Mechanical obstruction

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Mechanical obstruction is an uncommon cause of intestinal distension in ICU patients. However, it is important to exclude this diagnosis through careful consideration of the common causes of small and large bowel occlusion. FigureJ presents an algorithm for the investigation of intestinal distension with the focus on distinguishing obstruction from ileus.

Approach Ileus

Fig. 1 Algorithm for the approach to ileus versus obstruction in the ICU patient: SIRS, systemic inflammatory response syndrome; TPN, total parenteral nutrition.

Patients experience crampy abdominal pain as peristaltic contractions continue against obstruction in the early phase. As ICU patients are often comatose, hyperactive bowel sounds, visible peristalsis, absence of stool, and compatible abdominal radiographs showing fixed-position air-fluid levels on serial films all promote the diagnosis of obstruction.

Before extensive investigation is undertaken for possible bowel obstruction, it is prudent to assess any intraintestinal or intraperitoneal tubes or drains present. Balloon catheters used as feeding or drainage conduits may cause intraluminal obstruction. Internal hernias and volvulus may occur around the point of fixation of jejunal feeding catheters, and extrafascial stomal prolapse at colostomy or ileostomy sites may also cause remediable obstruction. A digital rectal examination (or digital exploration of stomas), followed by gentle saline enemas, is an often neglected yet essential initial maneuver, which may relieve existing fecal impaction. Aside from the more common surgical causes of obstruction, one etiology seen occasionally in the coagulopathic patient is a submucosal intestinal hematoma which can arise spontaneously. The typical finding on an upper gastrointestinal contrast study is the 'picket-fence' appearance of the mucosa at the site of obstruction.

A closed-loop obstruction is a surgical emergency often caused by an internal small bowel hernia due to previous postoperative adhesions or distal colorectal occlusion (neoplasm or diverticulitis) with a competent ileocecal valve. Acute cecal distension to greater than 12 cm should prompt consideration of surgical decompression. A loop transverse colostomy, which may be performed under local anesthesia in an unstable patient, affords highly effective decompression and facilitates rapid stabilization of the patient in preparation for a delayed definitive procedure.

Luminal sequestration of fluids and electrolytes causing significant third-space losses occurs within 12 h of small bowel occlusion. When intraluminal pressure exceeds 20 cmH2O, venous congestion of the bowel wall ensues and augmented capillary filtration enhances the accumulation of intraluminal and peritoneal free fluid. Bacterial overgrowth follows, and translocation of gut bacteria and endotoxin may occur. Overgrowth is fostered by gastric achlorhydria, diminished gut motility, obstruction, reflux, villus atrophy (as seen with prolonged total parenteral nutrition), altered gut flora (secondary to antibiotic use), intestinal distension, and sepsis.

The management of intestinal obstruction is surgical. Swift involvement of a general surgeon is warranted as soon as the diagnosis is suspected. Bowel obstruction is usually diagnosed clinically and confirmed by surgical exploration. Less commonly, radiological imaging is required to establish the diagnosis. If distal colonic obstruction is a possibility, a saline rectal lavage should be performed followed by a gastrograffin enema. If normal, the small bowel should be imaged using barium since water-soluble contrast media dilute readily in intestinal fluid, making interpretation difficult.

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