Figure 1

The inferior vena cava is the large vein that returns deoxygenated blood to the heart (Figure 1). Vena cava interruption is the placement of a filter in the inferior vena cava to trap clots and prevent pulmonary embolism (clot in lung). This "interrupts" or interferes with the free flow of blood through the vein. Methods have been developed that allow vena caval interruption devices to be placed directly into the vena cava through the femoral (in the thigh) or jugular (in the neck) vein. An example of such a device is a Greenfield umbrella filter, which is placed inside the vessel to trap clots. Filters have improved greatly and are widely used as both treatment for and prophylaxis (prevention) of thromboembolic disease (blockage by a clot carried in the bloodstream from another site). The Greenfield filter has successfully maintained long-term vein patency (condition of being open) in over 95% of patients.

Figure 1. Major veins of the pelvis, abdomen, and chest. Note that the inferior vena cava is the large vessel in the center of the figure. (From Gloviczki P, Yao, JST, eds. Handbook of Venous Disorders, 2nd ed. London: Arnold, 2001:20, Fig. 2.11.)

Before placement of a vena caval filter, a venacavogram (x-ray of the vena cava) is taken to determine the best site for placement. Techniques for placing a filter differ according to the type of filter chosen by the physician. Besides the Greenfield filter, the Bird's Nest filter, the Vena Tech filter, and the Simon Nitinol filter are possibilities.

In critically ill patients, those who are pregnant, those who have a contraindication to contrast material, or those whose weight exceeds the weight limits of standard x-ray equipment, vena caval filters can be safely placed at the bedside using fluoroscopy and ultrasound or ultrasound alone for guidance. Fluoroscopy is a diagnostic method by which x-ray images are projected onto a fluoroscopic screen.