Understanding Small Bowel Obstruction


A small-bowel obstruction (SBO) is caused by a variety
of pathologic processes. The leading cause of SBO in
developed countries is postoperative adhesions (60%)
followed by malignancy, Crohn disease, and hernias,
although some studies have reported Crohn disease as
a greater etiologic factor than neoplasia. Surgeries
most closely associated with SBO are appendectomy,
colorectal surgery, and gynecologic and upper
gastrointestinal (GI) procedures. One study from
Canada reports a higher frequency of SBO after
colorectal surgery, followed by gynecologic surgery,
hernia repair, and appendectomy. Lower abdominal and
pelvic surgeries lead to obstruction more often than
upper GI surgeries.

SBOs can be partial or complete, simple (ie,
nonstrangulated) or strangulated. Strangulated
obstructions are surgical emergencies. If not diagnosed
and properly treated, vascular compromise leads to
bowel ischemia and r. This bowel dilatation
stimulates cell secretory activity resulting in more fluid
accumulation. This leads to increased peristalsis both
above ant below the obstruction with frequent loose
stools and flatus early in its course.

Vomiting occurs if the level of obstruction is proximal.
Increasing small-bowel distention leads to increased
intraluminal pressures. This can cause compression of
mucosal lymphatics leading to bowel wall lymphedema.
With even higher intraluminal hydrostatic pressures,
increased hydrostatic pressure in the capillary beds
results in massive third spacing of fluid, electrolytes,
and proteins into the intestinal lumen. The fluid loss and
dehydration that ensue may be severe and contri intraluminal pressures. This can cause compression of
mucosal lymphatics leading to bowel wall lymphedema.
With even higher intraluminal hydrostatic pressures,
increased hydrostatic pressure in the capillary beds
results in massive third spacing of fluid, electrolytes,
and proteins into the intestinal lumen. The fluid loss and
dehydration that ensue may be severe and contri inflammatory bowel
% % disease (5%), volvulus (3%), and miscellaneous causes
(2%). The causes of SBO in pediatric patients include
congenital atresia, pyloric stenosis, and
intussusception. Strangulated SBOs are most
commonly associated with adhesions and occur when a
loop of distended bowel twists on its mesenteric
pedicle. The arterial occlusion leads to bowel ischemia
and necrosis. If left untreated, this progresses to
perforation, peritonitis, and death.

Bacteria in the gut proliferate proximal to the
obstruction. Microvascular changes in the bowel wall
allow translocation to the mesenteric lymph nodes. This
is associated with an increase in incidence of
bacteremia due to Escherichia wel ischemia
and necrosis. If left untreated, this progresses to
perforation, peritonitis, and death.

Bacteria in the gut proliferate proximal to the
obstruction. Microvascular changes in the bowel wall
allow translocation to the mesenteric lymph nodes. This
is associated with an increase in incidence of
bacteremia due to Escherichia coli, but the clinical
significance is unclear. In the US: SBO accounts for
20% of all acute surgical admissions.


Diagnosing Small Bowel Obstruction

Order plain radiographs first for patients in whom SBO is
suspected. At least 2 views, supine or flat and upright,
are required. While plain radiographs are diagnostically
more accurate in cases of simple obstruction;
diagnostic failure rates of as much as 30% have been
reported. It must also be noted that plain radiography
is of little assistance in differentiating strangulation
from simple obstruction. Enteroclysis is valuable in
detecting the presence of obstruction and in
differentiating partial from complete blockages.
This study is useful when plain radiographic findings are
normal in the presence of clinical signs of SBO or if plain
radiographic findings are nonspecific. CT scanning is
useful in making an early diagnosis of strangulated
obstruction and in delineating the myriad other causes
of acute abdominal pain, particularly when clinical and
ral
pain, and/or leukocytosis.