Brian Lacy, MD, and David Tendler, MD, on Mesenteric Ischemia: Part 1

In this 2-part podcast, Drs Brian Lacy and David Tendler, from Duke University in Durham, North Carolina, discuss the symptoms, diagnosis, and treatment of acute and chronic mesenteric ischemia.

For Part 2 of this podcast, click here.

Brian Lacy, MD, is a professor of medicine at the Mayo Clinic in Jacksonville, Florida. David Tendler, MD, is clinical associate in medicine at Duke University in Durham, North Carolina.

For more insights from experts like Dr Tendler, click here.
 

TRANSCRIPT:

Dr. Brian Lacy:  Welcome to this "Gastroenterology Learning Network" podcast. My name is Brian Lacy. I'm a professor of medicine at the Mayo Clinic in Jacksonville, Florida. I am absolutely delighted to be speaking today with Dr. David Tendler, clinical associate in medicine at Duke University in Durham, North Carolina.

Our topic today is one that is important for every GI provider, mesenteric ischemia. Dr. Tendler, welcome. Mesenteric ischemia is a broad term. Is this still the best approach to break this down into acute mesenteric ischemia and chronic mesenteric ischemia, or do you think there's a better way to tackle this topic?

Dr. David Tendler:  First of all, thank you for inviting me on, Dr. Lacy. I appreciate the invitation. Who amongst us would not relish the opportunity to talk about intestinal ischemia? To your point or to your question, I do think breaking down mesenteric ischemia into acute and chronic ischemia is helpful. The presentations tend to be distinct.

Those are worthwhile ways to initially categorize the condition. I generally will then further break down acute mesenteric ischemia into four relatively distinct pathophysiological subtypes, which include acute embolic ischemia, acute thrombotic ischemia, non-occlusive ischemia, and then finally acute mesenteric venous ischemia.

Dr. Lacy:  David, That's a really good approach, and thank you for setting the stage. We're going to circle back to that in a little bit. Now that we're thinking about your diagnostic approach of acute versus chronic and then your four subtypes of acute mesenteric ischemia, how common is this problem?

Dr. Tendler:  Thankfully, it remains a relatively rare condition. Epidemiologically, the incidence is estimated to be somewhere between 2 and 7 per 100,000 patients, so it is relatively rare. However, the exception to this is in the subgroup of patients who are over age 70 and present to the emergency department with an acute abdomen.

In that particular population of over 70-year-old patients with acute abdomens, it could account for up to 10 percent of those emergency department visits. That's an important subtype.

Dr. Lacy:  Wow, that's a nice fact to know. It's almost speaking to my next question about risk factors. Which populations are at risk? Certainly, in the ER, severe abdominal pain and acute abdomen and an older patient. How about the general population at risk? Is this more of a problem in women, or in those who smoke, or those on estrogen-containing medications?

Dr. Tendler:  That's a great question and an important one because probably the most important thing to thinking about and making the diagnosis is understanding the right patients to think about it. The risk factors for intestinal ischemia vary according to the underlying cause. In general, the same risk factors that are associated with other forms of vascular disease apply to mesenteric ischemia.

For example, women or those that are on prothrombotic medications such as estrogen are at a higher risk for acute mesenteric vein thrombosis. The same is true for other hypercoagulable states, both primary hypercoagulable states and secondary hypercoagulable states, such as malignancy or those associated with abdominal trauma.

Whereas those with underlying cardiovascular disease are the ones that tend to be at risk for acute thromboembolic ischemia. That tends to occur in older patients with arrhythmias like Afib, valvular disease, history of myocardial infarction, history of congestive heart failure, history of stroke. That's the population.

Finally, the non-occlusive ischemia group are typically the critically ill patients who are at risk for acute drops in intestinal perfusion. They may have cardiogenic or septic shock, acute arrhythmias could even happen on dialysis or during cardiac bypass.

