The placement of a inferior vena cava (IVC) filter is interesting.  An IVC filter is a web like structure that sits in the largest vein in the body that delivers blood from abdomen, kidneys, liver, pelvis, and lower extremities to the right atrium of the heart.  The purpose of an IVC filter is to reduce the risk of a pulmonary embolism.  A pulmonary embolism results when a blood clot usually in the lower extremity travels to the lungs.  Patients are at increased risk of developing clots in their lower extremities if they are immobile for long periods of time.  A pulmonary embolism (PE) can be a life threatening event because it can cut off blood supply to the entire pulmonary vessels leading to hemodynamic collapse or less lethal when a PE cuts off blood supply to a portion of lungs leading to a pulmonary infarct.

IVC filters have been shown to decrease the risk of developing a pulmonary embolism.  The filter will "catch" the clot before it reaches the lungs.

IVC filters are usually placed in patients who have developed a clot in their legs.  It could be that the surgeons prophylactically placed a filter before a clot in the legs actually formed.   The reason to do this is because if a patient does develop a pulmonary embolsim, then the patient would need to have his/her blood thinned.  After a intracerebral bleed, thinning the blood would not be a good idea as it would increase the risk for a rebleed.