Acute Mesenteric Ischaemia
Sudden loss of blood supply to the small bowel, most often an embolus from the heart lodging in the superior mesenteric artery, causes rapidly progressive transmural infarction; the hallmark is severe pain out of proportion to a soft abdomen, and survival depends on revascularising the gut before it dies.
Definition
Acute mesenteric ischaemia is a sudden reduction in blood supply to the small intestine, usually from superior mesenteric artery embolism or thrombosis, non-occlusive low-flow states, or mesenteric venous thrombosis, causing rapidly progressive bowel infarction if not reversed.
First principles
The small bowel cannot tolerate sudden total occlusion
The small intestine has a very high metabolic demand and, unlike the colon, little time to recruit collateral flow when a main artery is abruptly blocked. When the superior mesenteric artery is suddenly occluded, ischaemia progresses from the metabolically active mucosa outward to full-thickness (transmural) infarction within hours. Once the bowel wall is dead, no amount of reperfusion can save it, which is why acute mesenteric ischaemia is a time-critical emergency and why the entire management is a race to restore flow before infarction is established.
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