Pulmonary embolism and infarction
LIFE-THREATENING DISORDERPulmonary embolism is an obstruction of the pulmonary arterial bed by a dislodged thrombus or foreign substance. Although pulmonary infarction (tissue death) may be so mild as to be asymptomatic, massive embolism (more than 50% obstruction of pulmonary arterial circulation) and infarction can be rapidly fatal.
Causes
Pulmonary embolism generally results from dislodged thrombi originating in the leg veins. More than half of such thrombi arise in the deep veins of the legs and are usually multiple.
Other less-common sources of thrombi are the pelvic veins, renal veins, hepatic vein, right side of the heart, and upper extremities. Such thrombus formation results directly from vascular wall damage, venostasis, or hypercoagulability of the blood.
Rare causes
Rarely, the emboli contain air, fat, amniotic fluid, talc (from drugs intended for oral administration that are injected I.V. by addicts), or tumor cells. Thrombi may embolize spontaneously during clot dissolution or may be dislodged during trauma, sudden muscular action, or a change in peripheral blood flow.
Rarely, pulmonary infarction may evolve from pulmonary embolism, especially when pulmonary embolism occurs with chronic cardiac or pulmonary disease. However, if the embolus obstructs a large vessel, bronchial circulation may provide an inadequate oxygen supply to the lung supplied by the occluded vessel.
Risk factors
Predisposing factors to pulmonary embolism include:
long-term immobility
chronic pulmonary disease
heart failure or atrial fibrillation
thrombophlebitis, polycythemia vera, thrombocytosis, autoimmune hemolytic anemia, and sickle cell disease
varicose veins and vascular injury
recent surgery
advanced age
pregnancy
lower-extremity fractures or surgery
burns
obesity
malignancy
use of hormonal contraceptives.
Signs and symptoms
Total occlusion of the main pulmonary artery is rapidly fatal; smaller or fragmented emboli produce symptoms that vary with the size, number, and location of the emboli. Usually, the first symptom of pulmonary embolism is dyspnea, which may be accompanied by angina or pleuritic chest pain.
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