How should I work up an adult with acute severe abdominal pain out of proportion to exam and risk factors such as atrial fibrillation, recent myocardial infarction, atherosclerotic disease, heart failure, or hypercoagulable state for suspected bowel ischemia?

Work-up for Bowel Ischemia

In an adult with acute severe abdominal pain out of proportion to exam findings and risk factors such as atrial fibrillation, recent MI, atherosclerotic disease, heart failure, or hypercoagulable state, immediately obtain a triple-phase CT angiography (CTA) of the abdomen and pelvis—this is the gold standard diagnostic test with 95-100% sensitivity and specificity for detecting acute mesenteric ischemia. 1, 2

Clinical Recognition: High Index of Suspicion Required

Maintain an extremely high index of suspicion in patients with cardiovascular disease presenting with severe abdominal pain, as this is a Class I recommendation from the ACC/AHA. 1

Key Clinical Features to Identify:

• "Pain out of proportion to physical findings" is the pathognomonic presentation—severe periumbilical abdominal pain with initially absent peritoneal signs 1, 2
• Approximately 50% of embolic acute mesenteric ischemia patients have atrial fibrillation 1, 2
• One-third have prior history of arterial embolus 1
• Recent myocardial infarction is a major risk factor for arterial thrombosis 1
• Median age is 70 years, with two-thirds being women 1
• The triad of abdominal pain, fever, and hemocult-positive stools occurs in approximately one-third of patients 1

Laboratory Evaluation: Supportive but Not Diagnostic

No laboratory test can confirm or exclude bowel ischemia, but certain findings support the diagnosis and indicate disease severity. 1

Order These Labs Immediately:

• Serum lactate: Elevated levels >2 mmol/L associated with irreversible intestinal ischemia (Hazard Ratio 4.1), though elevation can occur from dehydration alone 1, 2
• Complete blood count: Leukocytosis present in >90% of cases 1
• D-dimer: If normal, essentially excludes intestinal ischemia; if >0.9 mg/L, has 82% specificity and 60% sensitivity 1
• Metabolic panel: Metabolic acidosis present in 88% of cases 1
• Amylase: Elevated in approximately 50% of patients 1
• Stool occult blood: Positive in approximately 25% of patients 1

Critical pitfall to avoid: The combination of lactic acidosis with abdominal pain in a patient who does not otherwise appear clinically ill should prompt immediate CTA, not reassurance. 1

Imaging: The Definitive Diagnostic Step

First-Line Imaging: Triple-Phase CT Angiography

CT angiography with non-contrast, arterial, and portal venous phases is the single best test and should be performed immediately. 1, 2, 3

Why Triple-Phase Protocol is Essential:

• Non-contrast phase: Detects intramural hyperdensity suggesting hemorrhage or ischemia 3
• Arterial phase: Identifies arterial stenosis, embolism, thrombosis, or dissection in the superior mesenteric artery (SMA) 1, 3
• Portal venous phase: Detects mesenteric vein thrombosis 3
• Simultaneous evaluation: Assesses both mesenteric vasculature and bowel viability to guide whether patient needs immediate surgery versus endovascular intervention 1, 2

Critical Imaging Findings to Identify:

• Arterial occlusion or filling defects in the SMA (present in 40-50% of embolic cases) 1, 2, 3
• Bowel wall thickening with abnormal enhancement 3
• Pneumatosis intestinalis or portal/mesenteric venous gas (late findings indicating infarction) 1, 3
• Mesenteric edema and ascites 3
• Atherosclerotic disease of intestinal arteries 1

Another critical pitfall to avoid: Do not delay CTA due to elevated creatinine—the mortality risk of missing acute mesenteric ischemia (30-90%) far outweighs the risk of contrast-induced nephropathy. 2

What NOT to Order:

Plain abdominal radiography is strongly contraindicated as the primary diagnostic test. 1, 2

• 25% of patients with acute mesenteric ischemia have completely normal radiographs 1, 2
• Findings appear only after bowel infarction has occurred, associated with high mortality 1, 2
• Most commonly shows nonspecific dilated loops of intestine 1
• Has low diagnostic yield and cannot exclude the diagnosis 1

Duplex ultrasound of the abdomen is contraindicated for suspected acute intestinal ischemia (Class III recommendation). 1

• Requires ideal conditions (fasting patients, early morning examinations) that are not present in acute settings 1
• Abdominal distention and fluid present with acute ischemia preclude successful scanning 1
• Time required to attempt scanning delays emergent treatment 1

Barium enema has absolutely no role in acute mesenteric ischemia evaluation, as it does not visualize mesenteric vessels and delays definitive diagnosis. 2

Alternative Imaging if CTA Contraindicated:

MR angiography (MRA) is the alternative if CTA cannot be performed, offering similar 95-100% sensitivity and specificity for grading mesenteric vessel stenosis. 2 However, MRA is limited in evaluating ischemic bowel changes such as pneumatosis or portal venous gas compared to CT. 1

Conventional catheter angiography should be reserved for cases where CTA is negative yet clinical suspicion remains high, or when endovascular intervention is planned. 2

Immediate Management While Awaiting Imaging

Start these interventions immediately upon clinical suspicion, before imaging is completed: 2, 3

• Aggressive fluid resuscitation 3
• Broad-spectrum antibiotics 3
• Systemic anticoagulation with intravenous unfractionated heparin 3
• Obtain surgical consultation immediately if any peritoneal signs are present 3

Treatment Algorithm Based on CTA Findings

Endovascular revascularization is first-line treatment for arterial occlusion without peritonitis. 2, 3

Emergency laparotomy is mandatory for: 2, 3

• Signs of bowel infarction or peritonitis
• Septic shock
• Markedly elevated lactic acid levels suggesting infarcted bowel

Most patients will still require laparotomy even if percutaneous therapy successfully relieves obstruction, because most have at least some nonviable intestine at presentation. 1

High-Risk Features Requiring Immediate Action

These findings mandate immediate surgical consultation before completing imaging: 3

• Any peritoneal signs on examination
• Age >75 years combined with leukocytosis and metabolic acidosis
• Elevated lactate suggesting advanced disease

Natural History and Prognosis

The natural history of acute intestinal ischemia without treatment is nearly always fatal, leading to infarction, perforation, peritonitis, and death in the vast majority of patients. 1 The mortality rate ranges from 30-90% even with treatment, making rapid diagnosis essential for survival. 1, 2