Acute Mesenteric Ischaemia
Acute mesenteric ischaemia is the sudden decrease in blood supply to the bowel, resulting in bowel ischaemia and, if not promptly treated, rapid gangrene.
In this article, we shall look at the causes, clinical features and management of a patient with acute mesenteric ischaemia.
The common causes of the any acute mesenteric ischaemia can be classified into:
- Thrombus-in-situ (Acute Mesenteric Arterial Thrombosis, AMAT)
- Embolism (Acute Mesenteric Arterial Embolism, AMAE)
- Non-occlusive cause (Non-Occlusive Mesenteric Ischemia, NOMI)
- Venous occlusion and congestion (Mesenteric Venous Thrombosis, MVT)
|Type||Proportion of Cases||Underlying Cause|
|AMAE||50%||Cardiac causes, such as arrhythmia (e.g. AF), post-MI mural thrombus, or prosthetic heart valve, or abdominal or thoracic aneurysm|
Rarer causes include Takayasu’s arteritis, fibromuscular dysplasia, polyarteritis nodosa, and thoracic aorta dissections
The risk factors for acute mesenteric ischaemia depend on the underlying cause.
Importantly for AMAE, the main reversible risk factors are smoking, hyperlipidaemia, and hypertension.
Traditionally, mesenteric ischaemia presents with a generalised abdominal pain, out of proportion to the clinical findings – yet it can often be more variable or subtle than this. The patient will typically complain of a diffuse, usually constant, pain. Nausea and vomiting present in around 75% of cases.
It is a diagnosis that should be considered in all older patients presenting with abdominal pain, especially in those with risk factors for thrombosis or embolism*.
*A history of AF or other cardiovascular disease increase the likelihood towards this diagnosis. Other points in the history to consider are previous DVT or PE or hypercoaguable states (e.g. active neoplasia or anti-phospholipid syndrome)
On examination, the abdomen is often unremarkable and the patient may find it difficult to localise the pain. However, remember late stage bowel ischaemia and necrosis can present as bowel perforation. Other signs may include tachycardia, tachypnea and delirium.
Importantly, take note of any potential embolic sources, such as AF, heart murmurs, or signs of previous valvular replacement surgery.
Mesenteric ischemia should always be considered in cases of severe acute abdomen, especially where there is no other obvious cause.
Other causes of acute abdomen that may have similar presentations include peptic ulcer disease, bowel obstruction, and symptomatic AAA
An arterial blood gas (ABG) should be performed urgently, to assess the degree of acidosis and serum lactate, secondary to the severity of bowel infarction.
Other blood tests that should be performed include: FBC (raised WCC with a SIRS response from bowel ischaemia), U&Es, Clotting (especially if AF patients on warfarin), Amylase*, and LFTs (if the coeliac trunk is affected, ischemia of the liver may cause derangement).
*Whilst an amylase is commonly measured to exclude pancreatitis as a cause of the abdominal pain, counter-intuitively amylase also rises in mesenteric ischaemia, as well as ectopic pregnancy, bowel perforation, and DKA.
A Group and Save should be taken as the patient will likely need operative intervention.
An initial AXR and erect CXR may show free gas under the diaphragm if perforated.
If there is any degree of suspicion, then a CT abdomen with contrast is indicated, commonly showing thickened and odematous bowel.
For the definitive diagnosis, for both arterial and venous mesenteric disease, CT angiography in the arterial phase with thin slices is warranted.
Acute mesenteric ischaemia is a surgical emergency, thus requires urgent resuscitation with early senior involvement.
Ensure the patient receives IV fluid resuscitation with a fluid balance chart started immediately and the insertion of urinary catheter to facilitate this.
Prescribe broad-spectrum antibiotics (depending on local guidelines), due to the risk of faecal contamination in case of perforation of the ischaemic (and potentially necrotic) bowel.
The patient will have a significant acidosis and is at a high risk of developing multiorgan failure, therefore early ITU input to optimise the patient and determine their ceiling of treatment is necessary. Taking a patient to theatre for potential bowel resection without the support of ITU is likely to be futile.
The location, timing, and severity of the mesenteric ischaemia, among other factors, will determine the surgical intervention performed. The basic principle is 2-fold:
- Excision of necrotic or non-viable bowel – with the patient kept on the intensive care unit under sedation for relook laparotomy in 24-48 hours. The majority of patients will end up with a stoma and there is a high chance of short gut syndrome.
- Revascularisation of the bowel – removal of any thrombus or embolism depends upon the state of the patient, the bowel, and the angiographic appearance of the mesenteric vessels. This would preferably be done through angioplasty due to the risk of aortic contamination in open surgery, however open embolectomy is possible either through the Coeliac axis, SMA or IMA, or through the aorta.
The main risks from mesenteric ischaemia are bowel necrosis and perforation.
Mortality is around 50-80%, even if the diagnosis is made and treatment performed. Those that survive may have short gut syndrome.