.

Vena caval filters: keeping big clots down Pulmonary emboli are usually unexpected, and research has concentrated on eliminating the source, deep vein thrombosis .' Once a deep vein thrombosis has developed we rely heavily on anticoagulation, even though evidence that this works is poor.2 Surgeons have thus been attracted by the idea of trapping clots in the leg or pelvic veins, where they are no threat to life. After an unproductive flirtation with femoral-vein ligation, vena caval occlusion was favoured for several years. As this prevented large pulmonary emboli the consequent swelling of the legs was tolerated despite the high morbidity and mortality of retroperitoneal operations in severely ill and anticoagulated patients. This policy was, however, misguided as we now know that multiple small pulmonary emboli may shower into the lungs via large collateral veins in 30-50% of patients.3 The current vogue for intraluminal filters began with the Mobin-Uddin umbrella (figure), which is passed under radiographic control via the internal jugular vein through the right atrium and lodged in the inferior vena cava below the renal veins.4 Blockage by a large embolus tends, however, to ft The Mobin-Uddin filter (left) may be displaced from the inferioir vena cava when a large embolus occludes the filter and causes .distension In the Kimray-Greenfield filter (right) emboli would be captured centrally and usually lyse without obstructing the inferior vena cava. dilate the inferior vena cava and-collapse the original 23 mm umbrella, occasionally, causing disastrous displacement into the heart or pulmonary artery. The introduction of a heparin bonded 28-mm filter reduced this risk, but caval occlusilon still occurred in about half of patients, leading to the expansion of collateral -veins' through which emboli could pass. 4 a. Thes p4 rolem0z s wes_re sole by 'the, ineiuly simple, thug exenive; (aou £80) K .: ..imray.; ..-Grenild ven caval i-Udi filter (fgr)Thseemlest may bedspidedro w thsxsanes harinfelike legs formiwhng a conge intoluwhchlde temboie maynldg wtoustrocudting bloo fler o w. Large emblifoceth terminal hooks on these spring loaded legs deeper into the vein wall and prevent migration.5 As the embolus lyses no collateral veins develop, and-blood from the legs continues to be filtered.6 Insertion via either the femoral or internal jugular veins has been eased by redesigned catheters from which the filter is ejected.7 Complications are few and usually result from inaccurate placement and occasionally from tears in the inferior vena cava. In 156 patients who either …