Acute Mesenteric Ischemia

• Margaret Tryforos, M.D.
• Paul George, M.D., M.H.P.E.

 Basic Information

Definition

Acute mesenteric ischemia (AMI) is the sudden onset of intestinal hypoperfusion to all or part of the small bowel caused by emboli, arterial or venous thrombosis (Fig. E1), or vasoconstriction from low-flow states.

Synonyms

1. AMI

2. Mesenteric ischemia, acute

ICD-10CM CODES
K55.0	Acute vascular disorders of intestine

Epidemiology & Demographics

Incidence

1. •

   AMI accounts for 0.1% of hospital admissions.

2. •

   The incidence appears to be increasing. Factors for this include increased awareness among clinicians, the aging of the population, and improved intensive care, leading to longer survival of sicker patients. The mortality rate is 60% to 85%.

Predominant Sex and Age

1. •

   AMI caused by arterial embolism or thrombosis occurs more frequently in the elderly.

2. •

   AMI due to mesenteric venous thrombosis often presents in younger age groups.

Genetics

No specific genetic predisposition but may be related to underlying factors such as cardiac disease, atherosclerosis, and hypercoagulable states.

Risk Factors

1. •

   Advanced age, atherosclerosis, low cardiac output (especially atrial fibrillation), severe cardiac valvular disease, intraabdominal malignancy.

2. •

   In the subgroup of cases caused by venous thrombosis, risk factors include hypercoagulable states, portal hypertension, abdominal infection, blunt trauma, pancreatitis, and portal malignancy.

3. •

   Additional risk factors for AMI caused by nonocclusive mesenteric ischemia include recent cardiac or aortic surgery, dialysis, hypovolemia, and vasoconstrictive medications (including illicit drugs such as cocaine).

4. •

   Table 1 summarizes risk factors for ischemic bowel disease.

   TABLE1 Risk Factors for Ischemic Bowel Diseases^∗From Adams JG et al: Emergency medicine, clinical essentials, ed 2, Philadelphia, 2013, Elsevier.

   Risk Factor	Arterial Thrombosis	Embolus	Mesenteric Vein Thrombosis	Nonobstructive Mesenteric Ischemia
   Advanced age	+	+	+	+
   Atherosclerosis	+
   Aortic dissection	+
   Low cardiac output	+	+		+
   Congestive heart failure				+
   Shock				+
   Severe dehydration	+		+
   Cardiac arrhythmias, especially atrial fibrillation		+		+
   Severe cardiac valvular disease		+
   Recent myocardial infarction	+			+
   Intraabdominal malignancy			+
   Abdominal trauma			+
   Intraabdominal infection			+
   Intraabdominal inflammatory conditions			+
   Parasitic infection (ascariasis)			+
   Hypercoagulable states (venous thrombosis)			+
   Sickle cell anemia			+
   Recent cardiac surgery	+	+		+
   Recent abdominal surgery			+
   Vascular aortic prosthetic grafts proximal to the superior mesenteric artery		+
   Hemodialysis				+
   Vasculitis	+		+
   Pregnancy			+
   Decompression sickness			+
   Blast lung caused by systemic air embolism		+
   Drugs that cause constriction
   • Digitalis				+
   • Cocaine				+
   • Amphetamines				+
   • Pseudoephedrine				+
   • Vasopressin			+†	+
   Estrogen therapy			+

5. •

   AMI may occur rarely in patients with no identifiable risk factors.

Physical Findings & Clinical Presentation

1. •

   The classic presentation is rapid onset of severe periumbilical pain “out of proportion to physical examination findings.” An epigastric bruit may be present in some patients. Generally, patients with mesenteric venous thrombosis tend to present with a less abrupt onset of abdominal pain than those with acute arterial occlusion.

2. •

   Nausea and vomiting are commonly associated.

3. •

   Initial abdominal examination may be normal, with no rebound or guarding, or may include minimal distention or stool positive for occult blood.

