4.10
肺塞栓症 I: 概要
血餅、または血栓は、フィブリン、血小板、赤血球からなる半固形塊です。血管内に形成されると、血流を遮断することがあり、これは血栓症と呼ばれます。血餅の一部が剥離すると塞栓子となり、移動して離れた血管を閉塞することがあります。これが肺動脈で起こると、肺塞栓症、またはPEと呼ばれる状態を引き起こします。
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血栓、すなわち血栓は血管内に形成され、血流を部分的または完全に遮断することがあります。この状態は血栓症として知られています。
血栓の一部が剥がれて血流を通過すると塞栓になります。
塞栓が肺動脈に詰まると、肺塞栓症(PE)を引き起こすことがあります。ほとんどの場合、塞栓は脚の深部静脈にある血栓、すなわち深部静脈血栓症から始まります。
PEの発症は、静脈停滞、凝固過、内皮損傷という三つの要因を含むヴィルショウ三位一体によって説明されます。
静脈停滞は、整形外科手術後の長時間の動かなさや、長時間の座り込み(例えば長時間の飛行機での飛行など)によって生じることがあります。
抗トロンビンIII欠乏症、妊娠、エストロゲン含有避妊薬の使用などが高凝固症を引き起こすことがあります。
内皮損傷は外傷や中心静脈カテーテル置管によって引き起こされることがあります。
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Q1: What is the difference between a thrombus and an embolus?
A thrombus is a blood clot that forms within blood vessels and can block blood flow, a condition called thrombosis. An embolus forms when part of the thrombus breaks away and travels through the bloodstream. If the embolus lodges in a pulmonary artery, it causes a pulmonary embolism.
Q2: What is deep vein thrombosis and how does it relate to pulmonary embolism?
Deep vein thrombosis (DVT) is a blood clot that forms in the deep veins of the legs. In most cases, the embolus that causes pulmonary embolism originates from a thrombus in these deep leg veins. DVT and PE together are considered part of the same disease process called venous thromboembolism.
Q3: What are the three factors in Virchow's triad that contribute to blood clot formation?
Virchow's triad includes venous stasis, hypercoagulability, and endothelial injury. Venous stasis occurs when blood flow slows due to immobility from surgery or prolonged sitting. Hypercoagulability results from conditions like antithrombin III deficiency or pregnancy. Endothelial injury may be caused by trauma or catheterization.
Q4: What causes venous stasis and who is at risk?
Venous stasis occurs when blood flow becomes stagnant due to immobility. Risk factors include prolonged bed rest after orthopedic surgery, extended plane flights, heart failure, obesity, pregnancy, and catheter use. Any condition limiting movement can slow blood circulation in the veins.
Q5: What conditions increase blood coagulability and raise pulmonary embolism risk?
Hypercoagulability can be inherited, such as factor V Leiden or protein C/S deficiency, or acquired through malignancy, oral contraceptives, pregnancy, or inflammatory disorders. These conditions increase the tendency of blood to clot, raising the risk of thrombus formation and subsequent pulmonary embolism.
Q6: How can endothelial injury contribute to pulmonary embolism development?
Endothelial injury damages the inner lining of blood vessels, activating clotting pathways that promote thrombus formation. Trauma, surgery, or prior thrombosis can cause this vessel wall damage. When a resulting clot dislodges and travels to the lungs, it causes pulmonary embolism.
Q7: Why are hospitalized and cancer patients at higher risk for pulmonary embolism?
Hospitalized and cancer patients face increased risk due to immobility, inflammation, and procoagulant states that promote blood clotting. These factors align with Virchow's triad mechanisms: reduced blood flow, increased clotting tendency, and vessel damage. Understanding these mechanisms supports early detection and prevention strategies in chronic obstructive pulmonary disease clinical contexts.