Over the years, numerous attempts have been made to use groupings of clinical criteria to establish

the diagnosis of complete and irreversible intestinal obstruction, as distinguished from partial intestinal

obstruction that might improve without operative intervention or other abdominal pathology. In recent

studies, computer-assisted analysis has been used to identify such criteria.37 Key factors in the history

and clinical examination38 include previous abdominal surgery, quality of pain (colic/intermittent

versus steady), abdominal distention, and hyperactivity of bowel sounds. Not surprisingly, the use of

such computer-assisted algorithms confirms that the most important clues to the diagnosis of simple

obstruction of the small intestine are obtained in a complete and careful history and physical

examination. As discussed below, the role of plain abdominal radiographs and other imaging studies is

to confirm the clinical diagnosis of simple obstruction. It should be emphasized that, in simple

obstruction, laboratory studies do not play a direct role in diagnosis, but aid in understanding the extent

of complications such as dehydration, strangulation, and sepsis.

Strangulation obstruction is accompanied by symptoms and signs suggesting peritonitis, large fluid

shifts, or systemic toxicity. These symptoms and signs include abdominal tenderness or involuntary

guarding localized to the area of the strangulated loop of bowel, decreasing urine output, fever, and

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tachycardia. There have been attempts to use common clinical and laboratory test criteria to identify

the likelihood that the obstruction is associated with strangulation. Stewardson et al.39 observed that the

risk of strangulation was low in patients with partial (i.e., incomplete) or complete SBO if feve

perfusion pressures, inflammatory cells are recruited from surrounding peritoneal structures. This

sequence of events leads to intense inflammation, release of exudate in the area of the appendix and the

first localization of pain from the umbilicus to the area of peritoneum lying nearest the inflamed

appendix. Peritoneal findings (localized tenderness, involuntary guarding, rebound, or referred

tenderness) and fevers appear. Subsequently, 20 to 24 hours into the illness, the blood supply of the

appendix is compromised. Gangrene and perforation follow and, if not contained by surrounding

structures, free perforation leads to a rigid abdomen. Toxins from necrotic tissue and bacterial

overgrowth are released into the systemic circulation and shock ensures. Torsion of a loop of small

intestine around an adhesive band or inside a hernia leads to a similar pattern of events. As discussed

below, torsions of the large bowel are usually accompanied by massive distention of the loop by air and

feces, but the compromise of intestinal wall perfusion and evolution into peritonitis, systemic toxicity,

and shock are similar.

Open-Loop Obstructions. Complications in open-loop obstructions do not necessarily evolve as rapidly

as in closed-loop obstructions. Not uncommonly, an open-loop obstruction located in the proximal

jejunum can be decompressed by the patient’s ability to vomit. Proximal obstruction is characterized by

vomiting and loss of gastric, pancreatic, and biliary secretions, with resulting electrolyte disturbances.

These disturbances include dehydration, metabolic alkalosis, hypochloremia, hypokalemia, and usually

hyponatremia. In contrast, obstructions of the distal ileum may lead only to a slowly progressing

distention of the small intestine, with accommodation by intestinal myoelectrical function and minor

alterations in fluid and electrolyte balances. Open-loop obstructions located in the midgut are often

complicated by events similar to those seen in closed-loop obstructions or combinations of events seen

in high and low obstructions (Table 49-2). Patients with distal jejunal obstruction tend to present with a

combination of complications resulting from loss of intestinal contents from vomiting, as well as

distention and compromise of intestinal wall perfusion.

2 In simple or uncomplicated obstruction, the intestinal lumen is partially or completely occluded

without compromise of intestinal blood flow. Simple obstructions may be complete, meaning that the

lumen is totally occluded, or incomplete, meaning that the lumen is narrowed but permitting distal

passage of some fluid and air. In strangulation obstruction, blood flow to the obstructed segment is

compromised and tissue necrosis and gangrene are imminent.

