Ischaemic bowel can be classified anatomically into ischaemia of small bowel (mesenteric ischaemia) and large bowel (ischaemic colitis). Both conditions may be caused by:
- arterial thromboembolism
- non-occlusive ischaemia (due to hypoperfusion, vasospasm)
- venous thrombosis.
They may be acute or chronic.
This pathway deals with acute mesenteric ischaemia and acute ischaemic colitis. Diagnosis of both conditions is challenging and requires a high index of clinical suspicion.
Table 1: Differentiating acute mesenteric ischemia from acute colonic ischemia1
| Acute mesenteric ischaemia | Acute colonic ischaemia |
|---|---|
Age varies with etiology of ischemia | 90% of patients over 60 years |
Acute precipitating cause is typical | Acute precipitating cause is rare |
Patients appear seriously ill | Patients do not appear severely ill |
Pain is usually severe, tenderness is not prominent early | Mild abdominal pain, tenderness present |
Bleeding uncommon until very late | Rectal bleeding. Bloody diarrhoea typical |
Acute mesenteric ischaemia
Mesenteric ischemia is a medical emergency and will often lead to bowel necrosis. Early diagnosis and intervention are key. Mortality for patients undergoing revascularisation ranges from 44% to 90%.
Treatment pathway
Step 1: Pathway entry
Severity of abdominal pain out of proportion to physical findings.
May be associated with shock from dehydration and excessive fluid loss - mental confusion, tachycardia, tachypnoea and circulatory collapse.
In bowel infarction - peritoneal signs, haemodynamic instability, signs of sepsis with multiorgan failure.
Risk factors to consider for arterial thromboembolism:
- Age >60
- Atrial fibrillation
- Recent acute myocardial infarction
- Valvular heart disease
- Aortic atherosclerosis or aneurysm
- Aortoiliac instrumentation or surgery.
Venous thrombosis is uncommon. It occurs in younger patients. Risk factors include:
- hypercoagulable states
- dehydration
- portal hypertension
- abdominal infections
- blunt abdominal trauma
- pancreatitis
- splenectomy
- malignancy in the portal region.
Step 2: Patient stabilisation
Initiate resuscitation measures. IV fluid resuscitation with crystalloids and blood products should be started promptly to correct the volume deficit and metabolic derangement.
Consider other life- threatening diagnoses:
- acute pancreatitis
- perforated viscus
- ruptured abdominal aortic aneurysm (AAA)
- septic shock from intra-abdominal source.
Step 3: Initial assessment
History and examination concurrent with resuscitation.
Bedside tests:
- 12 lead ECG
- Venous blood gases
- Focused assessment with sonography in trauma (FAST) to rule out ruptured AAA if this is a differential.
An elevated or rising lactate is suggestive of ischaemic bowel. However it is non-specific and a normal lactate does not exclude the diagnosis (sensitivity 77-100%, specificity 42%).
A systematic review reported a pooled sensitivity for l-lactate for acute mesenteric ischemia of 86% and a pooled specificity of 44%.
The specificity of an elevated serum lactate level does improve significantly when conditions such as shock, diabetic ketoacidosis and renal and hepatic failure can be excluded.1
Blood tests should include:
- full blood count
- urea and electrolytes tests
- liver function tests
- lipase
- coagulation profile
- group and hold.
Normal D-dimer levels may help to exclude acute intestinal ischemia, but elevated levels are less useful for making a diagnosis. However, elevated levels can also be seen in a variety of conditions, such as in patients with acute pancreatitis and those with an abdominal aortic aneurysm.
In a systematic review, the pooled sensitivity for D-dimer for acute mesenteric ischemia was 96 % with a pooled specificity of 40%.1
Step 4: Imaging
X-rays not diagnostic of ischaemic bowel but may help in exclusion of differential diagnoses.
Abdominal x-ray, if done, may show thumbprinting or thickening of bowel loops (40% of ischaemic gut), air in the portal vein is a late finding.
CT scan may show:
- focal or segmental bowel wall thickening
- intestinal pneumatosis with portal vein gas
- bowel dilation
- mesenteric stranding
- portomesenteric thrombosis, or
- solid organ infarction.
