Pulmonary
- Critical Care Associates
of East Texas
Jeffrey M.
Shea, M.D., F.C.C.P.
Catherine M. Martinez, M.D.
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Jeffrey M.
Shea, M.D., F.C.C.P. |
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Introduction Pulmonary embolism is one of the most important disorders affecting the pulmonary vasculature. The term pulmonary embolism refers to the movement of a blood clot from a vein through the right side of the heart to the pulmonary circulation; it then lodges in one or more branches of the pulmonary artery. The consequences of this problem are variable, ranging from none to sudden death, depending on the size of the clot and the pre-existing medical condition of the patient. Causes of PE & DVT In the majority of the cases, the legs are the source of thrombi (clot) that embolize to the lungs. Thrombi frequently originate in the veins of the calf; growth of the clots to the veins of the thigh is necessary to produce sufficiently large thrombi. Pulmonary emboli rarely originate in the arms, pelvis, or right-sided chambers of the heart, but these several sources combined may account for a small percentage of all pulmonary emboli. Three factors that potentially contribute to form venous thrombosis are (1) alteration in the mechanism of blood coagulation (hypercoagulability); (2) damage to the vessel wall, and (3) stasis or stagnation of blood flow. Risk factors for thrombo-emboli are: immobilization (bed rest, prolonged sitting during travel, immobilization of an extremity after a fracture), in postoperative conditions where patients are frequently bedridden, congestive heart failure, obesity, underlying cancers, pregnancy, and chronic deep venous thrombosis (DVT). Structure and Changes Pathologic changes from occlusion of a pulmonary artery depend upon the location of the occlusion and the presence of other underlying disorders that compromise oxygen supply to the pulmonary system. If minimal or no other oxygen supply reaches the essential parts of the pulmonary system, either from the airways or from the bronchial arterial circulation, then necrosis (death of tissue) of lung tissue (pulmonary infarction) will result. When the blood supply of the lung is maintained and infarction does not result, hemorrhage and edema are seen in lung tissue supplied by the occluded pulmonary artery. This is known as congestive atelectasis. Signs Pulmonary embolism usually develops in patients with one of the risk factors mentioned earlier. The embolus may not produce any significant symptoms. When the patient is symptomatic, sudden onset of shortness of breath is the most common complaint. Patients with a massive embolus may present with fainting spells, low blood pressure (shock), or suddenly die. On physical examination, the most common findings are rapid shallow breathing and a rapid heart rate. Examination of the lower extremities may show changes suggesting a thrombus, including tenderness, swelling, or a cord (clot within a vessel that can be felt by examination). Diagnosing PE & DVT An initial diagnostic evaluation of the patient with suspected pulmonary embolism includes a chest x-ray and arterial blood gases. Abnormalities on the chest x-ray may be atelectasis or elevation of a diaphragm, pleural effusions, showing volume loss but is usually normal. Over the past several years CT angiography (Helical CT) has become the mainstay in the diagnosis of PE's. This is done by infusing a contrast material into a peripheral vein and scanning the chest while the contrast material travels through the lung circulation. Blood clots are picked up directly by visualizing the clot as a filling defect in the artery. This scanning technique also allows the doctors to also evaluate the lungs to also rule out other diseases that may be causing breathing difficulties. Another screening test for pulmonary embolism is the ventilation (breathing) - perfusion(blood flow) lung scan. This scan is done instead of the CT if the patient is allergic to IV contrast or in addition to CT to evaluate equivocal cases. The scan demonstrates absence of perfusion to the region of lung supplied by the occluded vessel while showing maintenance of air delivery to that region. Treatment The standard treatment for a pulmonary embolus is the use of anticoagulant therapy, initially heparin and then a coumarin derivative (warfarin), the latter usually given for weeks to months. The use of anticoagulants is to prevent formation of new thrombi or reproduction of old ones (in the legs), not to dissolve clots that have already embolized to the lungs. Streptokinase or urokinase is other thrombolytic agents used in the treatment of massive pulmonary emboli. These must be give within the first several days of the embolic event in order to be effective. Prevention DVT and PE can be prevented in several high-risk groups. Patients that are scheduled for elective major abdominal, thoracic, or gynecologic procedures may receive subcutaneous heparin beginning shortly before the operation and continuing until they are fully ambulatory. The elderly and the obese should also receive prophylatic heparin during periods of immobilization in the hospital. Leg compression devices are also used frequently in order to maintain the venous blood flow when lying down.
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