Clinical diagnostics

Abdominal examination. Perform the examination in standard manner, i.e., inspection, auscultation, percussion, and palpation. LBO may be characterized by diminished or, in later stages, absent bowel sounds. The abdomen is distended and may be tender. The presence of true involuntary guarding or peritoneal signs should raise the specter of another intra-abdominal process, such as an abscess. The practice of seeking rebound tenderness is misleading and potentially cruel. Many patients without peritoneal signs complain vigorously after an aggressive rebound maneuver. Seeking tenderness and pain by having the patient cough or by shaking the bed probably is more useful.

Examination of inguinal and femoral regions. This should be an integral part of the examination. Incarcerated hernias represent a frequently missed cause of bowel obstruction. In particular, colonic obstruction often is caused by a left-sided inguinal hernia with the sigmoid colon incarcerated in the hernia.

Digital rectal examination. Perform this to verify the patency of the anus in a neonate. The examination focuses on identifying rectal pathology that may caus the obstruction and determining the contents of the rectal vault. Hard stools suggest impaction. Soft stools suggest obstipation. An empty vault suggests obstruction proximal to the level that the examining finger can reach. Faecal occult blood testing should be performed, and a positive result may suggest the possibility of a more proximal neoplasm.

Special examinations

Laboratory studies

Studies are directed at evaluating the dehydration and electrolyte imbalance that may occur as a consequence of LBO and at ruling out ileus as a diagnosis. Suggestion of an abnormal anion gap also should prompt an arterial blood gas measurement and/or a serum lactate level measurement. A decreased haematocrit level, particularly with evidence of chronic iron-deficiency anemia, may suggest chronic lower gastrointestinal bleeding, particularly due to colon cancer. A stool test also should be performed, for similar reasons. Although bowel obstruction, or even constipation, may mildly elevate the WBC count, substantial leukocytosis should prompt reconsideration of the diagnosis. Ileus, secondary to an intra-abdominal or extra-abdominal infection or another process, is a possibility.

Imaging studies

Flat and upright abdominal roentgenography demonstrates dilation of the large bowel and air fluid levels. Сolonic air suggests the anatomic location of the obstruction. A dilated colon without air in the rectum is more consistent with obstruction. The presence of air in the rectum is consistent with obstipation, ileus, or partial obstruction. This finding can be misleading, particularly if the patient has undergone rectal examinations or enemas. The characteristic bird’s beak of volvulus may be seen.

If differentiation between obstipation and obstruction is required, imaging with contrast is indicated (fig. 22). If localization is required for surgical intervention, imaging with contrast is indicated. Water-soluble gastrografin has important advantages over barium as a contrast agent and generally should be employed first. It usually does not cause chemical peritonitisk, if the patient has colonic perforation.

Figure 22 – Left side colonic cancer with obstruction

CT scanning is not used initially in patients with large bowel obstruction unless a diagnosis has been made. CT scan, particularly with rectal contrast, may demonstrate a mass or evidence of metastatic disease.

Other tests. Fiber-optic endoscopy may be useful in evaluating left-sided colonic obstruction, including the anatomic location and pathology of the lesion. Because the cecum is not reached in such cases, the endoscopist must be alert to the possibility of incorrectly identifying anatomic landmarks and the location of the obstruction. Although flexible endoscopy is relatively comfortable for the patient and provides a better view than rigid sigmoidoscopy, the latter also may be used, depending on the availability of resources and training of personnel. Right-sided colonic obstruction is more difficult to evaluate without first administering an oral bowel preparation, which is contraindicated in the setting of bowel obstruction.