Definitions

the interruption of normal passage through the bowel

• Mechanical bowel obstruction: the interruption of normal passage through the bowel due to a structural barrier (e.g., a tumor, adhesions)

• Paralytic ileus (functional bowel obstruction): temporary functional impairment of peristalsis in the absence of a mechanical obstruction (see “Mechanical bowel obstruction vs. paralytic ileus”

• According to the site of obstruction, mechanical bowel obstruction can be classified as:

  • Large bowel obstruction (LBO): obstruction at the level of the cecum, colon, or rectum

  • Small bowel obstruction (SBO): obstruction at the level of the duodenum, jejunum, or ileum

  • Gastric outlet obstruction (GOO): obstruction at the level of the pyloric channel or duodenum

• Bowel obstruction → stasis of luminal contents and gas proximal to the obstruction → ↑ intraluminal pressure, which leads to the following: [1][3]

  • Gaseous abdominal distention → sequestration of fluids within the distended bowel loops (third spacing) → dehydration and hypovolemia

  • Vomiting → loss of fluid and Na+, K+, H+, and Cl- → hypokalemia, metabolic alkalosis, and hypovolemia

  • Compression of intestinal veins and lymphatics → bowel wall edema → compression of intestinal arterioles and capillaries → bowel ischemia, which leads to:

    • ↑ Bowel wall permeability → translocation of intestinal microbes to the peritoneal cavity → sepsis

    • Necrosis and perforation of the bowel wall → peritonitis

    • Anaerobic metabolism and lysis of ischemic cells → accumulation of lactic acid and release of intracellular K+ → metabolic acidosis and hyperkalemia