- Clinical science
Intestinal ischemia occurs when blood flow to the bowels is reduced. The condition can be acute or chronic and may affect the large and/or the small intestine. Possible causes for decreased blood flow include thromboembolism, atherosclerosis, and severe hypotension. Mild forms of intestinal ischemia lead to abdominal discomfort (e.g., postprandial pain) and a change in bowel habits (e.g., bloody diarrhea). In severe cases, infarction of intestinal tissue leads to perforation of the bowel, sepsis, and death. Early diagnosis and therapy are, therefore, essential and sometimes emergency surgery is vital. Imaging techniques (e.g., CT angiography, ultrasound, colonoscopy) are used to detect stenoses, occlusions, and/or mucosal changes. Chronic and mild acute forms are associated with a better prognosis and patients benefit from revascularization procedures (e.g., stents, bypass surgery) and symptomatic therapy. Complications such as peritonitis and sepsis result in a poor prognosis.
Intestinal ischemia is classified into three main types:
- Ischemic colitis (colonic ischemia): hypoperfusion of the large bowel, which is mostly transient and self-limiting (non-gangrenous form), but can also lead to severe acute ischemia with bowel infarction (gangrenous form)
- Acute mesenteric ischemia: acute inadequate blood flow to the small intestine (arterial or venous) that can result in bowel infarction
- Chronic mesenteric ischemia: constant or episodic hypoperfusion of the small intestine, usually due to atherosclerosis
- Most common form of intestinal ischemia
- Mainly occurs in adults > 60 years
- In ∼ 80–85% mild, non-gangrenous form
Usually caused by transient hypoperfusion
- Hypotension, hypovolemia (e.g., sepsis, dehydration, hemorrhage)
- Cardiovascular surgery (especially aortic repairs or cardiac bypass)
- Vasoconstrictive drugs
- Thrombophilias (e.g., anticardiolipin syndrome)
- Colonic obstruction from tumors, adhesions, etc.
- Intestinal blood flow of the superior mesenteric artery (SMA) and/or inferior mesenteric artery (IMA) is suddenly compromised; (see “Etiology” for causes) → intestinal hypoxia → intestinal wall damage → mucosal inflammation + possibly bleeding → may progress to infarction and necrosis (gangrenous type) → disruption of mucosal barrier and perforation → release of bacteria, toxins, vasoactive substances → life-threatening sepsis
- Depending on the degree of ischemia, there may be two types:
- Non-gangrenous (80–85%)
- Gangrenous (15–20%)
- Sites of compromise
- Superior mesenteric artery (SMA): supplies the distal duodenum, jejunum, ileum, and the right colon from the cecum to the splenic flexure
- Inferior mesenteric artery (IMA): supplies the left colon from the splenic flexure to the rectum
- The splenic flexure and the rectosigmoid junction are at high risk for colonic ischemia because they are “watershed areas”.
The intestines can tolerate a state of ischemia for approx. 6 hours!
Typically presents with 3 clinical stages:
- Hyperactive phase
- Pain more diffuse
- Bowel sounds become absent.
- Bloody stools cease
- Shock phase
- No specific laboratory findings in mild ischemic colitis
- In severe ischemic colitis:
- Plain abdominal radiograph: insensitive, unspecific (air-filled, distended bowel), but helps exclude other disorders
- CT scan: wall thickening, pneumatosis intestinalis (suggests transmural ischemia or infarction)
- Exploratory laparotomy in severe cases
- Mild to medium-severe forms:
- Severe forms (signs of peritonitis, sepsis): surgical intervention (laparotomy and bowel resection)
- Non-gangrenous form: strictures or chronic ischemic colitis
- Gangrenous form: peritonitis → sepsis → multi-organ failure
- Non-gangrenous ischemic colitis:mortality rate of approx. 6%
- Gangrenous ischemic colitis: mortality rate of ∼ 50–75%
- Mainly occurs in adults > 60 years
- Young people with A-fib, vasculitis (e.g., ), or hypercoagulable states can also be affected
- Acute mesenteric ischemia: 0.1% of all hospital admissions
- Acute arterial embolism; (∼ 50% of cases): generally resulting from atrial fibrillation, myocardial infarction, valvular heart disease, or endocarditis
- Arterial thrombosis; (∼ 25% of cases): due to preexisting visceral atherosclerosis, arteritis, aortic aneurysm, or dissection
- Nonocclusive mesenteric ischemia (NOMI; ∼ 20% of cases)
- Mesenteric venous thrombosis; (< 10% of cases): Predisposing factors include infection, malignancies, estrogen therapy, and hypercoagulability disorders.
