Ischemia

Ischemia is the medical term for an inadequate blood supply to the tissue. If severe enough, infarction occurs, which is the local death of the tissue affected by the severe ischemia.

With over 25 feet of the small and large bowel, the blood supply has to be fanned out over a vast distance. The primary arteries supplying the small and large intestines are the

• superior and inferior mesenteric arteries, and the
• internal iliac arteries, with branches to the different parts:
  • most of the duodenum, the jejunum, and ileum of the small intestines; and the
  • ascending, transverse, descending colon, and
  • rectum of the large intestines.

Any reduction or occlusion of blood flow in the blood supply to the GI tract is considered intestinal ischemia (mesenteric ischemia).

 

Causes of Mesenteric Ischemia

Ischemia can either be acute or chronic.

Causes:

ACUTE: 

• Arterial spasm.
  Sudden transient hypotension, which can occur in cardiac arrhythmias, medication overdose, or anesthesia-related hypotension.
• Arterial embolization.
• Cardiac arrhythmia, specifically, atrial fibrillation.
• Temporary episodes of hypotension, as can occur in general anesthesia.

In fact, passage of bloody stools, with or without fever, should raise suspicion of ischemia to the bowel after any surgery in which a patient may have experienced a transient hypotension.

Symptoms of Acute Mesenteric Ischemia:

[SEE Signs & Symptoms: the 3 Phases of Mesenteric Ischemia, BELOW]

CHRONIC:

• Atherosclerosis: a reduction in intestinal blood flow over time instead of suddenly (as an embolus would act). Also called "intestinal angina," there is hypoperfusion of the small intestines due to stenosis or occlusion from atherosclerosis.

  Symptoms of "intestinal angina":

  • Recurrent episodes of abdominal pain after eating.
  • Dull, crampy, epigastric pain within the first hour after eating usually subsides over the next two hours.
  • The pain may radiate to the back.
  • Weight loss due to food aversion (fear of pain).

Risk factors are those that promote thrombus formation and embolization of the thrombus, such as arrhythmias (atrial fibrillation) and hyper-coagulation disorders. Atherosclerosis, which can be further advanced because of diabetes, hypertension, and smoking, increases the risk to the GI blood supply, as it does to the blood supply to other parts of the body.

NOTE: The large bowel is more frequently involved with mesenteric ischemia, and it is more prevalent in women.

 

Signs & Symptoms: the 3 Phases of Mesenteric Ischemia

Mesenteric ischemia is characterized by three specific progressive phases:

1. HYPERACTIVE PHASE: includes severe abdominal pain and frequent passage of bloody stools.
2. PARALYTIC PHASE: includes a change in the abdominal pain to a more widespread distribution with diffuse abdominal tenderness. Decreased bowel motility can cause bloating/distension, absent stools, and absent bowel sounds on examination.
3. SHOCK PHASE: when massive fluids, protein, and electrolytes start to leak through the damaged, gangrenous colon lining, resulting in

• shock,
• metabolic acidosis,
• dehydration,
• hypotension,
• tachycardia, and
• confusion.

Shock Phase affects 10-20% of patients. It requires intensive care and has a high mortality rate.

 

Treatment for Injury to the Bowel from Mesenteric Ischemia

Once the decrease in blood supply outpaces the colon's tolerance for hypoperfusion, this will result in gangrene and death to the portion of the bowel involved. At this point, surgery is necessary to remove the dead bowel.

PREVENTION: No one has a crystal ball, but the most common causes of mesenteric ischemia, arterial embolism, means the best way to prevent it is to use anticoagulants in those with aortic atherosclerotic plaques or atrial fibrillation (which loosens "vegetations" of thrombus on heart valves).

Before reaching the point of actual mesenteric ischemia, prevention also can include surgery (endovascular interventions, i.e., endarterectomy) for atherosclerosis.

When the entire wall of the colon dies, it can perforate to cause peritonitis or even generalized sepsis.

 

Management

CAVEAT: Anyone with new onset of lower abdominal pain and bloody diarrhea should be suspected of mesenteric ischemia, especially with a history of recent surgery. Fever indicates the presence of dead bowel.

In the field, prehospital management should focus on

• strict attention to BSI and PPE,
• ABC: airway, breathing, and circulatory support,
• IV fluid replacement,
• medication administration, as well as
• rapid transport to definitive care and pain management.