Flashcards in Gastroenterology - Ischaemic gut injury Deck (13):
What areas of the bowel are supplied by the superior mesenteric artery (SMA)?
Most of the small bowel
Ascending and transverse colon up to the left colic flexure (splenic flexure)
SMA and IMA overlap at the splenic flexure making the splenic flexure a watershed area
What areas of bowel are supplied by the IMA?
Descending and sigmoid colon
Upper half of the anal canal
What types of infarction can affect the bowel?
1) Transmural = full thickness haemorrhagic infarction
- usually involves all or part of the small bowel
- usually due to thrombosis of the SMA
2) Mural and mucosa infarctions
- usually occur in hypoperfusion states (e.g. shock)
What are the causes of acute ischaemia involving the small bowel?
1) Acute mesenteric ischaemia accounts for 50% of all cases:
i) embolism from the left side of the heart to the SMA
- AF is the most common predisposing arrhythmia
- SMA has the greatest velocity of blood flow and the most acute angle off the aorta of all the arteries originating from the abdominal aorta
ii) thrombosis of the SMA
2) Non occlusive ischaemia (25%)
i) Hypotension secondary to heart failure
ii) Hypovolaemic shock
iii) Digitalis - ?vasospasm
3) Mesenteric vein thrombosis
i) Pro thrombotic states - e.g. polycythaemia vera, antiphospholipid syndrome
ii) Extension of renal cell carcinoma into vena cava
Why is the small bowel more susceptible to ischaemic injury than the large bowel?
The colon has the benefit of two blood supplies - the SMA and the IMA, whereas the small bowel only has one (the SMA).
What are the clinical features of acute small bowel ischaemia?
Abdominal pain develops suddenly which is more impressive than the physical findings. In the early stages the abdomen may be distended, with absent or diminished bowel signs and peritonitis is a later feature. Early on there is no rebound tenderness. There is also bloody diarrhoea.
What are the important investigations in acute small bowel ischaemia?
Raised phosphate and amylase
"Thumb printing" on AXR due to mucosal oedema
An occluded or narrowed major artery on mesenteric or CT angiography
How is acute small bowel ischaemia managed?
Resuscitation, management of cardiac disease and IV antibiotic therapy should be followed by laparotomy, embolectomy and vascular reconstruction. In patients at high surgical risk, thrombolysis may sometimes be effective. Survivors often develop short bowel syndrome requiring nutritional support, sometimes including home parenteral nutrition, as well as anticoagulation. Small bowel trans- plantation is promising in selected patients.
What are the main causes of ischaemic colitis?
Ischaemic colitis refers to ischaemic injury to the large bowel. Causes include:
1) Watershed infarct to the splenic flexure of the large bowel
- hypotension, shock
2) Atherosclerotic narrowing of SMA causes mesenteric angina
- splenic flexure pain after eating
- leads to fear of eating and weight loss
3) Arterial thromboembolism
4) Systemic vasculitis
5) Abdominal aortic aneurysm surgery
6) Strangulated hernia
What are the clinical features of acute ischaemic colitis?
The patient is usually elderly and presents with sudden cramping left-sided lower abdominal pain and rectal bleeding. The diagnosis is established by colonoscopy within 48 hrs of onset. Symptoms usually resolve spontaneously over 24–48 hrs and healing occurs within 2 wks. Some have a residual fibrous stricture or segment of colitis.
What is chronic mesenteric ischaemia?
This results from atherosclerotic stenosis affecting at least 2 of the coeliac axis, SMA and IMA. Patients present with dull but severe mid or upper abdominal pain 30 mins or so after eating, weight loss and sometimes diarrhoea.
Examination reveals generalised arterial disease and sometimes an audible abdominal bruit. Mesenteric angiography confirms at least two affected arteries. Vascular reconstruction or percutaneous angioplasty is sometimes possible. Left untreated, many patients develop intestinal infarction.
What is angiodysplasia?
Dilation of mucosal and submucosal venules in caecum and right colon
- usually occurs in elderly individuals
- vascular ectasias in the ceacum increase with age
Increased wall stress in the caecum stretches the venules
- recall that the caecum has an increased diameter and according to the law of Laplace increasing diameter increases wall stress