Laboratory And Radiographic Findings

All patients with suspected obstruction should have a flat and upright abdominal radiograph and upright chest x-ray or a lateral decubitus view if the patient cannot be upright. An abdominal radiograph can confirm the diagnosis, identify free air or masses, and localize the site to large or small bowel ( Fig 7.5z3.^,Fj.9.; 7.5.-.3B).

Laboratory work usually includes a complete blood count and electrolyte measurements. Depending on the duration of symptoms and site of obstruction or whether there is bowel necrosis, one may find a wide range in white blood cell (WBC) counts and hemoglobin, hematocrit, and electrolyte values. Patients will usually have some elevation in WBC. A white count >20,000/pL or left shift should make one suspect bowel gangrene, intra-abdominal abscess, or peritonitis. 5 Extreme WBC elevation (>40,000/pL) suggests mesenteric vascular occlusion. The serum anylase and lipase levels may be mildly elevated. Levels of serum electrolytes are usually normal or mildly reduced,4 depending on whether the obstruction is of short or long duration or whether there is associated emesis. An increase in Hct, 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.

FIG. 75-3. A. Flat plate abdominal film illustrates distended loops of small bowel. B. Upright film demonstrates multiple air-fluid levels and "step-ladder" appearance.

(From Harris JH, Harris WH: The Radiology of Emergency Medicine, 3d ed. Baltimore, Williams and Wilkins, 1993, p 843, with permission.)

Further investigations to determine the site or etiology of obstruction include sigmoidoscopy or barium enema. Upper gastrointestinal studies are rarely indicated.

Barium enema can determine the cause and site of large bowel obstruction (Fig 7.5-4). Sigmoidoscopy can identify friable mucosa, intraluminal lesions, or the dark-blue gangrenous mucosa associated with dead bowel. If the diagnosis is unclear, repeated examination, preferably by the same examiner, will be necessary. Ihe use of contrast enhanced CI has been advocated to delineate partial from complete bowel obstruction. 78

FIG. 75-4. Barium enema examination demonstrating incomplete filling of the sigmoid secondary to volvulus. Note the "parrot-beak" appearance of the point of the volvulus. (From Schwartz GR: Principles and Practice of Emergency Medicine, 3d ed. Malvern, PA, Lea & Febiger, 1992, p 1720, with permission.)

If a true mechanical obstruction is diagnosed, then surgical intervention is often required. Ihe frequently quoted adage "never let the sun rise or set on a mechanical bowel obstruction" likely refers to the philosophy advocated by surgeons who have noted increased morbidity and mortality when the obstruction has not been treated within 24 h.6 Prior to surgical intervention, emergency department efforts should be made to decompress the bowel with nasogastric intubation. A nasogastric tube is generally effective in removing excess bowel contents and air. Likewise, because of loss of absorptive capacity, decreased oral intake, and vomiting, most patients will require intravenous fluid replacement. Patients can be monitored prior to surgical intervention by the response of blood pressure and heart rate and measurement of urine output. Surgery should not be delayed unnecessarily by attempting to use long intestinal tubes (Baker, Cantor, or Miller-Abbott) or excessive testing. A volvulus of the sigmoid colon will usually decompress via sigmoidoscopy and insertion of a rectal tube. Should a closed-loop obstruction, bowel necrosis, or cecal volvulus be suspected, then surgical intervention should be performed without delay. 4 All patients with mechanical obstruction require broad-spectrum antibiotic coverage preoperatively, as the risk of infection and septicemia is significant in most conditions. -i1,, If adynamic ileus is the primary problem or the diagnosis is uncertain, conservative measures, including intravenous fluids, nasogastric decompression, and observation, are generally effective in allowing the bowel to resume normal activity and function. Any medication that inhibits bowel mobility should be discontinued. Radiologic examination to confirm nasogastric tube placement or long-tube location is also advised. Some authors advocate contrast radiography to distinguish partial SBO from ileus or for the differentiation of strangulated from simple SBO.9,10

Intestinal pseudo-obstruction (Ogilvie's syndrome) may also mimic bowel obstruction. Although any segment of bowel may be affected, low colonic obstruction is the most common clinical presentation. Large amounts of gas will be present in the large intestine. Radiographs reveal a dilated colon with well-defined septae and haustral markings and very little fluid, making air-fluid levels uncommon.11 Patients may be using anticholinergic or tricyclic antidepressants, which depress motility. One must avoid the use of barium studies as the patient may be unable to evacuate the barium. Preference should be given to colonoscopy after digital rectal examination as an early intervention to rule out true obstruction or significant lesions. Colonoscopy will also treat the pseudo-obstruction by decompression. Surgery is not usually helpful and may be harmful.1 I2

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