Acute mesenteric ischemia: Clinical sciences

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Introduction0:00–1:50

Acute mesenteric ischemia, or AMI, occurs when there is a sudden decrease of blood flow within the mesenteric vasculature, which can lead to infarction or necrosis of the bowel wall.
Depending on the blood vessels involved, mesenteric ischemia can affect either the small or large bowel. Mesenteric ischemia is divided into 3 types based on the type of vasculature involved: arterial occlusion, venous occlusion, and non-occlusive arterial vasospasm.
While each type can be acute or chronic, acute presentations require timely diagnosis and treatment, as they can rapidly progress to bowel necrosis, perforation, sepsis, and even death.
Now, here’s a high-yield fact to keep in mind! The superior mesenteric artery, or SMA, supplies the GI tract from the small intestine to the proximal transverse colon, while the inferior mesenteric artery, or IMA, supplies the distal one-third of the transverse colon to the rectum.
The celiac artery, which mainly supplies the stomach and the proximal portion of the duodenum, can provide some collateral flow to the proximal small bowel and transverse colon via communications called confluences.
The intestines can actually survive off of only one of these major vessels. Venous drainage of the gut is quite similar to the arterial supply.
The superior mesenteric vein, or SMV, drains the midgut organs, while the inferior mesenteric vein, or IMV, drains the hindgut.
When approaching a patient who presents with signs and symptoms suggestive of acute mesenteric ischemia, your first step is to do an ABCDE assessment to determine if the patient is stable or unstable.

Unstable patient1:50–4:15

If the patient is unstable, you should initiate acute management to stabilize their airway, breathing, and circulation. This means you might need to obtain IV access, administer IV fluids, begin empiric broad-spectrum antibiotics, make sure the patient is NPO, and insert an NG tube if needed to decompress the bowel.
These measures are important, as there's a high risk for bowel necrosis and sepsis. Once you have initiated acute management, your next step is to obtain a focused history and physical examination.
Typically, patients with acute mesenteric ischemia report sudden onset of severe abdominal pain, which may be out of proportion to physical exam, and is usually associated with nausea and vomiting, as well as diarrhea and bloody stools.
Additionally, the history might reveal risk factors for AMI, such as atrial fibrillation, diabetes mellitus, hypercoagulable disorders, or hypertension.
Finally, on a physical exam, you might find abdominal distension, diffuse abdominal tenderness with rebound and guarding, as well as tachycardia and hypotension.
The abdominal exam may also be completely normal despite severe pain, which is typically described as pain out of proportion to the physical exam.
Alright, if you see these findings, obtain an abdominal x-ray to look for signs of bowel infarction or perforation. The x-ray might reveal pneumatosis intestinalis, or gas within the intestinal wall, which indicates bowel infarction and necrosis; or pneumoperitoneum, which means that perforation occurred.
If you see any of these findings, obtain an emergent surgical consultation for an exploratory laparotomy, which will be both diagnostic and therapeutic.
Remember, the only treatment for a necrotic bowel is surgical resection.Okay, now that the treatment for unstable patients is complete, let’s go back to the ABCDE assessment and discuss how to manage stable patients.

Stable patient4:15–6:38

If the patient is stable, you should first obtain a focused history and physical exam to identify the nature of the presentation, as well as the patient’s risk factors.
Patients might report varying degrees of abdominal pain, ranging from prior episodes of postprandial colicky abdominal pain, sometimes referred to as intestinal angina, which indicates that the blood flow is not meeting the bowel’s demands, to sudden onset severe constant pain that may indicate progression to complete vessel occlusion.
Keep in mind that postprandial pain is more likely in chronic mesenteric ischemia. They may also experience nausea and vomiting, as well as diarrhea and bloody stools.
Make sure to perform a thorough risk assessment of underlying conditions that may increase the risk of AMI, like arrhythmias such as atrial fibrillation, prior myocardial infarction, uncontrolled hypertension, venous thromboembolism, hypercoagulable disorders, malignancy, diabetes, smoking, or oral contraceptive use.
Patients with a history of prior blood clots are at a higher risk of developing clots within the mesenteric vasculature.
Now, the physical exam is typically not as severe as their pain. You might find a soft, non-distended, non-tender, or mildly tender abdomen, without guarding or rebound.
In fact, if the patient complains of abdominal pain that is out of proportion to the physical exam findings, you should have a high suspicion of acute mesenteric ischemia.
Be sure to order labs for lactate, which will be needed for serial monitoring; and start supportive care, including IV fluids, broad-spectrum IV antibiotics, and bowel rest.
Now that the supportive care is initiated, your next step is to obtain a CT or CTA of the abdomen and pelvis to visualize the mesenteric vessels.
Alright, once you’ve obtained the CT or CTA, you can look for findings associated with different types of AMI. Now, the CT or CTA might show diffuse luminal narrowing of the superior mesenteric artery or some of its distal branches, or evidence of atherosclerotic disease but without fully occluded arteries.

