Intestinal Ischemia

Intestinal ischemia is the term used to describe the result of a variety of disorders that cause insufficient blood flow to the gastrointestinal tract. Such ischemic injuries can manifest with symptoms ranging from a mild bout of short-lived abdominal pain or diarrhea to bloody diarrhea or a more serious situation, such as gangrene that may require surgery and even end in death.

Current management of intestinal ischemia has evolved from simply managing the grave consequences after an acute event to more aggressive and proactive methods aimed toward recognizing and exploring early warning signs and preventing potentially catastrophic complications.

It is essential to emphasize that successful management of intestinal ischemia involves a partnership between patients and their physicians. Recognition of the early symptoms and risk factors for the disease by patients greatly enhances their physicians’ ability to offer a diagnosis and appropriate management.

Ischemia either can be localized to a relatively small part of the small intestine or colon, or it may be more widespread and involve significant portions of both.

The time course of the ischemic event also may vary and be acute (new), chronic (long-standing), or recurrent.

An ischemic problem may be caused by an interruption in blood passage through an artery (a blood vessel that brings blood to the intestines) or vein (a blood vessel that returns blood from the intestines to the heart).

There are several ways in which arterial blood supply to the intestines can be restricted:

• an embolus (a migrating blood clot that can form a blockage),
• a thrombus (a stationary clot attached to the wall of a blood vessel that can prohibit blood passage),
• or a so-called non-occlusive state (spasm of a blood vessel, but without permanent obstruction, that restricts blood flow through an artery).

Venous problems also may result in intestinal ischemia, although less commonly than arterial causes. The most common cause of ischemia from venous obstruction is a thrombus which interferes with the return of blood flow from the intestines, produces intestinal congestion, and results in intestinal swelling, and occasionally bleeding.

Signs and symptoms of intestinal ischemia can develop suddenly (acute) or gradually (chronic).

The most common form of ischemic injury to the intestines is colon ischemia. Colon ischemia usually manifests as sudden, mild-to-moderate left-sided lower abdominal pain with an urgent desire to defecate, and the passage, within 24 hours, of bright red or maroon blood mixed with the stool.

Alternatively, some patients with colon ischemia manifest severe right-sided lower abdominal pain with minimal to no bleeding. The vast majority of patients with colon ischemia do well; a minority develops irreversible disease such as chronic ischemic colitis, stricture (narrowing) formation or gangrene.

Patients who have colon ischemia that is confined to the right side of the colon have a worse prognosis with a greater need for surgery and a higher mortality rate than patients whose colon ischemia affects other parts of the colon, alone or in combination with right-sided involvement.

Most patients with an acute episode of small intestinal ischemia present with the sudden onset of severe abdominal pain. Early in the process, the abdomen is usually soft, flat, and not tender to touch. Most patients with small intestinal ischemia do not have diarrhea or rectal bleeding. Abdominal distention may be the first sign of a serious injury to the intestines. A sudden, forceful bowel movement associated with severe abdominal pain suggests an acute arterial occlusion caused by an embolus.

A more slowly developing course usually occurs when small intestinal ischemia is caused by an arterial obstruction from a thrombus. The obstruction is usually clinically silent but causes pain when blood flow is insufficient to permit the basic activities of the intestines, such as normal motility and digestion. The presence of abdominal pain specifically after meals in the weeks to months before an acute thrombosis is sometimes prelude to such an occurrence.

Patients with acute small intestinal ischemia resulting from a thrombus in a vein rather than an artery also experience abdominal pain. The pain is more variable and typically less severe than with arterial thrombosis; it may occur in a so-called “tumbleweed” type of recurring and remitting abdominal pain.

Other symptoms may include:

• nausea,
• vomiting,
• diarrhea with or without blood.

Here again, patients usually have already had more subtle symptoms prior to the sudden event. Many patients with a venous thrombus have been diagnosed with blood clots in the past or have a high risk of developing clots because of a familial clotting problem, or underlying conditions like cancer, inflammatory bowel disease (IBD), or lupus, or because they take medications that may promote clotting such as oral contraceptives.

The presence of non-occlusive acute small intestinal ischemia (from spasm of the blood vessels) may be overshadowed by the other illnesses a patient might have, such as:

• heart failure,
• hypotension (low blood pressure),
• aheart attack,
• cardiac arrhythmia (irregular heart beat).

A patient in these settings may already be quite ill and abdominal pain may be absent. Unexplained abdominal distention or bleeding from the rectum may be the only signs of intestinal ischemia in these circumstances.

Chronic small intestinal ischemia (or “intestinal angina”) is typically associated with dull, cramping abdominal pain felt 10 to 30 minutes after eating and reaching its peak 1 to 3 hours after a meal. The pain can increase in severity to where the patient fears eating and therefore reduces the size of meals or eats less frequently and loses weight.

Symptoms of this condition, in contrast to those of the other intestinal ischemic disorders, usually become progressively more severe over an extended period of time, without resulting in a severe crisis until late in the picture.

There are several possible causes of intestinal ischemia and infarction.