4. •

   Later in the course the patient may present with gross distention, absence of bowel sounds, and peritoneal signs. In the elderly, mental status changes may occur.

Etiology

The pathophysiology of the four different causes of acute mesenteric ischemia are summarized in Table 2. Causes and approximate frequencies of acute mesenteric ischemia are summarized in Table 3. The pathophysiologic mechanisms that cause AMI include:

1. •

   Mesenteric arterial embolism (40% to 50% of cases of AMI): typically from the left atrium, left ventricle, or cardiac valves. The superior mesenteric artery is most commonly affected.

2. •

   Mesenteric arterial thrombosis: often in patients with prior progressive atherosclerotic stenoses, with superimposed abdominal trauma or infection. Thrombotic occlusion of previously stenotic mesenteric vessels accounts for 20% to 35% of cases of AMI.

3. •

   Mesenteric venous thrombosis may occur in the setting of hypercoagulable states (acquired or inherited), blunt trauma, abdominal infection, portal hypertension, pancreatitis, and portal malignancy.

4. •

   Nonocclusive mesenteric ischemia is caused by reduced intestinal perfusion, as seen with hypotension, hypovolemia, vasoconstricting drugs, and hemodialysis.

5. •

   Dissection or inflammation of the mesenteric artery accounts for less than 5% of cases of AMI.

Diagnosis

Differential Diagnosis

Initially include other causes of abdominal pain of acute onset, including perforated peptic ulcer and early appendicitis, as well as the varied causes of peritonitis.

Workup

1. •

   Early diagnosis is key. Treatment success is related to the duration of symptoms prior to diagnosis.

2. •

   Consider early laparotomy for diagnosis in cases with a high index of suspicion when imaging is not readily available.

Laboratory Tests

1. •

   Laboratory test results are nonspecific, especially early in the course. Elevated lactic acid, leukocytosis, acidosis, and elevated hematocrit from hemoconcentration can occur later in the course, often after progression to bowel necrosis has occurred, hence are not useful for early diagnosis.

2. •

   When a hypercoagulable state is suspected, workup may include proteins C and S, antithrombin III, and factor V Leiden. This will likely not affect the diagnosis of AMI but may help guide long-term therapy.

3. •

   Amylase levels may be elevated in up to 50% of individuals with intestinal ischemia; phosphate levels may be elevated in up to 80% of affected individuals.

4. •

   Normal D-dimer testing may help rule out AMI. Elevated levels are nonspecific.

Imaging Studies

1. •

   Biphasic contrast-enhanced CT is the preferred diagnostic mode (Fig. E2). It is more easily available and has similar sensitivity to angiography, the prior gold standard test. Computed tomographic angiography (CTA) has 95% to 100% accuracy for the diagnosis of visceral ischemic syndromes and is also useful in detecting potential sources of emboli and other pathologic processes.

   

2. •

   Plain CT findings are nonspecific and more often found late in the course. Portal venous gas or intramural gas may be seen after the development of gangrene (Fig. 3). In many cases, CT findings remain nonspecific even at advanced stages.

   

3. •

   MR angiography (MRA) may be more useful in cases of mesenteric vein thrombosis causing AMI. It has also been found useful in monitoring the progress of patients with superior mesenteric venous thrombosis who are treated nonsurgically. MRA, however, takes longer than CTA to perform and can overestimate the degree of stenosis.

4. •

   Angiography may be considered if the diagnosis remains unclear after CT or MR imaging.

5. •

   Plain films are normal 25% of the time in early stages. Suggestive findings may include ileus (Fig. 4), bowel wall thickening, or intramural gas. Free air under the diaphragm may support early surgical intervention prior to further radiologic evaluation.

   

6. •

   Doppler ultrasound evaluation of intestinal blood flow is often limited by the presence of air-filled loops of bowel and is not an appropriate part of the diagnostic workup if AMI is the leading working diagnosis.

Treatment

1. •

   The goal of treatment is to restore blood flow to ischemic bowel as rapidly as possible before the occurrence of infarction.

2. •

   Treatment varies depending on etiology.

