Risk Factors/Etiology
- Small bowel obstruction is typically caused by postoperative adhesions, hernias, or
tumors.
- Large bowel obstruction is caused by carcinoma, colonic diverticulitis, volvulus, inflammatory
bowel disease, radiation colitis, or foreign bodies. It is primarily a disease of the elderly.
- Sigmoid volvulus in the United States occurs in debilitated elderly people secondary
to chronic severe constipation.
- Cecal volvulus is most common in 25-35 yr olds but may occur at any age. It is likely
due to a hereditary hypofixation of the cecum to the posterior abdominal wall. Risk
factors include marathon running, pregnancy, and prior abdominal surgery.
Clinical Presentation and Diagnoses
- Acute onset of severe intermittent abdominal pain followed by nausea and vomiting is
the common clinical manifestation. Vomiting may be absent in distal obstructions.
The abdomen is diffusely tender and becomes progressively distended. Obstipation
may be absent early on or in a partial obstruction, and its absence does not exclude the
diagnosis. Peritoneal signs or fever suggest strangulation or perforation.
- Signs include a tympanitic distended abdomen, high pitched "tinkling" bowel sounds,
or a tender mass in closed loop obstructions.
- Laboratory values are nonspecific. An elevated WBC count may be present in both
simple and strangulated obstructions. Electrolyte abnormalities are late findings. Hemoconcentration
may reflect third spacing of fluid.
- Plain radiographs are often diagnostic, demonstrating small bowel obstruction (SBO)
in 50-60% of cases and suggesting it in 20-30% more. A supine abdominal film along
with either a lateral decubitus or upright abdominal films are minimally needed for
diagnosis. An upright chest film may be added to search for free air under the diaphragm
indicating a perforated viscous. CT scan is 94% sensitive and 83% specific in
diagnosing SBO. Ultrasound is 88% sensitive and 96% specific in diagnosing SBO.
Plain abdominal films are the test of first choice.
- In small bowel obstruction, distension of the small bowel is seen, often with distal
collapse. The small bowel is differentiated from the large bowel by the presence of
"valvulae conniventes" which are numerous, narrowly spaced and cross the entire lumen.
A "string of pearls" sign is highly suggestive of small bowel obstruction and is
described as a line of air pockets in a fluid filled small bowel. Air fluid levels in a
stepladder pattern are also suggestive of a small bowel obstruction.
- A large bowel obstruction is suggested by dilation of bowel with "haustra", which are
widely spaced, do not cross the entire lumen, and are less numerous than the "valvulae
conniventes." A sigmoid volvulus is diagnosed by a single dilated loop of large bowel
in the mid abdomen in the classic "bent inner tube" configuration, 80% of the time.
If not, sigmoid volvulus can be diagnosed by the classic "birds beak" sign on barium
enema. Distended large bowel in the left lower quadrant with absence of right-sided
gas may indicate a cecal volvulus.
- Differential diagnoses include gastroenteritis, mesenteric ischemia, adynamic ileus,
and incarcerated hernia. The intermittent nature of the pain is suggestive of bowel
obstruction but is also present in mesenteric ischemia.
Treatment
- Early nasogastric decompression, aggressive fluid resuscitation, broad spectrum antibiotics
including coverage of Gram negatives and anaerobes, and early surgical consultation
are the mainstays of treatment of small and large bowel obstructions. Up to
75% of partial small bowel obstructions and up to one-third of complete small bowel
obstructions will resolve with decompression and fluid resuscitation alone. Strangulated
obstructions indicated by fever, tachycardia, and/or localized tenderness are operative
cases. Uncomplicated obstructions are usually initially treated conservatively,
with surgery reserved for treatment failures.
- Octreotide may be useful in nonoperative cases of bowel obstruction by decreasing GI
emergencies and motility.
- Sigmoid volvulus is treated with rectal tube decompression or surgery and usually
does not require aggressive fluid resuscitation as there is little third spacing. Cecal
volvulus often requires surgery.
Disposition
- These patients are all admitted to the hospital, almost always under the care of a surgeon.
- "Never let the sun rise or set on a bowel obstruction."
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