Overview
Acute Mesenteric Ischaemia
1. Clinical Overview
Summary
Acute mesenteric ischaemia (AMI) is sudden reduction of blood flow to the intestines, causing bowel infarction if not treated urgently. Causes include arterial embolism (most common — often from AF), arterial thrombosis, mesenteric venous thrombosis, and non-occlusive mesenteric ischaemia (NOMI). Classic presentation is severe abdominal pain out of proportion to physical findings. CT angiography is the gold standard. Treatment is emergency revascularisation and/or bowel resection. Mortality is high (50-70%) if diagnosis is delayed.
Key Facts
- Classic presentation: Severe pain "out of proportion" to examination
- Causes: Arterial embolism (AF), arterial thrombosis (atherosclerosis), venous thrombosis, NOMI
- Investigation: CT angiography (gold standard)
- Treatment: Resuscitation + anticoagulation + surgery (embolectomy/bypass + bowel resection)
- Mortality: 50-70% (diagnosis often delayed)
Clinical Pearls
"Pain out of proportion to examination" + AF = think SMA embolism
Lactate elevation and metabolic acidosis are late signs — don't wait for these to act
Early CT angiography is life-saving — have a low threshold
Why This Matters Clinically
AMI is a vascular emergency with very high mortality. The classic presentation is often missed because early examination is unremarkable. A high index of suspicion saves lives.
2. Epidemiology
Visual assets to be added:
- Mesenteric vascular anatomy diagram
- CT angiography showing SMA occlusion
- AMI causes comparison table
- Management algorithm
Epidemiology
Incidence
- 1-2 per 100,000/year
- Increasing with ageing population
- Accounts for 0.1% of hospital admissions
Demographics
- Elderly (mean age 70s)
- Patients with AF, cardiovascular disease
- Critical illness (NOMI)
Causes
| Cause | Frequency | Notes |
|---|---|---|
| Arterial embolism | 40-50% | Usually SMA; AF, recent MI, valve disease |
| Arterial thrombosis | 20-30% | Atherosclerotic disease; may have chronic symptoms |
| Venous thrombosis | 10-15% | Hypercoagulable states, portal hypertension |
| NOMI | 20% | Critical illness, shock, vasopressors |
3. Pathophysiology
Mechanism
- Sudden reduction in mesenteric blood flow
- Intestinal mucosal ischaemia → mucosal sloughing
- Full-thickness bowel wall infarction
- Bacterial translocation → sepsis
- Bowel perforation → peritonitis
Arterial Anatomy
- Superior mesenteric artery (SMA) supplies jejunum, ileum, right colon
- Inferior mesenteric artery (IMA) supplies left colon
- SMA occlusion is most common and most devastating
Why "Pain Out of Proportion"
- Early ischaemia causes visceral pain (severe) but minimal peritoneal irritation
- Examination is initially unremarkable
- Peritonism occurs only after transmural infarction (late finding)
NOMI Mechanism
- Low cardiac output states (cardiogenic shock, sepsis)
- Vasopressor use → mesenteric vasoconstriction
- No occlusion — ischaemia from low flow
4. Clinical Presentation
Symptoms
Signs — Early
Signs — Late (Bowel Infarction)
Red Flags
| Finding | Significance |
|---|---|
| AF + sudden abdominal pain | SMA embolism |
| Metabolic acidosis | Bowel ischaemia/infarction |
| Elevated lactate | Late sign — tissue necrosis |
| Peritonism | Transmural infarction — poor prognosis |
Severe abdominal pain — diffuse, poorly localised
Common presentation.
Sudden onset (embolism) or subacute (thrombosis, venous)
Common presentation.
Nausea, vomiting
Common presentation.
Diarrhoea (may be bloody — late sign)
Common presentation.
History of "fear of eating" (chronic mesenteric ischaemia)
Common presentation.