Clinical Presentation and Differential Diagnosis

3 The four key symptoms associated with acute mechanical bowel obstruction include abdominal pain,

vomiting, distention, and obstipation. When bowel obstruction is the most likely diagnosis, “abdominal

pain out of proportion to physical findings” represents a surgical emergency. Colon obstruction is

usually accompanied by varying levels of pain with massive abdominal distention and obstipation. As

noted earlier, the signs and symptoms of acute but simple small intestinal obstructions are related to the

level of the obstruction and the closed- or open-loop nature of the obstruction. Other abdominal

conditions, such as appendicitis, diverticulitis, perforated peptic ulcer, cholecystitis, or

choledocholithiasis can usually be distinguished from SBO, by clinical examination and basic laboratory

data. It should be emphasized that bowel obstruction can complicate any of these abdominal conditions.

The presence of another abdominal process does not exclude the complication of SBO.

Over the years, numerous attempts have been made to use groupings of clinical criteria to establish

the diagnosis of complete and irreversible intestinal obstruction, as distinguished from partial intestinal

obstruction that might improve without operative intervention or other abdominal pathology. In recent

studies, computer-assisted analysis has been used to identify such criteria.37 Key factors in the history

and clinical examination38 include previous abdominal surgery, quality of pain (colic/intermittent

versus steady), abdominal distention, and hyperactivity of bowel sounds. Not surprisingly, the use of

such computer-assisted algorithms confirms that the most important clues to the diagnosis of simple

obstruction of the small intestine are obtained in a complete and careful history and physical

examination. As discussed below, the role of plain abdominal radiographs and other imaging studies is

to confirm the clinical diagnosis of simple obstruction. It should be emphasized that, in simple

obstruction, laboratory studies do not play a direct role in diagnosis, but aid in understanding the extent

of complications such as dehydration, strangulation, and sepsis.

Strangulation obstruction is accompanied by symptoms and signs suggesting peritonitis, large fluid

shifts, or systemic toxicity. These symptoms and signs include abdominal tenderness or involuntary

guarding localized to the area of the strangulated loop of bowel, decreasing urine output, fever, and

1252

tachycardia. There have been attempts to use common clinical and laboratory test criteria to identify

the likelihood that the obstruction is associated with strangulation. Stewardson et al.39 observed that the

risk of strangulation was low in patients with partial (i.e., incomplete) or complete SBO if fever,

tachycardia, localized abdominal tenderness, or leukocytosis were not present. These authors suggested

that, in a setting consistent with bowel obstruction, any one of these four cardinal signs indicated a

small risk for strangulation. The presence of any two of these signs increased the risk of strangulation so

high as to warrant immediate surgery. These authorities and others have stressed, however, that when

complete obstruction is present, no satisfactory clinical criteria are available to reliably exclude the

possibility of strangulation.39–43

Different laboratory tests have been advocated for early detection of strangulated intestine. Metabolic

(i.e., lactic) acidosis and increases in serum amylase, inorganic phosphate, hexosaminidase, intestinal

fatty acid–binding protein, and serum D-lactate levels have all been associated with intestinal

ischemia.44,45 Such laboratory abnormalities may be helpful in diagnosing established strangulation in a

small group of patients where the diagnosis of necrotic bowel is not clear. However, a noninvasive and

rapid test has not yet been developed that can provide information to suggest that tissue necrosis is

imminent but not yet established.43

Radiographs and Imaging

Plain Films

The role of plain abdominal radiographs and imaging studies is to confirm the diagnosis of bowel

obstruction, locate the site of obstruction, and gain insight into the lesion responsible for the

obstruction. On plain radiographs of the abdomen, the key findings of SBO reflect the accumulation of

air and fluid proximal, and clearance of fluid and air distal to the point of obstruction. Dilated loops of

small intestine are defined as those greater than 3 cm in diameter. Free air represents perforation of a

viscus and mandates immediate operation. Such findings include dilated loops of small bowel on the flat

plate (Fig. 49-3) and multiple air–fluid levels located at different levels on the upright film or lateral

decubitus film (Fig. 49-4). Based on these criteria plain abdominal radiography is diagnostic in 67% to

80% of patients.46,47 Plain radiographs, however are only accurate in 46% to 85% of the time and can

miss SBO in patients without air–fluid levels because of fluid-filled distended loops.48 In complete

obstruction of the small intestine, the colon loops and rectum do not contain air. If there is air in the

colon, the obstruction may be complete, but early, or it may be incomplete.

