Bowel Ischemia

What is Bowel Ischemia?

Bowel ischemia happens when blood flow to the intestines is reduced, affecting either a small or large section of the gut. While it’s not a common condition, it’s very serious as it has a high mortality rate. The blood supply to the intestine comes from two main arteries – the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA). Each artery supplies different sections of the gut, and a third artery, the celiac artery, can also provide some blood supply.

Bowel ischemia can be split into two types: small intestine ischemia, or mesenteric ischemia, and large intestine ischemia, usually referred to as colonic ischemia. Certain areas in the large intestine are more vulnerable to ischemia, particularly where two arteries come together to supply the colon. These areas, known as the ‘watershed’ areas, make up around 70% of ischemic colitis (inflammation and injury of the colon due to inadequate blood supply) cases. Half of the population have a poorly developed artery supplying these areas. Just like the blood coming in, the blood going out also follows the same arterial structure.

Acute or sudden drops in mesenteric arterial blood flow are responsible for most cases of mesenteric ischemia. The other causes are usually related to colonic ischemia. Abdominal pain is the most frequent symptom of intestinal ischemia. There may be other signs, like rectal bleeding or bloody diarrhea, which are more common in acute colonic ischemia, particularly in people over 60 years old who have mild abdominal pain and don’t seem severely ill.

A CT scan of the abdomen is typically used for patients who are stable but have acute abdominal pain. For patients where there is a strong suspicion of intestinal ischemia, special CT or MR angiography tests are used. Depending on the specific type of acute mesenteric ischemia, different medications can be used to treat it. One of these, papaverine, relaxes the blood vessels. It can be used to treat various forms of arterial mesenteric ischemia and nonocclusive mesenteric ischemia.

What Causes Bowel Ischemia?

Intestinal ischemia happens when blood flow to the intestine is cut down by at least 75% for over 12 hours. This condition can impact the small intestine (known as mesenteric ischemia) or the large intestine (often referred to as colonic ischemia).

Mesenteric Ischemia

Mesenteric Ischemia (MI) can happen suddenly (acute) or over time (chronic). The body’s natural system can handle up to a 75% sudden drop in blood flow to the gut for up to 12 hours without serious damage. Acute intestinal ischemia can be caused by a blood clot in the intestinal artery (50% of cases), reduced blood supply to the gut or non-blockage related ischemia (20-30% of cases), a blood clot in the mesenteric artery (15-25% of cases), or a blood clot in the mesenteric vein (5% of cases).

1- A blood clot in the intestinal artery often affects people with heart disease. Common heart causes include heart attacks, narrowed heart valves, irregular heartbeat, weak heart walls, and bacterially infected heart valves. Other vascular factors include infected blood vessels, plaque in the aorta, or artificial vessel grafts in the aorta.

2- Reduced blood supply or non-blockage related ischemia typically happens in those who experience a drastic drop in blood pressure, which could be due to heart disease, infection, or severe dehydration. This type accounts for about 95% of colonic ischemia cases.

3- The risk for a blood clot in the mesenteric artery is higher in older people or in those with peripheral artery disease, severe injury, or poor heart function.

4- A blood clot in the mesenteric vein can occur in individuals with conditions that increase the ability of the blood to form clots.

Chronic Mesenteric Ischemia

In chronic mesenteric ischemia, widespread hardening of the arteries is the cause in 95% of cases. Women over the age of 60, smokers, those with a history of stroke, heart disease, or peripheral artery disease, are at an increased risk of chronic intestinal ischemia. The remaining 5% is caused by conditions such as vessel inflammation, abnormal muscle and artery development, Takayasu arteritis, cancer, and radiation.

Risk Factors and Frequency for Bowel Ischemia

Mesenteric ischemia, a condition caused by a sudden decrease in blood flow to the intestines, is a concern for 60% to 70% of patients. The remaining causes relate to colonic ischemia and chronic mesenteric ischemia. Despite this being a relatively rare condition, accounting for only 0.1% of all hospital admissions, it has high mortality rates, ranging from 24% to 94%.

• Mesenteric ischemia is caused by a decrease in blood flow to the intestines in 60% to 70% of patients.
• The rest of the cases are linked to colonic ischemia and chronic mesenteric ischemia.
• While the condition is rare, making up only 0.1% of all hospital admissions, it comes with high mortality rates of 24% to 94%.
• Colonic ischemia occurs in 16 cases per 100,000 person-years and is on the rise.
• Ischemic colitis is reported for 1 in 2000 hospital admissions.
• This medical condition is more commonly seen in females.

Signs and Symptoms of Bowel Ischemia

Intestinal ischemia, a condition characterized by inadequate blood flow to the intestines, can be serious if not identified and treated early. Knowing a patient’s medical and family history can help in diagnosing this disorder. This includes any history of heart disease, aortic surgery, peripheral artery disease, hemodialysis, vasoconstrictive medication use, clotting disorders (either hereditary or acquired), hypovolemia, and current or previous inflammation or infections.

