GI: Mesenteric Ischaemia

Question 1

describe the 4 possible causes of mesenteric ischaemia

Answer 1

1. acute mesenteric arterial embolism (50%)
2. acute mesenteric arterial thrombosis
3. mesenteric venous thrombosis (usually superior mesenteric vein)
4. non-occlusive mesenteric ischaemia (e.g. low BP, arterial spasms, DIC, HF)

All cause bowel ischaemia, eventually leading to bowel wall necrosis, oedema and haemorrhage.

Question 2

which 2 areas of the colon are watershed areas? what type of ischaemic colitis are they more prone to?

Answer 2

1. Splenic flexure (sup. and inf. mesenteric artery watershed)
2. Sigmoid colon (inf. mesenteric and hypogastric artery watershed)

Protected from occlusive types of ischaemia due to dual blood supply, but more prone to non-occlusive ischaemia as supplied by most distal branches of their arteries.

Question 3

describe symptoms of mesenteric ischaemia

Answer 3

• sudden, severe, poorly localised abdo. pain (out of proportion to physical exam)
• +/- bloody stool (mucosal sloughing)
• +/- diarrhoea
• +/- nausea and vomiting (bowel wall spasms)

Question 4

describe the early and late signs of mesenteric ischaemia

Answer 4

Early: minimal tenderness

Late:

• peritonism (guarding and rebound tenderness)
• shock (hypotension, tachycardia and confusion)

Question 5

why can mesenteric ischaemia pts develop shock?

Answer 5

Fluid leaks through damaged bowel wall… dehydration… hypotension, tachycardia and confusion.

Or septic shock from bowel wall necrosis and perforation.

Question 6

describe possible aetiologies for acute mesenteric arterial embolus

Answer 6

Often cardiac:

1. Post-MI (mural thrombi)
2. Mitral stenosis or AF (atrial thrombi)
3. Vegetative endocarditis
4. Ruptured atheromatous plaques, e.g. in aorta

Question 7

which Ix would you request in a pt with suspected mesenteric ischaemia?

Answer 7

1. Bedside tests:
   - ECG: may show AF or MI
2. Bloods:
   - FBC: raised WCC as disease progresses
   - Clotting studies (PT, aPTT and INR)
   - ABG: raised lactate, metabolic acidosis
3. Imaging:
   - AXR: typically normal (use to exclude DDx), may show: SBO, thickened bowel wall (thumbprinting) and pneumatosis intestinalis (wair within intestinal wall from necrosis) in later stages
   - CT angiography (gold standard): shows arterial blockage due to thrombus/embolus
   - abdo CT: typically shows mesenteric oedema with irregular thickening or small or large bowel wall >3mm +/- portal venous air in L hepatic lobe. Can depict underlying aetiology and complications.

Question 8

how would you manage a pt with mesenteric ischaemia?

Answer 8

Initial:

1. O2
2. fluid resuscitation
3. analgesia
4. early broad spectrum antibiotics

Definitive:

5. re-perfusion:
   
   • stable pts may benefit from non-surgical interventions, e.g. IV heparin infusion or percutaneous intervention (angioplasty after thrombolysis, stent placement)
   • surgery, e.g. arteriotomy or bowel resection, should be performed immediately in those with peritoneal signs