Intestinal Obstruction

An intestinal obstruction is a partial or complete blockage of the lumen in the small or large bowel. A small-bowel obstruction is far more common (90% of patients) and usually more serious. A complete obstruction in any part of the bowel, if untreated, can cause death within hours from shock and vascular collapse. Intestinal obstructions are most likely to occur from adhesions caused by previous abdominal surgery, external hernias, volvulus, Crohn's disease, radiation enteritis, intestinal wall hematomas (after trauma or anticoagulant therapy), and neoplasms

Causes

Adhesions and strangulated hernias usually cause small-bowel obstructions; carcinomas usually cause large-bowel obstructions. A mechanical intestinal obstruction results from foreign bodies (fruit pits, gallstones, worms) or compression of the bowel wall due to stenosis, intussusception, volvulus of the sigmoid or cecum, tumors, or atresia.

A nonmechanical obstruction results from physiologic disturbances, such as paralytic ileus, electrolyte imbalances, toxicity (uremia, generalized infection), neurogenic abnormalities (spinal cord lesions), and thrombosis or embolism of mesenteric vessels.

The three forms of intestinal obstruction are:

• simple: blockage prevents intestinal contents from passing with no other complications
• strangulated: blood supply to part or all of the obstructed section is cut off in addition to blockage of the lumen
• close-looped: both ends of a bowel section are occluded, isolating it from the rest of the intestine.

In all three forms, the physiologic effects are similar; When intestinal obstruction occurs, fluid, air, and gas collect near the site. Peristalsis increases temporarily as the bowel tries to force its contents through the obstruction, injuring intestinal mucosa and causing distention at and above the site of the obstruction. This distention blocks the flow of venous blood and halts normal absorptive processes. As a result, the bowel begins to secrete water, sodium, and potassium into the fluid pooled in the lumen. This results in distention and enormous amounts of fluid in the gut.

An obstruction in the upper intestine results in metabolic alkalosis from dehydration and loss of gastric hydrochloric acid; a lower obstruction causes slower dehydration and loss of intestinal alkaline fluids, resulting in metabolic acidosis. Ultimately, an intestinal obstruction may lead to ischemia, necrosis, and death.

Sign and symptoms

An obstruction in the small intestine is usually signaled by cramps in the area of the belly button, vomiting, severe constipation if the obstruction is total, or diarrhea if the obstruction is partial. As time passes, the abdomen becomes distended and tender. Symptoms of a blockage in the large intestine are similar, but develop more gradually and may not include vomiting.

Diagnosis

Progressive, colicky abdominal pain and distention, with or without nausea and vomiting, suggest bowel obstruction. Plain abdominal radiography confirms the diagnosis.

CLINICAL TIP

Small-bowel obstruction must be distinguished from adynamic ileus. Pancreatitis, acute gastroenteritis, appendicitis, and acute mesenteric ischemia must be ruled out.

Abdominal films show the presence and location of intestinal gas or fluid. In small-bowel obstructions, a typical "stepladder" pattern emerges, with alternating fluid and gas levels apparent in 3 to 4 hours. In large-bowel obstructions, a barium enema reveals a distended, air-filled colon or a closed loop of sigmoid with extreme distention (in sigmoid volvulus).

Laboratory results that support this diagnosis include:

• decreased sodium, chloride, and potassium levels (due to vomiting)
• slightly elevated white blood cell count (with necrosis, peritonitis, or strangulation)
• increased serum amylase level (possibly from irritation of the pancreas by a bowel loop).

Treatment

Initial therapy consists of correcting fluid and electrolyte imbalances, decompressing the bowel to relieve vomiting and distention, and treating shock and peritonitis. A strangulated obstruction usually necessitates blood replacement as well as I.V. fluid administration. Nasogastric tube suction is necessary to relieve vomiting and abdominal distention.

Close monitoring of the patient's condition determines the duration of treatment; if the patient fails to improve or if his condition deteriorates, surgery is necessary. Surgery is performed on all patients with large-bowel obstruction.

Total parenteral nutrition may be appropriate if the patient suffers a protein deficit from chronic obstruction, postoperative or paralytic ileus, or infection.

Drug therapy includes analgesics and sedatives. Antibiotics are given for peritonitis due to bowel strangulation or infarction. Broad-spectrum antibiotics should be given to provide anaerobic and gram-negative coverage.

Prevention

Prevention depends on the cause. Treatment of conditions (such as tumors and hernias) that are related to obstruction may reduce the risk.

Some causes of obstruction are not preventable.