The Greenfield Vena Cava Filter
Tnterruption of the inferior vena cava (IVC) has been used for several decades as a means of protecting patients with lower extremity deep venous thrombosis (DVT) from pulmonary embolism (PE). The long history of this approach has been marked, as expected, by an evolution of the techniques employed. It took some years before it became apparent that unilateral interruptive procedures (femoral vein ligation) were inadequate and needed to be replaced by I VC interruption. It took additional time to appreciate that I VC ligation had a number of deficiencies and was best replaced by partially-occlusive, and preferably less invasive, procedures. During the past 20 years, trans-venous approaches have developed that obviate the need for general anesthesia with its attendant risks, costs, and delays. A number of transvenous devices have been described; however, only two have gone into widespread use: the Mobin-Uddin umbrella filter, and more recently, the Greenfield filter. Other devices, such as the Hunter balloon, birds nest filter, and the nitinol wire filter, have been reported, but are not in general use.
The value of any form of therapy in venous thromboembolism is dictated chiefly by the attendant risk/ benefit ratio. This ratio is not accurately predicted by theoretical considerations or by preliminary reports; such evaluation must await general application. This is because a given risk/benefit defined in carefully structured investigations may not reflect the results when the approach is applied to a diverse universe of patients. Due to the context of general use, risk/ benefit is conditioned by the experience and skill of those using the approach and the particular patients involved. “Murphys Law” then operates; modifications of the technique often result, and the true (or “real”) risk/benefit ratio slowly emerges. These basic considerations apply to the use of the Greenfield filter. This approach now has been available for a sufficient period to allow a reasonable assessment of both its risks and benefits as found in current practice. We have undertaken this appraisal based on review of the available literature and our own experience.
In preparing this review, we have had to contend with the diversity of clinical practice. Specifically, investigators have used different insertion techniques, varying criteria for defining complications, monitored different parameters, had diverse follow-up periods and protocols, etc. However, this compilation reasonably represents the actual variety of “state of the art” to which any given patient may be exposed.