Critical Care Medicine

Ileus and small bowel obstruction

Ileus defined as nonmechanical obstruction of bowel usually secondary to inhibition of peristalsis.

Small bowel obstruction defined as mechanical obstruction of small bowel due to adhesions, mass, volvulus or other internal or external compression.

Synonyms

Ileus: paralytic ileus, adynamic ileus, non mechanical obstruction, intestinal pseudo obstruction

Small bowel obstruction: mechanical ileus, obstructive ileus, dynamic ileus

Related conditions

Post operative ileus, internal hernia, midgut volvulus, gall stone ileus, incomplete and complete small bowel obstruction, colonic obstruction

1. Description of the problem

What every clinician needs to know

Ileus can be caused by indolent factors such drugs or electrolyte abnormalities as well as abdominal catastrophes. In the ICU patient who may not be able to communicate change in toleration of enteral feeds, increased gastric output, distended abdomen, or decreased stool output should prompt investigation for cause.

Clinical features

Signs of Ileus in the ICU patient can include abdominal distention, intolerance to enteral feeds, increased gastric output, increase in abdominal pressure, decreased flatus, decreased bowel sounds and decreased stool output. Sypmptoms of ileus can include abdominal pain, nausea,vomiting.

Bowel obstruction in the ICU patient can have very similiar signs, such as abdominal distention, intolerance to feeds, increased gastric output and decreased flatus and stool. But often the distinguishing feature can be cramping abdominal pain and hyperactive or high pitched bowel sounds.

Key management points

As ileus is caused by other factors including life threatening intra-abdominal processes such as peritonitis, it is necessary to quickly determine first this is an ileus vs. a small bowel obstruction. If ileus, is there a life threatening procress associated with it? If bowel obstruction, is it partial, complete or closed loop? Bowel decompression, fluid resuscitation and diagnosis are mainstays of initial treatment for both ileus and bowel obstruction.

2. Emergency Management

Gastric decompression with gastric tube. Resuscitation with isotonic fluid. No need for antibiotics for ileus or obstruction unless associated infectious cause or perforation suspected. Assess for intra-abdominal hypertension with bladder pressure. Correct electrolyte abnormalities, specifically potassium. Rule out life threatening cause of ileus (intra-abdominal sepsis) or small bowel obstruction with CT scan.

Emergency management steps

  • Gastric decompression.

  • Stop enteral feeds and medications.

  • IV resuscitation.

  • Monitor vital signs and urine output.

  • Measure bladder pressure.

  • Assess abdominal exam for peritoneal signs, present or absence of bowel sounds, presence of hernias.

  • Obtain X-ray studies: kub,upright cxr, decubitus abdominal film.

  • Obtain electrolytes, complete blood count, amylase, lipase.

  • CT scan consistent with Ileus r/o cause: drugs, infection, pancreatitis, electrolyte abnormality.

  • CT scan consistent with obstruction: assess; if partial: NGT decompression, bowel rest; if complete: NGT decompression, surgical consult.

3. Diagnosis

Establishing a specific diagnosis

Signs of paralytic ileus are very similar to bowel obstruction. Nausea, abdominal pain, bloating with vomiting, abdominal distention and obstipation being accompanying symptoms. Classically paralytic ileus is suggested by hypoactive bowel sounds whereas small bowel obstruction is described with rushes and bowel sounds consistent with peristalsis against the obstruction.

However, if obstruction has led to ischemia and intra-abdominal sepsis, the patient may have hypoactive bowel sounds. In a critically ill patient who is sedated and has impaired mental status, it may be difficult to elicit complaints of nausea or pain. Anasarca can mask abdominal distention. Obstipation and constipation may be overlooked as secondary to medications.

Diagnostic approach

A high index of suspicion should be maintained in patients who develop high gastric tube residuals or become intolerant of tube feeding. Patients with electrolyte abnormalities are at a higher risk for paralytic ileus, as are multiple trauma, burn, and post operative patients, as well as patients with any inflammatory response. Patients who are status post abdominal surgical procedure can develop post operative bowel obstruction from adhesions.

The key is to distinguish ileus from obstruction as early as possible since small bowel obstruction can lead to ischemia and perforation.

