Ischemic Bowel (Ischaemic colitis, mesenteric ischaemia) Flashcards
What is acute mesenteric ischaemia? (including pathophysiology)
Umbrella term covering:
- Acute mesenteric arterial embolus and thrombus
- Mesenteric venous thrombus
- Non-occlusive mesenteric ischaemia (NOMI)
All have pathological features of:
- Impaired blood flow to the intestine
- Bacterial translocation - intraluminal flora crossing into normally sterile tissue
- Systemic inflammatory response
Mostly affects the small bowel
What is the epidemiology of acute mesenteric ischaemia?
Most common in the >50yrs
- Venous thromboses are more common in younger patients however
Overall incidence 0.09-0.2% of hospital admissions
What are some risk factors for acute mesenteric ischaemia by pathophysiology?
Arterial emboli risk factors: (most common causes overall)
- Mural thrombus post MI
- Auricular thrombus from mitral stenosis and AF
- Septic emboli from valvular endocarditis
- Fragments of proximal aortic thrombus
- Arterial catheterisation dislodging bits of plaque
- (FATBAT)
Arterial thrombosis risk factors:
- Atherosclerosis
- Aortic aneurysm or dissection
- Arteritis
- Low CO e.g. MI, CHF, dehydration
Mesenteric venous thrombosis (MVT) risk factors:
- Hypercoagulabiltiy disorders/states
- Tumour causing venous compression or hypercoag
- Infection - usually intra-abdo e.g. appendicitis, diverticulitis, abscess
- Venous congestion e.g. portal HTN
- Venous trauma from accidents or surgery (esp portocaval surgery, pancreatitis, decompression sickness) `
Non-occlusive mesenteric ischaemia (NOMI) risk factors:
- Hypotension
- Vasopressive drugs
- Ergotamines
- Cocaine
- Digitalis
How does acute mesenteric ischaemia present?
Pain:
- Moderate-severe
- Colicky or constant
- Poorly localised
- Physical findings are often out of proportion to degree of pain i.e. in the early stages, there may be no/minimal tenderness and no signs of peritonitis
Peritonism develops later:
- Rebound tenderness
- Guarding
Mass is sometimes palpable
Examination may reveal associated causes e.g. AF, peripheral vascular disease
How do you investigate acute mesenteric ischaemia?
CT angiography (IV contrast + thin slicing in arterial phase):
- Gold standard, will show arterial blockage (embolic/thrombotic)
- May also show gas in ecoptic places e.g. bowel wall, portal vein; bowel wall/mesenteric oedema; thumbprinting; solid organ infarction
- High level of suspicion and low threshold for delivering CT is required to reduce mortality
AXR:
- May be done initially if Dx unclear and can be helpful to rule out other causes
- In the later stages, may show SBO, ileus and thickened bowel wall
Other:
- Bloods - raised WCC; metabolic acidosis
- ECG - AF or infarct?
- CXR erect - bowel perforation?
- USS/MRI?
How do you manage acute mesenteric ishcaemia?
Initial medical:
- Early involvement of seniors, surgical referrals and notifying ITU
- Initial resuscitation with IV fluids + O2
- NG tube insertion
- IV broad spec Abx
- IV anticoagulant drugs e..g unfractioned heparin
Surgical:
- Prompt laparotomy for patients with overt peritontis
- Goals of surgery are to re-establish circulation to ischaemic bowel + resection of non-viable regions + preservation of viable bowel
What is the prognosis of acute mesenteric ischaemia?
If Dx missed - mortality = 90%
- Bowel necrosis, perforation, overwhelming sepsis or haemorrhage
With treatment - mortality is still 50-90%
- Often have to have a re-look laparotomy 24-48hrs after first
- Time spent on ICU
Survivors of extensive bowel surgery will often end up with a stoma and short gut syndrome
What is chronic mesenteric ischaemia?
Chronic atherosclerotic disease of (usually) all three major mesenteric arteries
What is the epidemiology of chronic mesenteric ischaemia?
Very low incidence:
- <1/1000 hospital admissions for acute abdo
- Most often are female aged 50-70
- Usually co-existing manifestations of and risk factors for vascular disease
How does chronic mesenteric ischaemia present?
Pain:
- Moderate-severe
- Colicky or intermittent
- Poorly localised
- Postprandial (‘abdominal angina’), associated with a fear of eating
Weight loss
Nausea/vomiting
Bowel irregularity
Hx CVD
How do you investigate chronic mesenteric ischaemia?
CT angiography:
- Gold standard investigation to show the site of arterial blockage or stenosis
USS doppler of mesenteric arteries may also be useful
- Laboratory tests such as FBC, LFTs and U&E may reflect malnutrition or dehydration
- CXR should be carried out to exclude pneumonia, and cardiac scanning to exclude comorbidity
How do you manage chronic mesenteric ischaemia?
Asymptomatic:
- Conservative i.e. smoking
- Anti platelet therapy
- 5yr mortality of 40% - most deaths due to MI/CVD death
Symptomatic:
- Open/endovascular revascularisation as 5yr mortality is c.100%
- TPN may be needed preoperatively to build health again as patients are usually malnourished
What is ischaemic colitis? (including the aetiology and pathophysiology)
Caused by a compromised blood supply to the colon
- Marginal branches of the middle colic (superior mesenteric artery - supplying distal duodenum through to splenic flexure) and left collic (inferior mesenteric artery - supplying splenic flexure to rectum) arteries supply the transverse and descending segments of the colon
- An arterial (and lymphatic) watershed exists near the splenic flexure meaning that when blood flow to either is compromised, this area is at risk of:
Hypoxia - intestinal wall damage - mucosal inflammation +/- bleeding - infarction +/- necrosis (gangrenous type, 15-20%) - disruption of mucosal barrier - translocation of bacteria/toxins - sepsis
Most forms are caused by transient hypoperfsion (80-85%) e.g. hypovolaemia, sepsis, haemorrhage
Other causes:
- Thromboembolism
- Colonic distension (area immediately proximal to an obstruction is at risk)
- CV surgery esp. aortic repair, cardiac bypass
- Vasoconstrictive drugs
- Thrombophilias
- Colonic obstruction e.g. tumour, adhesions, strangulated hernias, volvulus
- Drugs - Cocaine, digitalis, oestrogens, vasopressin, antihypertensives etc.
- Vasculitic diseases
- Coagulopathies
What is the epidemiology of ischaemic colitis?
Increasingly common
- As most common (non-transient) form is due to atherosclerosis
- Thus also more common >60yrs
How does ischaemic colitis present?
Non-specific acute abdomen
Pain:
- Acute (hrs) onset (unlike inflammatory or infective colitis = subacute or even more insidious) that (often) continues to worsen
- Worse hours after eating - due to increased demand for blood flow to the bowel
- Mostly left iliac fossa (but may not be so focal)
- Localised tenderness in LIF; but if generalised indicates peritonitis (and a more severe presentation)
Nausea + vomiting
Loose stools containing dark blood - in later stages