The most common symptom is abdominal pain, which, along with other patient characteristics, can provide hints on differentiating between acute small bowel and colonic ischemia. The former is more likely in patients over the age of 60 who might not appear severely ill, with symptoms like mild abdominal pain, tenderness, rectal bleeding, or bloody diarrhea.

The nature of the pain, accompanying symptoms, and physical examination results can help pinpoint the root cause of the intestinal ischemia. Here are some key symptoms to note:

• Mesenteric artery embolism: sudden, severe, belly-button level pain often accompanied by nausea and vomiting.
• Thrombotic mesentery ischemia: pain commonly occurs after eating.
• Mesenteric veins thrombosis: the pain described as coming and going before a definitive diagnosis.
• Nonocclusive mesenteric ischemia: patients don’t typically have sharp pain and usually have a history of low blood pressure, hypovolemia, irregular heartbeat, and heart failure.
• Chronic mesenteric ischemia: recurring abdominal pain after eating which can lead to weight loss.
• Acute colonic ischemia: sudden onset cramping abdominal pain, usually on the left side, accompanied by an urgent desire to defecate. The pain will typically feel more on the side rather than around the belly button, which is more common in small intestine ischemia.

Physical examination results can vary from normal to showing signs of peritoneal irritation (such as rebound tenderness and guarding) depending on when the symptoms started.

Testing for Bowel Ischemia

In simple terms, tests to diagnose intestinal ischemia, a condition where the blood flow to the intestines is reduced, might not always yield clear results. At the start of the condition, a complete blood cell count (which measures the amounts of various cells in the blood) might be completely normal. However, as intestinal ischemia progresses, you might see an increase in white blood cells (a condition known as leukocytosis), as well as higher levels of amylase and lactate dehydrogenase enzymes in your blood.

The exact results of these laboratory tests can depend on other risk factors. For example, in a condition called mesenteric venous thrombosis (MVT), patients are tested for issues related to blood clotting. In another condition known as chronic mesenteric ischemia (CMI), patients may show abnormal results due to being malnourished, such as a lower than normal number of white blood cells, low levels of a protein called albumin, and abnormalities in electrolyte levels.

How to proceed in diagnosing patients with intestinal ischemia heavily depends on the severity of their symptoms. If a patient is showing signs of peritonitis, a severe abdominal inflammation, their diagnosis might have to involve physically examining the abdomen.

Various imaging techniques are also commonly used, including X-rays, computed tomography angiography (CTA), magnetic resonance angiography (MRA), invasive angiography, and duplex ultrasound. An X-ray of the abdomen might show features like an obstruction of the bowel, the thickening of the bowel wall, or the presence of particular types of gas, all of which could suggest mesenteric ischemia.

In patients who are stable and experiencing acute abdominal pain, abdominal CT scans are used to check for other potential causes of the pain. This might include the presence of particular types of gas, fluid or inflammation in the abdomen. The abdominal CT scans should, however, be done without oral contrast because that can sometimes interfere with the results.

If intestinal ischemia is highly suspected, CTA and MRA are the first tests done usually. But CTA is preferred over MRA due to lower cost, wider availability, and speed. Angiography is usually reserved for patients with a high suspicion of Acute Mesenteric Ischemia with negative CTA.

Duplex ultrasound, which uses sound waves to create a picture of the blood vessels, is limited in what it can detect. It can identify blood clots in the main blood vessels. Other factors, like the presence of gas in the peritoneum, previous abdominal surgery, or obesity, can make it less effective.

In stable patients who show signs of acute colonic ischemia, which includes symptoms like abdominal pain, the immediate need to defecate, diarrhea, and lower gastrointestinal bleeding, other tests like sigmoidoscopy or colonoscopy (examinations of the lower part of the colon) and biopsy (tissue sample examination) may be necessary. If colonic ischemia is suspected, it’s best to perform the colonoscopy within 48 hours from when the symptoms were first observed.

Treatment Options for Bowel Ischemia

Acute Mesenteric Ischemia (AMI) is a severe health condition with a high death rate, needing urgent treatment. The initial steps include maintaining adequate oxygen supply, stabilizing blood pressure and heart rate, and correcting any imbalance of electrolytes (minerals in the body). Typically, 2 to 4 units of blood should be on hand, and drugs that constrict blood vessels (vasopressors) should be avoided. To prevent and treat infections, doctors recommend a broad-spectrum antibiotic that fights many types of bacteria. Other measures include inserting a bladder catheter and a nasogastric tube, fixing any acid/base abnormalities, and administering fluids intravenously, all before surgery. It’s also essential to keep the patient comfortable, usually through injectable painkillers.

Depending on the type of intestinal ischemia, different treatments might be needed. There is evidence that both endovascular intervention (a minimally invasive procedure inside blood vessels) and traditional surgery can be successful in cases of acute mesenteric arterial occlusion (blockage).

Endovascular intervention includes either drug treatment or mechanical removal of the blockage, such as pulling it out via a large tube (catheter) with a stiff wire. In special cases, drugs that dissolve blood clots are used. Current evidence suggests that certain medications have a lower risk of non-brain bleeding, and so tend to be favored. An initial heparin injection, a blood thinner, helps prevent further clotting. This is followed by warfarin, another blood thinner, administered orally for at least six months.

