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Gastroenterology - Intestinal Ischemia - Fast Facts | NEJM Resident 360

Intestinal ischemia can be broadly categorized as either mesenteric (small bowel) ischemia or colonic ischemia and can present as acute or chronic disease. Patients often have underlying conditions (e.g., atrial fibrillation or vasculitis) that predispose to the formation of blood clots (thrombosis).

The cardinal sign of intestinal ischemia is abdominal pain. Although intestinal ischemia is largely considered a rare cause of abdominal pain, delayed diagnosis can be associated with significant morbidity and mortality.

Mesenteric Ischemia

Causes

• acute arterial embolism, usually from a cardiac source (e.g., atrial fibrillation)

• acute arterial thrombosis, generally in the presence of preexisting atherosclerotic disease

• nonocclusive mesenteric ischemia, usually from underlying atherosclerosis and acute low-flow state (e.g., systemic hypotension)

• mesenteric venous thrombosis, either idiopathic or secondary to an intra-abdominal process

Evaluation and Diagnosis

Mesenteric ischemia can be difficult to diagnose because of the rare incidence and nonspecific symptoms. Therefore, diagnosis requires a high index of suspicion.

• Clinical features: The hallmark of early presentation is abdominal pain out of proportion to physical exam. In addition to abdominal pain, patients with chronic mesenteric ischemia can present with other gastrointestinal symptoms, such as postprandial pain, nausea, vomiting, weight loss related to food avoidance, or change in bowel habits.

• Laboratory studies: Although laboratory studies are nonspecific, evaluation of arterial blood gas for acidosis should be considered in patients with suspected mesenteric ischemia.

• Diagnostic imaging: Definitive diagnostic tests should be initiated immediately in patients with suspected mesenteric ischemia and risk factors (e.g., atherosclerosis, atrial fibrillation). Imaging options include:

• • computed tomography angiography (CTA)

  • magnetic resonance (MR) angiography if CTA is not possible (e.g., secondary to contrast allergy or renal failure)

  • mesenteric angiography: the gold standard (although invasive, it can be therapeutic if a lesion is found that is amenable to intervention)

Computed Tomographic Angiography (CTA) in a Patient with Acute Mesenteric Ischemia Due to Embolus in the Superior Mesenteric Artery

Panel A shows a sagittal CTA image of a long-segment occlusion of the superior mesenteric artery (arrow). The occlusion was caused by an acute embolism beyond the origin of the superior mesenteric artery.
(Source: Mesenteric Ischemia. N Engl J Med 2016.)

Treatment

The focus of initial treatment is fluid resuscitation and monitoring of electrolytes because infarction can progress quickly to acidosis and hyperkalemia, both of which rapidly progress to sepsis associated with a systemic inflammatory response. Anticoagulation with heparin infusion should also be initiated as soon as possible once a diagnosis is made.

Definitive treatment can then be pursued through a range of interventions, including endovascular or surgical repair. In cases that require vascular reconstruction or where there is suspicion of intestinal ischemia, open surgery is required, generally with a “second look” surgery within 48 hours to assess the viability of the bowel after revascularization.

Colonic Ischemia

Causes

Colonic ischemia is the most frequent form of intestinal ischemia. Colonic ischemia generally results from nonocclusive causes, such as small-vessel disease, systemic hypotension, decreased cardiac output, or aortic surgery, but in most patients a specific inciting factor cannot be identified.

Evaluation and Diagnosis

Evaluation and diagnosis of colonic ischemia are similar to that of mesenteric ischemia except that large-vessel thrombus or embolus are seldom the cause of colonic ischemia. Clinically, patients also present with pain that is out of proportion to physical exam, although bright, blood-stained stools can also be present.

Abdominal and pelvic CT scan is the investigation of choice for making the initial diagnosis, followed by colonoscopy for confirmation if needed. Angiography is not required except in patients with both small bowel and colonic ischemia.

Management

Treatment is generally supportive, with aggressive hydration, bowel rest, and occasionally antibiotics. Surgery is reserved for peritonitis, fulminant colitis, persistent hypotension, pneumatosis intestinalis on imaging, or massive bleeding.

The American College of Gastroenterology (ACG) guidelines for diagnosing and managing colonic ischemia can be found here.

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