Etiology and Pathogenesis Top
Acute mesenteric (small bowel) ischemia results from a sudden occlusion and/or insufficiency of the mesenteric arteries or veins that reduces intestinal perfusion and thus threatens the viability of the small intestine.
Causes include mesenteric artery embolism (45%-50% of cases); nonocclusive mesenteric ischemia (NOMI) (20%-30%) due to low cardiac output secondary to shock, drugs (cocaine, ergotamine, vasopressin analogues, norepinephrine), or after intestinal revascularization interventions; mesenteric arterial thrombosis (15%-25%); or mesenteric venous thrombosis, which by itself may lead to impaired microvascular perfusion (5%).
Clinical Features and Natural HistoryTop
Mesenteric ischemia most commonly occurs in the elderly.
1. Symptoms: Because symptoms are nonspecific, diagnosis requires a high degree of clinical suspicion. The dominant feature is severe abdominal pain that is out of proportion to physical examination and is most frequently located in the periumbilical area. Nausea and vomiting are frequent. Diarrhea, which may be bloody with transmural infarction, may occur.
Initially physical examination may be unremarkable (eg, abdominal distension) or even normal. In the early stages of ischemia bowel sounds may be hyperactive but in later stages they can be reduced to complete cessation. Subsequently fever, diffuse peritonitis, and shock develop if intestinal necrosis or perforation occurs. Only 20% to 25% of patients present with an acute abdomen.
2. Risk factors: Risk factors differ by etiology. Mesenteric arterial embolism commonly occurs in patients with atrial fibrillation, cardiac valvular disease, or recent myocardial infarction. Mesenteric arterial thrombosis frequently occurs in patients with underlying chronic intestinal ischemia from atherosclerosis (see Chronic Mesenteric (Small Bowel) Ischemia). Mesenteric venous thrombosis tends to occur in patients with acquired (eg, secondary to malignancy) or hereditary hypercoagulable states (eg, factor V Leiden mutation, protein C or S deficiency, polycythemia). Trauma, recent abdominal surgery, and inflammatory conditions such as pancreatitis or diverticulitis are also risk factors for mesenteric venous thrombosis. NOMI occurs frequently in critically ill ventilated patients.
1. Laboratory tests: The most common findings are hemoconcentration and leukocytosis (usually >20,000/microL). In patients developing intestinal necrosis, nonrespiratory (lactic) acidosis, hyperphosphatemia, elevated levels of serum liver and pancreatic enzymes, and elevated creatine kinase levels may be seen as early as in the first few hours.
2. Imaging studies: Abdominal radiographs are nonspecific, and more than 25% radiographs are normal. Radiographic features of intestinal necrosis (including the presence of gas in the intestinal wall) appear late; they are only helpful when findings suggest perforation or a different diagnosis, such as obstruction. Computed tomography angiography (CTA) (without oral contrast) has replaced conventional angiography with its high sensitivity and specificity (94% and 95%, respectively). However, arteriography is still considered by some to be the definitive diagnostic method if there is uncertainty (with sensitivity of about 90%) or if required for therapeutic purposes. It should not delay surgery, if indicated.
Although specific treatment depends on etiology, the initial management for all patients focuses on resuscitation and prevention of complications.
1. Appropriate treatment of shock (see Shock).
2. Conservative management: Medications that may exacerbate mesenteric ischemia, such as vasoconstricting agents, should be avoided. If required, vasopressors with a relatively smaller effect on mesenteric circulation, such as dobutamine, low-dose dopamine, and milrinone, are preferred. Consider nasogastric decompression.
3. Anticoagulation is recommended in occlusive mesenteric ischemia.Evidence 1Strong recommendation (benefits clearly outweigh downsides; right action for all or almost all patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to the evidence being based on small case series. Joh JH, Kim DI. Mesenteric and portal vein thrombosis: treated with early initiation of anticoagulation. Eur J Vasc Endovasc Surg. 2005 Feb;29(2):204-8. PubMed PMID: 15649730. It may be the only treatment necessary in mesenteric venous thrombosis.
4. Endovascular treatment (local thrombolysis, percutaneous thrombectomy, balloon angioplasty, stenting) may be considered in selected patients without intestinal necrosis.Evidence 2Weak recommendation (benefits likely outweigh downsides, but the balance is close or uncertain; an alternative course of action may be better for some patients). Low Quality of Evidence (low confidence that we know true effects of the intervention). Quality of Evidence lowered due to variable results from retrospective studies that do not directly compare endovascular and open surgical procedures. Ryer EJ, Kalra M, Oderich GS, et al. Revascularization for acute mesenteric ischemia. J Vasc Surg. 2012 Jun;55(6):1682-9. doi: 10.1016/j.jvs.2011.12.017. Epub 2012 Apr 12. PubMed PMID: 22503176. Schermerhorn ML, Giles KA, Hamdan AD, Wyers MC, Pomposelli FB. Mesenteric revascularization: management and outcomes in the United States, 1988-2006. J Vasc Surg. 2009 Aug;50(2):341-348.e1. doi: 10.1016/j.jvs.2009.03.004. Epub 2009 Apr 16. PubMed PMID: 19372025; PubMed Central PMCID: PMC2716426. In the case of arterial vasospasm or NOMI found on arteriography, intra-arterial administration of vasodilators may be considered if the patient is not responding to conservative management.
5. Early surgical treatment is indicated if perforation or infarction is suspected. Otherwise surgical treatment is usually reserved for failure of nonoperative management, as endovascular procedures are increasingly performed for revascularization. The goals of surgery include assessment of bowel viability, resection of the nonviable bowel, and revascularization. Revascularization options include embolectomy in patients with embolism and thrombectomy or bypass anastomosis in patients with mesenteric artery thrombosis.
In patients with intestinal necrosis mortality rates are up to 90%. However, with early surgical intervention, mortality decreases to ~10% if the patient is operated within 24 hours. Comorbidities, age, and etiology also affect mortality; patients with arterial occlusions have worse survival rates.