Nonthrombotic Pulmonary Embolism
Nonthrombotic sources of pulmonary embolism include air, fat, amniotic fluid, infected material, foreign bodies, and tumors.
Pulmonary embolism can arise from nonthrombotic sources. PE caused by nonthrombotic sources results in clinical syndromes that differ from those caused by thrombotic PE. Diagnosis is usually based in part or completely on clinical criteria, including in particular the patient's risk. Treatment includes supportive measures.
Air embolism is caused by introduction of large amounts of air into systemic veins or into the right side of the heart, which then move to the pulmonary arterial system. Pulmonary outflow tract obstruction may occur, which can be rapidly fatal. Causes include surgery, blunt trauma, defective or uncapped venous catheters, and errors occurring during the insertion or removal of central venous catheters.
Treatment includes placement of the patient in the left lateral decubitus position, preferably in the Trendelenburg position (ie, head lower than the feet), to trap air in the apex of the right ventricle and thus prevent brain embolism and main pulmonary artery outflow obstruction. Supportive measures are also needed.
Rapid decompression after underwater diving may cause microbubble formation in the pulmonary circulation, a different problem, which results in endothelial damage, hypoxemia, and diffuse infiltrates (see Arterial Gas Embolism).
Fat embolism is caused by introduction of fat or bone marrow particles into the systemic venous system and then into pulmonary arteries. Causes include fractures of long bones, orthopedic procedures, microvascular occlusion or necrosis of bone marrow in patients with sickle cell crisis, and, rarely, toxic modification of native or parenteral serum lipids.
Fat embolism causes a pulmonary syndrome similar to acute respiratory distress syndrome (ARDS), with severe hypoxemia of rapid onset often accompanied by neurologic changes and a petechial rash.
Early splinting of fractures of long bones and operative rather than external fixation are thought to help prevent fat embolism.
Amniotic fluid embolism is a rare syndrome caused by introduction of amniotic fluid into the maternal venous and then pulmonary arterial system. The syndrome occurs around the time of labor (amniotic fluid embolism) or, even less often, during prepartum uterine manipulations.
Patients can have cardiac and respiratory distress due to anaphylaxis, vasoconstriction causing acute severe pulmonary hypertension, and direct pulmonary microvascular toxicity with hypoxemia and pulmonary infiltrates.
Septic embolism occurs when infected material embolizes to the lung. Causes include IV drug use, right-sided infective endocarditis, and septic thrombophlebitis.
Septic embolism causes symptoms and signs of pneumonia (eg, fever, cough, sputum production, pleuritic chest pain, dyspnea, tachypnea, and tachycardia) or sepsis (eg, fever, hypotension, oliguria, tachypnea, tachycardia, and confusion). Initially, nodular opacities appear on the chest x-ray; the appearance may progress to peripheral infiltrates, and emboli may cavitate (particularly emboli caused by Staphylococcus aureus).
Treatment includes that of the underlying infection.
Tumor embolism is a rare complication of cancer (usually adenocarcinoma) in which neoplastic cells from an organ enter the systemic venous and pulmonary arterial system, where they lodge, proliferate, and obstruct flow.
Patients typically present with dyspnea and pleuritic chest pain and signs of cor pulmonale that develop over weeks to months.
The diagnosis, which is suggested by micronodules or diffuse pulmonary infiltrates on chest x-ray, can be confirmed by biopsy or occasionally by cytologic aspiration and histologic study of pulmonary capillary blood.