Acute mesenteric ischaemia

Acute mesenteric ischaemia is a form of intestinal ischaemia and is mostly a disease of elderly. It’s relatively rare but has a mortality rate of > 60%. It is most often due to embolism, but may also be due to thrombosis or decreased CO. The superior mesenteric artery is most commonly affected. The ischaemic tolerance time is approximately 40 minutes.

Ischaemia causes infarction, leading to disruption of the mucosal barrier, causing bacteria and toxins from the GI tract to be released into the circulation. This may cause sepsis, leading to a high mortality rate.

There are three stages:

1. Mucosal necrosis
2. Muscular necrosis
3. Transmural necrosis

The latter two are irreversible.

Etiology

• Embolism
  • Atrial fibrillation
  • Valvular heart disease/endocarditis
• Thrombosis
  • Atherosclerosis
  • Arteritis
  • Aortic aneurysm
  • Aortic dissection
• Nonocclusive mesenteric ischaemia
  • Severe hypotension or shock
  • Abdominal compartment syndrome
• Venous thrombosis (mesenteric vein)

Clinical features

Depending on the etiology, the presentation may be anywhere from abrupt (embolism) to gradual (nonocclusive ischaemia). The typical symptoms are severe periumbilical abdominal pain, nausea/vomiting, and bloody diarrhoea.

The pain follows a characteristic pattern. Initially (1 – 2 hours), there is intense diffuse abdominal pain and tenesmus. In the next 12 hours the pain disappears due to the necrosis. Later, pain may return along with sepsis due to bowel perforation and leakage of bowel contents into the abdominal cavity.

Classically, the pain is “out of proportion to the physical examination”, meaning that the patient is in much more severe pain than the results of their physical examination would indicate (as the physical examination is usually normal in the initial stages).

Diagnosis

Invasive or CT angiography will show the occlusion. However, in severely ill patients where the clinical suspicion is high, the diagnosis is made during emergency laparotomy.

In many cases of acute abdomen, an abdominal CT is made. An abdominal CT in case of acute mesenteric ischaemia will show bowel wall thickening, intestinal pneumatosis. If done with contrast, it may show the etiology.

Treatment

In most cases, surgery is necessary to look for necrotic bowel. Any necrotic bowel must be resected. Re-examining the intestines during a so-called second-look laparotomy 24 – 36 hours later is mandatory to look for further necrotic sections.

Revascularisation must also be performed, if possible before the bowel resection. This may involve arterial bypass surgery, thrombectomy/embolectomy, stenting, etc.

In advanced cases with peritonitis or sepsis, emergency laparotomy with arterial bypass and resection of necrotic bowel segments is necessary. In less severe cases, interventional methods like angioplasty, stenting, and thrombectomy should be performed instead.