The Greenfield Vena Cava Filter: Anticoagulation
Anticoagulation remains the primary therapy for deep venous thrombosis. Caval filtration serves to protect the patient from one complication of this disease (pulmonary embolism) but has no effect on venous thrombosis. Therefore, anticoagulation should be administered as usual if no contraindication exists. While he prefers to discontinue heparinization briefly prior to insertion, Greenfield contends that anticoagulation is not an absolute contraindication to filter placement. This assertion is supported by the experience of Gomez et al who routinely administered 7,500 units of heparin immediately prior to venotomy in those patients without contraindication and noted no increase in complications. In the two reported cases of retroperitoneal hematoma in association with a filter, both patients received excessive anticoagulation therapy. In one of the cases, the patient underwent laparotomy 18 months later (for another condition), at which time, one arm of the filter was noted to have perforated the I VC. The actual timing could not be proven, and the earlier bleed would suggest that the perforation took place during or shortly after insertion. There is no other evidence that patients receiving anticoagulation therapy are at increased risk of caval hemorrhage. starlix 60 mg
The construction of the Greenfield filter is such that the curved prongs of the struts effectively anchor the filter to the caval wall. When the introducer is loaded with the filter, the struts are under tension. During the insertion, the filter springs open to engage the caval wall; the prongs may actually perforate the cava at this point. Among nine series (258 insertions), possible filter movement occurred in 27. All cases were confined to two series and comprise a significant percentage of their patients. Apparent migration, as little as 2 mm, was reported, with no significant proximal migrations. An argument has been put forth that some of those “migrations” actually represent parallel-related discrepancies between fluoroscopy at insertion and later roentgenograms. Only one significant proximal migration has been reported, this due to unrecognized placement in a dilated segment of vein that was too large to engage the filter.