Pulmonary embolism: incidence, diagnosis, prevention, and treatment.

Abstract

Focus in this discussion of pulmonary embolism is on the following: risk factors (age heredity and blood type obesity estrogen and oral contraceptive use/pregnancy cardiovascular disease cancer and other risk factors); pathophysiology and presenting symptoms; laboratory procedures and findings (radiography electrocardiography lung scanning and evaluation of lower extremity veins); treatment modalities (heparin therapy thrombolysis and surgery); and prevention. Pulmonary embolism may be the primary cause or a major contributory cause in as many as 200000 deaths per year in the US. Most of these deaths occur in patients in whom the diagnosis is not suspected and thus not treated. The mortality rate for untreated pulmonary embolism is approximately 30%. 90% of patients survive the initial embolic event but the correct diagnosis is made in no more than 2/3 of cases. Risk factors for the development of deep venous thrombosis are based upon the Virchow-Aschoff postulates which include: trauma or disruption of the vein wall; stasis of blood flow in the veins; and increased coagulability of the blood. More than 85-90% of all pulmonary emboli originate from deep venous thromboses in the popliteal and femoral deep veins. Other important although less frequent sites of origin of venous thromboembolism include the pelvic veins the renal and hepatic veins the axillary veins in the upper extremities and the right atrium. Accurate diagnosis and effective prevention and treatment depend on the clinicians awareness of risk factors for development of deep vein thrombosis. Estrogen may accelerate intimal proliferation in arteries and veins and it may also increase permeability of venous vascular endothelium. The risk of thromboembolism increases as the dose of estrogen increases. Both pregnancy and oral contraceptive use significantly decrease venous tone and the velocity of blood flow in the calf of the leg. Appropriate treatment includes thrombolytic therapy for patients with massive pulmonary embolism which results in hypotension or shock. Anticoagulant therapy with herapin followed by an oral anticoagulant is the primary treatment for most patients with submassive emboli in which there is less cardiovascular compromise. When thrombolytic therapy is used it should always be followed by anticoagulant therapy. Prevention of primary or recurrent deep vein thrombosis is directed toward improving venous blood flow and reducing hypercoagulability.