Acute General Rx

1. •

   Initial management should include hemodynamic monitoring and support, correction of acidosis, pain control (using parenteral opioids), administration of broad-spectrum antibiotics, and gastric decompression by nasogastric tube.

2. •

   Vasoconstricting agents should be avoided.

3. •

   In the absence of active bleeding, the use of systemic anticoagulation is usually indicated. The optimal timing of initiation is unclear.

Nonpharmacologic Therapy

1. •

   Signs of peritonitis mandate early laparotomy and resection of infarcted bowel.

2. •

   Specific management will depend on patient status and most likely etiology of the ischemia.

3. •

   When workup is positive for major superior mesenteric artery (SMA) embolus, embolectomy is considered standard treatment in the absence of peritoneal signs. Depending on the location and degree of occlusion of the embolus, surgical revascularization, intraarterial infusion of thrombolytics or vasodilators, or systemic anticoagulation may be considered.

4. •

   In cases of SMA thrombosis, emergency surgical revascularization is the treatment of choice; stent placement may be a viable alternative.

5. •

   Angiography is needed to diagnose nonocclusive mesenteric ischemia before infarct and should be followed up by intraarterial vasodilator infusion. This approach has been shown to reduce mortality rate significantly. Underlying risk factors for reduced blood flow should be assessed and mitigated.

6. •

   In patients with mesenteric vein thrombosis, treatment depends on the presence or absence of peritoneal signs. Laparotomy and resection of infarcted bowel is indicated in more advanced cases. If there are no peritoneal signs, immediate anticoagulant therapy with heparin, and ultimately warfarin, may be adequate treatment.

7. •

   In general, percutaneous treatment with lytic therapy, balloon angioplasty, or stenting may be limited by the frequent presence of nonviable bowel, which would require laparotomy despite success with percutaneous treatment.

8. •

   A “second look” procedure is indicated in most patients, 24-48 hours after initial revascularization.

Chronic Rx

1. •

   In the subgroup of patients with mesenteric venous thrombosis, prevention of further thrombosis is indicated. The optimal duration of anticoagulation is unclear.

2. •

   Patients who receive endovascular treatment should be managed with 1-3 months of clopidogrel; additionally, periodic surveillance for restenosis with duplex ultrasound or CTA is indicated.

Disposition

1. •

   Prognosis is best in AMI due to mesenteric venous thrombosis and after surgical treatment for acute arterial embolism. It remains poor in cases of arterial thrombosis and nonocclusive ischemia.

2. •

   With delayed diagnosis, intestinal infarction—resulting in perforation or gangrenous bowel, sepsis, shock, and death—is typical.

Referral

1. •

   Early surgical consultation should be considered. There should be no delay with peritoneal signs.

2. •

   Surgery may be warranted for diagnostic purposes.

Pearls & Considerations

Comments

1. •

   The diagnosis of AMI should be considered in any patient with acute onset of abdominal pain out of proportion to physical findings, particularly in at-risk patients.

2. •

   Early diagnosis, before intestinal infarction occurs, is critical and correlates with improved survival rates.

3. •

   The use of endovascular procedures for AMI is becoming more common and may be most appropriate for patients with ischemia that is not severe and for those who have severe coexisting conditions that place them at high risk for complications and death associated with open surgery.

Prevention

Prevention of underlying factors, most notably atherosclerotic disease (smoking cessation, management of hypertension, and use of statins) is indicated for primary prevention as well as prevention of recurrence.

Suggested Readings

• S. Acosta, M. Björck: Modern treatment of acute mesenteric ischaemia. Br J Surg. 101 (1):e100–e108 2014 Jan 24254428

• D.L. Clair, J.M. Beach: Mesenteric ischemia. N Engl J Med. 374:959–968 2016 26962730

• Zhao Y, et al.: Management of acute mesenteric ischemia: a critical review and treatment algorithm, Vasc Endovascular Surg 50:183–192, 2016.

Related Content

1. Mesenteric Venous Thrombosis (Related Key Topic)