Acute
mesenteric ischaemia
Mesenteric vein thrombosis
Definition
Ischaemic bowel injury in the distribution of the superior mesenteric
vessels. Ranges from reversible alterations in bowel function to transmural
necrosis of the bowel wall
Aetiology
SMA embolus
- 40-50% of episodes of acute mesenteric ischaemia
- emboli usually originate from LA or LV mural thrombus
- approx 20% have synchronous emboli in other arteries
Non occlusive mesenteric ischaemia
- 20-30% of episodes
- probably results from splanchnic vasoconstriction initiated by vasoactive
medication or a period of decreased cardiac output. Vasoconstriction may persist
even after the precipitating cause has been eliminated or corrected
- predisposing factors: MI, CCF, aortic, hepatic and renal disease, major
cardiac and intra-abdominal operations
- a more immediate precipitating cause (eg pulmonary oedema, arrhythmia, shock) is
frequently present although the consequent mesenteric ischaemia may not become
manifest for hrs-days
SMA thrombosis
- acute ischaemic episode often superimposed on chronic ischaemia so 20-50%
of patients have a history of abdominal pain +/- malabsorption for weeks-months
- associated with cardiac, cerebral and peripheral vascular disease
Mesenteric vein thrombosis
- may present acutely, subacutely or as a chronic process
- < 5% of cases of acute mesenteric ischaemia
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Clinical features
- early identification requires high index of suspicion
- acute abdominal pain varying in severity, nature and location in 75-98%
- pain is usually out of proportion to physical findings in early stages
- rapid and forceful bowel evacuation
- unexplained abdominal distension or GI bleeding may be only features,
especially in non-occlusive disease
- distension is a late feature and is often the first sign of impending bowel
infarction
- stool +ve for occult blood in 75%. May precede all other features
- right-sided abdominal pain associated with the passage of maroon or bright red
blood in stool, although characteristic of colonic ischaemia, also suggests the
diagnosis of acute mesenteric ischaemia
- no abdominal findings early in course of intestinal ischaemia but as
infarction develops there is increasing tenderness, rebound tenderness, and
guarding
- nausea, vomiting, melaena, haematemesis, massive abdominal distension, back
pain and shock are late features indicating compromise of bowel viability
- metabolic acidosis in 50%
- plain AXR normal in early stages. Late: formless loops of small bowel or
small intestinal "thumbprinting". Less commonly "thumbprinting"
of right colon
- laparoscopy may be useful in patients whose clinical condition precludes
angiography but examination is limited to the serosal surface making it
unreliable for identifying mucosal necrosis early in its course
- angiography: mainstay of diagnosis of and initial treatment of both
occlusive and non-occlusive forms. (NB mesenteric vasoconstriction can occur
in hypotensive patients and those with pancreatitis as well as in patients
with non-occlusive mesenteric ischaemia)
- duplex scanning: can identify portal and superior mesenteric vein
thrombosis and, in some patients, SMA occlusion
- CT has also been used to identify arterial and venous thromboses as well
as ischaemic bowel, but only in the late stages of the disease
Management
- aggressive resuscitation
- plain AXR to exclude other diagnoses and to look for infarcted bowel. NB
normal AXR does not exclude diagnosis
- angiography. Should be performed even if decision to operate has been made
on clinical grounds in order to manage the patient properly at laparotomy.
Moreover relief of mesenteric vasoconstriction is essential to treat emboli
and thromboses as well as non-occlusive ischaemia
- intra-arterial papaverine via angiographic catheter placed in SMA: 30-60
mg/h. Majority of papaverine is cleared during passage through the liver but
there is a risk of systemic hypotension. Daily repeat angiogram to determine
whether papaverine should be continued
- laparotomy to restore blood flow and to resect non-viable bowel. If
diagnosis of non-occlusive ischaemia is made, laparotomy should be performed
if there is clinical suspicion of infarcted bowel
- post-operative anti-coagulation: probably advisable 48 h post op in order
to prevent late thrombosis following embolectomy or arterial reconstruction
- broad spectrum antibiotics (associated with improved survival)
Prognosis
Approx 50% mortality even with vasodilator therapy
Infrequent but distinct form of gut ischaemia
Associated with:
Hypercoagulable states
- peripheral DVT
- neoplasms
- protein C & S deficiency
- antithrombin III deficiency
- oral contraceptive
- pregnancy
- polycythaemia vera
- thrombocytosis
Inflammation
- pancreatitis
- peritonitis
- inflammatory bowel disease
- pelvic or intra-abdominal abscess
Portal hypertension
- cirrhosis
- congestive splenomegaly
- following sclerotherapy of varices
Trauma
- post-op
- following splenectomy
- blunt abdominal trauma
Other
- decompression sickness
Pathology
Thrombosis due to cirrhosis, or operative injury starts at site of injury and
extends peripherally whereas thromboses caused by hypercoagulable states start
in smaller veins and propagate into major trunks. When collateral circulation is
inadequate and venous drainage from a segment of bowel is compromised there is
increasing congestion of the affected bowel with oedema, cyanosis, and
thickening with intramural haemorrhage. Ultimately similar changes affect the
mesentery. Serosangineous peritoneal fluid accompanies early haemorrhagic
infarction. Late in the process when transmural infarction occurs it may be
impossible to distinguish venous from arterial occlusion
Clinical features
- varied and non-specific
- abdominal pain usual but location, duration, nature and severity vary widely
- nausea and vomiting
- GI bleeding (bloody diarrhoea and haematemesis) indicate bowel infarction
- abdo tenderness in almost all patients
- decreased bowel sounds, abdo distension in most patients
- clear signs of peritonitis in only 2/3 initially
- guarding and rebound develop as bowel infarction occurs
- pyrexia
Investigations
- AXR. When abnormal almost always reflects presence of infarcted bowel
- angiography can establish definitive diagnosis before infarction occurs
- CT can establish diagnosis in over 90%
- ultrasound may be difficult because of overlying gas
Management
In absence of evidence of bowel infarction a trial of anticoagulant or
thrombolytic therapy may prove worthwhile but immediate laparotomy is indicated
if signs of infarction develop. Infarcted bowel should be resected and
anticoagulation started immediately post-op (recent studies show clear evidence
of benefit from immediate anti-coagulation)
Prognosis
Mortality 20-50%
Further reading
Kaleya RN, Boley SJ. Acute mesenteric ischaemia. Crit Care Clin, 1995;
11(2):479-512
© Charles Gomersall December 1999
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