DEFINITIONS

Acute mesenteric ischaemia (AMI) is defined as the occurrence of an abrupt cessation of the mesenteric blood flow with an acute onset of symptoms (8).

Severe abdominal pain is the main symptom, whereas other pathological signs during clinical investigation of the abdomen are often disproportionately mild.

Onset of symptoms may vary from minutes (in embolism) to hours (in atherothrombosis) (8) and may not be clearly identifiable in patients with impaired mental status or analgesia-related sedation, or in cases of non-occlusive mesenteric ischaemia (NOMI).

Acute mesenteric ischaemia may be occlusive or non-occlusive in origin.

Forms of AMI:

Occlusive intestinal ischaemia: Decreased mesenteric blood flow due to acute thrombo-embolic high-grade stenosis or occlusion of mesenteric vessels with further subdivision:

· arterial embolism

· arterial thrombosis

· venous thrombosis

Non-occlusive intestinal ischaemia (NOMI): Acute severe ischaemia of the intestine develops without an acute thrombo-embolic high-grade stenosis or occlusion. The mechanisms include severe hypovolaemia, severe vasoconstriction (especially if accompanied by hypovolaemia), very low cardiac output, and compression of mesenteric vessels due to increased intra-abdominal pressure. Critically decreased mesentericblood flow leading to damage of intestinal cells occurs without acute thrombo-embolichigh-grade stenosis or occlusion of specifically identifiable (larger) mesenteric vessels. Previous chronic high-grade stenosis of mesenteric vessels may be a contributing factor and pertinent revascularisation may play a role also in cases of NOMI (9).

Intestinal ischaemia in specific conditions or via unclear mechanisms

· AMI due to abdominal compartment syndrome

· AMI due to occlusion of the inferior mesenteric artery during abdominal aortic aneurysm repair

· AMI due to aortic dissection

· AMI in patients with intra-aortic balloon counterpulsation

· AMI due to mechanical compression/distortion (e. g. volvulus, strangulation)

· Acute-on chronic mesenteric ischaemia (chronic mesenteric ischaemia that led to emergency admission due to an acute ischaemic event with intestinal infarction).

· Intestinal infarction due to any other cause or an unclear mechanism

Intestinal infarction refers to irreversible transmural necrosis of the intestine due to ischaemia independent of its mechanism.

Chronic mesenteric ischaemia (CMI) is defined as ischaemic symptoms caused by insufficient blood supply to the gastrointestinal tract with a duration of at least 3 months (8). The typical presentation includes postprandial pain, weight loss resulting from fear of eating, or unexplained diarrhoea.

Acute ischaemic event in a patient with known or suspected CMI refers to acute onset of more severe symptoms of mesenteric ischaemia necessitating hospitalisation.

Acute care hospital admissions include all patients receiving active treatment for a severe injury or episode of illness, an urgent medical condition, or during recovery from surgery (patients after elective surgery).

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