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530 SECTION 9: Gastrointestinal Disorders Bowel Obstruction Timothy G. Price INTRODUCTION 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. Mechanical obstruction is caused by either intrinsic or extrinsic fac tors. It requires identification of the cause and definitive intervention in a relatively short period of time to minimize morbidity and mortality (Tables 83-1 and 83-2). Adynamic ileus (paralytic ileus) is usually selflimiting and does not require surgical intervention. Both large and small intestines may be obstructed by various patho logic 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. PATHOPHYSIOLOGY Normal bowel contains gas as well as gastric secretions and food. Intra luminal accumulation of gastric, biliary, and pancreatic secretions con tinues 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. 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 is high 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 ileo cecal valve.  SMALL BOWEL OBSTRUCTION Small bowel obstruction accounts for most bowel obstructions. 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 incar ceration of a hernia. See Chapter 84, “Hernias, ” for detailed descrip tion of types of hernias. In the elderly, adhesions and hernias are still common causes of small bowel obstruction. Bariatric surgery may be complicated by internal hernias after Roux-en-Y gastric bypass. 2,3 Other causes of small bowel obstruction are much less common and generally are the result of intraluminal or intramural processes. Primary small bowel lesions include polyps, lymphoma, or adenocarcinoma. Hamartomatous polyps are common in Peutz-Jeghers syndrome; polyps occur in patients between the ages of 10 and 30 years and can cause obstruction.

struction are much less common and generally are the result of intraluminal or intramural processes. Primary small bowel lesions include polyps, lymphoma, or adenocarcinoma. Hamartomatous polyps are common in Peutz-Jeghers syndrome; polyps occur in patients between the ages of 10 and 30 years and can cause obstruction. 4 An unusual cause of intra luminal obstruction is gallstone ileus, in which a gallstone has eroded from the gallbladder through the bowel wall and causes obstruction at the ileocecal valve. Signs of gallstone ileus include bowel obstruc tion and pneumobilia. Lymphomas may be the leading point of intus susception and present as small bowel obstruction. Bezoars are most commonly composed of vegetable matter or pulp from persimmons. Patients who have undergone GI pyloroplasty or pyloric resection are most susceptible to intraluminal obstruction by bezoars. Inflammatory bowel disease or its complications may obstruct the small bowel at various sites. Radiation enteritis is a possible cause of small bowel obstruction in patients who have undergone radiation therapy. Blunt abdominal trauma may cause a duodenal hematoma. This condi tion is seen in individuals restrained solely by a lap belt or as a result of striking the handlebar of a bicycle and may present as intra-abdominal pain and vomiting similar to other causes of small bowel obstruction. Capsule endoscopy, used to visualize the entire small bowel, may be complicated by capsule retention, with literature-reported frequencies of 1% to 20%. 5 Capsule retention can lead to obstruction and perforation, so patients with abdominal pain after capsule introduction should be carefully evaluated for these complications.  LARGE BOWEL OBSTRUCTION Neoplasms are by far the most common cause of large bowel obstruction, especially in the elderly. However, incidence is rising in younger patients, even those <40 years old. Colonic obstruction is almost never caused by hernia or surgical adhesions and should prompt an evaluation for a neoplasm. Diverticulitis may create significant mesenteric edema and secondary obstruction. Stricture formation may occur with chronic inflammation and scarring. Fecal impaction is a common problem in the elderly or debilitated and may present with symptoms of colonic obstruction. The next most frequent cause of large bowel obstruction after cancer and diverticulitis is sigmoid volvulus. Elderly, bedridden, or psychiatric patients who are taking anticholinergic medication are most at risk for volvulus. Cecal volvulus has been reported in pregnant patients. CLINICAL FEATURES  HISTORY The site and nature of the obstruction and the preexisting condition of the patient will determine the clinical presentation. Although some generalizations are possible, there are no components of the history able CHAPTER TABLE 83-1 Common Causes of Intestinal Obstruction Duodenum Small Bowel Colon Stenosis Adhesions Carcinoma Foreign body (bezoars) Hernia Fecal impaction Stricture Intussusception Ulcerative colitis Superior mesenteric artery syndrome Lymphoma Volvulus Stricture Diverticulitis (stricture, abscess) Intussusception Pseudo-obstruction TABLE 83-2 Key Features of Ileus and Mechanical Bowel Obstruction Ileus Bowel Obstruction Pain Mild to moderate Moderate to severe Location Diffuse May localize Physical examination Mild distention, ± tenderness, decreased bowel sounds Mild distention, tenderness, high-pitched bowel sounds Laboratory Possible dehydration Leukocytosis Imaging May be normal Abnormal Treatment Observation, hydration Nasogastric tube, surgery Tintinalli_Sec09_p0473-0562.indd 530 8/2/19 6:49 PM

