Acute Mesenteric Ischaemia

Question 1

… ischaemia refers to insufficient blood supply to the small intestines leading to ischaemic and inflammatory changes.

Answer 1

Mesenteric ischaemia refers to insufficient blood supply to the small intestines leading to ischaemic and inflammatory changes.

Question 2

Colonic ischaemia: refers to ischaemia affecting the colon.

Mesenteric ischaemia: this term tends to be reserved to describe ischaemia affecting the … intestines.

Answer 2

Colonic ischaemia: refers to ischaemia affecting the colon.

Mesenteric ischaemia: this term tends to be reserved to describe ischaemia affecting the small intestines.

Question 3

The blood supply to the small intestines is primarily from the … … with additional contribution from the coeliac axis.

Answer 3

The blood supply to the small intestines is primarily from the superior mesenteric artery with additional contribution from the coeliac axis.

Question 4

Foregut (duodenal component) - is it common to have duodenal ischaemia? Why/why not?

Answer 4

The foregut extends from the mouth through to the second part of the duodenum (until the ampulla of Vater). As such only a short segment of the small intestines is part of the foregut. The gastroduodenal artery supplies blood to the stomach, duodenum and pancreas. It is a branch of the common hepatic artery, itself a branch of the coeliac axis.

The anatomy of the gastroduodenal artery (its origin and branching) is highly variable. However, the duodenum typically receives blood supply from the anterior and posterior superior pancreaticoduodenal artery.

The anastomosis of the superior pancreaticoduodenal artery and inferior pancreaticoduodenal artery (from the superior mesenteric artery) means the duodenum has a rich, well-collateralised dual blood supply. It is therefore relatively rare to suffer from duodenal ischaemia.

Question 5

Midgut (small intestinal component) - is it common to have ischaemia? Why/why not?

Answer 5

The midgut extends from the second part of the duodenum to approximately two-thirds along the way of the transverse colon. The superior mesenteric artery (SMA), the major artery of the midgut, arises from the abdominal aorta at the L1 vertebral level. It supplies the small intestines, ascending and transverse colon (see our notes on Colonic ischaemia for more on the SMA’s supply to the colon).

It provides a number of branches that supply the small intestines:

Inferior pancreaticoduodenal artery: comes off the right side of the SMA supplying both the pancreas and duodenum. It anastomoses with the superior pancreaticoduodenal artery.
Jejunal branches: these come off the left side of the SMA. There are typically 4-6 branches supplying the jejunum.
Ileal branches: these come off the left side of the SMA distal to the jejunal branches. There tend to be more, typically 8-12 branches.

The superior mesenteric vein (SMV) drains the distribution of the SMA. It joins the splenic vein to form the portal vein which travels to the liver.

Question 6

Aetiology

The common causes of acute mesenteric ischaemia can be classified into:

Answer 6

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)

Question 7

The risk factors for acute mesenteric ischaemia depend on the underlying cause.

Specifically, however for AMAE, the main reversible risk factors are …, …, and hypertension, much the same as for chronic mesenteric ischaemia.

Answer 7

The risk factors for acute mesenteric ischaemia depend on the underlying cause.

Specifically, however for AMAE, the main reversible risk factors are smoking, hyperlipidaemia, and hypertension, much the same as for chronic mesenteric ischaemia.

Question 8

AMI refers to a collection of conditions causing acute intestinal ….

Answer 8

AMI refers to a collection of conditions causing acute intestinal hypoperfusion.

Question 9

Acute mesenteric ischaemia - causes overview

Answer 9

Question 10

Acute mesenteric arterial embolism (AMAE) is caused by emboli blocking the …

Answer 10

Acute mesenteric arterial embolism (AMAE) is caused by emboli blocking the SMA. An embolus is a mass that passes through blood vessels eventually blocking it if the calibre narrows sufficiently given the size of the embolus. An embolus can be theoretically anything from air to fat. In the case of AMAE, it is normally a blood clot that becomes detached from the heart or vessel wall and floats through the blood before becoming stuck.

Question 11

It is estimated that around 50% of cases of AMI are due to …(AMAE).