It may also rule out other causes of acute abdominal pain.
The CT scan should be performed without oral contrast, which can obscure the diagnosis.
CT is preferred over MRI because of its lower costs, speed and wide availability. However, MR angiography may be more sensitive for the diagnosis of mesenteric venous thrombosis and may be necessary for those with an allergy to iodinated contrast.
If the diagnosis is still in question then options are:
- laparotomy (which may be diagnostic and therapeutic).
- arteriography (facilitates therapies such as vasodilators or thrombolytic agents, angioplasty, placement of a vascular stent, and embolectomy).
Step 5: Management
Early notification of surgeons and intensive care unit (and interventional radiology if appropriate).
Early laparotomy or arteriography.
Broad spectrum IV antibiotics (ampicillin and gentamicin or 3rd generation cephalosporin and metronidazole).
IV heparin if no contraindications to anticoagulation.
Supportive measures:
- fluid resuscitation
- oxygen to correct hypoxia
- analgesia
- nasogastric tube for gastric decompression.
Ischaemic colitis
Ischaemic colitis is usually not related to blood vessel occlusion but to a compressive lesion in the large bowel (e.g. colon carcinoma, stricture, diverticulosis, faecal impaction).
Approximately 15% of patients with colonic ischemia develop necrotic bowel. this can have life-threatening consequences. Rapid diagnosis and treatment is imperative. Most cases of colonic ischemia are usually transient and resolve without sequelae. However, some patients will have a more prolonged course or develop long-term complications, such as stricture or chronic ischemic colitis.1
Treatment pathway
Step 1: Pathway entry
- Mild-moderate abdominal pain, often left sided. Pain is not as severe as that of mesenteric ischaemia.
- diarrhoea
- per rectal bleeding.
Risk factors are similar to those for mesenteric ischaemia.
Step 2: Patient stabilisation
Commence resuscitation measures if unstable.
Consider other life-threatening diagnoses:
- aortoenteric fistula
- ruptured AAA
- perforated viscus
- septic shock from intraabdominal source (e.g. diverticulitis).
Step 3: Initial assessment
History and examination concurrent with resuscitation.
Bedside tests:
- 12 lead ECG
- Venous blood gases
- Focused assessment with sonography in trauma (FAST) to rule out ruptured AAA if this is a differential.
An elevated or rising lactate is suggestive of ischaemic bowel but not specific.
Blood tests should include:
- full blood count
- urea and electrolytes tests
- liver function tests
- lipase
- coagulation profile
- group and hold.
Step 4: Imaging
Abdominal X-rays non-specific, may show distension, pneumatosis, thumbprinting.
CT abdomen with IV contrast: non-specific and may be normal. May show:
- segmental bowel wall thickening
- pneumatosis
- mesenteric vein
- hepatic portal vein gas.
Arteriography rarely helpful (unless small bowel ischaemia needs to be excluded).
If diagnosis unclear then will require colonoscopy.
Step 5: Management
Supportive measures:
- IV fluids
- oxygen to correct hypoxia
- analgesia
- nasogastric tube if ileus present.
Broad spectrum IV antibiotics (ampicillin and gentamicin or 3rd generation cephalosporin and metronidazole).
Anticoagulant therapy is not normally indicated except for patients who develop ischemia due to mesenteric venous thrombosis or due to cardiac embolisation.
Patients with colonic infarction and necrosis require urgent surgical intervention, which can be lifesaving.
Change log
| Date | Section updated | Change |
|---|---|---|
| June 2024 | Table 1 | Updated characteristics |
| June 2024 | Acute mesenteric ischaemia | Pathophysiology section removed. Updated text in Step 3 and 4 of treatment pathway. |
| June 2024 | Acute ischaemic colitis | Introduction updated. Pathophysiology section removed. |
| June 2024 | Omental infarction | Section removed. |
References
- UptoDate. Overview of intestinal ischemia in adults. Ver.34.0, 29 Jan 2024 [cited 20 Jun 2024].
Accessed from the Emergency Care Institute website at https://aci.health.nsw.gov.au/networks/eci/clinical/tools/ischaemic-bowel