It sounds like it's been recommended that she have an inferior vena cava filter (the vena cava is a large blood vessel that everyone has; see http://wiki.medpedia.com/Inferior_Vena_Cava and http://wiki.medpedia.com/Superior_Vena_Cava ). An IVC filter is a device which is placed inside the inferior vena cava, designed to prevent blood clots from traveling past it. A pulmonary embolism ( http://wiki.medpedia.com/Pulmonary_Embolism ) is thought to most commonly come from a blood clot in the legs ( http://wiki.medpedia.com/Deep_Vein_Thrombosis ), which travels through the IVC into the lungs.

IVC filters are not designed to prevent blood clots themselves, but to stop them from travelling to the heart and lungs. Many patients at risk of DVT or PE are on "blood thinners", medications designed to decrease a patient's formation of blood clots. Since blood must be able to clot well to undergo surgery safely, patients must often stop taking the blood thinners before having a procedure performed. Gastric bypass is a procedure which may take as much as several hours, and the longer a surgery takes, the more likely a patient is to form a blood clot in her legs during the surgery. Since she cannot be on a blood thinner, an IVC filter is the next best choice to prevent PE.

The insertion of an IVC filter is a relatively simple procedure, most often performed under mild sedation. Typically, a small puncture is made into the vein in the thigh, and the filter, a small piece of metal mesh, is threaded into the inferior vena cava under the guidance of X rays. The major risks of the procedure, like any surgical procedure, include bleeding and infection. One other potential complication is badly positioning the filter, which can lead to the need for more surgery; since most filters placed today are "retrievable", they can typically be repositioned rather easily if this complication is recognized during the procedure. Finally, there is the (rare) risk of puncturing the IVC, either with the filter or with the wires used to guide the filter into place. This can lead to the need for emergency surgery to stop the bleeding.

Over the long term, two major complications are described. The first, and likely most common, complication is the formation of a blood clot around the filter. Since this is a foreign device in the blood stream, it can promote clot formation. Again, however, this is not as serious as having the blood clot travel to the heart or lungs. Much more rare is the potential erosion of the filter through the wall of the IVC. While this does not usually lead to bleeding, it may also require surgery.

While IVC filters are not without risk, they are often appropriate for people who are at higher risk of DVT and PE, especially those who are unable to take blood thinners, and especially as a temporary or short-term solution.