Page created on September 9, 2021. Last updated on November 10, 2021 at 20:38
Intestinal or abdominal ischaemia occurs when the blood flow to the large or small bowels is reduced. We can distinguish three types:
- Acute mesenteric ischaemia
- Chronic mesenteric ischaemia
- Acute colonic ischaemia
The small intestine is supplied by the coeliac trunk and superior mesenteric artery. The large intestine is supplied by the inferior mesenteric artery as well as a few branches from the superior mesenteric artery.
Acute mesenteric ischaemia
Definition and epidemiology
Acute mesenteric ischaemia 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:
- Mucosal necrosis
- Muscular necrosis
- Transmural necrosis
The latter two are irreversible.
- Atrial fibrillation
- Valvular heart disease/endocarditis
- Aortic aneurysm
- Aortic dissection
- Nonocclusive mesenteric ischaemia
- Severe hypotension or shock
- Abdominal compartment syndrome
- Venous thrombosis (mesenteric vein)
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).
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.
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 section.
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.
Chronic mesenteric ischaemia
Definition and etiology
Chronic mesenteric ischaemia is also a disorder of the elderly. Like acute ischaemia, chronic ischaemia is also relatively rare.
The condition occurs due to slowly progressive atherosclerotic stenosis of two or more of the mesenteric arteries. People with chronic mesenteric ischaemia are at higher risk for acute-on-chronic ischaemia, leading to infarction.
Symptoms include intestinal angina, referring to dull, cramping, postprandial epigastric pain which occurs within the first hour of eating. The pain subsides over the next couple of hours. This usually leads to food aversion and weight loss. The oxygen demand of bowel increases while digesting, which explains the origin of the pain.
On auscultation, an abdominal bruit may be heard due to stenosis of the mesenteric arteries.
In a patient with other clinical features of atherosclerosis (AMI, stroke, PAD), the diagnosis of chronic mesenteric ischaemia is likely in the case of typical symptoms. CT angiography will reveal the stenoses themselves.
As for all atherosclerotic disorders, reducing the risk factors of atherosclerosis is essential. Revascularisation procedures (angioplasty, stenting, bypass surgery) is the definitive treatment and also reduces the risk for infarction.
Acute colonic ischaemia
Not included in lecture, probably not that important.
Definition and etiology
Acute colonic ischaemia, also called ischaemic colitis, is the most frequent form of intestinal ischaemia, although also a disorder of elderly. Although it is more frequent than small mesenteric ischaemia, it is less deadly, as the colon handles ischaemia better than the small intestine. In 80% of cases it is mild, the so-called nongangrenous form. In the remaining cases however, it is severe and causes colonic gangrene.
Colonic ischaemia mostly occurs at the “watershed” areas of the colon, as these areas has the poorest perfusion. The splenic flexure and rectosigmoid junction are watershed areas; thus, the left colon is mostly affected.
Many conditions may predispose to acute colonic ischaemia, and in some cases no specific cause is identified:
- Mesenteric arterial or venous occlusion
- Myocardial infarction
- Diabetes mellitus
- Abdominal aortic aneurysm repair
- Constipation-inducing drugs
- Immunomodulator drugs (anti-TNF, interferon)
- Illegal drugs
Patients usually have mild abdominal pain and tenderness over the left colon, as well as rectal bleeding or bloody diarrhoea.
The diagnosis may be made clinically, in the context of typical history, physical examination, and clinical features. Abdominal CT with contrast is usually the initial study in patients with suspected intestinal ischaemia. Although there are no specific findings for colonic ischaemia on CT, it will exclude other differential diagnoses.
Colonoscopy confirms the diagnosis, and shows an oedematous, friable mucosa with erythematous and pale areas. Histology by biopsy shows necrotic changes.
Supportive care, nil per mouth, and broad-spectrum antibiotic therapy should be performed in all cases. In mild and moderate cases, these measures are usually enough. If due to a treatable etiology like vessel occlusion, these should be treated.
In severe, gangrenous cases, laparotomy with segmental resection is necessary.