In the colon, tight closed-loop obstructions (i.e., volvulus of the cecum, transverse colon, or sigmoid

colon) are accompanied by distention of the obstructed segment (Fig. 49-5). The proximal colon is

considered dilated when it reaches 8 to 10 cm; the sigmoid colon is considered dilated at 4 to 5 cm. In

contrast, obstruction by carcinoma or diverticulitis presents with massive distention of the entire colon

from the point of obstruction to the ileocecal valve. From this standpoint, any large bowel obstruction

may represent a “closed loop” if the ileocecal valve is competent. Although plain film findings can be

used to differentiate obstruction of the small bowel from that of the large bowel, they are not

consistently accurate in localizing the specific site of obstruction.

Figure 49-3. Plain supine abdominal film of a patient with small-intestinal obstruction. Note the multiple dilated loops of small

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intestine (black arrow) in the left upper quadrant, characterized by complete markings of the plicae. Also note the absence of air in

colon and rectum.

Figure 49-4. Plain upright abdominal film of a patient with small-intestinal obstruction. Note the air–fluid levels in the stomach

and multiple dilated loops of small intestine (black arrows), and absence of air in the colon or rectum.

Figure 49-5. Plain upright abdominal film of a patient with sigmoid volvulus. The dilated centrally located sigmoid loop is seen

(arrowheads). The proximal colon is dilated and gas filled. T, transverse colon; D, descending colon.

Contrast Studies

The diagnosis of bowel obstruction can generally be made by considering the clinical history, physical

examination, laboratory, and plain radiograph findings. Contrast studies (i.e., small bowel followthrough, enteroclysis, and contrast enema) may provide specific localization of the point of obstruction

and the nature of the underlying lesion. When obstruction of the small intestine is not progressing or

resolving, a small bowel follow-through may be performed to confirm the presence and location of the

obstruction. Also, even under acute circumstances, diagnosis and management of colonic obstructions

are generally enhanced by the use of a contrast enema. Under some circumstances, however, contrast

studies are unnecessary and may be contraindicated. For example, in the classic setting of abdominal

pain, nausea, vomiting, and a plain film indicating multiple air–fluid levels in the small intestine and

colonic collapse, the diagnosis of acute obstruction can be made clinically. Failure to improve in a short

period of time will mandate operation and contrast studies are unnecessary. When strangulation or

perforations are strongly suspected, contrast studies are contraindicated.

4 The choice of contrast materials includes water-insoluble suspensions of barium and water-soluble

agents such as Gastrografin® or Hypaque®. Barium studies provide the clearest images, in both small

bowel studies where the contrast is given from above and colon/rectum studies in which the contrast is

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given by enema. If barium leaks into the peritoneum, it elicits intense peritonitis. If there is any

possibility of bowel perforation or gangrene, barium should not be used. Water-soluble agents such as

sodium amidotrizoate/meglumine amidotrizoate oral solution (Gastrografin®) or diatrizoate

sodium/diatrizoate meglumine (Hypaque®) are hyperosmotic and can elicit fluid translocation into the

gut. When the obstruction of the small intestine is incomplete the use of these agents may facilitate

resolution. Gastrografin is hyperosmolar (1,900 mOsm/L). Its administration permits mobilization of

fluid into the bowel lumen which decreases edema of the intestinal wall and increases the pressure

gradient across obstructive site. It is thought that these fluid and pressure shifts can contribute to

resolution in cases of incomplete obstruction. The 2013 Bologna guidelines for diagnosis and

management of adhesive SBO recommended a dosage of 50 to 150 mL of Gastrograffin administered

either orally or via NGT immediately on admission or after an attempt of conservative treatment for 48

hours.49 The appearance of contrast in the colon within 4 to 24 hours after administration had a

sensitivity of 96% and specificity of 98% in predicting resolution of SBO.50 A prospective randomized

trial confirmed that gastrograffin significantly reduced the need for surgery by 74%.51 Some studies

showed that water-soluble contrast medium reduces hospital stay but does not reduce need for

surgery52,53 but recent meta-analysis showed that it is effective in reducing the need for surgery and

shortening length of stay.50 Use of water-soluble contrast may thus be both diagnostic and can be

therapeutic.