5. Clinical Examination
Early
- Tachycardia
- Abdominal tenderness (mild, diffuse)
- Soft abdomen — deceptively normal
Late
- Fever
- Hypotension (shock)
- Abdominal distension
- Peritonism (guarding, rigidity)
- Absent bowel sounds
- PR: Blood on glove
6. Investigations
Blood Tests
| Test | Finding |
|---|---|
| WCC | Elevated |
| Lactate | Elevated (late sign) |
| ABG | Metabolic acidosis (late) |
| Amylase | May be elevated |
| LDH, D-dimer | Elevated (non-specific) |
| U&E | AKI |
Imaging
| Modality | Role |
|---|---|
| CT angiography | Gold standard; shows occlusion, bowel wall changes |
| Plain AXR | Late signs — thumbprinting, pneumatosis, portal venous gas |
| Conventional angiography | Diagnostic and therapeutic (rarely first-line now) |
CT Findings
| Finding | Significance |
|---|---|
| SMA occlusion | Confirms diagnosis |
| Bowel wall thickening | Ischaemia |
| Bowel wall enhancement loss | Infarction |
| Pneumatosis intestinalis | Air in bowel wall — late/severe |
| Portal venous gas | Very poor prognosis |
Classification & Staging
By Cause
| Type | Mechanism |
|---|---|
| Arterial embolism | Thrombus from heart (AF, valve) lodges in SMA |
| Arterial thrombosis | Atherosclerotic plaque in SMA |
| Venous thrombosis | SMV/portal vein thrombosis |
| NOMI | Low-flow state, no occlusion |
By Severity
- Reversible ischaemia (early)
- Irreversible infarction (late)
7. Management
Immediate Resuscitation
| Action | Details |
|---|---|
| IV access | Large bore |
| IV fluids | Aggressive resuscitation |
| NBM | Nil by mouth |
| NG tube | Decompress |
| Urinary catheter | Monitor output |
| Analgesia | IV opioids |
| Anticoagulation | IV heparin (unless contraindicated) |
| Broad-spectrum antibiotics | Cover bacterial translocation |
Surgical Management
Arterial Occlusion:
- Emergency laparotomy
- SMA embolectomy or bypass
- Assess bowel viability
- Resect non-viable bowel
- Second-look laparotomy 24-48 hours
Venous Thrombosis:
- Anticoagulation (may be mainstay)
- Surgery if peritonitis/infarction
NOMI:
- Treat underlying cause (optimise cardiac output)
- Vasodilators (papaverine) via angiography
- Surgery if infarction
Endovascular Options
- Catheter-directed thrombolysis
- Mechanical thrombectomy
- Stenting (in selected cases)
Second-Look Laparotomy
- Recommended 24-48 hours after initial surgery
- Reassess bowel viability
- Further resection if needed
8. Complications
Of AMI
- Bowel infarction
- Perforation
- Peritonitis
- Sepsis
- Multi-organ failure
- Short bowel syndrome (if extensive resection)
- Death
Of Treatment
- Bleeding
- Reperfusion injury
- Anastomotic leak
- Stoma complications
9. Prognosis & Outcomes
Mortality
- Overall 50-70%
- Higher if diagnosis delayed beyond 12-24 hours
- Lower with early revascularisation
Factors Affecting Outcome
- Time to diagnosis and surgery
- Extent of bowel infarction
- Patient age and comorbidities
- Cause (NOMI has highest mortality)
Survivors
- May have short bowel syndrome
- Need long-term anticoagulation if embolic cause
10. Evidence & Guidelines
Key Guidelines
- ESVS Clinical Practice Guidelines on Acute Mesenteric Ischaemia
- World Society of Emergency Surgery (WSES) Guidelines
Key Evidence
- Early CT angiography improves outcomes
- Revascularisation before bowel resection improves survival
11. Patient/Layperson Explanation
What is Acute Mesenteric Ischaemia?
This is when the blood supply to part of the bowel is suddenly blocked. Without blood, the bowel can die, which is very serious.
Symptoms
- Severe abdominal pain that comes on suddenly
- Feeling very unwell
- Sometimes bloody diarrhoea
Treatment
- Emergency surgery to restore blood flow and remove any damaged bowel
- Blood thinning medication
What Happens Next?
- Recovery in intensive care
- Some patients may need further surgery
Resources
12. References
Primary Guidelines
- Bjorck M, et al. Editor's Choice – Management of the Diseases of Mesenteric Arteries and Veins: Clinical Practice Guidelines of the ESVS. Eur J Vasc Endovasc Surg. 2017;53(4):460-510. PMID: 28359440
Key Reviews
- Clair DG, Beach JM. Mesenteric Ischemia. N Engl J Med. 2016;374(10):959-968. PMID: 26962730
- Bala M, et al. Acute mesenteric ischemia: guidelines of the World Society of Emergency Surgery. World J Emerg Surg. 2017;12:38. PMID: 28794797