Pocket Medicine

GASTROENTEROLOGY

INTESTINAL ISCHEMIA

ACUTE MESENTERIC ISCHEMIA (25%)

Etiologies

•  SMA embolism (50%): from LA (AF), LV (↓ EF) or valves; SMA most prone to embolism

•  Nonocclusive mesenteric ischemia (25%): transient intestinal hypoperfusion due to ↓ CO, atherosclerosis, sepsis, drugs that ↓ gut perfusion (pressors, cocaine, dig, diuretics)

•  SMA thrombosis (10%): usually at site of atherosclerosis, often at origin of artery

•  Venous thrombosis (10%): hypercoagulable states, portal hypertension, IBD, malignancy, inflammation (pancreatitis, peritonitis), pregnancy, trauma, surgery

•  Focal segmental ischemia of the small bowel (<5%): vascular occlusion to small segments of the small bowel (vasculitis, atheromatous emboli, strangulated hernias, XRT)

Clinical manifestations

•  Occlusive: sudden abd pain out of proportion to abdominal tenderness on exam at leastinitially (2–4 h) until severe ischemia → frank infarction w/ peritoneal signs

•  Nonocclusive: abd distention & pain, though up to 25% may be pain-free,  N/V; often in setting of CHF ± h/o chronic mesenteric ischemia sx

•  Hematochezia due to mucosal sloughing (right colon supplied by SMA)

•  “Intestinal angina”: postprandial abd pain, early satiety, & ↓ wt from gastric vascular “steal”; may occur wks to mos before onset of acute pain in Pts w/ chronic mesenteric ischemia

Physical exam

•  May be unremarkable, or may only show abdominal distention;  FOBT ~75% of Pts

•  Bowel infarction suggested by peritoneal signs (diffuse tenderness, rebound, guarding)

Diagnostic studies

•  Dx relies on high level of suspicion; rapid dx essential to avoid infarction (occurs w/in h)

•  Laboratory: often nl; ~75% ↑ WBC; ↑ amylase, LDH, phosphate, D-dimer; ~50% acidosis w/ ↑ lactate (late)

•  KUB: nl early before infarct; “thumbprinting,” ileus, pneumatosis in later stages

•  CT angiography (arterial phase imaging): noninvasive test of choice; can detect thrombi in mesenteric vessels, colonic dilatation, bowel wall thickening, pneumatosis/ portal venous gas; venous phase imaging for dx of mesenteric vein thrombosis

•  Angiography: gold standard; potentially therapeutic; indicated if vasc occlusion suspected

Treatment

•  Fluid resuscitation, optimize hemodynamics (minimize pressors); broad-spectrum abx

•  Emergent surgery for prompt resection of necrotic bowel if evidence of peritonitis

•  Anticoagulation for arterial & venous thrombosis and embolic disease

•  Papaverine (vasodilator) catheter-directed infusion into SMA, typically in nonocclu- sive ischemia when spasm is considered the primary cause of the ischemia

•  SMA embolism: consider fibrinolytic; if no quick improvement → surgical embolectomy if possible, o/w aortomesenteric bypass

•  SMA thrombosis: percutaneous or surgical revascularization (J Vasc Surg 2009;50:341)

•  Nonocclusive: correct underlying cause (esp. cardiac)

•  Consider angioplasty/stent vs. surg revasc in cases of chronic mesenteric ischemia if: ≥2 vessels or occl SMA, supportive clinical hx, & other etiologies for abd pain excluded

Prognosis

•  Mortality 20 to >70% if bowel infarcted; dx prior to infarction strongest predictor of survival

ISCHEMIC COLITIS (75%)

Definition & pathophysiology

•  Nonocclusive disease 2° to Ds in systemic circulation or anatomic/fxnal Ds in local mesenteric vasculature; often underlying etiology unknown, frequently seen in elderly

•  “Watershed” areas (splenic flexure & rectosigmoid) most susceptible, 25% involve R side

Clinical manifestations, diagnosis, & treatment

•  Disease spectrum: reversible colopathy (35%), transient colitis (15%), chronic ulcerating colitis (20%), resulting stricture (10%), gangrene (15%), fulminant colitis (<5%)

•  Usually p/w cramping LLQ pain w/ overtly bloody stool; fever and peritoneal signs should raise clinical suspicion for infarction

•  Dx: r/o infectious colitis; consider flex sig/colonoscopy if sx persist and no alternative etiology identified (only if peritonitis not present, o/w avoid overdistention of colon)

•  Treatment: bowel rest, IV fluids, broad-spectrum abx, serial abd exams; surgery for infarction, fulminant colitis, hemorrhage, failure of med Rx, recurrent sepsis, stricture

•  Resolution w/in 48 h w/ conservative measures occurs in >50% of cases