- This article concerns ischemia of the small bowel. See ischemic colitis for ischemia of the large bowel
|Synonyms||mesenteric ischaemia, mesenteric vascular disease|
|Computer tomography (CT) showing dilated loops of small bowel with thickened walls (black arrow), findings characteristic of ischemic bowel due to thrombosis of the superior mesenteric vein.|
|Classification and external resources|
Mesenteric ischemia is a medical condition in which injury of the small intestine occurs due to not enough blood supply. It can come on suddenly, known as acute mesenteric ischemia, or gradually, known as chronic mesenteric ischemia. Acute disease often presents with sudden severe pain. Symptoms may come on more slowly in those with acute on chronic disease. Signs and symptoms of chronic disease include abdominal pain after eating, unintentional weight loss, vomiting, and being afraid of eating.
Risk factors include atrial fibrillation, heart failure, chronic renal failure, being prone to forming blood clots, and previous myocardial infarction. There are four mechanisms by which poor blood flow occurs: a blood clot from elsewhere getting lodged in an artery, a new blood clot forming in an artery, a blood clot forming in the mesenteric vein, and insufficient blood flow due to low blood pressure or spasms of arteries. Chronic disease is a risk factor for acute disease. The best method of diagnosis is angiography, with computer tomography (CT) being used when that is not available.
Treatment of acute ischemia may include stenting or medications to break down the clot provided at the site of obstruction by interventional radiology. Open surgery may also be used to remove or bypass the obstruction and may be required to remove any intestines that may have died. If not rapidly treated outcomes are often poor. Among those affected even with treatment the risk of death is 70% to 90%. In those with chronic disease bypass surgery is the treatment of choice. Those who have thrombosis of the vein may be treated with anticoagulation such as heparin and warfarin, with surgery used if they do not improve.
Acute mesenteric ischemia affects about five per hundred thousand people per year in the developed world. Chronic mesenteric ischemia affects about one per hundred thousand people. Most people affected are over 60 years old. Rates are about equal in males and females of the same age. Mesenteric ischemia was first described in 1895.
Signs and symptoms
- A hyper active stage 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.
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 in 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 atrial fibrillation who complains of abdominal pain is highly 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".
It is difficult to diagnose mesenteric ischemia early. One must also differentiate ischemic colitis, which often resolves on its own, from the more immediately life-threatening condition of acute mesenteric ischemia of the small bowel.
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)
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.
- 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%
- 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
As the cause of the ischemia can be due to embolic or thrombotic occlusion of the mesenteric vessels or nonocclusive ichemia, the best way to differentiate between the etiologies is through the use of mesenteric angiography. Though it has serious risks, angiography provides the possibility of direct infusion of vasodilators in the setting of nonocclusive ischemia.
NG tube decompression, angiogram for diagnosis and treatment, heparin anticoagulation. Papaverine to decrease arterial vasospasm.
"Surgical revascularisation remains the treatment of choice for mesenteric ischaemia, but thrombolytic medical treatment and vascular interventional radiological techniques have a growing role".
If the ischemia has progressed to the point that the affected intestinal segments are not savable, a bowel resection of those segments is called for. Often, obviously dead segments are removed at the first operation, and a second-look operation is planned to assess segments that are borderline that may be savable after revascularization.
- venous thrombosis: 32% mortality
- arterial embolism: 54% mortality
- arterial thrombosis: 77% mortality
- non-occlusive ischemia: 73% mortality.
In the case of prompt diagnosis and therapy, acute mesenteric ischemia can be reversible.
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