Bowel obstruction occurs when the normal flow of intraluminal contents is interrupted. Obstruction can be mechanical or functional. Bowel obstruction may occur in the small or large bowel. The small bowel is involved in about 80 percent of cases of mechanical intestinal obstruction. Ischemia, which complicates up to 42 percent of bowel obstructions, significantly increases mortality associated with bowel obstruction.
Mechanical bowel obstruction may be classified as partial (incomplete) or complete (see Table 1), simple or complicated (see Table 2). A complete bowel obstruction may progress to complicated bowel obstruction when intestinal ischaemia, necrosis, and/or perforation develop.
Table 1: Partial vs Complete bowel obstruction
Partial Bowel Obstruction
Complete Bowel Obstruction
Partial passage of flatus or stool
Failure to pass flatus or stool
Not usually associated with peritonitis
Generally associated with peritonitis
Table 2: Simple vs Complicated bowel obstruction
Simple Bowel Obstruction
Complicated Bowel Obstruction
Absence of peritonitis
Associated with perionitis
Generally reflects early or partial obstruction
Obstruction has progressed to intestinal ischaemia/ gangrene and/or perforation
Ileus and colonic pseudo-obstruction cause functional obstruction, because of uncoordinated or attenuated intestinal muscle contractions. Functional bowel obstruction is characterized by signs and symptoms of a mechanical obstruction of the small or large bowel in the absence of an anatomic lesion that obstructs the flow of intestinal contents.
Paralytic ileus occurs to some degree after almost all open abdominal operations. Other causes include peritonitis, trauma, intestinal ischemia, and medications (eg, opiates, anticholinergics). It is exacerbated by electrolyte disorders, particularly hypokalemia. Symptoms are similar to that of mechanical obstruction. However, on imaging there is air in the colon and rectum, and on CT abdomen there is no demonstrable mechanical obstruction. Treatment is dependent on the cause. Prolonged post-operative ileus often responds to conservative treatment with bowel rest, correction of electrolyte disorders and reduction of opioid medications, and drug induced ileus responds to cessation of the precipitating drug.
Acute colonic pseudo-obstruction, or Ogilvie's syndrome, is a variant of ileus, characterized by massive colonic dilatation and is discussed later. Chronic idiopathic pseudo-obstruction may be due to an underlying neuropathic disorder (involving the enteric nervous system or extrinsic nervous system), a myopathic disorder (involving the smooth muscle), or abnormality in the interstitial cell of Cajal.