Definition

Acute Mesenteric Ischaemia: Overview

• Definition: Sudden disruption of blood flow to intestines, primarily mesenteric vessels.
• Causes: Blood clot (thrombus) or blocked artery (embolism).
• Consequence: Inadequate blood supply leading to intestinal damage, tissue death, and life-threatening complications.
• Immediate Attention Required: Urgent medical intervention needed.
• Complications: Intestinal damage, tissue necrosis, life-threatening outcomes.

Aetiology

Common Causes of Acute Mesenteric Ischaemia

• Arterial Embolism (50%)
  • Risk Factors: Cardiac causes (e.g., AF, post-MI mural thrombosis, prosthetic heart valve), Abdominal/thoracic aneurysm.
• Arterial Thrombosis (25%)
  • Risk Factors: Atherosclerosis.
• Non-Occlusive Disease (20%)
  • Risk Factors: Low flow states (e.g., recent cardiac surgery, cardiac failure, renal failure), Hypovolaemic shock, Cardiogenic shock.
• Venous Thrombosis (<10%)
  • Risk Factors: Younger patients with hypercoagulable states, Malignancy, Inflammatory conditions (e.g., pancreatitis, diverticulitis), Trauma.

Risk Factors

Risk Factors for Acute Mesenteric Ischaemia

• Advanced Age
• Cardiovascular Disease (e.g., atherosclerosis)
• Atrial Fibrillation
• Hypercoagulable States
• History of Blood Clotting Disorders or Thrombosis
• Abdominal Surgery
• Aortic dissection or aneurysm
• Decreased cardiac output: myocardial infarction, heart failure

Pathophysiology

Acute Mesenteric Ischaemia: Pathophysiology

• Definition: Sudden reduction in blood flow to intestines, causing tissue hypoxia and ischemia.
• Obstruction: Mesenteric vessel blockage (arterial or venous) leads to diminished oxygen and nutrient delivery.
• Consequences:
  • Reduced oxygen supply causes tissue damage.
  • Prolonged interruption may lead to tissue necrosis if not treated.
• Severity: Depends on:
  • Extent of blood flow disruption.
  • Duration of interruption.

Differential Diagnosis

Differential Diagnosis of Acute Mesenteric Ischaemia

• Similar Conditions: Other causes of acute abdominal pain.
• Examples:
  • Abdominal aortic aneurysm.
  • Appendicitis
  • Biliary disease.
  • Chronic mesenteric ischaemia.
  • Cholecystitis
  • Diverticulitis.
  • Ectopic pregnancy.
  • Gastrointestinal perforation
  • Helicobacter pylori infection.
  • Intestinal obstruction
  • Multisystem organ failure due to sepsis.
  • Myocardial infarction.
  • Pancreatitis
  • Pneumonia.
  • Pneumothorax.
  • Acute intermittent porphyria.
  • Testicular torsion.

Epidemiology

Epidemiology of Acute Mesenteric Ischaemia

• Incidence: Approximately 1 in 100,000 population per year in the UK.
• Age: More common in individuals over 50 years of age, especially those over 60.
• Overall Incidence: Accounts for 0.09-0.2% of all hospital admissions.

Clinical Presentation

Clinical Presentation of Acute Mesenteric Ischemia:

• Varied clinical presentation
• Typical signs and symptoms:
  • Severe abdominal pain
  • Pain is disproportionate to physical findings
  • Sudden onset of pain
  • Tenderness upon examination
  • Nausea and vomiting
  • Signs of systemic illness:
    • Tachycardia
    • Hypotension

Diagnosis of Acute Mesenteric Ischemia:

• Patients present with:
  • Acute onset of severe generalized abdominal pain
  • Abdominal pain is disproportionately severe
  • Diffuse and constant pain
  • Nausea and vomiting in about 75% of cases

Presentation of Acute Mesenteric Ischemia Types:

• Presentation of various types is similar
• Common features:
  • Moderate-to-severe colicky or constant poorly localized pain
  • Physical findings are disproportionate to pain severity
  • Early stages may have minimal or no tenderness and no signs of peritonitis
  • Later stages exhibit typical peritonism symptoms:
    • Rebound guarding
    • Tenderness
  • Palpable mass may sometimes be present
  • Associated causes may be revealed upon examination (e.g., atrial fibrillation).

