Intestinal Obstruction

A blockage of the intestinal tract, preventing the passage of intestinal contents.

An obstruction may be acute or chronic, mechanical or adynamic, simple or strangulated; it may occur in the small or large intestine. Certain features are common to all types, but the choice of therapy depends on a specific diagnosis.

Adhesions and hernias are the most common lesions of the small intestine causing acute intestinal obstruction; cancer predominates in the colon. Adynamic ileus occurs when the absence of reflex nerve stimulation precludes peristalsis in an otherwise normal bowel. In a simple obstruction, the blood supply to the intestine is not compromised; in a strangulated obstruction, the vessels to a segment are occluded, usually by adhesions or bands.

Symptoms and Signs

Symptoms and signs are highly variable and depend chiefly on the site and cause of the obstruction and the time since onset.

A patient with an acute obstruction characteristically presents with a rapid onset of abdominal cramps, vomiting, distention, and obstipation. Cramps tend to recur about every 3 minutes and are associated with high-pitched bowel sounds caused by peristalsis (borborygmi). Although wide individual variation may exist, crampy pain usually occurs in the epigastrium and periumbilically with small-bowel obstruction and in the lower abdomen with colonic obstruction; cramps may not occur with high jejunal obstruction. Abdominal distention usually occurs and increases. In a simple obstruction, the abdomen is not tender; abdominal tenderness and continuous pain indicate strangulation. Because a simple obstruction can lead to strangulation in as little as 6 hours, every patient with a suspected intestinal obstruction should be hospitalized immediately.

With a small-bowel obstruction, vomiting usually occurs early; it may progress to fecal emesis (a misnomer, given that the etiology is bacterial overgrowth secondary to luminal stasis), which can be distinguished from coffee-ground vomit (caused by upper GI hemorrhage) with a guaiac test. With a large-bowel obstruction, vomiting occurs much later or not at all and is usually preceded by distention and cramps. Initially, scanty diarrhea may occur; complete obstruction is followed by obstipation.

Diagnosis

The abdomen should be inspected for scars from previous abdominal operations and for groin or incisional hernias. The abdomen is auscultated for several minutes to detect bowel sounds and palpated for tenderness or masses. A rectal examination and, in women, a vaginal examination should be performed.

A complete blood cell count, blood chemistry tests, and urinalysis should be performed. An indwelling bladder catheter and central venous pressure line are usually advisable. If the patient has a history of myocardial dysfunction, a pulmonary arterial catheter may be necessary to guide resuscitation.

X-rays are extremely important but should be performed only after a nasogastric tube has been inserted. Plain abdominal films should be taken in the supine and upright positions. Lateral decubitus films sometimes are helpful, particularly in cases of external hernias.

With a typical small-bowel obstruction, a ladderlike pattern of distended intestinal loops appears. With strangulation, however, a mass rather than distended loops may be visible. Distended loops may also be absent in a high jejunal obstruction, particularly if the patient has had a gastric resection.

Obstruction of the ascending colon may resemble a small-bowel obstruction when reflux occurs through an incompetent ileocecal valve. Obstruction of the descending colon leads to distention of the entire proximal large bowel because of gas. A single large gas-filled loop of colon in the midabdomen or left upper quadrant usually results from a cecal volvulus, and a single loop of distended sigmoid usually results from a sigmoid volvulus. If gas appears in the intrahepatic bile ducts, a gallstone obstruction is likely (secondary to cholecystenteric or choledochoenteric fistula).

Colonoscopy or a barium enema is used when the site of an obstruction is unclear. Oral barium may be administered to confirm and better localize small-bowel obstruction but should not be used with a colonic obstruction.

Differential diagnosis of intestinal obstruction includes acute appendicitis, acute cholecystitis, diverticulitis, and pancreatitis. Also, thoracic disease (eg, pneumonia) may cause adynamic ileus.

Treatment

Acute mechanical obstruction requires surgery. Nasogastric intubation and preoperative antibiotics should be started early.

Certain types of intestinal obstruction, including adynamic ileus, early postoperative obstruction, and recurrent obstruction caused by adhesions from previous intra-abdominal surgery, can be treated by GI intubation and IV alimentation. Some surgeons believe that simple obstruction can be treated by intubation, but others believe that surgery is the treatment of choice.

In cases of small-bowel obstruction without evidence of strangulation (ie, audible peristalsis and no abdominal tenderness) but with marked dehydration, several hours may be needed to rehydrate the patient and establish adequate urinary output. A severely dehydrated patient who has advanced strangulation and is in shock may require immediate surgery, thus appropriate and aggressive resuscitation is critical.

Adynamic Ileus

Adynamic ileus should be suspected in patients with symptoms of obstruction and a history of recent surgery, back injury, severe trauma, or thoracic or renal disease. Peristalsis (and thus bowel sounds) is absent or infrequent, and abdominal x-rays show gas in scattered areas of the small intestine and colon. Treatment consists of nasogastric suction and IV alimentation. Administration of metoclopramide or cisapride usually is not beneficial.

In pseudo-obstruction of the colon, or Ogilvie's syndrome, the colon distends as if obstructed, although there is no mechanical obstruction and a colonoscope can be passed easily. The cause of Ogilvie's syndrome is unknown, although it occurs most often in elderly, debilitated patients with restricted mobility (eg, in an obese elderly patient after a hip replacement). A supine x-ray of the abdomen often shows a dilated proximal colon, but the distention can also involve the splenic flexure and left colon. Colonoscopy, a barium enema, or surgery reveals no obstructing lesion. Usually, advanced colonic ileus can be treated effectively by colonoscopy, which may need to be repeated.

Mechanical Obstruction

Mechanical obstruction may be caused by an impacted gallstone in the terminal ileum; the stone may not appear on x-ray or may appear considerably smaller than it actually is. However, gas in the intrahepatic biliary tree is diagnostic.

Mechanical obstruction may also occur when a patient with false teeth and a partial gastrectomy swallows masses of indigestible fiber. The mass forms an obstructing bezoar in the small intestine. Bezoars also can cause obstruction in patients treated in the intensive care unit with large doses of antacid to prevent bleeding stress ulcers.

Richter's hernia is a nonpalpable, small hernia involving strangulation of only part of the intestinal wall in a small hernial sac.

Fecal impaction is common and rarely produces complete obstruction. More commonly, repeated attempts to evacuate produce small diarrheal stools. If the condition is detected early by rectal examination, the impaction can be removed digitally or with warm mineral oil retention enemas. If the condition is advanced, the patient may require sedation to facilitate complete fecal removal. Fecal impaction high in the rectum or in the sigmoid can lead to obstruction, perforation, and fecal peritonitis.

Apparent intestinal obstruction accompanied by shock, marked leukocytosis, and variable abdominal tenderness can be caused by mesenteric artery occlusion from thrombosis or embolism. This condition is not a true mechanical obstruction but an ileus caused by aperistalsis. If surgery is performed before infarction of all or most of the small bowel, embolectomy or thrombectomy should be attempted (in a few cases, this may result in survival).