Those are the main groups. I guess the other group that's also important to think about which breaks the pattern here are those that are at risk for non-occlusive ischemia outside of that setting.

Those tend to be people that are on drugs that compromise intestinal blood flow, and that includes cocaine. That's an important subgroup. Younger patients that present with acute abdomen, that's certainly a worthy consideration.

Dr. Lacy:  David, you've once again beat me to the punch. Thinking about the pathophysiology and etiology of this disorder, as you mentioned, embolic disease, thrombotic disease, non-occlusive disease, and acute venous thrombosis, but to even tease that a little bit more, could you maybe speak a little bit about other potential factors such as dehydration, hypovolemia, and maybe diabetes?

Dr. Tendler:  At the root of all forms of intestinal ischemia, very simply is a mismatch between intestinal blood supply and demand. All of the subtypes still follow that basic premise. While the gut is blessed with a wonderful system of collaterals, that safety valve can easily be compromised in a variety of settings. Again, that hearkened back to the subtypes of ischemia.

In general, physiologically, what we find is that two of the three major mesenteric arteries, which of course include the celiac artery, the superior mesenteric artery, and the inferior mesenteric artery, that two of those three generally have to suffer some form of high-grade compromise to the caliber of the lumen, which we usually find to be greater than 70 percent.

Whether that's from an embolism or thrombosis, that's generally the issue. In the conditions you spoke about before, particularly in patients who might have diabetes or other forms of diseases that may be associated with vascular disease, those are the patients that generally are more likely to present with thrombotic ischemia.

In those situations, that tends to be more of a sub-acute or chronic process that then leads into an acute thrombotic event. We can certainly touch on that again also.

Dr. Lacy:  Those are two great teaching points that I want to reiterate is that for many providers who may not see as many patients with these conditions as you do, it should be typically two of the three arteries, not just one, and 70 percent is a great threshold for stenosis. That 30 percent stenosis of the celiac artery is probably not enough to cause these symptoms.

Dr. Tendler:  That's right. It's also worth noting that while that obviously pertains to those three forms or at least the two forms of occlusive ischemia that involve the arteries, in the case of acute venous mesenteric ischemia, there's a thrombosis that impairs the drainage of the small bowel through the SMV, the superior mesenteric vein.

In that case, the valve becomes edematous, blood flow is hampered, and then the bowel can become ischemic and necrose. Then finally, in the non-occlusive ischemic patient, there's just an acute drop in perfusion.

Dr. Lacy:  Great, thank you. You hinted at this early on, but what are the typical symptoms our listeners should be aware of?

Dr. Tendler:  Classically, what we have ingrained in us which holds true is that patients present with acute severe, generally mid abdominal, but doesn't have to necessarily be focal, abdominal pain, it's out of proportion to the physical exam. Why is that? In the early stages of ischemia, before there's infarction, there's not an inflammatory component that irritates the perineum.

Unlike conditions like diverticulitis, appendicitis, cholecystitis, where there's peritoneal inflammation that comes along with acute abdomen, that's not the case in a vascular condition. Generally, the pain can be quite severe, but the physical exam findings don't show those peritoneal signs of an acute abdomen like you might have in other conditions.

Otherwise, nausea, vomiting, abdominal distension are common symptoms. The context is the key. In the patient who's presenting with acute severe pain, who may be elderly, at risk for vascular disease, or even a younger patient that might be taking cocaine or birth control, in that context, an acute abdomen should trigger the thought at least of mesenteric ischemia.

Dr. Lacy:  That key phrase pain out of proportion to the physical exam still holds true. Mentioned, I think in Cope's diagnosis of the abdomen in the 1920s still holds true. Now that we're thinking about some of those classic symptoms, what tests are required to accurately make the diagnosis of acute mesenteric ischemia?

Dr. Tendler:  I keep harking back to this, but it remains true that the most important "diagnostic test" still remains having heightened awareness. Without that, there's almost no chance of making the diagnosis promptly enough to change outcome. That said, there are a few points that are worth making.

