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INTRODUCTION AND EPIDEMIOLOGY

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Intestinal obstruction is the inability of the intestinal tract to allow for regular passage of food and bowel contents secondary to mechanical obstruction or adynamic ileus. Intestinal obstruction accounts for approximately 15% of all ED visits for acute abdominal pain.1

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Mechanical obstruction can be caused by either intrinsic or extrinsic factors and generally requires definitive intervention in a relatively short period of time to determine the cause and minimize subsequent morbidity and mortality (Tables 83-1 and 83-2). Adynamic ileus (paralytic ileus) is more common but is usually self-limiting and does not require surgical intervention.

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TABLE 83-1Common Causes of Intestinal Obstruction
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Both large and small intestines may be obstructed by various pathologic processes (Table 83-1). Extrinsic, intrinsic, or intraluminal processes precipitate mechanical obstruction. Differentiating small bowel obstruction from large bowel obstruction is important, because the incidence, clinical presentation, evaluation, and treatment vary depending on the anatomic site of obstruction. Intestinal pseudo-obstruction (Ogilvie's syndrome) may mimic bowel obstruction.

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PATHOPHYSIOLOGY

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Normal bowel contains gas as well as gastric secretions and food. Intraluminal accumulation of gastric, biliary, and pancreatic secretions continues even if there is no oral intake. As obstruction develops, the bowel becomes congested and intestinal contents fail to be absorbed. Vomiting and decreased oral intake follow. The combination of decreased absorption, vomiting, and reduced intake leads to volume depletion with hemoconcentration and electrolyte imbalance, and may lead to renal failure or shock.

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Bowel distention often accompanies mechanical obstruction. Distention is due to the accumulation of fluids in the bowel lumen, an increase in intraluminal pressure with enhanced peristaltic contractions, and air swallowing. When intraluminal pressure exceeds capillary and venous pressure in the bowel wall, absorption and lymphatic drainage decrease, the bowel becomes ischemic, and septicemia and bowel necrosis can develop. Shock ensues rapidly. Mortality approaches 70% if bowel obstruction has progressed to this degree. This sequence of events may occur more rapidly in a closed-loop obstruction with no proximal escape for bowel contents. Examples of closed-loop obstruction include an incarcerated hernia and complete colon obstruction in the presence of a closed ileocecal valve.

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SMALL BOWEL OBSTRUCTION

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Small bowel obstruction is approximately four times more common than large bowel obstruction. The most common cause of small bowel obstruction is adhesions after abdominal surgery. Although in most cases several months to years have passed from the time of the previous surgery, small bowel obstruction may occur within the first few weeks after surgery. The second most common cause of small bowel obstruction is incarceration of ...

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