Another endovascular method is balloon angioplasty, often followed by inserting a stent to keep the artery open. This method depends on the condition and might get used in chronic cases of ischemia. If the occlusion cannot be removed or surgical bypass is not possible, a device can be introduced to restore blood flow.

Surgery might involve exploring the abdomen and taking control of the damage. In other words, if there’s suspicion of serious damage to the intestines or intestinal perforation based on clinical tests, immediate exploratory surgery is necessary. Sometimes, parts of the dead intestine might need to be removed. Special tests can help doctors identify low blood flow areas in the intestines during the surgery.

Revascularization, or restoring blood flow, can take different forms. If open surgery is necessary, embolectomy, or removal of an embolus (blockage), can be a good option. If reperfusion, restoring blood flow, fails, a mesenteric bypass could be required. In this procedure, surgeons create a bypass to reroute the blood from a source area to a specific point after the obstruction. It’s often necessary to recheck bowel conditions 24 – 48 hours after the initial operation.

In the case of NOMI (Non-occlusive Mesenteric Ischemia) or Colonic Ischemia, treatment is usually about dealing with known causative factors, providing supportive care, and treating underlying conditions. Some patients might need open surgery. The severity of ischemia varies according to many factors like heart rate, blood pressure, lab test results, etc. In severe cases, urgent surgical referral and intensive care unit monitoring are required.

What else can Bowel Ischemia be?

When it comes to diagnosing bowel ischemia, doctors have to consider a variety of other conditions that also cause abdominal pain. Depending on where the pain is located, some other conditions to consider include:

If the pain is in the upper abdomen, possibilities might include:

• Gallstones
• Medical conditions affecting the gallbladder like acute cholecystitis or cholangitis
• Liver-based problems such as hepatitis, perihepatitis, or liver abscess
• General upper stomach pain
• Pancreatitis, an inflammation of the pancreas
• Peptic ulcer disease, which is a sore that’s on the inside of the stomach lining
• Gastroparesis, a condition that affects the stomach muscles and prevents proper stomach emptying

When the pain is in the lower abdomen, the conditions could include:

• Acute appendicitis, which is inflammation of the appendix
• Diverticulitis, a condition that occurs when small bulging pouches or diverticula in the digestive tract get inflamed or infected
• Problems related to kidney stones or kidney infection called pyelonephritis
• Infectious colitis, an inflammation of the large intestine due to infection

If the pain is all over the abdomen, it could be because of:

• Obstruction, or blockage, in the intestines
• Inflammatory bowel disease, a disorder that results in inflammation of the digestive tract
• Spontaneous bacterial peritonitis, an infection in the abdomen
• Cancers such as colorectal, gastritis, or pancreatic

Thus, doctors must take a comprehensive approach to accurately diagnose bowel ischemia by considering all the possible alternative conditions.

What to expect with Bowel Ischemia

The outcome for patients with intestinal ischemia can vary greatly, dependent on the root cause of the condition. In cases of acute mesenteric ischemia, mortality rates can sometimes reach above 60%. Acute mesenteric venous thrombosis, a specific type of the condition, tends to have a lower overall mortality rate compared to other forms.

Thanks to improved recognition and early treatment of mesenteric venous thrombosis, both death and health-complicating rates have improved over time. If this condition is diagnosed early and treated with anticoagulation therapy, mortality rates drop to between 10 and 20%.

For patients with Chronic Mesenteric Ischemia (CMI), the chance of death during or immediately after surgery can vary widely, from 0 to 16%, but this increases to up to 50% if acute symptoms develop.

The outlook for patients with Non-occlusive Mesenteric Ischemia (NOMI) or ischemic colitis is influenced by the cause, the severity, and the extent of their illness. If the colonic tissue is not gangrenous, the mortality rate is less than 5%. However, patients who have colonic necrosis and gangrene face higher death rates.

Possible Complications When Diagnosed with Bowel Ischemia

These are several serious conditions that can occur due to complications in the intestines and the rest of the body:

• Bowel Infarction and bowel perforation (tissue death and rupture in the intestine)
• Gangrenous and necrotic bowel (decaying tissue in the intestine)
• Sepsis (a severe infection that can spread throughout the body)
• Endotoxemia with bacterial translocation (when bacteria escape from the intestine and enter the bloodstream, releasing toxins)
• Toxic megacolon (severe inflammation and enlargement of the colon)
• Multiple organ failure (when several organs stop working at the same time)
• Fibrosis (thickening and scarring of connective tissue)
• Fistula (an abnormal connection between two body parts)
• Colonic stricture (narrowing of the colon)

Preventing Bowel Ischemia

Teaching patients about their diseases in various ways can be really important for their care. In the beginning, it’s crucial to inform patients about how the disease might show itself. Recognizing the signs and symptoms early on can make a huge difference in their health. Acting quickly and getting treatment as soon as possible is key to managing the disease well. This is more likely to happen if patients get help as soon as they notice the symptoms.