Intestinal obstruction results from either mechanical or nonmechanical (neurogenic) blockage of the lumen. Causes of mechanical obstruction include adhesions and strangulated hernias (usually associated with small-bowel obstruction); carcinomas (usually associated with large-bowel obstruction); foreign bodies, such as fruit pits, gallstones, and worms; compression of the bowel wall from stenosis; intussusception; volvulus of the sigmoid or cecum; tumors; and atresia.

Nonmechanical obstruction usually results from paralytic ileus (the most common intestinal obstruction). Paralytic ileus is a physiologic form of intestinal obstruction that usually develops in the small bowel after abdominal surgery. Other nonmechanical causes of obstruction include electrolyte imbalances; toxicity, such as that associated with uremia or generalized infection; neurogenic abnormalities such as spinal cord lesions; and thrombosis or embolism of mesenteric vessels.

Although intestinal obstruction may occur in several forms, the underlying pathophysiology is similar.

Intestinal obstruction can lead to perforation, peritonitis, septicemia, secondary infection, metabolic alkalosis or acidosis, hypovolemic or septic shock, intestinal necrosis and, if untreated, death.

Investigation of the patient’s history often reveals predisposing factors, such as surgery (especially abdominal surgery), radiation therapy, and gallstones. The history may also disclose certain illnesses, such as Crohn’s disease, diverticular disease, and ulcerative colitis, that can lead to obstruction. Family history may reveal colorectal cancer among one or more relatives.

Hiccups are a common complaint in all types of bowel obstruction. Other specific assessment findings depend on the cause
of obstruction—mechanical or nonmechanical—and its location in the bowel.

In mechanical obstruction of the small bowel, the patient may complain of colicky pain, nausea, vomiting, and constipation. If obstruction is complete, he may report vomiting of fecal contents. This results from vigorous peristaltic waves that propel bowel contents toward the mouth instead of the rectum.

Inspection may reveal a distended abdomen, the hallmark of all types of mechanical obstruction. Auscultation may detect bowel sounds, borborygmi, and rushes (occasionally loud enough to be heard without a stethoscope). Palpation may disclose abdominal tenderness. Rebound tenderness may be noted in a patient with obstruction that results from strangulation with ischemia.

In mechanical obstruction of the large bowel, a history of constipation is common, with a more gradual onset of signs and symptoms than in small-bowel obstruction. Several days after constipation begins, the patient may report the sudden onset of colicky abdominal pain, producing spasms that last less than 1 minute and recur every few minutes.

The patient history may reveal constant hypogastric pain, nausea and, in the later stages, vomiting. He may describe his vomitus as orange-brown and foul smelling, which is characteristic of large bowel obstruction. On inspection, the abdomen may appear dramatically distended, with visible loops of large bowel. Auscultation may reveal loud, high-pitched borborygmi.

Partial obstruction usually causes similar signs and symptoms, in a milder form. Leakage of liquid stools around the partial obstruction is common.

In nonmechanical obstruction, such as paralytic ileus, the patient usually describes diffuse abdominal discomfort instead of colicky pain. Typically, he also reports frequent vomiting, which may consist of gastric and bile contents and, rarely, fecal contents. He may also complain of constipation and hiccups.

If obstruction results from vascular insufficiency or infarction, the patient may complain of severe abdominal pain. On inspection, the abdomen is distended. Early in the disease, auscultation discloses decreased bowel sounds; this sign disappears as the disorder progresses.