Embolism

An embolism is a detached intravascular solid, liquid, or gaseous mass carried by blood to a site distant from its point of origin. The vast majority, 99%, are from a dislodged thrombus and are so referred to as thromboembolism. Additionally, rare forms exist such as fat, bubbles of air or nitrogen, atherosclerotic debris, tumor fragments, bone marrow, or foreign bodies. Each of these forms can cause partial or complete vascular obstruction and may lodge anywhere in the vascular tree.

Pulmonary Thromboembolism

Pulmonary Thromemboli constitute 25 per 100,000 hospitalized patients. Patients who have a history of pulmonary embolus are at risk of having more. Sudden death, cor pulmonale, or cardiovascular collapse may occurs in 60% of pulmonary emboli. Typically they originate from deep vein thrombi, especially from above the level of the knee. The site of occlusion depends on largely on the size of the embolus. Larger emboli may occlude the main pulmonary artery. While others may impact across the bifurcation (saddle embolus) or pass out into branching arterioles. A paradoxical embolus refers to the rare event where an embolus passes through an interatrial or interventricular defect entering the systemic circulation.

- Most are clinically silent because they are small – eventually become organized and incorporated into vascular wall

- Obstruction of medium-sized arteries can cause pulmonary hemorrhage but usually not pulmonary infarction as the circulation has dual blood supply and intact bronchial arterial circulation - Embolus in setting of left-sided cardiac failure and small end-arteriolar pulmonary branches may result in large infarct - Occurring a period of time may cause pulmonary hypertension with right ventricular failure

Systemic thromboembolism - Emboli in arterial circulation - 80% arise from intracardiac mural thrombi ( associated with left ventricular wall infarcts and dilated atria) - Other causes – aortic aneurysm, thrombi on ulcerated atherosclerotic plaques or fragmentation of valvular vegetations - Arterial emboli can travel to a wide variety sites ( depends on origin and relative blood flow) - Major site of embolisation are lower extremities and brain with kidneys, spleen affected to lesser extent - Effects depends on – vulnerability to ischemia, caliber of occluded vessel and collateral blood supply - In general it will cause infarction of affected tissues Fat embolism - Found after fractures of long bones (which contain fatty marrow) or after soft-tissue trauma - Characterized by pulmonary insufficiency, anemia, and thrombocytopenia - Fatal in about 10% of cases - Symptoms appear 1 -3 days after injury with sudden onset of tachypnea, dyspnea, tachycardia, neurologic syndrome (irritability and restlessness with progressive delirium or coma) - Vascular occlusion is aggravated by local platelet and RBC aggregation - Further exacerbated by FFA release causing local toxic injury to endothelium - Recruitment of granulocyte further complete the vascular assault

Air embolism - Can obstruct vascular flow and cause distal ischemic injury as well - Get during obstretric procedures or consequence of chest wall injury - More than 100ml of air needed for clinical effect – may coalesce to form frothy masses - Decompression sickness – exposed to sudden change in atmospheric pressure - Scuba, deep sea divers and underwater construction workers are at risk - Air breathed at high pressure will increase amounts of gas becomes dissolved in blood and tissues - Depressurize too rapidly, nitrogen expands and bubbles out of solution to form gas emboli - Rapid formation gas bubbles responsible for painful condition called the bends ( characteristically arched their backs) - In lungs, it causes edema, hemorrhages and focal atelectasis or emphysema leading to respiratory distress called chokes - Chronic form of decompression sickness is called caisson disease – persistence of gas emboli in bones leads to multiple foci of ischemic necrosis - Treated b placing in compression chamber to increase barometric pressure and force the gas bubbles back into solution Amniotic fluid embolism - Fatal but uncommon complication of labor and the immediate postpartum period - Onset characterized by sudden severe dyspnea, cyanosis, and hypotensive shock followed by seizures and coma - Caused by entry of amniotic fluid into maternal circulation via a tear in placental membranes and rupture of uterine veins - Marked pulmonary edema and diffuse alveolar damage with pulmonary microcirculation containing squamous cells shed from fetal skin, lanugo hair, fat from vernix caseosa and mucin from the fetal respiratory or GIT