Answer 11

It is estimated that around 50% of cases of AMI are due to AMAE. Any condition that causes proximal thrombus formation can predispose patients to AMAE:

AF (thrombus formation in the left atrium due to turbulent blood flow)
Infective endocarditis (septic emboli)
Myocardial infarction (with mural thrombus secondary to impaired muscle function)
Aortic thrombus (often seen in aortic aneurysms)

Question 12

It is estimated that around 50% of cases of AMI are due to AMAE. Any condition that causes proximal thrombus formation can predispose patients to AMAE: (4)

Answer 12

AF (thrombus formation in the left atrium due to turbulent blood flow)
Infective endocarditis (septic emboli)
Myocardial infarction (with mural thrombus secondary to impaired muscle function)
Aortic thrombus (often seen in aortic aneurysms)

Question 13

Acute mesenteric arterial thrombosis (AMAT) is caused by thrombosis, normally on the background of pre-existing …. It is thought to account for around 20-25% of cases of AMI. There is often a history consistent with chronic mesenteric ischaemia (e.g. abdominal pain, weight loss). Though … is the most commonly implicated, other causes of arterial thrombus include:
(4)

Answer 13

Acute mesenteric arterial thrombosis (AMAT) is caused by thrombosis, normally on the background of pre-existing atherosclerosis. It is thought to account for around 20-25% of cases of AMI. There is often a history consistent with chronic mesenteric ischaemia (e.g. abdominal pain, weight loss). Though atherosclerosis is the most commonly implicated, other causes of arterial thrombus include:

Vasculitis
Traumatic injury
Infection
Mesenteric aneurysm/dissection

Question 14

… (NOMI) is caused by arterial spasm or vascoconstriction as opposed to occlusive disease. It is thought to be the cause of around 20% of cases of AMI and may involve the proximal colon.

The condition is most commonly seen in patients on ITU who are severely unwell, typically with impaired cardiac function and/or vasopressor use.

Answer 14

Non-occlusive mesenteric ischaemia (NOMI) is caused by arterial spasm or vascoconstriction as opposed to occlusive disease. It is thought to be the cause of around 20% of cases of AMI and may involve the proximal colon.

The condition is most commonly seen in patients on ITU who are severely unwell, typically with impaired cardiac function and/or vasopressor use.

Question 15

… (MVT) is caused by thrombosis of the venous drainage of the small intestines. It is thought to account for around 10% of cases of AMI.

Answer 15

Mesenteric venous thrombosis (MVT) is caused by thrombosis of the venous drainage of the small intestines. It is thought to account for around 10% of cases of AMI.

Question 16

Mesenteric venous thrombosis (MVT) is caused by thrombosis of the venous drainage of the small intestines. It is thought to account for around 10% of cases of AMI.

It tends to occur in patients with risk factors for hypercoagulability, these include:

Answer 16

Systemic factors:
Inherited thrombophilia (e.g. factor V Leiden, protein C and S deficiency)
Malignancy
Medications (e.g. oral contraceptive)
Local factors:
Venous compression (secondary to tumours)
Inflammatory conditions (e.g. pancreatitis, IBD)
Surgical trauma

Question 17

… … … is characteristic of AMI.

Answer 17

Severe abdominal pain is characteristic of AMI.

Question 18

AMI most commonly presents with abdominal pain that is often poorly …. The pain can be severe and may be out of keeping with what is expected based on the examination. Clinical examination reveals …, the development of peritonism is indicative of advanced ischaemia and necrosis. As the condition worsens fever becomes common and … instability can occur.

Answer 18

AMI most commonly presents with abdominal pain that is often poorly localised. The pain can be severe and may be out of keeping with what is expected based on the examination. Clinical examination reveals tenderness, the development of peritonism is indicative of advanced ischaemia and necrosis. As the condition worsens fever becomes common and haemodynamic instability can occur.

Question 19

Symptoms of AMI

Answer 19

Abdominal pain
Nausea
Vomiting
Diarrhoea
Blood in stools

Question 20

Signs of AMI

Answer 20

Abdominal tenderness
Guarding/peritonism
Tachycardia
Pyrexia
Hypotension

Question 21

What is the diagnostic modality of choice for AMI?

Answer 21

CT abdomen and pelvis with contrast is the diagnostic modality of choice for AMI.

Question 22

Bedside tests in AMI

Answer 22

Observations
Blood sugar
ECG (check for arrhythmias, particularly AF)
Pregnancy test (if appropriate)

Question 23

Blood tests in AMI?

Answer 23

FBC
Renal function
CRP
LFT
Amylase
Clotting screen
Group and screen
VBG/ABG (lactate, pH balance)

Question 24

Imaging in AMI

Answer 24

Erect CXR: may reveal pneumoperitoneum if necrosis and perforation have occurred.

CT abdominal/pelvis: this is generally the diagnostic modality of choice. It offers good sensitivity and also allows alternative causes of abdominal pain to be excluded.

Echocardiogram: may be ordered if a central source of embolus is suspected (e.g. valvular endocarditis, ventricular thrombus).

Question 25

In patients with MVT without signs of peritonitis or perforation, … can be used as the definitive management. Close monitoring is required and surgical intervention must be considered if the clinical situation deteriorates.

