Pulmonary Embolism Risk
Pulmonary Embolism is an extremely common condition that is a leading cause of death in all age groups. Pulmonary Embolism is caused when a thrombus (clot) travels up the major inferior vein (the vena cava) through the heart and into the blood vessels of the lungs. Once the thrombus is lodged in the lungs it causes acute respiratory and circulation problems that can result in the patient's death. More than 90% of Pulmonary Embolism cases are complications of Deep Vein Thrombosis which are thrombi originating in the leg or pelvic veins.
Pulmonary Embolism is especially common and lethal in the patient confined to bed rest during a hospital admission. It is estimated that Pulmonary Embolism accounts for approximately 10% of in-hospital deaths. Particular groups of patients are known to have an increased risk for developing Deep Vein Thrombosis, (such as: multiple trauma, orthopedic surgery, head injury, surgical oncology) and no group of patients is free of risk. Approximately 600,000 new cases of Pulmonary Embolism are reported in the U.S. each year with over 200,000 deaths, despite detailed prophylactic medication-based regimens for the prevention of venous thromboembolic disease. Many patients simply cannot receive adequate anticoagulation due to the type or severity of their condition. Mechanical filtration, as offered by vena cava filters, has become an accepted form of adjuvant therapy in selected high-risk patients.
Prophylactic Vena Cava Filter Use
In the last decade there have been an increasing number of reports of the prophylactic use of permanent filters in patient populations at risk of Deep Vein Thrombosis. These reports have demonstrated encouraging results both in the prevention of Pulmonary Embolism and a reduction in mortality.
These issues have led to the development of temporary and retrievable (or optional) vena cava filters. Retrievable filters can be implanted prophylactically and after a suitable period can be removed or left in place dependent on the patient's condition and further risk of thromboembolic phenomena. The classic example is the young multi-trauma patient with head injury and long bone fractures who cannot receive anticoagulation therapy and is at high risk for Pulmonary Embolism, yet after full recovery and mobilization carries no further significant risk. Another large group of candidates for retrievable vena cava filter implantation are patients undergoing orthopedic surgery for femoral neck fracture and total hip or knee replacement. These patients have a defined period of high risk for deep vein thrombosis and return to full mobilization subsequently. Other potential patient populations include neurosurgery, gynecology, obstetrics and general surgery.
To maximize the clinical potential of these filters a number of issues have to be addressed. A central issue is the period of time the filter remains retrievable. The risk of thromboembolism often extends beyond the hospital admission period, especially in the case of elective orthopedic surgery. Therefore an extended period of protection is essential.
An important factor in improving retrievable filter design is the minimizing of filter related morbidity. This includes filter stability, lack of migration and effective filtration with minimal interference to the blood flow in the inferior vena cava. Furthermore the delivery and retrieval systems should be low profile (less than 2mm for insertion sheath) to reduce patient discomfort and preserve the patency of the accessed vein.
Due to the limitations of existing vena cava filters on the market (such as permanency or limited retrieval period, vessel damage, risk of migration, difficult placement), their use is typically restricted to patients determined to be at high risk of developing Pulmonary Embolism and who exhibit contraindications to anticoagulation. Despite the growing interest of the medical community in expanding the use of vena cava filters, the safety and cost considerations associated with existing filters may be preventing prophylactic filter placements on a widespread basis.
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Background Information