Acute Mesenteric Ischemia
Thrombotic: due to an acute arterial thrombosis which occludes usually the orifice of the superior mesenteric artery (SMA),
resulting in massive ischemia of the entire small bowel plus the right colon — the area supplied by the SMA.
Embolic: due to a shower of embolic material originating proximally — from the heart (atrial fibrillation, post MI, diseased valve) or an aneurysmal or atherosclerotic aorta. Emboli lodge usually at the proximal SMA, but below the entry of the middle colic artery; therefore — as a rule — the most proximal segment of proximal SB is spared. Emboli tend also to fragment — and re-emboli distally — producing a patchy type, small bowel ischemia.
Non-occlusive: due to “low flow state”, in the absence of documented arterial thrombosis or embolus. Note, however, that an underlying mesenteric atherosclerosis may be a precipitating — contributory factor. The low flow state is a product of low cardiac output (e.g. cardiogenic shock), reduced mesenteric flow (e.g. intra-abdominal hypertension) or mesenteric vasoconstriction (e.g. administration of vasopressors) — usually, however, due to a combination of these factors, developing in the settings of pre-existent critical illness.
KeywordsSuperior Mesenteric Artery Short Bowel Syndrome Mesenteric Ischemia Acute Mesenteric Ischemia Middle Colic Artery
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