Non-Occlusive Mesenteric Ischemia6:38–8:36

If you see this, you can diagnose non-occlusive mesenteric ischemia. Keep in mind that patients with diabetes, hyperlipidemia, and hypertension are especially prone to developing atherosclerotic plaques within the mesenteric arterial wall.
These plaques can reduce the blood flow to the bowels, especially in the postprandial phase when the gut has a higher demand for perfusion.
These already narrowed blood vessels are also susceptible to vasospasms, which can further reduce the blood flow and cause colicky pain.
When it comes to treatment, the non-occlusive ischemic disease is treated with medical management. In the acute phase, you can give the patient vasodilators, like papaverine; and anticoagulation with heparin, or low molecular weight heparin drugs like enoxaparin.
Long-term management includes continuing oral anticoagulation, treating underlying conditions like atherosclerosis, and modifying risk factors, such as smoking cessation.
Lastly, patients that have thrombosis of an existing atherosclerotic lesion can be treated with mesenteric stenting or bypass.Okay, here’s a clinical pearl!
For people with acute mesenteric ischemia on nonsurgical management, you need to perform serial exams and monitor for rising lactate.
This is because the threshold for exploratory laparotomy to evaluate bowel viability is low and they might need to go to surgery at any time.
Let’s switch gears and talk about different CT and CTA findings. The CT or CTA may show a thrombus in the mesenteric veins or even the portal vein, as well as signs of venous congestion within the branches of the SMV or IMV such as distal venous distension or end tissue edema.

Mesenteric Venous Thrombosis8:36–9:48

If you see this, you can diagnose mesenteric venous thrombosis. Once the diagnosis is made, your next step is to start the treatment.
Treatment includes starting anticoagulation right away with IV heparin. In a patient with venous thrombosis, you will usually need to assess for an underlying hypercoagulable state, so make sure to send labs like PT, PTT, and INR.
Additionally, keep in mind that some patients may need further testing for inherited or acquired diseases like thrombophilia or antiphospholipid syndromes.
Finally, consult either interventional radiology or the surgical team for thrombolysis or a thrombectomy, since this can result in bowel necrosis requiring emergent surgical intervention.
Let’s go back to the CT/CTA and talk about the most serious findings. Now, if the CT or CTA shows signs of arterial occlusion with thrombosis, the diagnosis is mesenteric arterial thrombosis can be made.

Arterial Occlusion9:48–11:37

In a patient with chronic stenosis, thrombosis can occur causing ischemia. However, if you see an embolism and an abrupt cutoff of contrast distal to the blockage, this means that the patient is having a mesenteric arterial embolism.
Similar to venous occlusions, you should initiate anticoagulation with IV heparin right away. Remember that arterial occlusions can quickly lead to bowel infarction, necrosis, and perforation, so timely intervention is key.
One important element in managing patients with the arterial occlusive disease is to identify possible sources of emboli.
Cardiogenic emboli are a common type and are seen more often in patients with atrial fibrillation or patent foramen ovale, so make sure to order an electrocardiogram and an echocardiogram.
Finally, obtain an urgent IR or surgical team consultation for thrombolysis, thrombectomy or embolectomy, or even exploratory laparotomy to evaluate the intestinal viability.
Now, here’s a clinical pearl! All forms of acute mesenteric ischemia will have a low threshold to go for an exploratory laparotomy to evaluate the intestinal viability.
So, if your patient is treated with a less invasive approach, such anticoagulation, thrombectomy, or embolectomy, you need to perform serial exams and monitoring, including serial lactate levels.Lastly, the CTA might show patent mesenteric vessels with no signs of venous or arterial occlusion.

Alternative diagnosis11:37–11:55

If you see this, consider other alternative diagnoses for abdominal pain, like infectious colitis or inflammatory bowel disease.
Alright, as a quick recap… Patients with acute mesenteric ischemia can present as stable or unstable. Unstable patients should be assessed with an x-ray to look for signs of bowel infarction or perforation.

Review11:55–12:54

They require emergent surgical intervention, which will be both diagnostic and therapeutic. On the other hand, stable patients should have a CTA of the abdomen and pelvis performed to categorize AMI into one of three types.
Non-occlusive mesenteric ischemia can be treated with vasodilators, anticoagulation, and optimization of underlying conditions.
On the flip side, mesenteric venous thrombosis and thrombotic or embolic arterial occlusion can both be treated with anticoagulation and thrombolysis, thrombectomy or embolectomy, or even exploratory laparotomy.
Remember to order a hypercoagulation workup for mesenteric thrombosis and a cardiac workup for arterial occlusions.
Acute mesenteric ischemia: Video, Causes, Symptoms | Osmosis