Intestinal obstruction
LIFE-THREATENING DISORDERAn intestinal obstruction is a partial or complete blockage of the lumen in the small or large bowel. A small-bowel obstruction is more common (90% of patients) and usually more serious. A complete obstruction in any part of the bowel, if untreated, can cause death within hours from shock and vascular collapse. Intestinal obstructions are most likely to occur from adhesions caused by previous abdominal surgery, an external hernia, volvulus, Crohn’s disease, radiation enteritis, an intestinal wall hematoma (after trauma or anticoagulant therapy), or a neoplasm.
Causes
Adhesions and strangulated hernias usually cause small-bowel obstructions; carcinomas usually cause large-bowel obstructions. A mechanical intestinal obstruction results from a foreign body (fruit pits, gallstones, or worms) or compression of the bowel wall due to stenosis, intussusception, volvulus of the sigmoid or cecum, tumors, or atresia.
A nonmechanical obstruction results from a physiologic disturbance, such as paralytic ileus (see Paralytic ileus), electrolyte imbalance, toxicity (uremia or generalized infection), a neurogenic abnormality (spinal cord lesions), or thrombosis or embolism of mesenteric vessels.
The three forms of intestinal obstruction are:
simple—blockage prevents intestinal contents from passing with no other complications
strangulated—blood supply to part or all of the obstructed section is cut off in addition to blockage of the lumen
close looped—both ends of a bowel section are occluded, isolating it from the rest of the intestine.
In all three forms, the physiologic effects are similar. When intestinal obstruction occurs, fluid, air, and gas collect near the site. Peristalsis increases temporarily as the bowel tries to force its contents through the obstruction, injuring intestinal mucosa and causing distention at and above the site of the obstruction. This distention blocks the flow of venous blood and halts normal absorptive processes. As a result, the bowel begins to secrete water, sodium, and potassium into the fluid pooled in the lumen. This results in distention and enormous amounts of fluid in the gut.
An obstruction in the upper intestine results in metabolic alkalosis from dehydration and loss of gastric hydrochloric acid; a lower obstruction causes slower dehydration and loss of intestinal alkaline fluids, resulting in metabolic acidosis. Ultimately, an intestinal obstruction may lead to ischemia, necrosis, and death.
Signs and symptoms
Signs and symptoms depend on the location and extent of the obstruction.
Partial small-bowel obstruction
Colicky pain, nausea, vomiting, constipation, abdominal distention, and signs and symptoms of dehydration characterize small-bowel obstruction.
Auscultation reveals bowel sounds, borborygmi, and rushes; occasionally, they’re loud enough to be heard without a stethoscope. Palpation elicits abdominal tenderness with moderate distention; rebound tenderness occurs
when the obstruction has caused strangulation with ischemia. In late stages, signs of hypovolemic shock result from progressive dehydration and plasma loss.
when the obstruction has caused strangulation with ischemia. In late stages, signs of hypovolemic shock result from progressive dehydration and plasma loss.