Computed Tomography and Other Imaging Modalities

5 The potential benefits of computed tomography (CT) scanning in diagnosis of bowel obstruction include

the following.54–57 First, using radiographic contrast, the obstructing segment may be localized and

characterized as complete or incomplete. Second, the nature of the obstructing lesion, especially if it is

malignant, can be established. Third, additional abdominal pathology (e.g., metastases, ascites,

parenchymal liver abnormalities) may be identified. Fourth, anatomic information obtained from the CT

can be used in operative planning. There is also evidence that, in special circumstances, CT may

improve preoperative detection of strangulation.42,56 Coronal and sagittal reconstruction improve the

ability to identify transition point and IV contrast with delayed imaging should be considered to assess

for venous occlusion or delayed bowel wall enhancement.58 CT findings indicating the site of

obstruction and impending ischemia include beak-like narrowing, mesenteric edema, vascular

engorgement, moderate to severe intestinal wall thickening (greater than 2 mm) (Fig. 49-6). In

addition, high attenuation of bowel wall on unenhanced CT scans, low or reduced attenuation of bowel

wall on intravenous contrast CT scans, and presence of intramural air (pneumatosis) or portal venous

gas are CT findings suggestive of strangulation. Attenuation reflects increased energy absorption,

scattering, beam divergence, and other causes of energy loss. Thus, areas of high attenuation appear

darker than areas of low attenuation. CT scan has a 96% sensitivity and 93% specificity with a negative

predictive value of 99% in diagnosing intestinal strangulation.59 Although CT scan need not be routinely

performed unless history, physical examination, and plain films are not conclusive for SBO diagnosis,60

it is increasingly the “go-to” study for confirmation.

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Figure 49-6. Axial (A) and coronal (B) images of a closed-loop obstruction with strangulated small bowel secondary to a volvulus

from an adhesive band. Distended fluid-filled loops of small bowel (B) in a radial distribution converge toward the point of

torsion (white arrows). There is edema within the mesentery (M). Shown in (C) is a coronal view of vascular engorgement and

mesenteric edema in a closed-loop obstruction.

Ultrasound has a very limited use in diagnosing SBO and visualization can be obscured by the

intraluminal air but it has been suggested that real-time abdominal sonography could aid in the

diagnosis of strangulation obstruction. In studies conducted in two different institutions, Ogata and

colleagues

61,62 demonstrated that the presence of significant amounts of peritoneal fluid and of an

akinetic and dilated loop of bowel were strongly associated with the presence of strangulation. In

patients who had strangulation, but were thought to have simple obstruction only, these findings helped

to make the preoperative diagnosis of infarction.

Magnetic resonance imaging (MRI) has the sensitivity comparable to CT scan in diagnosing

obstruction but limitations include lack of availability after hours, poor definition of mass lesion, and

poor visualization of colonic obstructions.63 The use of MRI should be limited to patients who have

contraindications to CT or are allergic to contrast material.49

It should be emphasized that when the clinical picture suggests strangulation, unnecessary imaging

studies should not delay resuscitation or expeditious movement to the operating room. Such studies will

not necessarily be helpful when clinical criteria and basic abdominal radiographs have indicated the

presence of a simple and complete obstruction. By itself, this diagnosis mandates urgent exploration and

the information sought should be weighed against the risk of delay in going to the operating room. In

fact, in most studies evaluating the impact of imaging on diagnosis and timing of intervention, clinical

diagnosis is seldom incorrect – it is highly specific when multiple clinical signs (tenderness, peritoneal

signs, leukocytosis, and profound dehydration) of strangulation are present. However, such a picture

represents advanced disease and use of CT scan may detect strangulation before such signs are manifest.

These findings reinforce the dictum that when there are clinical signs of strangulation, surgery should

be performed without delaying for additional imaging studies. In patients with equivocal findings or

uncertain clinical diagnosis, CT can be highly useful in confirming the diagnosis, localizing the site and

detecting the cause of intestinal obstruction and strangulation.56

General Considerations in Management of the Patient with Bowel Obstruction

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