ize Physical examination Mild distention, ± tenderness, decreased bowel sounds Mild distention, tenderness, high-pitched bowel sounds Laboratory Possible dehydration Leukocytosis Imaging May be normal Abnormal Treatment Observation, hydration Nasogastric tube, surgery Tintinalli_Sec09_p0473-0562.indd 530 8/2/19 6:49 PM CHAPTER 83: Bowel Obstruction 531 to reliably predict small bowel obstruction. 7 Abdominal pain is nearly universal. Pain generally is crampy and intermittent. Pain of mechanical small bowel obstruction is often episodic, lasting for a few minutes at a time, and may be periumbilical or diffuse. Pain tends to be less intense and more constant in adynamic ileus. Proximal obstruction usually causes vomiting. Vomitus is usually bilious in proximal obstruction but is feculent in distal ileal or large bowel obstruction. The pain of large bowel obstruction is usually hypogastric. Other features that are consistently present with obstruction of small bowel or colon include the inability to have a bowel movement or pass flatus. “Constipation” is a common symptom of bowel obstruction. Partial bowel obstruction, however, is often associated with regular passage of stool and flatus. Additional risk factors are advanced age and anticholinergic or tricyclic antidepressant use, which depress bowel motility.  PHYSICAL EXAMINATION Physical findings vary depending on the site, duration, and cause of obstruction. In small bowel obstruction, distention is the most reliable sign, and some distention is usually present early in the disease process. Abdominal tenderness may be minimal to severe and localized or dif fuse. Peritonitis causes severe pain. The abdomen may be tympanitic to percussion. Mechanical obstruction produces active, high-pitched bowel sounds with occasional “rushes. ” If obstruction has been present for several hours, peristaltic waves and bowel sounds may be diminished. Localized or rebound tenderness may be a sign of gangrenous or per forated bowel, which requires immediate surgical intervention. Patients with an adynamic ileus may have some abdominal distention associated with diminished or absent bowel sounds. Careful examination coupled with radiographic investigation will often distinguish bowel obstruction from ileus. Emptiness of the left iliac fossa is a reliable sign of sigmoid volvulus. Organomegaly or masses may suggest a cause of the obstruction. The absence of stool or air in the rectal vault supports a diagnosis of obstruction and may aid in the diagnosis of bowel obstruction, but its presence does not eliminate a more proximal obstruction. A rectal examination may identify fecal impaction, rectal carcinoma, occult blood, or stricture. Consider a pelvic examination in women to identify gynecologic pathology caus ing obstruction. A vaginal pessary can cause colonic obstruction due to extrinsic compression of the colon. 8 See Table 83-2 for the key causes of ileus and mechanical bowel obstruction. DIAGNOSIS Consider bowel obstruction or ileus in any patient with abdominal pain and distention. Numerous other pathologic processes may also cause these symptoms, but additional evaluation guided by the history and physical examination may be necessary to confirm or rule out obstruc tion or ileus.  LABORATORY TESTING Laboratory studies usually include a CBC and electrolyte levels, the results of which may vary widely depending on the duration and site of obstruction and the presence of bowel necrosis. A leukocytosis of >20,000/mm or left shift should make one suspect bowel gangrene, intra-abdominal abscess, or peritonitis. Extreme leukocytosis (>40,000/mm 3) suggests mesenteric vascular occlusion. The serum amylase and lipase levels may be mildly elevated.

and site of obstruction and the presence of bowel necrosis. A leukocytosis of >20,000/mm or left shift should make one suspect bowel gangrene, intra-abdominal abscess, or peritonitis. Extreme leukocytosis (>40,000/mm 3) suggests mesenteric vascular occlusion. The serum amylase and lipase levels may be mildly elevated. Increases in hematocrit, BUN, and creatinine are consistent with volume depletion and dehydration. Other indications of the severity of obstruction or secondary complications include increased urine specific gravity, ketonuria, elevated lactate levels, and metabolic acidosis. Small studies suggest that procalcitonin may predict bowel ischemia or failure of conservative management.  IMAGING In the ED, flat and upright abdominal radiographs with an upright chest radiograph or a lateral decubitus view are of little utility. Plain films may reveal severe constipation, but be cautious of prematurely attributing symptoms to the presence of colonic stool, even large burdens. Perhaps the greatest value of the plain radiograph is in demonstrating free air secondary to rupture and expediting surgical management. CT scan with oral and IV contrast is the imaging method of choice in the ED (Figures 83-1 and 83-2). The CT scan provides information not only about the presence of an obstruction but often also its location, severity, and cause. 1 In the presence of renal insufficiency or contrast allergy, oral contrast alone may provide sufficient diagnostic information. US can identify small bowel obstruction, 10-12 but management relies on further imaging with CT.11 FIGURE 83-1. Distended loops of small bowel are evident, and decompressed loops are visible in the right lower quadrant. Findings suggest the presence of a transition point. [Reproduced with permission from Block J, Jordanov MI, Stack LB, Thurman RJ (eds): The Atlas of Emergency Radiology. New York, NY: McGraw-Hill Education, Inc.; 2013. Fig 7.38 Part B.] FIGURE 83-2. CT scan of large bowel obstruction. Arrow indicates an apple core lesion; C shows dilated colon proximal to the stricture; and F shows fluid in the right paracolic gutter. [Reproduced from Butler KL, Harisinghani M (eds): Acute Care Surgery: Imaging Essentials for Rapid Diagnosis. New York, NY: McGraw-Hill, Inc., 2015. Fig. 10-11.]Tintinalli_Sec09_p0473-0562.indd 531 8/2/19 6:49 PM