Bowel Ischaemia

 

• Pathophysiology

  Mesenteric ischaemia

  Acute mesenteric ischaemia (AMI)

  • Acute reduction in blood flow through the superior mesenteric artery (SMA) or (less commonly) the coeliac artery (CA), injuring the small bowel. It rarely affects the IMA.
  • Severe disease with >50% mortality (>90% if untreated). Often features bacterial translocation and sepsis.
  • Usually due to a left heart or aortic thromboembolism e.g. post MI, AF, infective endocarditis.
  • Other causes include hypoperfusion (non-occlusive mesenteric ischaemia, NOMI), SMA atherosclerosis, vasculitis, and mesenteric vein thrombosis.

  Chronic mesenteric ischaemia (CMI)

  • Usually due to atherosclerosis of the SMA, IMA, and/or CA.
  • Can affect the small or large bowel.
  • Aka intestinal angina.

  Ischaemic colitis

  • Large bowel ischaemia, typically transient, leading to inflammation.
  • Generally, commoner and milder than mesenteric ischaemia.
  • Usually due to atherosclerosis of the middle colic artery (SMA territory) and left colic artery (IMA territory).
  • Other causes include emboli, hypoperfusion (e.g. in sepsis), vasculitis, and drugs (contraceptive pill, cocaine, antihypertensives).
  • Splenic flexure is area most commonly affected, lying in the watershed area between both supplies (Griffith's area).
  • In rare cases, it can present as fulminant ischaemic colitis, in which there is necrosis, perforation, and sepsis.

• Signs and symptoms

  Abdominal pain:

  • Acute mesenteric ischaemia: moderate to severe pain, sudden onset, sometimes colicky, out of proportion to exam findings. Later progresses to peritonism.
  • Ischaemic colitis: moderate pain, onset over hours, sometimes colicky, with tenderness over affected bowel area, often LIF. In severe cases with necrosis and/or perforation, there may be peritonitis, with abdominal distention and guarding.

  Other features:

  • PR bleeding (mucosal sloughing) and diarrhoea, especially with ischaemic colitis.
  • Weight loss and postprandial pain in chronic mesenteric ischaemia. May have sitophobia (fear of eating).
  • Abdominal bruit.

• Investigations

  Bloods:

  • FBC: ↑WBC, ↓Hb.
  • ABG: metabolic acidosis, ↑lactate.
  • ↑Amylase

  ECG:

  • Arrhythmias including AF as a cause of acute mesenteric ischaemia.

  Imaging:

  • Abdo XR often obtained, though not required. May show bowel dilation and thumb-print sign (mucosal oedema).
  • Erect CXR: pneumoperitoneum if perforated.
  • CT abdo with IV contrast: mucosal oedema, ectopic gas, vessel occlusion.

  Further diagnostic tests:

  • Mesenteric angiography for acute mesenteric ischaemia.
  • Colonoscopy for ischaemic colitis: shows sloughing, friability, and ulceration. Should not delay surgery in an acute situation.

• Management

  Acute

  Supportive treatment, including antibiotics IV due to the risk of bacterial translocation.

  Acute mesenteric ischemia:

  • In severe illness (e.g. perforation or peritonitis), proceed to urgent laparoscopy/laparotomy for embolectomy or arterial bypass, and resection of any infarcted bowel.
  • Otherwise, thrombolysis or percutaneous angioplasty can be used.
  • Papaverine – an opioid antispasmodic which causes vasodilation – may be started as an infusion into the affected vessel in NOMI and continued 24 hours.
  • Heparin: give after surgery or thrombolysis, or standalone treatment in mesenteric vein thrombosis.

  Ischaemic colitis:

  • Fulminant disease usually requires partial or total colectomy.
  • In non-fulminant disease, symptoms usually self-resolve.

  Chronic

  Chronic mesenteric ischaemia:

  • Systemic-mesenteric bypass. Percutaneous angioplasty if unfit for open surgery.
  • Manage CVD risk factors.

  Ischaemic colitis:

  • Most can be managed conservatively.
  • Partial colectomy if there is recurrent sepsis or chronic segmental colitis.

• Complications

  • Perforation
  • Sepsis
  • Strictures