What we'll find in terms of diagnostic tests, patients may have elevated white blood cell counts, lactated levels, metabolic acidosis. It's important to remember that there is no lab test that has a high enough sensitivity or specificity to make a diagnosis of intestinal ischemia.

The same is true for plain films. You may see an ileus, you may see thumbprinting, but again, the predictive value just remains poor. In the right setting, you're thinking about it. The best initial diagnostic test remains CT angiogram, and that's without oral contrast. That's an important point because oral contrast can obscure the mesenteric vessels.

Then thereafter, if a patient does not have peritoneal signs, does not have signs of bowel infarction, then we will usually progress to angiography both for diagnosis as well as to initiate therapy, which we'll touch on. In patients that have peritoneal signs or concerned that there may be bowel infarction, there should be no delay to laparotomy. That's the most important test in that subgroup.

Dr. Lacy:  Wonderful. Recognizing that treatment options vary to some degree based on the four subtypes of embolic, thrombotic, non-occlusive, acute venous ischemia. What treatment options do we have?

Dr. Tendler:  There are some generalizations that apply irrespective of the subtype. Initial management is restoring good volume, good blood flow. IV fluids are important, oxygen. Because of the risk of bacterial translocation and infarction, broad-spectrum antibiotics are generally initiated. NG tube decompression in the acute ischemic patient. These basics all apply irrespective of the subtype.

Unless it's otherwise contraindicated, heparin is usually started in order to stop or prevent a propagation of a blood clot. Thereafter that, then therapy is geared towards restoring blood flow, and of course, resecting any non-viable bowel. Restoring blood flow in terms of treatment options can be accomplished either surgically or endovascularly.

Options there include thrombolysis, angioplasty, plus or minus stenting. The choice about whether to proceed with therapy that's endovascular versus surgical really depends on a lot of factors, whether the patient is a high surgical risk, what the underlying anatomy is like, and of course, the particular expertise to the institution makes a big difference.

Dr. Lacy:  Wonderful. Fluids, fluids, fluids still remain a mainstay of therapy, don't they?

Dr. Tendler:  Absolutely.

Dr. Lacy:  Let's think about maybe a younger patient with an episode of acute mesenteric ischemia for whatever reason. What do you tell him or her about future events? Is it going to happen again guaranteed or 10 percent risk? What do you tell them?

Dr. Tendler:  Thankfully, most patients that are younger, who have a [inaudible 12:01] of acute intestinal ischemia, tend to have reversible or at least manageable risk factors.

They may be on a medication. There may be drug use, like in the case of cocaine, or they may have a hypercoagulable state. Thankfully, most of those are addressable. The risk factors, if they're addressed appropriately, tend to obviate the risk for future events.

Dr. Lacy:  Wonderful. David, as a little bit of an aside since you've mentioned it twice now. Thinking about that patient with a hypercoagulable state, should all these patients see a hematologist or go back to their internist? Are we comfortable, maybe as gastroenterologists, checking the protein C, protein S, antithrombin level?

Dr. Tendler:  Again, if you have the ability and the expertise, hematology consultation is smart in this population unless there's another obvious reason for thrombosis.

Particularly in a younger patient, that is critical in that situation because you don't want to subject anybody, but certainly, a younger person who's got hopefully many years ahead of them, to a higher risk of recurrence than is otherwise necessary. Doing hypercoagulable workup by an expert is ideal simply because it's an evolving field.

There's always new genetic defects that are being recognized, new hypercoagulable states. Maybe not speaking for you, Brian, but for me, I'm probably not the best equipped to figure all that out.

Dr. Lacy:  I'm in 100 percent agreement. This is where you pull the experts in.

Thank you for listening in today with this great discussion with Dr. David Tendler, who's at Duke University in Durham, North Carolina. Please tune in for part 2 of our discussion on mesenteric ischemia. Looking forward to having you on that podcast.