The Greenfield Vena Cava Filter: Operative Technique
Anatomic definition of a patients IVC is mandatory prior to filter placement, as the device has a finite maximal diameter. In addition to congenital abnormalities in the venous system, cavae with diameters greater than 28 mm (so-called “megacavae”) may be encountered. Indeed, the one report of significant proximal filter migration was due to inadvertent placement in a massively dilated segment of the IVC. Venocavography will also alert the physician to the presence of clot in the IVC or the renal veins. Such clot may prevent the struts of the filter from completely opening and engaging the caval wall. This situation, once recognized, can be dealt with by suprarenal filter placement.
The filter can be introduced by either jugular or femoral venous cut-down. The procedures are dissimilar, however, in their use of guide wires and insertion catheters. A percutaneous approach has also been described. Techniques for insertion have been published, and instructions are packaged with the equipment. Like all new therapies, both the design and application of this device have evolved. These progressive changes are important because they have conditioned previously reported results. The most significant technical change occurred in 1983 when both the insertion catheter and the techniques of femoral and jugular placement were modified. The modifications included the following: (1) placement using Seldinger guide wire technique; (2) providing a disposable introducer; and (3) provision for continuous heparin irrigation of the system through an additional access port.
Most filters are placed via a right internal jugular approach. A cut-down is made to the internal jugular in line with the fibers of the sternocleidomastoid muscle. A segment of the vein is then mobilized. The introducer (which includes the filter and its carrier) can be inserted through a transverse incision in the jugular or the guidewire may be passed first, and then back-loaded through the carrier. The filter is then guided to a location below the lowest renal vein and above the bifurcation of the iliac veins. Knowledge of the venous anatomy is critical to avoid placement in a renal, hepatic, iliac, or other vessel. Once the device is in place, the carrier is removed while the filters position is maintained by use of a stylet within the introducer system. As the carrier is withdrawn from around the filter, the legs open and engage the caval wall. The guide wire running longitudinally through the filter helps to prevent angled insertion. The introducer assembly is removed, and the venotomy repaired.