Overview
Clinical Meaning
Bowel obstruction is classified as mechanical (physical blockage of intestinal lumen) or functional (paralytic ileus — impaired peristalsis without physical blockage).
Bowel obstruction is classified as mechanical (physical blockage of intestinal lumen) or functional (paralytic ileus — impaired peristalsis without physical blockage). Mechanical small bowel obstruction (SBO) is most commonly caused by adhesions (60%, typically post-surgical), hernias (15%), and tumors (15%). Large bowel obstruction (LBO) is most commonly caused by colorectal cancer (60%), diverticular disease (20%), and volvulus (5%). In mechanical obstruction, accumulated gas and fluid proximal to the obstruction cause bowel distension, which increases intraluminal pressure. This pressure compresses mucosal blood vessels, causing ischemia, bacterial translocation, and potential necrosis and perforation. Third-spacing of fluid into the bowel lumen and peritoneal cavity causes significant intravascular volume depletion and electrolyte imbalances (hypokalemia, hyponatremia, metabolic alkalosis from vomiting in proximal SBO or metabolic acidosis from ischemia). Closed-loop obstruction (both ends of a bowel segment are occluded, as in volvulus or incarcerated hernia) is a surgical emergency due to rapid progression to strangulation and perforation. Paralytic ileus results from temporary inhibition of peristalsis following surgery, electrolyte imbalances (hypokalemia), opioid use, peritonitis, or spinal injury.