Mesenteric Ischemia

Eight seasons ago (Can you believe we've been on the air for EIGHT seasons?), our residents had just entered their first year of residency – their "intern" year. They may have been invited into the OR with the big dogs, but they were barely allowed to hold a retractor. And now, as they have started their fifth year, they stand in the lead surgeon's spot. They're the ones that say: "Scalpel." They're the ones who make the first cut. They're the ones who make the difficult decisions. 

And what difficult decisions they can be. In tonight's episode, "Take The Lead," Alex chooses the hardest option a surgeon can face in an OR: to stop.

So wait, what did Alex's patient have?

The mesenteric arteries are the arteries that supply blood to the large and small intestines. Ischemia occurs when the blood cannot flow through the arteries as well as it should, and the intestines do not receive the necessary oxygen to function normally. Without an adequate source of oxygen, the cells in the intestine weaken and eventually die. Depending on the severity, infection and/or gangrene may ensue.

You've heard of a heart attack? Well, this is like an INTESTINAL attack.

Typically, mesenteric ischemia occurs when one or more of the arteries narrows or becomes blocked. Predisposed patients include those older than age sixty, smokers, or people with high cholesterol. It usually involves the small intestine, but it may involve other intra-abdominal organs such as the colon, liver, and stomach. The condition can either be chronic (such as Alex's patient Sam) or acute. Sam suffered from abdominal pain and complications for a few years, but acute mesenteric ischemia can present suddenly and worsen very quickly.

Atherosclerosis, a condition that slows the amount of blood flowing through the arteries, may also contribute to chronic mesenteric ischemia. Due to a build-up of plaque (a sticky substance made of fats and other materials circulating in the blood), the arteries can narrow or stiffen.

A common cause for acute mesenteric ischemia is an embolus, or clot, that travels to one of the mesenteric arteries and blocks blood flow. Clots often form in the heart, but they tend to be more frequent in patients with an irregular heartbeat or heart disease.

Other predisposing factors include:

• Low blood pressure.
• Congestive heart failure.
• Aortic dissection.
• Occlusion or blockage of the veins in the bowel.
• Coagulation disorders.
• Unusual disorders of the blood vessels.

Besides abdominal pain, what are other symptoms of the condition?

Chronic mesenteric ischemia typically presents with the following:

• Severe pain in the abdomen 15 to 60 minutes after eating.
• The pain may last from 60 to 90 minutes and then disappear.
• Weight loss.
• Diarrhea.
• Vomiting.
• Flatulence.
• Constipation.

Acute mesenteric ischemia usually involves a sudden onset of the following:

• Severe stomach pain.
• Nausea.
• Vomiting.

The symptoms seem fairly vague, right? It's hard even for the doctor to find sometimes.

Well, the pain is often out of proportion to the doctor's physical exam findings, which can be a clue. But, additional tests may be performed.

If the doctor suspects acute mesenteric ischemia and needs a rapid diagnosis, he may choose to run an angiogram – X-ray imaging of the blood vessels. The doctor injects a contrast dye through a catheter in the patient's groin or arm in order to visualize the blood vessels.

Doctors may also perform an ultrasound, which uses high-frequency sound waves that bounce off blood cells and vessels to determine blood flow. Even though it may take more time to perform, an ultrasound can be efficient in identifying blocked arteries.

A patient will have blood tests run because acute mesenteric ischemia can cause an elevated white blood cell count. Blood tests can also show the amount of acid in the body – high levels can indicate bowel injury.

CT scans and Magnetic Resonance Angiograms also may be helpful in that they project three-dimensional images of the body, potentially revealing any problems with the arteries or abdominal organs.

What kinds of treatments exist?

Regardless of the type of mesenteric ischemia, the doctor's priority is to try and re-open the artery to allow normal blood flow again. For chronic cases, the doctor may try a trans-aortic endarterectomy – a procedure in which the plaque is removed from the mesenteric artery through an incision in the abdomen. Or, bypass surgery may be attempted. The surgeon would create a "detour" around the narrowed/blocked section of the artery by either using one of the patient's veins or a man-made tube, just like in the heart. The bypass would be attached above and below the affected area, establishing a new path for blood to flow. A newer treatment option includes angioplasty with stenting. The surgeon would inflate a small balloon inside the narrowed artery, widen it, and then insert a stent to support the artery's walls in remaining open.

Due to the rapid damage caused by acute mesenteric ischemia, treatment must be emergent. If a clot exists, doctors first would try administering thrombolytic agents to dissolve it. However, the surgeon may have to remove the clot in the OR if it has already inflicted intestinal damage. Or similar to Sam's case, portions of the intestine may need to be surgically removed due to the extent of the damage.

You're probably wondering about that crazy fluorescent stuff that Alex was injecting into the patient.

That "stuff" would be a synthetic organic compound called fluorescein. General surgeons can use it in the middle of surgery to determine the viability of bowel tissue. In other words, the fluorescein helps determine if certain parts of the bowel have died. Surgeons inject the sodium fluorescein intravenously through a vein over 30 to 60 seconds. The OR staff then darkens the room, and the operative field is then illuminated with a standard ultraviolet, or "Woods" lamp. Only bowels with a good blood supply (and are therefore healthy) will receive the fluorescein through the veins. The dead or dying bowels have no blood supply and therefore do not light up with color. And so as we saw tonight, the lack of color or patterns indicates non-viable bowel.

For more information on mesenteric ischemia, please visit:

http://www.nlm.nih.gov/medlineplus/ency/article/001156.htm