The small bowel is the proximal portion of the intestine distal to the stomach, comprising the duodenum, jejunum, and ileum.

A small bowel obstruction or a small intestinal obstruction is either a mechanical or functional blockage of the intestinal tract. When detected, the patient must be monitored very closely. If untreated (sometimes due to a failure to diagnose or a misdiagnosis) the condition may become life-threatening.

A mechanical bowel obstruction occurs when the bowel is physically blocked and its contents cannot get past the obstruction. They can occur for several reasons:

  • The bowel can twist on itself (volvulus)
  • The bowel telescopes (intussusception)
  • Hernias
  • Impacted Feces
  • Abnormal tissue growth
  • Inflammatory bowel disease (Crohn’s disease)
  • Presence of naturally occurring foreign bodies in the intestines such as gallstones
  • Presence of a foreign body such as an adhesive band from prior surgery

Nonmechanical functional obstructions called ileus or paralytic ileus, occur because peristalsis stops. Peristalsis is the rhythmic contraction that moves material through the bowel. The ileus is most often associated with an infection of the peritoneum (the membrane lining the abdomen). Another common cause is a disruption of the blood supply to the abdomen. Handling the bowel during abdominal surgery can cause peristalsis to stop. People who have had abdominal surgery are more likely to experience ileus. 

Causes and symptoms may include:

  • Abdominal pain is one of the earliest signs of mechanical intestinal obstruction. Pains or cramps will come in waves. The cramping is caused by the inability of the contractions of the bowel to push digested food past any intestinal obstructions.
  • Vomiting is another symptom  Vomiting follows shortly after the pain if the obstruction is in the small intestine but is delayed if it is in the large intestine. Vomited material may be fecal.
  • Abdomen becomes sore to the touch and swollen when the body re-absorbs large amounts of fluid that cannot pass the obstruction. and the balance of certain important chemicals (electrolytes) in the blood is upset. 
  • Persistent vomiting can cause the patient to become dehydrated. Without treatment, the patient can suffer shock and kidney failure.
  • Strangulation occurs when a loop of the intestine is cut off from its blood supply and occurs in about 25% of cases of small bowel obstruction.