What is the workup, treatment, and pathophysiology of ischemic colitis, including risk factors?

Ischemic Colitis: Workup, Treatment, and Pathophysiology

Pathophysiology

Ischemic colitis results from acute or chronic reduction in blood flow to the large intestine, representing the most common form of intestinal ischemia. 1, 2 The condition manifests as a spectrum of injury ranging from transient mucosal and submucosal ischemia to transmural infarction with necrosis. 2 The most common mechanism involves acute, self-limited compromise in intestinal blood flow, though the etiology is multifactorial. 2, 3

The "watershed areas" of the colon—including the splenic flexure, right colon, and rectosigmoid junction—are particularly vulnerable due to their relatively poor collateral circulation. 4 When blood flow is severely or persistently interrupted, progression to bowel necrosis and perforation can occur, leading to peritonitis and potentially death. 1

Risk Factors

• Advanced age is the primary demographic risk factor, as ischemic colitis is predominantly an illness of the elderly 1, 2
• Low flow states or shock, particularly cardiogenic shock, significantly increase risk 4
• Vasoconstrictor medications including cocaine, ergots, vasopressin, norepinephrine, and NSAIDs are associated with increased incidence 4
• Post-surgical states including coarctation repair or revascularization procedures 4
• Comorbidities in patients over 60 years correlate with higher mortality 4

Clinical Presentation

Patients typically present with the triad of abdominal pain (usually left-sided), bloody diarrhea, and abdominal tenderness over the affected bowel segment. 5, 1, 2

Key clinical features include:

• Bloody diarrhea ranging from streaks to frank bleeding, though hemodynamically significant bleeding is unusual 5, 2
• Urgency to defecate is frequently reported 5
• Mild abdominal pain and tenderness localized to the involved segment 2
• Fever, nausea, and vomiting may accompany the presentation 5

Warning Signs Requiring Urgent Intervention

Abdominal pain out of proportion to physical examination findings should immediately raise concern for mesenteric ischemia and potential transmural involvement. 5

Critical red flags include:

• Peritoneal signs (rebound tenderness, guarding) suggesting bowel necrosis or perforation 5
• Hemodynamic instability with tachycardia, hypotension, or shock 5
• Lactic acidosis indicating transmural ischemia and bowel necrosis 5, 1
• Marked leukocytosis suggesting significant inflammation or infection 5

Diagnostic Workup

Initial Laboratory Studies

Obtain complete blood count, comprehensive metabolic panel, serum lactate, and inflammatory markers, though none are specific for ischemic colitis. 5

• Elevated lactate is particularly concerning for transmural ischemia 5, 1
• Stool studies must be performed to exclude infectious causes including Clostridioides difficile, CMV, and other pathogens 4
• Fecal lactoferrin and calprotectin can help stratify patients and determine urgency of endoscopy 4

Imaging

CT angiography of the abdomen and pelvis with intravenous contrast is the first-line imaging modality for suspected ischemic colitis. 5, 6

CT findings include:

• Bowel wall thickening in the affected segment 4
• Mesenteric vessel engorgement 4
• Fluid-filled colonic distention 4
• High sensitivity for detecting vascular abnormalities and signs of bowel ischemia 5
• Prognostic value in determining severity and distribution 6

However, CT patterns are indistinguishable from other forms of colitis (infectious, inflammatory), limiting specificity. 4 Plain radiographs and ultrasound are insufficiently sensitive and specific for definitive diagnosis in this population. 4

Endoscopy

Colonoscopy is the gold standard for diagnosis and should be performed within 48 hours in all but fulminant cases. 6, 2, 7

• Flexible sigmoidoscopy may be adequate as approximately 95% of patients have inflammation in the left colon, though the descending colon is most commonly involved 4
• Endoscopic findings include mucosal erythema, edema, ulceration, and hemorrhagic nodules 4
• Biopsy provides histological confirmation showing mucosal and submucosal necrosis, hemorrhage, and inflammatory infiltrates 6, 7
• Early endoscopy (within 7 days) is associated with shorter symptom duration and reduced steroid treatment duration 4

The rectum is typically spared in ischemic colitis, which helps distinguish it from other colitides. 4

Treatment

Conservative Management (Majority of Cases)

Most patients with non-gangrenous ischemic colitis improve with conservative management within 1-2 days and experience complete resolution. 1, 2, 3

The mainstay of treatment includes:

• Bowel rest with nothing by mouth 1, 2
• Intravenous fluid resuscitation to optimize hemodynamic status 1, 2
• Avoidance of vasoconstrictive medications including NSAIDs, vasopressors when possible, and other agents that may worsen ischemia 5, 1, 2
• Empiric broad-spectrum antibiotics to prevent bacterial translocation 1, 6, 2
• Correction of electrolyte abnormalities and anemia 4
• Thromboprophylaxis with subcutaneous low-molecular-weight heparin 4

Surgical Intervention

Twenty percent of patients will develop peritonitis or deteriorate despite conservative management and require urgent surgery. 2

Indications for surgical intervention:

• Peritoneal signs indicating perforation or necrosis 5, 2
• Hemodynamic instability despite resuscitation 5
• Clinical deterioration after 24-48 hours of conservative therapy 6, 2
• Gangrenous ischemic colitis with transmural infarction 3

Surgical treatment consists of resection of nonviable bowel, with consideration for "second look" operations 24-48 hours later to avoid excessive resection while ensuring all nonviable tissue is removed. 4

Monitoring and Follow-up

Close monitoring is essential with joint medical and surgical management. 4

• Daily physical examination to assess for peritoneal signs 4
• Vital signs monitored four times daily or more frequently if deterioration occurs 4
• Stool chart documenting frequency and character of bowel movements 4
• Serial laboratory studies (CBC, inflammatory markers) every 24-48 hours 4
• Repeat imaging if clinical deterioration or colonic dilatation (transverse colon >5.5 cm) develops 4

Prognosis and Complications

Most cases of transient, non-gangrenous ischemic colitis resolve spontaneously without complications. 3, 7 However, severe ischemia carries high morbidity and mortality, with overall mortality averaging approximately 70% in acute intestinal ischemia requiring surgical intervention. 4

Potential complications include:

• Bowel perforation and peritonitis 7
• Persistent bleeding 7
• Protein-losing colopathy 7
• Symptomatic intestinal strictures requiring surgical resection 7
• Progression to gangrene with transmural necrosis 3

The key to improved outcomes is early recognition and prompt initiation of appropriate therapy, as delayed diagnosis is associated with significantly worse prognosis. 4, 6