Chapter 3-8: Acute Mesenteric Ischemia

TEXTBOOK PRESENTATION

Acute mesenteric ischemia is a life-threatening condition that virtually always presents with the abrupt onset of acute severe abdominal pain that is typically out of proportion to a relatively benign physical exam. Acute mesenteric ischemia usually occurs in patients with risk factors of systemic embolization (eg, atrial fibrillation) or arterial thrombosis. Unexplained metabolic acidosis can be an important clue.

DISEASE HIGHLIGHTS

1. Etiology: Usually due to superior mesenteric artery or celiac artery embolism (50%). Other causes include thrombosis (15–25%), low flow states without obstruction (15–30%) (nonobstructive mesenteric ischemia), and mesenteric venous thrombosis (5%).

   1. Embolism

      1. Risk factors include atrial fibrillation, acute myocardial infarction, valvular heart disease, heart failure, ventricular aneurysms, angiography of abdominal aorta, and hypercoagulable states.

      2. The onset is often sudden without prior symptoms.

   2. Thrombosis

      1. Usually occurs in patients with atherosclerotic disease of the involved artery.

      2. Approximately half of such patients have a prior history of chronic mesenteric ischemia with intestinal angina.

   3. Nonobstructive mesenteric ischemia

      1. May have an insidious onset

      2. Often occurs in elderly patients with mesenteric atherosclerotic disease and superimposed hypotension (due to myocardial infarction, heart failure, dialysis, or sepsis). Alpha-agonists, digoxin, and beta-blockers may also increase the risk of nonobstructive mesenteric ischemia.

      3. Also seen in critically ill patients after cardiopulmonary bypass or other major surgery

      4. Other causes include cocaine use and following endurance exercise activities (eg, marathon, cycling).

   4. Mesenteric venous thrombosis is often secondary to portal hypertension, hypercoagulable states, and intra-abdominal inflammation.

2. Patients have acute abdominal pain that is often out of proportion to their abdominal exam. If left untreated, bowel infarction and peritoneal findings will develop.

3. Incidence: 0.1–0.3% of hospital admissions, 1% of patients presenting with abdominal pain, and up to 10% of patients > 70-years-old presenting with abdominal pain.

4. Mortality is high and increases with delay in treatment.

EVIDENCE-BASED DIAGNOSIS

1. Abdominal pain out of proportion to exam is a classic finding but is absent in 20–25%. Other common presenting symptoms are vomiting (71%) and diarrhea (42%).

2. 50% of patients have a prior history of intestinal angina.

3. Laboratory studies are nonspecific.

   1. The WBC is abnormal in 90% of patients and often markedly elevated (mean WBC 21.4 × 10⁹/mL).

   2. Lactate level has a sensitivity of 86% and specificity of 44%; LR+, 1.5; LR–, 0.32

A normal lactate level does not rule out acute mesenteric ischemia.

4. Standard CT scanning is insensitive for acute mesenteric ischemia (64%). It may demonstrate superior mesenteric artery occlusion or findings suggesting ischemic and necrosis such as segmental bowel wall thickening or pneumatosis. One study reported 100% sensitivity but patients were studied 3 days after symptom onset, when infarction may have been easier to demonstrate.

5. CT angiography is very accurate (93.3% sensitive, 95.9% specific), rapidly available and fast. It is the initial study prior to angiography. Magnetic resonance angiography has also been used.

   Routine CT scanning may not diagnose AMI. CTA is required.

6. Catheter angiography is the gold standard ...