IMPORTANT NOTE: JAAPA CME activities consist of 2 articles. To obtain credit, you must also read
Trigeminal neuralgia: Diagnosis and medical and surgical management; the post-test will include questions related to both articles. AAPA Fellow members should complete and submit the post-test on the AAPA Web site by going to
www.aapa.org and searching for keyword
JAAPA post-tests. All others may complete and submit the post-test online at no charge at
www.mycme.com. To obtain 1 hour of AAPA Category I CME credit, PAs must receive a score of 70% or better on each test taken.
KEY POINTS
■ Although relatively rare, mesenteric ischemia carries a high mortality rate, which ranges from 60% to 100% depending on the cause of the ischemia.
■ Mesenteric ischemia can be categorized as either acute or chronic.
■ Despite recent advancements in diagnostic technology, only one-third of patients with mesenteric ischemia present with the classic triad of abdominal pain, fever, and heme-positive stool. A positive outcome continues to depend on the clinician having a high index of suspicion and intervening promptly.
■ Angiography is the gold standard for diagnosing acute mesenteric ischemia because it is both diagnostic and potentially therapeutic when combined with emergent fibrinolytic intervention.
■ Supportive medical treatment is essential, and surgery is usually required as well.
Almost all PAs will encounter cases of mesenteric ischemia at some point during their career. Although relatively rare, accounting for 1 in every 1,000 hospital admissions, mesenteric ischemia carries a high mortality rate, which ranges from 60% to 100% depending on the cause of the ischemia.1,2 Recent data show that the true mortality rate of mesenteric ischemia may exceed 90%, and in only 33% of cases was the diagnosis considered prior to death.2 A high clinical suspicion is thus essential to reduce morbidity and mortality.
EPIDEMIOLOGY AND CAUSE
Mesenteric ischemia can be categorized as either acute or chronic (Table 1). Acute mesenteric ischemia (AMI) results from a diminution in the blood supply to the intestinal circulation that compromises the viability of the affected organs.3 An estimated one-third of AMI cases occur from arterial embolism, one-third from acute arterial thrombosis, and the remaining from nonocclusive and venous occlusive events.1 A recent review found that thrombosis of the arterial mesenteric blood supply accounts for only 15% to 30% of cases; when it does occur, however, the mortality rate is 90%.2
Because of its large intraluminal diameter and narrow take-off angle from the aorta, the superior mesenteric artery (SMA) is the intra-abdominal artery most susceptible to an occlusive event. Proximal SMA stenosis secondary to atherosclerosis increases this susceptibility.4 In an SMA occlusion, the mid-jejunum is at the highest risk of ischemic damage, primarily because of its distance from the collateral circulation of the celiac and inferior mesenteric arteries.4 In acute occlusion, collateral circulation is very limited, resulting in severe symptoms and rapid decompensation. Common risk factors for AMI are listed in Table 2.2 One study showed that patients with an in-hospital diagnosis of atrial fibrillation had an increased risk for thromboembolic events in the mesenteric arteries (a relative risk of 4.0 and 5.7 for men and women, respectively).5 In a review, 30% to 50% of AMI cases were attributed to emboli of the visceral vasculature of the intestines.4
Nonocclusive mesenteric ischemia (NOMI) usually occurs during periods of relative hypotension (or reduced flow), resulting in diminished blood supply to visceral vessels; hypovolemia with resultant hypoperfusion is typically a causative factor.3 Mesenteric venous thrombosis is more commonly associated with hypercoagulable states resulting from recent injury or surgery, prolonged bed rest, pregnancy, cancer, or inherited coagulopathies (Table 3). Chronic mesenteric ischemia (CMI) is defined as a continuous reduction in intestinal blood flow, more commonly due to severe stenosis or atherosclerotic plaque buildup in two or more mesenteric vessels. The occurrence of CMI is rarely associated with emboli.1 Chronic mesenteric ischemia is often asymptomatic; when signs and symptoms are present, they include abdominal pain after eating, avoidance of food to prevent pain, and weight loss.