LARGE BOWEL OBSTRUCTION

Background: A large bowel obstruction is an emergency condition that
normally requires early identification and prompt surgical
intervention. Colonic obstruction may result from
infectious/inflammatory, neoplastic or mechanical pathology. The
etiology is age dependent. Recognizing colonic obstruction is
essential. The serosa will only expand to a variable diameter before
rupture and fecal soilage of the peritoneal cavity occurs.

Pathophysiology: Colonic obstruction that occurs as a result of
rotation or twisting of the cecum or sigmoid colon normally causes the
abrupt onset of symptoms. Sigmoid volvulus usually occurs in an older
individual with a history of straining at stool. In cecal volvulus,
there is normally a congenital defect in the peritoneum with inadequate
fixation of the cecum and volvulus will occur in a much younger person
as opposed to sigmoid cecum. As the colon twists on its mesentery, the
venous drainage and arterial inflow is compromised and there is a
closed loop obstruction. The KUB appearance is classic as is the
gastrografin study, which demonstrates a bird’s beak at the level of
obstruction.

 CLINICAL

History: 

 Major complaints include abdominal distention, nausea, vomiting
and crampy abdominal pain. It is important to obtain a history of
bowel movements and flatus. The abrupt onset of symptoms would make an
acute obstructive event, such as a cecal or sigmoid volvulus, a more
likely diagnosis. A chronic history of constipation, cathartic use and
straining at stools would imply a diagnosis of diverticulitis or
carcinoma. A change in the caliber of the stools favors the diagnosis
of carcinoma. When associated with weight loss, this increases the
likelihood of carcinoma.

 Right-sided colonic lesions have an opportunity to grow quite
large before obstruction occurs, because of the compacity of the right
colon and the consistency of the stool. Tumors of the sigmoid colon
and rectum cause colonic obstruction much earlier in their development
since the colon is narrower and the stool harder in that area of the
colon.

 The colon has pain receptors that sense vigorous contraction or
distention. As a result, a large bowel obstruction causing dilatation
of the colon causes vague, visceral abdominal cramps unless perforation
occurs. This procedes to peritonitis. The physician’s role is to
intervene in order to prevent colonic perforation. A history of
obstipation (no gas or bowel movement) is important to obtain. Often
the patient will state that her/his belt or pants do not fit. 
Obstruction secondary to intussusception presents with a history of
intermittent, crampy abdominal pain that is colicky and relieved by
assuming the fetal position. Weight loss and a feeling of fatigue are
common.

 Symptoms of pneumaturia, mucasuria or fecaluria may occur when
fistulization of the sigmoid colon to the bladder occurs secondary to
diverticulitis or cancer.

Physical:

 Abdominal distention may be significant in patients with a large
bowel obstruction. Bowel sounds may be normal early on, but usually
become quiet. The abdomen is hyperresonant to percussion.

 Palpation reveals tenderness. Rebound is an ominous sign, which
implies peritonitis secondary to perforation.

 The cecum is the area most likely to perforate (following the law
of Le Place). Sigmoid diverticulitis and a perforated sigmoid
carcinoma are clinically difficult to differentiate.

 The stool may be guaiac positive if carcinoma is the etiology.

 A rectal or low sigmoid mass may be palpated on rectal
examination. A mass or fullness may be appreciated if the etiology is
a tumor of the cecum.

Causes: The obstruction that occurs as a result of a tumor is of
gradual onset and normally results from tumor ingrowth into the lumen
of the colon. Diverticulitis is associated with muscular hypertrophy
of the colonic wall and with repetitive episodes of inflammation, the
lumen becomes narrow as the colonic wall becomes fibrotic and
thickened. Intussusception commonly involves a tumor which acts as the
lead point and is located at the iliocecal valve. Normally,
peristalsis will invaginate the tumor through the iliocecal valve to
the right colon. In this process, the terminal ileum and a segment of
small intestine and mesentery will intussuscept into the right colon. 
Ogilvie's syndrome may occure in elderly individuals who abuse
cathartics or have diabetes. It is almost a neuropathy of the colonic
wall and a loss of peristalsis. There is no evidence of obstruction,
but the colon becomes significantly and dangerously dilated.


 DIFFERENTIALS

Bowel Obstruction, Small 
Constipation 
Diverticular Disease 

Other Problems to be Considered: 
Carcinoma
Cecal Volvulus
Intussusception
Ogilvie's Syndrome
Sigmoid Volvulus 

 WORKUP

Lab Studies: 

 Blood should be obtained for a CBC, electrolytes, PT and type and
crossmatch.

Imaging Studies:

 A chest x-ray (CXR), KUB and upright should be obtained. The CXR
demonstrates free air if perforation has occurred and a KUB may be
diagnostic of sigmoid or cecal volvulus (i.e., kidney bean appearance
on the radiograph).

 Additional contrast studies might include a gastrografin enema or
a computerized tomography with contract.

Procedures:

 A nasogastric tube should be inserted when symptoms of vomiting
are present. Intravascular volume is usually depleted and fluid
resuscitation is necessary early. The appropriate fluid is normal
saline or Ringer’s lactate.

 TREATMENT

Emergency Department Care: Initial therapy is directed at patient
comfort and volume resuscitation. The ultimate goal of therapy is to
decompress the large intestine.

Consultations:

 Early consultation from a general surgeon is indicated as
treatement for the causes of large bowel obstruction is frequently
surgical.

 Sigmoid volvulus: The first choice is a sigmoidoscopy with
volvulus reduction. The second choice is a sigmoid colectomy.

 Cecal volvulus: The first choice is a hemicolectomy. The
second choice is a colonoscopy.

 Sigmoid obstruction secondary to diverticulitis or carcinoma:
The solution is a sigmoid resection and Hartman procedure or a sigmoid
resection and primary anastomosis as an alternative.

 Obstruction of the splenic flexture: The first choice is an
extended hemicolectomy. The second choice is a proximal colostomy with
delayed resection.