Acute mesenteric ischaemia

• What is AMI?

  • Occurs when there is insufficient blood supply to the small intestines resulting in ischaemia
  • Can be caused by anything that results in acute hypoperfusion to the small intestines
  • Blood supply to the small intestines is primarily from the superior mesenteric artery (SMA)
  • If not promptly treated this can result in tissue necrosis and perforation
• Classification:

  • Thrombus in situ
  • Embolism (most common, cardiac causes)
  • Non-occlusive: arterial spasm or vasocontraction, hypovolaemia
  • Venous occlusion and congestion - thrombus in veins draining small intestine eventually leading to high pressure preventing arterial blood flow
• Cardiac causes of embolism:

  • Atrial fibrillation
  • Post MI mural thrombus
  • Prosthetic heart valve
  • Infective endocarditis
• The risk factors depend on the underlying cause but the main reversible risk factors for an embolus causing acute ischaemia are the same as chronic mesenteric ischaemia:

  • Smoking
  • Hyperlipidaemia
  • Hypertension
• Clinical features:

  • Generalised abdominal pain that is out of proportion to the clinical findings
  • Diffuse and constant pain
  • Nausea and vomiting
  • Non-specific tenderness on exam (peritonism if perforation)
  • Take note of any embolic sources - atrial fibrillation, heart murmurs, infective endocarditis
• Lab tests:

  • Urgent ABG - to asses degree of acidosis and serum lactate (degree of bowl infarction)
  • Routine - FBC, U&Es, clotting, LFTs
  • Amylase is normally done to rule out pancreatitis in an acute abdomen but mesenteric ischaemia also causes raised amylase
  • Special tests - echocardiogram if looking for central source of embolus e.g. valvular endocarditis or ventricular thrombus
• Imaging:

  • CT angiography
  • Initially shows oedematous bowel
  • Later shows loss of bowel wall enhancement - loss of blood supply so less contrast in bowel wall
• Initial management:

  • Acute mesenteric ischaemia is a surgical emergency, requiring urgent resuscitation with early senior involvement
  • IV fluids
  • Catheterisation
  • Broad spectrum antibiotics
  • Anticoagulation with heparin
  • early ITU input due to risk of acidosis causing organ failure
• Definitive management:

  • Revascularisation - removal of embolism or thrombus via radiological intervention - section thrombectomy or thrombolysis
  • If evidence of peritonitis or advances ischaemia then emergency laparotomy -excision of necrotic or non-viable bowel - most patients will end up with a loop or end stoma and there is a high chance of short gut syndrome . If due to vessel occlusion try to revascularize bowel during surgery via embolectomy (embolism) or bypass graft (thrombosis)
• Mortality rates are >50%

  Those that survive may have short gut syndrome if a significant amount of bowel needs to be resected
• Thrombosis causes:

  • Most commonly due atherosclerosis in mesenteric artery
  • Vasculitis
  • Infection
  • Trauma