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1006 PART 9: Gastrointestinal Disorders

the degree of the obstruction, the presence of complicating features such TABLE 104-7 Causes and Risk Factors of Intestinal Pseudoobstruction
as ischemia or perforation, as well as if any other intra-abdominal cause
of ileus is present should no obstruction be found. Recent studies have Intra-abdominal • Postoperative
demonstrated CT to have an accuracy of 85% to 100% 86,87 in diagnosing • Prolonged mechanical bowel obstruction
strangulation, with accuracy increased when combined with classical • Trauma
clinical criteria such as the presence of tachycardia, fever, abdominal • Peritonitis (chemical, infectious, autoimmune)
tenderness, and leukocytosis. CT findings suggestive of ischemia • Impaired bowel perfusion
87
include mesenteric haziness, reduced wall enhancement, wall thickening, Retroperitoneal • Orthopedic, spinal, vascular, renal, or other surgery
mesenteric fluid, mesenteric venous congestion, and ascites. • Trauma, hematoma, infection
A partial small bowel obstruction can be treated successfully • Pancreatitis
with nonoperative management in over 80% of cases, with a risk of Thoracic • Myocardial infarction
progression to strangulation in 3% to 6%. As the vast majority of patients • Infection
being treated nonoperatively improve within 48 hours, those that do
not improve after such a trial should with rare exception be taken for Systemic • Medications (eg, narcotics, anticholinergics)
surgery. Patients with complete small bowel obstruction require surgery • Electrolyte imbalances
with resection of compromised bowel in approximately 30% of cases. • Increasing age
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As mortality is increased by up to sevenfold when an operation is per- • Bedrest
formed for intestinal strangulation compared with simple obstruction, • Uremia
earlier surgery is preferred. Of note, there is no evidence supporting • Sepsis
the use of routine antibiotics as adjunctive therapy in the nonoperative • Neurologic disorders, spinal cord injury
treatment of small bowel obstruction, and as such, antibiotics should • Hypothyroidism, hypo/hyperparathyroidism
only be used for patients with signs of intestinal compromise who are on
their way to the operating theatre. There is also no evidence of benefit
of long intestinal tubes over conventional oro- or nasogastric tubes. 86
■ LARGE BOWEL OBSTRUCTION PSEUDOOBSTRUCTION

The investigation and management of large bowel obstruction have Paralysis of the gastrointestinal tract, or ileus, is a common response
in patients undergoing abdominal surgery, but it can also develop in
evolved considerably over the last decade. Etiologies of large bowel response to a number of acute extra-abdominal and intra-abdominal
obstruction are listed in Table 104-6, with the most common causes in conditions (see Table 104-7). Studies have demonstrated that ileus
North America being malignancy (60%), volvulus (10%-15% of which complicates up to 40% of ICU patients who have not had antecedent
75% are sigmoidal and 20% cecal), and strictures (10%). Large bowel abdominal surgery. 32,33
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obstruction can be diagnosed on plain abdominal x-rays with a sensitiv- The pathophysiology of ileus is incompletely understood, although is
ity of 84%, although differentiation from acute colonic pseudoobstruc- best described as multifactorial, involving abnormalities of the enteric
89
tion may require additional imaging. When differentiating acute colonic nervous system, autonomic nervous system, neurohormonal pathways,
pseudoobstruction from true obstruction, the use of a rectal contrast and local and systemic inflammatory processes. 96-98 Vasoactive intestinal
study is recommended. This may be in the form of a water-soluble peptide, substance P, and nitric oxide have all been shown to play a
enema or potentially CT scan with rectal contrast. Use of barium con- role in the development of postoperative ileus. The body’s inflamma-
trast is contraindicated in an obstructed colon as it is not necessary to tory response, whether as a result of direct intestinal manipulation by
make the diagnosis of obstruction, it can precipitate barium peritonitis surgeons or from systemic illness, also plays a significant role in the
in the setting of compromised bowel at risk of perforation, and its reten- development of ileus and helps explain the frequent occurrence of this
tion in the bowel will hamper any future radiographic imaging as it is condition in nonsurgical ICU patients. 32,98
extremely radiodense and causes significant artifact. A water-soluble Postoperative ileus is manifested by atony of the stomach, small
contrast enema may be used in the investigation of volvulus where plain bowel, and colon that usually resolves spontaneously within a few days.
abdominal films are not diagnostic, but CT scan (± rectal contrast) is Typically the small bowel regains motility first, followed by the stom-
being increasingly used to diagnose these conditions. 90 ach then colon. Initial therapy is directed at identifying and correctly
Management of volvulus of the sigmoid colon is emergent endoscopic reversible causes (see Table 104-7) and providing relief of symptoms
detorsion and elective resection to prevent recurrence, or emergent such as distension, nausea, or vomiting. Many studies have investigated
surgical exploration in the setting of bowel compromise. Cecal volvu- methods of preventing or shortening the duration of postoperative ileus.
91
lus generally does not respond to endoscopic therapy and thus emergent While no such methods are universally accepted nor employed, the
surgery is the procedure of choice. Similarly, malignant colonic obstruc- following have support for their use in the literature: laparoscopic surgical
tion generally requires surgical resection for definitive management, technique, postoperative gum chewing, 99,100 judicious perioperative
98
although sometimes either endoscopy or interventional radiology can intravenous fluid administration, 101-103 nonopioid pain control medica-
place stents in nonoperative candidates. 92,93 tions (eg, NSAIDS), use of local anesthetic epidural anesthesia instead
98
■ AN APPROACH TO ILEUS AND/OR FEED INTOLERANCE IN THE ICU of epidural or systemic narcotics, and most recently, alvimopan and
105
104
methylnaltrexone. Use of promotility agents such as erythromycin
106
107
Unfortunately, up to 60% of ICU patients will experience gastrointestinal or metoclopramide have not been shown to decrease postopera-
symptoms during their stay. 31-33 Both surgical and nonsurgical ICU patients tive ileus, 108,109 although they are useful in assisting with enteral feed
often have multiple causes for ileus or pseudoobstruction (Table 104-7), in tolerance in ICU patients and diabetic gastroparesis. It is important to
34
addition to being at risk for mechanical bowel obstructions. An algorithm note that according to the SCCM/ASPEN guidelines, in the ICU setting
for assessing ileus and/or abdominal distension is provided in Figure 104-6. the resolution of clinical ileus is not required in order to initiate enteral
In the case of a likely mechanical obstruction, remember that delay in nutrition, and in fact, NPO status may prolong ileus. 34
surgical management increases morbidity and mortality. Indeed, even Ileus without antecedent abdominal operation also commonly occurs
94
experienced surgeons have been shown to be able to accurately predict the in the ICU. Although the treatment of ileus in these patients is the
development of intestinal ischemia in only 50% of cases of complete small same, it is important that the etiology is clarified sufficiently to exclude
bowel obstruction. Thus, if mechanical obstruction is high on the differ- anything more ominous that may require surgery or other interventions.
95
ential, early surgical consultation should be obtained. Similarly, when an ileus persists for an inappropriate length of time,

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