Investigations

Diagnostic Investigations for Acute Mesenteric Ischemia:

Blood Tests:

• ABG (Arterial Blood Gas):
  • Raised lactate and metabolic acidosis
• FBC (Full Blood Count):
  • Raised Hb (due to plasma loss)
  • Raised WCC (White Cell Count)
• U&Es (Urea and Electrolytes):
  • Monitor kidney function (especially urea, creatinine, and eGFR)
  • IV contrast used for CT angiography may impact kidney function
• LFTs (Liver Function Tests):
  • Raised AST and ALT (indicate poor prognosis)
• Clotting profile (especially important if the patient is on anticoagulation medication)
• Amylase: Rule out acute pancreatitis (may also be elevated in acute mesenteric ischemia)
• G&S (Group and Screen):
  • Prepare for potential blood transfusion during an urgent laparotomy
  • Crossmatch 4 units of blood if the patient is known to be anemic

Imaging:

• CT Angiography (Gold Standard)
• AXR (Abdominal X-ray):
  • May reveal small bowel obstruction, ileus, and thickened bowel wall (in later stages)
• Erect CXR (Chest X-ray):
  • Used if bowel perforation is suspected
• Ultrasound or MRI scan: May provide additional information
• Electrocardiogram (ECG):
  • May show atrial fibrillation or signs of infarction
• Echocardiogram: To investigate the cause of embolism or valvular pathology
• Intraoperative fluorescein administration: Highlights areas of bowel requiring resection

Key Points:

• Early diagnosis with CT angiography is crucial for lower mortality rates.
• No specific laboratory tests exist, but a raised white cell count and metabolic acidosis can be indicators.
• Plain abdominal X-ray and CT scans may show bowel abnormalities, gas in unusual locations (pneumatosis intestinalis), and signs of infarction.
• CT angiography with intravenous contrast is the preferred diagnostic tool.
• Ultrasound, MRI, ECG, and echocardiogram may be useful in specific cases.

Management

Management of Acute Mesenteric Ischaemia (UK):

• Treatment Goals: Restore blood flow, address underlying causes.

• Medical Interventions:
  • Initial resuscitation with IV fluids and oxygen.
  • Nasogastric tube placement.
  • Intravenous broad-spectrum antibiotics.
  • Intravenous unfractionated heparin if not contraindicated.

• Surgical Interventions:
  • Prompt laparotomy for patients with overt peritonitis.
  • Surgical goals: re-establish blood supply, resect non-viable regions, preserve viable bowel.
• Endovascular Procedures: Consider for partial arterial occlusion.

• Long-Term Management:
  • Lifelong therapy with anticoagulants or antiplatelet agents may be required.

• Mortality and Complications:
  • Mortality ranges from 50-80%, even with treatment.
  • Survivors may face short gut syndrome.

Emergencies and Immediate Management:

• Acute mesenteric ischaemia is a surgical emergency.
• Life-threatening complications include septic peritonitis and multi-organ failure.
• Urgent interventions: IV fluids, broad-spectrum antibiotics, LMWH.
• Urgent exploratory laparotomy to remove necrotic bowel.
• High mortality rate; survivors may have short gut syndrome.

Prognosis

Prognosis of Acute Mesenteric Ischaemia

• Factors Affecting Prognosis:
  • Duration of ischemia.
  • Extent of intestinal damage.
  • Presence of complications (e.g., bowel perforation, peritonitis).
  • Timeliness of intervention.
• Outcome Range:
  • If diagnosis is missed, mortality rate can reach 90%.
  • Even with treatment, mortality rate remains at 50-90%.
• Survivors’ Challenges:
  • Survivors of extensive bowel surgery may experience significant disability.

Complications

Complications of Acute Mesenteric Ischaemia

• Bowel Infarction (Tissue Death): Due to inadequate blood supply, leading to tissue damage.
• Peritonitis: Inflammation of the abdominal lining, often due to bacterial translocation from dying gut tissue.
• Sepsis: Systemic infection resulting from bacterial spread.
• Bowel Perforation: Rupture of intestinal wall, leading to contamination of abdominal cavity.
• Multiple Organ Failure: Progressive dysfunction of multiple organ systems.
• Impact on Morbidity and Mortality: These complications can significantly worsen morbidity and mortality if not promptly managed.

References

• • Oxford Handbook of Clinical Medicine, 10th edition, page 620-21
• • https://teachmesurgery.com/vascular/peripheral/mesenteric-ischaemia/
  • https://patient.info/doctor/bowel-ischaemia