Ischaemic Colitis

Ischaemic colitis is a medical condition where inflammation and injury of the large intestine occur due to inadequate blood supply. This condition is uncommon in the general population but is more frequent in the elderly and is the most common form of bowel ischaemia.

Causes include systemic changes like low blood pressure or local factors such as blood vessel constriction or blood clots. Often, no specific cause is identified.

Signs and Symptoms

Three progressive phases of ischaemic colitis have been identified:

1. Hyperactive Phase: Characterised by severe abdominal pain and the passage of bloody stools. Many patients recover and do not progress beyond this phase.
2. Paralytic Phase: If ischaemia continues, this phase follows with widespread abdominal pain, tenderness, decreased bowel motility, abdominal bloating, and absent bowel sounds.
3. Shock Phase: Fluids leak through the damaged colon lining, leading to shock and metabolic acidosis with dehydration, low blood pressure, rapid heart rate, and confusion. Patients are often critically ill in this phase and require intensive care.

Common early signs include left-sided abdominal pain and mild to moderate rectal bleeding. Other findings among patients include abdominal pain (78%), lower gastrointestinal bleeding (62%), diarrhoea (38%), and fever (34%).

Causes

Ischaemic colitis is classified based on the underlying cause.

Non-occlusive Ischaemia

This form develops due to conditions like low blood pressure or vessel constriction, often seen in haemodynamically unstable patients.

Occlusive Ischaemia

Typically caused by a thromboembolism, possibly resulting from conditions like atrial fibrillation, valvular disease, myocardial infarction, or cardiomyopathy. Ischaemic colitis is also a recognised complication of abdominal aortic aneurysm repair, especially when the origin of the inferior mesenteric artery is obstructed.

Pathophysiology

Colonic Blood Supply

The colon receives blood from both the superior and inferior mesenteric arteries, with abundant collateral circulation via the marginal artery of the colon. However, watershed areas like the splenic flexure and rectosigmoid junction are most vulnerable to ischaemia when blood flow decreases.

Development of Ischaemia

Under normal conditions, the colon receives 10-35% of the total cardiac output. Ischaemia develops if blood flow drops by more than 50%. The arteries feeding the colon are sensitive to vasoconstrictors, potentially leading to non-occlusive ischaemic colitis during periods of low blood pressure or due to vasoconstricting drugs.

Pathologic Findings

Pathologic findings range from mucosal and submucosal haemorrhage and oedema to transmural infarction with perforation. Reperfusion injury may also contribute to damage.

Diagnosis

Ischaemic colitis must be differentiated from other causes of abdominal pain and rectal bleeding. Devices testing colon oxygen delivery, like visible light spectroscopy, are used for diagnosis during procedures like aortic aneurysm repair.

Diagnostic Tests

There are no specific blood tests for ischaemic colitis. Plain X-rays and CT scans may suggest the diagnosis or identify complications. Endoscopic evaluation via colonoscopy or flexible sigmoidoscopy is the preferred method when the diagnosis remains unclear. Visible light spectroscopy can also assist in diagnosis.

Treatment

Most cases are treated with supportive care, including IV fluids and bowel rest. Cardiac function and oxygenation should be optimised. Antibiotics may be given in moderate to severe cases to prevent bacterial translocation. Surgical intervention is required if symptoms worsen.

Prognosis

Most patients recover fully, though the prognosis depends on the ischaemia's severity. Non-gangrenous ischaemic colitis has a mortality rate of approximately 6%. In contrast, gangrenous colitis has a higher mortality rate of 50-75% with surgical treatment.

Long-term Complications

Approximately 20% of patients may develop chronic ischaemic colitis, treated with surgical removal of the diseased bowel portion. Colonic strictures may heal spontaneously, but severe cases may require surgical resection or endoscopic dilatation and stenting.

Epidemiology

Ischaemic colitis is responsible for about 1 in 2000 hospital admissions and 1 in 100 endoscopies. It affects men and women equally, primarily occurring in individuals over 60 years old.

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Self-assessment MCQs (single best answer)

What is the primary cause of ischaemic colitis?

Which age group is most commonly affected by ischaemic colitis?

What characterises the hyperactive phase of ischaemic colitis?

Which diagnostic method is preferred when the diagnosis of ischaemic colitis remains unclear?

What percentage of patients with ischaemic colitis may develop chronic ischaemic colitis?

Which artery is NOT involved in the blood supply to the colon?

What is the mortality rate for non-gangrenous ischaemic colitis?

What is a common early sign of ischaemic colitis?

Which of the following is NOT a cause of occlusive ischaemia?

What type of care is typically provided for most cases of ischaemic colitis?