Removable Filter Catches Deadly Blood Clots Red-Handed

November 08, 1996

A team of Johns Hopkins physicians placed a temporary metal filter inside a major vein to catch a life-threatening blood clot in a bedridden patient. The successful procedure is believed to be the first use of the temporary filter in the United States and is of potential use in thousands of accident victims to catch pulmonary emboli.

The 35-year-old patient had suffered a broken pelvis in a motorcycle crash and was confined to bed for almost two weeks, according to Anthony Venbrux, associate professor of radiology.

Previous studies have found that most emboli--blood clots that break free and travel in the blood--form in the lower body and travel to the lungs where they can block blood flow and kill. They occur in up to 22 percent of accident patients and are the third most common cause of death in patients who survive the first 24 hours after a major accident.

With the patient's approval, the Hopkins physicians--interventional radiologists-- inserted the finger-like filter into his inferior vena cava via a catheter inserted into the neck. The vena cava is a large vein that returns blood from the lower part of the body to the heart. The physicians later discovered by means of an X-ray that the removable filter had indeed caught an embolus, interrupting its potentially catastrophic journey to the lungs.

"A patient who must lie flat for many days because of an injury tends to form blood clots, especially in the legs," says Venbrux. "These clots are like time bombs. If they break off from where they form and get to the lungs, they may block off the blood flow and kill the patient."

Drugs like heparin, which reduce clot formation, cannot be used if the patient has internal injuries that might bleed, Venbrux says.

In the past, only permanent filters have been available to reduce the risk of blood clot migration to the lungs. In up to 20 percent of patients with a permanent filter, however, blood clots may block the vena cava, says Venbrux. And permanent filter removal requires major surgery because body tissue grows around it and anchors it in place.

The temporary filter, trademarked Tempofilter (manufactured by B. Braun Celsa), is made of a biocompatible metal called Phynox, which resists clot formation.

Like the permanent filter, a catheter with the temporary filter attached to it is inserted into a neck vein through a small incision and threaded into the inferior vena cava. The filter is pushed out of a sheath and opens into an oval array of metal fingers that permits blood but not large clots to flow through.

"We put the filter below the level of the kidneys to prevent the clot from going to the kidney, as well as to protect the lungs," Venbrux says.

The filter is later removed by drawing out the end of the catheter from the small incision in the neck.

Venbrux and his co-workers first published results of animal tests with the filter in the November-December 1995 issue of the Journal of Vascular and Interventional Radiology.

His co-authors on that paper include Brian S. Kuszyk, Michael A. Samphilipo, Carolyn A. Magee, Jean L. Olson, and Floyd A. Osterman, Jr.

Note: The patient and Venbrux are available for interviews and photos of the filter in the vena cava are available to the media.


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