• Abdominal radiographs can demonstrate

obstruction, but computed tomography is more

sensitive.

INTRODUCTION

Intestinal obstruction refers to failure of intestinal contents

to pass through the bowel lumen. Mechanical obstruction

refers to physical blockage of luminal contents. This occurs

in either small bowel (80% of cases) or large bowel (20%

of cases). The most common cause of mechanical obstruction is adhesions from prior abdominal surgery (SOo/o),

followed by malignancy (20%), hernias ( 10%), inflammatory bowel disease (So/o), and volvulus (3%).

Intestinal obstructions can be either partial or com ­

plete. Partial obstructions are often managed nonopera ­

tively. Complete obstructions carry more risk of morbidity

and can result in strangulation. As bowel contents are

prevented from forward flow, increased secretions result in

overdistention, which causes bowel wall edema and

reduced lymphatic and venous outflow. This is referred to

as strangulation and can progress to bowel ischemia,

necrosis, perforation, and peritonitis. Up to 40% of small

bowel obstructions become strangulated, most commonly

from volvulus, adhesions, and hernias. A closed-loop

obstruction occurs when there is mechanical blockage

both proximal and distal to a bowel segment. This results

in very high risk of strangulation because bowel contents

are prevented from both forward and retrograde flow.

Small bowel obstructions represent lSo/o of hospital

admissions for acute abdominal pain. Approximately

1 3 1

• Intesti nal obstruction is treated with intravenous fluids,

nasogastric suctioning, antiemetics, narcotic pain medications, and anti biotics in select cases.

• Strangulation is a compl ication of obstruction that can

lead to bowel ischemia, peritonitis, and sepsis.

300,000 operations are performed every year in the United

States for obstruction. Mortality rate overall is approximately So/o, whereas the mortality rate from strangulated

obstructions approaches 30%.

In contrast to mechanical obstruction, functional

obstruction (eg, adynamic ileus) occurs when intestinal

contents fail to pass because of disturbances in gut motility.

It most commonly occurs immediately after surgery, but

can also be seen in inflammatory conditions, electrolyte

abnormalities, and from certain medications (namely,

narcotics). Unless noted otherwise, the remainder of this

chapter refers to mechanical obstruction.

CLINICAL PRESENTATION

.... History

The most common initial complaint is intermittent colicky

abdominal pain. If the obstruction is proximal, the patient

may also complain of nausea and vomiting. More distal

obstructions can result in delayed onset of vomiting.

Although obstipation (lack of flatus and bowel movements) can suggest an obstruction, the presence of flatus or

bowel movements should not be used as evidence that an

obstruction has not occurred, as these can be seen early in

the course of even complete obstructions. The patient history should include questions about prior surgeries, history

CHAPTER 31

of hernias, and history of obstruction in the past, as prior

intestinal obstructions have up to SOo/o recurrence rate.

� Physical Examination

Vital signs may be normal or abnormal. Fever, tachycardia,

and hypotension are ominous signs and may suggest peritonitis or sepsis. Patients will usually appear uncomfortable regardless of their position. Physical exam is significant

for a distended, diffusely tender abdomen, tympany to

percussion, and hyperactive bowel sounds. If strangulation

has occurred there may be peritonitis on exam. Patients

should be examined for evidence of prior abdominal surgeries (eg, incision scars) and examined for hernias.

DIAGNOSTIC STUDIES

� Laboratory

Electrolyte abnormalities such as hypokalemia and acidbase disturbances can occur due to vomiting. Third spac- A

ing of fluid and dehydration from vomiting may cause

elevated blood urea nitrogen or creatinine. Intestinal ischemia can cause an anion gap metabolic acidosis with an

elevated lactic acid. Leukocytosis may be present on a

complete blood count and also suggests ischemia or peritonitis. Consideration should be given to checking liver

function studies, amylase, lipase, and urinalysis to evaluate

for other etiologies of the patient's symptoms.

� Imaging

Radiographs are 50-66% sensitive in diagnosing an intestinal obstruction. An "obstructive series" classically consists

of 3 radiographs: upright chest film, supine abdominal

film, and upright abdominal film. A lateral decubitus x-ray

may also be included. The upright chest film is used to

evaluate for evidence of perforation (free air under the

diaphragm). The upright abdominal film will show dilated

loops of bowel (>3 em), air-fluid levels (layering of

intestinal contents), and absence of air in the rectum

(Figure 31-1A). The "string of pearls" sign is a series of

small pockets of gas in a row. It represents a predominance

of fluid in the bowel lumen with small amounts of air

trapped between the valvulae conniventes of the bowel. In

adynamic ileus, radiographs will demonstrate dilation of

the bowel without air-fluid levels.

An abdominal CT scan is much more sensitive than

radiographs (92-100% sensitive) (Figure 31- lB). CT also

has the advantage of being able to determine the location

of obstruction, as well as bowel wall edema, and findings

suggestive of bowel ischemia. A CT scan may also show the

cause of the obstruction (eg, hernia, malignancy). If no

cause is identified, adhesions may be the etiology. In

patients with fever, localized abdominal pain, or abnormal

vital signs, a CT scan should be the initial study of choice

owing to its greater sensitivity and the need for timely

diagnosis.