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Kufe DW, Pollock RE, Weichselbaum RR, et al., editors. Holland-Frei Cancer Medicine. 6th edition. Hamilton (ON): BC Decker; 2003.

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Holland-Frei Cancer Medicine. 6th edition.

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Ileus and Bowel Obstruction

, MD, FACP.

Ileus, obstipation, and bowel obstruction are encountered frequently in the cancer patient. Intestinal obstruction refers to the interference of the normal passage of luminal contents through the gastrointestinal tract, caused by an intraluminal process or by extrinsic compression. The obstruction can be partial or complete. Ileus is a failure of normal intestinal motility in the absence of mechanical obstruction. Toxic megacolon is a type of ileus that can occur in patients with ulcerative colitis and in which there is transmural inflammation and colonic dilatation. Obstipation refers to acute abdominal pain, the ability to pass flatus, but with cessation of bowel movements. Obstipation is associated with both mechanical obstruction and functional ileus. The term strangulated obstruction is used if the blood supply of the involved bowel is compromised. Idiopathic dilatation of the colon in the absence of mechanical obstruction is referred to as acute colonic pseudoobstruction or Ogilvie syndrome.

Clinical Manifestations

Whenever a patient presents with abdominal pain, vomiting, abdominal distention, and obstipation, intestinal obstruction is the first diagnostic consideration. A detailed history is a key element in pinpointing the site of obstruction. It is also important to ascertain the duration of symptoms to distinguish acute from chronic conditions. A history of previous abdominal surgery, previous episodes of obstruction, inflammatory bowel disease, herniation in the abdominal wall or previous incisions, prior abdominal or pelvic radiation, or previous cancers provide important clues as to cause of obstruction. A careful medication review that includes narcotic history is important in discovering the underlying cause of ileus. The clinical features of ileus or bowel obstruction are dependent on the site of involved intestine. Proximal obstructions (gastric outlet, duodenum) are associated with persistent and copious vomiting, modest abdominal pain, and minimal abdominal distention. Distal small-bowel obstruction is associated with vomiting that can be malodorous, significant abdominal distention, and pain. Vomiting is uncommon in colonic obstruction, but pain and distention are pronounced. The competency of the ileocecal valve is important in the pathophysiology of colonic obstruction because a competent value precludes decompression of fluid and gas into the small bowel, resulting in a closed-loop obstruction. Cecal diameters ≥ 13 cm carry a risk of perforation, particularly when the obstruction is relatively acute in onset. Ileus is thought to result from an imbalance between sympathetic and parasympathetic motor activity, resulting in intestinal atony. In cases of ileus, vomiting is usually infrequent; pain is mild, and distention is moderate to severe. Typically, the pain in small-bowel obstruction is crampy, with paroxysms occurring at 4- to 5-min intervals for proximal obstruction and less frequently for more distal obstruction. The development of continuous, localized, and intense pain suggests the possibility of strangulated obstruction.

Etiology

While there are many causes of small-bowel obstruction, the three most common etiologies are adhesions resulting from prior abdominal surgery, hernias, and neoplasms, especially malignancy. Obstruction may occur anytime after the initial abdominal surgery, but the average interval between the initial operation and development of adhesive obstruction reported in one study was 6 years.84 Hernias are the second leading cause of obstruction. Neoplasms cause obstruction of the small intestine as well as the colon. Malignant etiology should be one's first impression in a large-bowel obstruction. Obstruction can be caused by primary tumors or by metastatic cancer, including metastases to the mesentery, serosa of the intestine, or peritoneal carcinomatosis. In contrast to mechanical obstruction, the cause of ileus or pseudoobstruction is usually occult and multifactorial. In cancer patients, the most common causes include opioid use, electrolyte imbalance, certain chemotherapeutic agents (such as vincristine), and metabolic disturbances.

Vincristine treatment is associated with adynamic ileus and has been implicated in some cases of cecal perforation.85 Although the etiology of vincristine-induced ileus is unknown, improvement has been reported with the use of metoclopramide.86 Cisapride may also be beneficial in that this agent improves motility throughout the intestinal tract whereas metoclopramide's effect is limited to the upper GI tract. Patients with vincristine-induced ileus often have obstipation, and aggressive use of cathartics may be needed.

