Normal bowel contents contain gas as well as gastric secretions and food. Intraluminal accumulation of gastric, biliary, and pancreatic secretions continues even if there is no oral intake. As obstruction develops, the bowel becomes congested and there is failure of intestinal contents to be absorbed. Vomiting and decreased oral intake follow. The combination of decreased absorption, vomiting, and reduced intake leads to volume depletion with hemoconcentration and electrolyte imbalance, and ultimately can cause renal failure or shock.5
Bowel distension often accompanies mechanical obstruction. Distension is due to the accumulation of fluids in the bowel lumen, an increase in intraluminal pressure with enhanced peristaltic contractions, and air swallowing. When intraluminal pressure exceeds capillary and venous pressure in the bowel wall, absorption and lymphatic drainage decrease. At this stage, bacteria may enter the bloodstream, the bowel becomes ischemic, and septicemia and bowel necrosis can develop. Shock rapidly ensues. Mortality approaches 70 percent if bowel obstruction has been allowed to progress this far. With a closed-loop obstruction this sequence of events may occur more rapidly. In this instance, there is no proximal escape for bowel contents. Examples of closed-loop obstruction include an incarcerated hernia and complete colon obstruction in the presence of a closed ileocecal valve.
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