- Sudden interruption of blood flow to small bowel (see “Etiology” above for cause) → intestinal hypoxia → hemorrhagic infarction and necrosis → disruption of mucosal barrier and perforation → release of bacteria, toxins, vasoactive substances → life-threatening sepsis
- Sites of interruption
- Periumbilical pain that is disproportionate to physical findings
- Nausea and vomiting
- Diarrhea (bloody in later stages)
- Gangrenous bowel: rectal bleeding and signs of sepsis (e.g., tachycardia, hypotension)
- Clinical courses
- Acute arterial embolism: most abrupt and painful onset of all types (“abdominal apoplexy”)
- Acute arterial thrombosis: presentation less severe because patients have better collateral supply
- Nonocclusive ischemia: symptoms develop over several days
- Venous thrombosis: symptoms less dramatic, worsen gradually (e.g., abdominal discomfort evolves over a week)
A patient with acute arterial embolism typically presents with severe abdominal pain, fever, bloody diarrhea, leukocytosis and atrial fibrillation!
A patient with acute arterial thrombosis typically has a known cardiovascular or peripheral vascular disease and/or symptoms of chronic mesenteric ischemia in addition to acute symptoms!
- Laboratory findings
- CT angiography (confirmatory test)
- Detection of distended intestinal loops and free fluid in the abdominal cavity in case of perforation
- Color Doppler ultrasound to detect stenosis in arterial branches
- Evaluation of underlying disease (e.g., ECG for atrial fibrillation or myocardial infarction)
If an acute mesenteric ischemia is suspected, quickly initiating imaging studies (CT angiography, color Doppler sonography) is essential. In cases with peritonitis or risk of shock, however, emergency surgery without prior imaging is indicated!
- If signs of advanced ischemia (e.g., peritonitis, sepsis) or hemodynamically unstable patient → emergency laparotomy
- Hemodynamically stable patients without signs of advanced ischemia → endovascular approach
- Supportive: IV fluids, nasogastric tube; , analgesics and broad-spectrum antibiotics
- Infusion of a vasodilator (e.g., papaverine) during arteriography to relieve occlusion and vasospasm
- Heparin anticoagulation in cases of venous thrombosis
- Long-term measures
Acute management checklist for acute mesenteric ischemia 
- Urgent general/vascular surgery and interventional radiology consults
- IV access with two large-bore peripheral IVs.
- Aggressive IV fluid resuscitation
- Avoid vasopressors, if feasible
- Nasogastric tube insertion
- Administer supplemental oxygen.
- IV anticoagulation: unfractionated heparin infusion 
- Parenteral analgesics (see ) 
- Broad-spectrum IV antibiotics: See empiric antibiotic therapy for intra-abdominal infection.
- ondansetron or promethazine ) (such as
- Serial abdominal examination
- Admit to surgical service/ICU or transfer to OR.
- Multi-organ failure
- Acute mesenteric arterial ischemia: mortality rate of 60–80%
- In cases of bowel infarction, mortality rate is 90–100%
- A clinically manifested chronic mesenteric ischemia is rare
- Generally occurs in adults > 60 years
- Slowly progressing stenosis of two or more main arteries (SMA, IMA; , or celiac artery) → postprandial mismatch between splanchnic blood flow and intestinal metabolic demand → postprandial pain
- If only one main artery is affected, collateral connections between the arteries can form and compensate for the reduced flow → patient may be asymptomatic
- Thrombus formation in addition to progressive stenosis can lead to acute-on-chronic mesenteric ischemia → acute mesenteric ischemia
- Some patients may be asymptomatic (see “Pathophysiology”)
- So-called 'abdominal/intestinal angina'
- Bloating, nausea, occasional diarrhea
- Abdominal bruit caused by stenosis of mesenteric vessels
- No specific laboratory findings in chronic mesenteric ischemia
- Clinical suspicion → CT scan of the abdomen (identifies atherosclerotic vascular disease and rules out other abdominal disorders)
- CT angiography or MR angiography: High-grade stenoses of at least two major vessels must be established for diagnosis
- Duplex sonography of the mesenteric vessels: best screening modality in an office setting
- Nutritional support (frequent, small meals; low-fat diet) 
- Long-term anticoagulation for patients not healthy enough for vascular repair
- Revascularization procedures to prevent bowel infarction in patients with abdominal pain and weight loss:
- In chronic mesenteric ischemia, surgical revascularization and reduction of risk factors can lead to significant pain reduction.