Mesenteric ischemia

Mesenteric ischemia (Mesenteric ischaemia - British English) is a medical condition in which inflammation and injury of the small intestine result from inadequate blood supply. Causes of the reduced blood flow can include changes in the systemic circulation (e.g. low blood pressure) or local factors such as constriction of blood vessels or a blood clot. It is more common in the elderly.

Diagnosis

It is important to differentiate ischemic colitis, which often resolves on its own, from the more immediately life-threatening condition of acute mesenteric ischemia of the small bowel.

Signs and symptoms

Three progressive phases of ischemic colitis have been described:

• A hyperactive phase occurs first, in which the primary symptoms are severe abdominal pain and the passage of bloody stools. Many patients get better and do not progress beyond this phase.

• A paralytic phase can follow if ischemia continues; in this phase, the abdominal pain becomes more widespread, the belly becomes more tender to the touch, and bowel motility decreases, resulting in abdominal bloating, no further bloody stools, and absent bowel sounds on exam.

• Finally, a shock phase can develop as fluids start to leak through the damaged colon lining. This can result in shock and metabolic acidosis with dehydration, low blood pressure, rapid heart rate, and confusion. Patients who progress to this phase are often critically ill and require intensive care.

Symptoms of mesenteric ischemia vary and can be acute (especially if embolic), subacute, or chronic.

Case series report prevalence of clinical findings and provide the best available, yet biased, estimate of the sensitivity of clinical findings. In a series of 58 patients with mesenteric ischemia due to mixed causes:

• abdominal pain was present in 95% (median of 24 hours duration). The other three patients presented with shock and metabolic acidosis.
• nausea in 44%
• vomiting in 35%
• diarrhea in 35%
• heart rate > 100 in 33%
• 'blood per rectum' in 16% (not stated if this number also included occult blood - presumably not)
• constipation 7%

In the absence of adequate quantitative studies to guide diagnosis, various heuristics help guide diagnosis:

• Mesenteric ischemia "should be suspected when individuals, especially those at high risk for acute mesenteric ischemia, develop severe and persisting abdominal pain that is disproportionate to their abdominal findings"
• Regarding mesenteric arterial thrombosis or embolism: "...early symptoms are present and are relative mild in 50% of cases for three to four days before medical attention is sought".
• Regarding mesenteric arterial thrombosis or embolism: "Any patient with an arrhythmia such as auricular fibrillation who complains of abdominal pain is hghly suspected of having embolization to the superior mesenteric artery until proved otherwise".
• Regarding nonocclusive intestinal ischemia: "Any patient who takes digitalis and diuretics and who complains of abdominal pain must be considered to have nonocclusive ischemia until proved otherwise".

Blood tests

In a series of 58 patients with mesenteric ischemia due to mixed causes:

• White blood cell count >10.5 in 98% (probably an overestimate as only tested in 81% of patients)
• Lactic acid elevated 91% (probably an overestimate as only tested in 57% of patients)

Devices for Diagnosis During Endoscopy

A number of devices have been used to assess the sufficiency of oxygen delivery to the colon. The earliest devices were based on tonometry, and required time to equilibrate and estimate the pHi, roughly an estimate of local CO2 levels. The first device approved by the U.S. FDA (in 2004) used visible light spectroscopy to analyze capillary oxygen levels. Use during Aortic Aneurysm repair detected when colon oxygen levels fell below sustainable levels, allowing real-time repair. In several studies, specificity has been 83% for chronic mesenteric ischemia and 90% or higher for acute colonic ischemia, with a sensitivity of 71%-92%. This device must be placed using endoscopy, however.

Plain x-ray

Plain X-rays are often normal or show non-specific findings.

Computed tomography

Computed tomography (CT scan) is often used. The accuracy of the CT scan depends on whether a small bowel obstruction (SBO) is present.

SBO absent

• prevalence of mesenteric ischemia 23%
• sensitivity 64%
• specificity 92%
• positive predictive value (at prevalence of 23%) 79%
• negative predictive value (at prevalence of 23%) 95%

SBO present

• prevalence of mesenteric ischemia 62%
• sensitivity 83%
• specificity 93%
• positive predictive value (at prevalence of 62%) 93%
• negative predictive value (at prevalence of 62%) 61%

Findings on CT scan include:

• Mesenteric edema
• Bowel dilatation
• Bowel wall thickening
• Intramural gas
• Mesenteric stranding

Treatment

"Surgical revascularisation remains the treatment of choice for mesenteric ischaemia, but thrombolytic medical treatment and vascular interventional radiological techniques have a growing role".

Prognosis

The prognosis depends on prompt diagnosis (less than 12-24 hours and before gangrene) and the underlying cause:

• venous thrombosis - 32% mortality
• arterial embolism - 54% mortality
• arterial thrombosis - 77% mortality
• non-occlusive ischemia - 73% mortality