Answer 25

In patients with MVT without signs of peritonitis or perforation, anticoagulation (with UFH) can be used as the definitive management. Close monitoring is required and surgical intervention must be considered if the clinical situation deteriorates.

Question 26

Medical management of AMI

Answer 26

IV access with wide-bore cannula should be gained. Appropriate fluid resuscitation should be commenced with close monitoring of haemodynamic stability. A nasogastric tube should be placed.

Broad-spectrum antibiotics should be started due to the risk of bacterial translocation across the gut wall and the risk of perforation. Anticoagulation with unfractionated heparin (UFH) is typically started unless there is a contra-indication.

Question 27

NOMI - treatment

Answer 27

In patients with non-occlusive disease treatment of the underlying cause is of the utmost importance. This may involve optimisation of cardiac output and altering or reducing the vasopressors used.

Vasodilators like papaverine may be used to improve blood flow to the intestines. Again surgical management can be required if there are signs of peritonitis, perforation or clinical deterioration. This is not a decision taken lightly as given the often poor pre-morbid state the mortality of any surgery is very high.

Question 28

MVT - treatment

Answer 28

In patients with MVT without signs of peritonitis or perforation, anticoagulation (with UFH) can be used as the definitive management. Close monitoring is required and surgical intervention must be considered if the clinical situation deteriorates.

Question 29

Surgical management of AMI

Answer 29

Prompt laparotomy is typically required in patients with peritonitis or radiological evidence of advanced ischaemia.

All emergency laparotomies should be recorded with data submitted to NELA. The NELA risk calculator can be used to give an estimate of a patient’s 30-day mortality.

Laparotomy allows for direct assessment of the intestines. Non-viable sections of bowel will require resection, decisions regarding stoma formation or primary anastomosis should be made at a consultant level. In occlusive disease (AMAT, AMAE), laparotomy can also be used to attempt revascularisation:

AMAE: SMA emboli can be treated with embolectomy.
AMAT: Diffuse thrombosis may be treated with a bypass graft.
It may not be possible to conclusively assess and treat AMI during a single operation. A re-look laparotomy is often required to check the viability of intestines and to make final decisions regarding resection, creating an anastomosis or forming a stoma.

Question 30

Laparotomy allows for direct assessment of the intestines. Non-viable sections of bowel will require resection, decisions regarding stoma formation or primary anastomosis should be made at a consultant level. In occlusive disease (AMAT, AMAE), laparotomy can also be used to attempt …:

AMAE: SMA emboli can be treated with embolectomy.
AMAT: Diffuse thrombosis may be treated with a bypass graft.

Answer 30

Laparotomy allows for direct assessment of the intestines. Non-viable sections of bowel will require resection, decisions regarding stoma formation or primary anastomosis should be made at a consultant level. In occlusive disease (AMAT, AMAE), laparotomy can also be used to attempt revascularisation:

AMAE: SMA emboli can be treated with embolectomy.
AMAT: Diffuse thrombosis may be treated with a bypass graft.

Question 31

AMAE: SMA emboli can be treated with ….
AMAT: Diffuse thrombosis may be treated with a … graft.

Answer 31

AMAE: SMA emboli can be treated with embolectomy.
AMAT: Diffuse thrombosis may be treated with a bypass graft.

Question 32

Endovascular management - AMI

Answer 32

Endovascular techniques may be used in appropriately selected patients where local expertise allows. It can only be used in stable patients without any clinical or radiological evidence of advanced ischaemia and necrosis. Research is ongoing to define the patient population in whom endovascular intervention should be used, and the relative risks and benefits.

In patients with AMAE/AMAT, endovascular interventions involve obtaining vascular access (typically via the femoral or brachial artery) and identifying the arterial occlusion. The blockages may be resolved through a variety of techniques including mechanical aspiration, localised thrombolysis and/or angioplasty +/- stenting.

Some studies have looked at localised thrombolysis/thrombectomy for patients with MVT. This therapy is in the early stages of development and is typically only performed at specialist centres as part of research.

Question 33

Acute mesenteric ischaemia causes - AMAT underlying cause is typically what?

Answer 33

Acute mesenteric ischaemia causes - AMAT underlying cause is typically what? Atherosclerosis

Question 34

Acute mesenteric ischaemia causes - AMAT underlying cause is typically what? Atherosclerosis

Answer 34

Acute mesenteric ischaemia causes - AMAE underlying cause is typically what? Cardiac causes* or thoraco-abdominal aneurysm

Question 35

Acute mesenteric ischaemia causes - NOMI underlying cause?

Answer 35

Hypovolaemic shock, cardiogenic shock

Question 36

Acute mesenteric ischaemia causes - MVT underlying causes?

Answer 36

Coagulopathy, malignancy, autoimmune disorders