Hernia

If the intestine moves into the wrong place or becomes tangled, this can cut off blood flow.

Adhesions

The intestine may become trapped in scar tissue from past surgery (adhesions). This can lead to ischemia if left untreated.

Embolus

A blood clot from the heart or main blood vessels may travel through the bloodstream and block one of the arteries supplying the intestine. People who have had a heart attack or who have arrhythmias, such as atrial fibrillation, are at risk for this problem.

Arterial thrombosis

The arteries that supply blood to the intestine may become so narrowed or blocked from atherosclerotic disease (cholesterol buildup). When this happens in the arteries to the heart, it causes a heart attack. When it happens in the arteries to the intestine, it causes intestinal ischemia.

Venous thrombosis

The veins carrying blood away from the intestines may become blocked by blood clots. This interrupts blood flow in the intestines. This is more common in people with liver disease, cancer, or blood clotting disorders.

Low blood pressure

Very low blood pressure in patients who already have narrowing of the intestinal arteries may also cause intestinal ischemia. This often occurs in people with other serious medical problems.

Early diagnosis of intestinal ischemia is essential to improve the chances for a good outcome. In general, the longer the injury is sustained without treatment, the greater the chance that the damage done to the intestines will be irreversible.

The first considerations for a physician in diagnosing intestinal ischemia are the patient’s past medical history, his or her current symptoms, and results of a thorough physical examination. The diagnostic tools most commonly used to supplement this information include

• routine blood tests,
• colonoscopy,
• ultrasound,
• abdominal radiologic studies including CAT or MRI scans,
• mesenteric angiography,
• exploratory abdominal surgery.

Angiography is a special radiologic study of one’s blood vessels. Contrast material is injected through a small catheter placed into an abdominal artery or vein, after which radiologic images of the vessels are generated.

Angiography is considered the gold standard for diagnosis and is usually performed after a CT scan has shown that the abdominal pain is not caused by any other disorder that is mimicking intestinal ischemia. Sometimes a CT-angiogram, which is a non-invasive way of studying the intestine and its blood vessels, obviates the need for a formal angiographic study.

When a venous obstruction is suspected, CT scan has been used successfully for diagnosis. Angiography can be used more selectively to aid in treatment of a particular vein.

In cases of non-occlusive intestinal ischemia, there is no identifiable point of blockage seen by angiography. Rather, the blockage is caused by diffuse spasm in the blood vessels supplying the intestines and the spasm is precipitated by underlying medical conditions such as

• heart failure,
• cardiac arrhythmias,
• hypotension;

these underlying conditions must be addressed to help restore blood delivery to the intestines.

In colon ischemia, the extent and severity of the injury again dictates the action taken. If the patient is stable, colonoscopy is ideally performed within 24-48 hours of the onset of symptoms. Patients in this situation can expect to be placed on a restricted diet in the short-term, and given antibiotics to prevent serious infection.

In most cases, symptoms abate within 1 to 2 days and the injury to the colon resolves in 1 to 2 weeks. A minority of patients develops more significant consequences and is treated accordingly, possibly with surgery.

Treatment methods for intestinal ischemia are:

• Surgical: Embolectomy, revascularization, with or without bowel resection.
• Angiographic: Vasodilators or thrombolysis.
• Long-term anticoagulation or antiplatelet therapy

If diagnosis is made during exploratory laparotomy, options are surgical embolectomy, revascularization, and resection. A “second look” laparotomy may be needed to reassess the viability of questionable areas of bowel.

If diagnosis is made by angiography, infusion of the vasodilator papaverine through the angiography catheter may improve survival in both occlusive and nonocclusive ischemia. Papaverine is useful even when surgical intervention is planned and is sometimes given during and after surgical intervention as well. In addition, for arterial occlusion, thrombolysis or surgical embolectomy may be done.

The development of peritoneal signs at any time during the evaluation suggests the need for immediate surgery. Mesenteric venous thrombosis without signs of peritonitis can be treated with papaverine followed by anticoagulation with heparin and then warfarin.

Patients with arterial embolism or venous thrombosis require long-term anticoagulation with warfarin. Patients with nonocclusive ischemia may be treated with antiplatelet therapy.

Preventive measures for intestinal ischemia include:

• Control risk factors, such as irregular heartbeat, high blood pressure, and high cholesterol
• Do not smoke
• Eat a nutritious diet
• Quickly treat hernias

There are several risks and complications associated with intestinal ischemia.

The ultimate effects of reduction in intestinal blood flow vary. The milder forms of ischemic injury may involve several days of abdominal discomfort and altered bowel habits (e.g., diarrhea, bloody stool) or chronic low-grade cramping abdominal pain associated with eating (“intestinal angina”).

The more severe cases may present with life-threatening gangrene and rupture of the intestines or bleeding, and may require hospitalization and surgery.

In order to take full advantage of the advances made in the diagnosis and treatment of these disorders and to improve the chances of recovery, early diagnosis is essential.

Individuals who experience the symptoms, particularly those persons who are identified at greatest risk for intestinal ischemia, should seek the attention of their physician immediately.