Question 12

College answer

Mesenteric ischaemia occurs when blood flow is inadequate to meet the metabolic demands of the small bowel or colon.

Pathophysiology

• Occlusion of the arterial supply leads to ischaemia of the mucosa, before progressing to full thickness ischaemia and infarction with subsequent bacterial translocation leading to localised abscess formation, peritonitis and systemic sepsis depending of the extent of ischaemia.
• Arterial embolism – generally originates from atrial thrombi and therefore tends to occur with tachyarrhythmias, cardiac failure or rheumatic heart disease
• Arterial thrombosis – occlusion of atherosclerotic mesenteric vessel
  • Dissection of the aorta
  • Torsion
  • Closed loop bowel obstruction (intraluminal pressure > arterial pressure)
  • Surgical misadventure
• Venous thrombosis – venous occlusion generally in prothrombotic state e.g.: factor deficiency, malignancy, abdominal trauma, closed loop obstruction
• Mesenteric ischaemia may also occur as a near terminal event in low cardiac output states with poor global oxygen delivery
   

Diagnosis

• History:
  • Acute onset of central colicky or constant abdominal pain, often associated with nausea, vomiting, and constipation
  • May have history of pre-disposing condition e.g.
    • Atrial fibrillation
    • Mechanical cardiac valve
    • Predisposing conditions for atherosclerosis
    • Previous bowel surgery
• Examination:
  • General
    • Often look unwell, tachycardiac (?AF) tachypnoiec (related to metabolic acidosis), hypotensive
  • Abdomen
    • At first may be soft and non-tender in spite of quite severe pain (while only mucosa is ischaemic) progressing then to localised or generalised peritonism
• Investigations:
  • Laboratory
    • Lactate is often raised but may be normal
    • Non-specific markers of inflammation
  • Plain AXR -Riegler’s sign (gas on both sides of bowel wall), thickening of bowel wall
  • Ultrasound
    • May detect proximal vessel occlusion/narrowing
    • Images often inadequate due to pain, bowel gas, obesity etc.
  • CT
    • CT Angiography – information on vasculature as well indication of bowel injury (stranding, lack of enhancement, free air etc.)
    • Two phase imaging(contrast) for optimal venous images
    • Poor sensitivity
  • MRI
    • Good vascular images, but often unacceptable delay in image acquisition
  • Endoscopy
    • May identify ischaemic changes in bowel and rectum
  • Diagnostic surgery
    • May be only way to confirm diagnosis

Treatment

• General resuscitative
  • Fluid resuscitation and judicious vasoactive support
  • Anticoagulation – generally with heparin
  • Antibiotics – controversial but often given as gut translocation and perforation common
• Disease specific
  • Arterial thrombus/embolism
    • Reperfusion
    • Endovascular – mechanical thrombectomy, angioplasty and stenting or thrombolysis
      • Requires close monitoring and often require laparotomy for peritonitis and bowel resection
  • Open
    • Revascularisation – thrombectomy and or arterial bypass
    • Assessment of bowel viability
    • Resection of necrotic bowel
    • Often require “second look” operation
  • Venous thrombosis
    • Systemic anticoagulation
    • Consider percutaneous thrombectomy
    • Laparotomy for complications – peritonitis
  • Low output state
    • Optimise haemodynamic stability
    • Minimising vasoconstrictors controversial
    • Laparotomy for complications – peritonitis

Additional Examiners’ Comments:

The template above is only a guide to the expected answer.Important points sought by the Examiners were: the different categories of mesenteric ischaemia, comments about importance of history, examination and suspicion; it was essential to mention surgery as a diagnostic tool.

Discussion

The template below is also only a guide.

Pathophysiology

• Acute mesenteric ischaemia
  • Arterial embolism (40% of cases)
  • Arterial thrombosis from ruptured atheroma (20-35% of cases)
  • Arterial dissection (<5% of cases)
  • Non-occlusive mesenteric hypoperfusion (10-15% of cases)
  • Venous infarction (5-15% of cases)
• Chronic mesenteric ischaemia
  • Gradual onset of arterial insufficiency due to atherosclerosis

History

• History of atherosclerosis
• Hypercoagulable background
• AF
• Vasculitis
• Recent abdominal surgery
• Historical features associated with chornic mesenteri ischaemia, eg:
  • Postprandial pain ("mesenteric angina"), 30-60 minutes after eating
  • Weight loss
  • Diarrhoea or constipation
  • Early satiety

Examination

• Classic “pain out of proportion to examination”
• Epigastric bruit
• Peritonism
• Clinical features of shock

Biochemistry

• Features of organ system dysfunction, eg. rising creatinine
• Raised lactate
• Neutrophilia

Imaging

• Doppler ultrasound of the mesenteric vessels
• CT with IV contrast, two-phase to detect venous thrombosis
• Catheter angiography (also allows thrombolysis)
• Diagnostic laparotomy (the college felt this was an essential part of the answer)

Specific management

• Aggressive:
  • Endovascular repair
  • Open repair with or without vascular bypass
  • Catheter-directed clot aspiration or  thrombolysis
  • Stenting of dissected segments
• Conservative:
  • Heparin infusion (this is probably the only therapy required for venous mesenteric ischaemia)

Supportive management

• Airway protection may be required (high risk of aspiration)
• Mechnical ventilation (increased work of breathing due to acidosis)
• Circulatory support (vasodilated shock state)
• Analgesia and anaesthesia (opiates may actually be preferred, as they "rest the gut" by paralysing its motility)
• Neuromuscular junction blockers may help organ perfusion by their effect on abdominal compartment pressure
• Electrolyte correction (particularly correction of acdi-base balance)
• Fluid resuscitation (extensive third-space losses are to be expected)
• Abdominal compartment pressure - serial measurements 
• Parenteral nutrition (the patient should remain fasted)
• Antibiotics of a broad spectrum, eg. piperacillin/tazobactam or meropenem