Entrapment of sized emboli by the KMA-Greenfield intracaval filter.

Clinical studies demonstrating the effectiveness of the Kim-Ray Greenfield vena caval filter in the management of pulmonary emboli have stimulated efforts to accurately define this filter's capability to entrap sized emboli and maintain caval patency. Twenty-three dogs had filters inserted and positioned distal to the renal veins. Radiopaque emboli measuring 2 to 5 mm were introduced via the femoral vein. Cineradiography allowed direct observation of emboli capture and filter flow dynamics. Probability of entrapment was found to be related to (1) emboli size, (2) depth of filling of the conical-shaped filter by prior entrapment of emboli, and (3) absence of distal venous hypertension. The geometric design of the filter, which allows progressive vertical filling while maintaining circumferential blood flow, is thought to be responsible for entrapment of emboli and avoidance of venous thrombosis and hypertension.