Intestinal Ischaemia
Inadequate blood supply to the gut, spanning three entities that differ in vessel, tempo and danger: acute mesenteric ischaemia (a small-bowel emergency), chronic mesenteric ischaemia (intestinal angina from symptomatic mesenteric arterial disease), and ischaemic colitis (usually a low-flow colonic injury); telling them apart drives urgency.
Definition
Intestinal ischaemia is insufficient blood supply to the bowel, comprising acute mesenteric ischaemia (sudden small-bowel arterial occlusion), chronic mesenteric ischaemia (atherosclerotic multi-vessel narrowing causing postprandial pain) and ischaemic colitis (low-flow injury of the colonic watershed zones).
First principles
One organ, two circulations, three syndromes
The gut is supplied by the coeliac axis, superior mesenteric artery (SMA, small bowel and right colon) and inferior mesenteric artery (IMA, left colon), linked by collaterals. Ischaemia produces three different pictures depending on which supply fails and how fast. Sudden occlusion of the SMA infarcts the small bowel: acute mesenteric ischaemia, a true emergency. Atherosclerotic mesenteric arterial disease causes chronic mesenteric ischaemia when symptoms and haemodynamically important disease align, commonly with multivessel disease but sometimes with severe isolated SMA disease. A global fall in perfusion injures the colon at its watershed zones: ischaemic colitis. Same principle, three very different clinical problems.
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