Diagnosis

Inspection of the abdomen may reveal distention, previous surgical scars, hernias, or masses. The degree of distention varies depending on the level of obstruction. Distention is marked in distal small-bowel obstruction and long-standing colonic obstruction. In cases of ileus, the degree of distention is quite variable. Palpation of the abdomen may reveal areas of marked tenderness, rebound guarding, or rigidity, indicating a strangulated hernia or a localized perforation requiring immediate surgical attention. Auscultation of the abdomen may reveal periods of increasing bowel sounds with periods of relative quiet. With obstruction, the bowel sounds are usually high-pitched or musical. In cases of prolonged obstruction and ileus, bowel sounds may disappear as a consequence of decreased motility. Laboratory studies are useful in the diagnosis of ileus or pseudoobstruction which can be caused by an electrolyte imbalance. Metabolic abnormalities and electrolyte derangements are commonly associated with, and are a consequence of, prolonged intestinal obstruction.

Abdominal radiography is extremely helpful in confirming the diagnosis of obstruction, differentiating ileus from obstruction, and localizing the level of obstruction. A complete abdominal series that includes an upright chest film, an upright and supine abdominal film, and a lateral decubitus abdominal film should be obtained. Patients with a complete small-bowel obstruction generally have dilated intestinal loops proximal to the obstruction and no gas in the colon or rectum. Abdominal radiography may also show multiple air-fluid levels with distended loops of bowel. The rectum will be devoid of any gas in cases of colonic obstruction, but the proximal colon may or may not have gas. Abdominal radiography may also show free air, indicating perforation, or air in the intestinal wall, indicating pneumatosis or bowel ischemia. Approximately 20% to 30% of patients with small-bowel obstruction produce equivocal or normal abdominal radiographs.87,88 In cases of ileus, gas is generally present throughout the intestinal tract, including the rectum, but it is sometimes difficult to distinguish obstruction from ileus on the basis of abdominal plain radiography alone.

Contrast studies are helpful in differentiating between obstruction and ileus, identifying the site of obstruction, and differentiating between partial and complete obstruction. If colonic obstruction has been ruled out or is deemed very unlikely, barium sulfate can be given orally for an antegrade contrast study since net secretion in the intestinal lumen keeps the barium in solution. Water-soluble contrast agents such as diatrizoate meglumine (Gastrografin) usually get diluted (because of the large amount of fluid present within the obstructed bowel) and prevent the definition of distal obstruction. If colonic obstruction is suspected, a Gastrografin or barium enema should be done as the first test. Care is taken to avoid getting a large amount of barium above the obstruction, which can become inspissated due to net absorption of fluid in the colon, and which can be removed only at the time of operation.

Computed tomography is an excellent test in patients with suspected or known malignancy and in identifying recurrence, inflammatory mass, and extrinsic obstruction by masses. The demonstration of a transition zone with dilated fluid-, air-, or air-fluid-filled loops above collapsed loops of bowel distally suggests the presence of small-bowel obstruction. CT is very sensitive (90%) for high-grade obstruction, but sensitivity is low (50%) for low-grade obstruction.89 Computed tomography also detects air in the bowel wall or in the peritoneal cavity in cases of perforation.

Treatment

The most important principle for the treatment of ileus is to treat the underlying cause. Other important steps to take are (1) limiting oral intake; (2) maintaining intravascular volume; (3) correcting electrolyte abnormalities, especially hypokalemia; (4) stopping the administration of the offending drugs, if possible; (5) using nasogastric suction; (6) decompressing the rectum with a tube; and (7) frequently changing the position of the patient. These conservative measures are successful in the majority (85%) of patients in a mean of 3 days.90 In patients with bowel obstruction, a Foley catheter is suggested to measure intake and output and also to assess the immediate effects of fluid resuscitation on urine output. A nasogastric tube should be placed to decompress the stomach and intestine and to avoid further abdominal distention. A surgical consultation should be obtained to determine whether operative treatment or expectant management should be employed. This decision depends on the patient's clinical condition and underlying pathology, the degree of obstruction, the rapidity with which the obstruction developed, the presence of strangulation or perforation, and any signs of peritonitis. Intravenous antibiotics covering gram-negative and anaerobic bacteria should be started in cases of suspected inflammatory mass or perforation. A cautious endoscopy may be attempted in cases of distal obstructions that require further diagnostic evaluation or in cases of pseudoobstruction with a very dilated bowel segment, for placement of a decompression tube. In some patients with unresectable solid malignancy, intestinal bypass procedures can be performed for palliation and to improve the quality of their remaining life. Alternatively, decompressive gastrostomy tube placement can be used for palliation of patients with multiple sites of malignant small intestinal obstruction, and in some cases, for peritoneal carcinomatosis. Recently, the use of self-expanding metal stents for acute colonic obstruction before elective surgery has been reported as having a high success rate. The mean time between stent placement and surgery was 8.6 days.91

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2003, BC Decker Inc.
Bookshelf ID: NBK13786

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