Diagnostic tests

Although plain abdominal films - flat, upright and decubitus films - are often initial tests ordered outside the ICU, inside the ICU these films are often of poor quality for discerning ileus from small bowel obstruction. Ileus usually has air throughout colon into rectum compared to small bowel obstruction, which when complete does not show colonic air. However these findings are not consistant when dealing with partial or early small bowel obstruction. Air fluid levels are difficult to ascertain in the critically ill, as upright and decubitus films are usually inadequate. (Figure 1 and Figure 2)

Figure 1.

KUB showing air in small and large bowel suggesting an ileus.

Figure 2.

KUB showing dilated small bowel loops with minimum air in colon suggesting small bowel obstruction

CT scan with oral water soluble contrast can help distinguish ileus from obstruction and also determine partial vs. complete obstruction. CT scan can also reveal causes for ileus or obstruction such as pancreatitis, retroperitoneal bleed, mass or hernia. CT scan is also sensitive in assessing for ischemic bowel in cases of obstruction. (Figure 3)

Figure 3.

CT scan showing dilated proximal small bowel with collapsed distal small bowel consistent with complete bowel obstruction

Findings such as mesenteric edema, asymmetrical bowel wall enhancement, pneumotosis intenstinalisis and portal vein air are all signs of possible bowel ischemia. The whirl sign, when the mesentery of small bowel is wrapped around its vessel, is in some reports predictive of small bowel obstruction that will require surgery.

4. Specific Treatment

Ileus

Most ileus care is supportive, treating the underlying correctable cause, if any. Since ileus can be caused by innumerable things, treating life threatening conditions such as infection and bleeding are first priority. Keeping electrolytes, especially potassium, normal is essential in these patients.

Removing dysmotility type of medications such as opiates, anticholenergics and calcium channel blockers may be helpful. Gastric decompression can help relieve abdominal distention and allow for more controlled account of output. It also may help with diaphragmatic excursion. The distended bowel can sequester large amounts of fluid, so fluid resuscitation may be necessary. Patient mobilization has mixed reviews for shortening duration of ileus.

Small bowel obstruction

In comparison, small bowel obstruction should be diagnosed as early as possible from ileus since the treatment for worsening clinical signs is most often surgical. Involvement of surgeon is paramount early in course especially for any complete or closed loop obstruction.

As the abdominal exam in critical ill patient is often nonspecific, close monitoring of pulse, minute ventilation, acid base, wbc and immature forms is critical. Lactate is often a late finding in intestinal ischemia and should not be used to rule it in or out as a single factor. Gastric decompression again maybe helpful. If there is no obvious finding of ischemic bowel on initial studies, there is no overwhelming data for antibiotics.

Parenteral nutrition support should be considered in patients at risk of malnutrition.

Drugs and dosage

Promotility agents such as metoclopramide or erythromyacin have not been shown to decrease duration of postoperative ileus and few studies show much improvement in non operative ileus. Use of alvimopan, a highly selective mu opioid receptor antagonist has been shown to decrease postoperative ileus at dose of 6mg twice a day. However only case reports of off label use for non operative ileus have been published.

Because of the multifactorial cause of ileus, systemic and continued correction of underlying abnormalities such as electrolytes, withdrawal of contributive medications and nutritional support are the mainstay.

5. Disease monitoring, follow-up and disposition

Expected response to treatment

Most postoperative ileus lasts 3-6 days. The average duration of non post operative ileus in the critically ill is unclear.

Partial small bowel obstruction may take several days to resolve. However, prolonged small bowel obstruction often requires surgery. If the obstruction is complete, early surgery is usually the best therapy.

Follow-up

In low grade or intermittent obstruction, CT scan may be less sensitive, thereby presenting as an ileus. Therefore, prolonged ileus should have additional contrast studies such as repeat CT scan, small bowel follow through or enterolysis to r/o low grade obstruction.

Pathophysiology

Ileus mechanism is complex but thought to be multifactorial, including stress induced sympathetic (inhibitory) reflexes, inflammatory mediators and effects of medications. Although bowel may contract, the coordinated forward peristalsis is impaired.

At onset of intestinal obstruction, gas and fluid accumulate proximal to the obstruction. Initially, the bowel becomes hyperdynamic, peristalsing against the obstruction causing the classic colicky pain. As more fluid and gas accumulate, the bowel distends, causing rise in pressure against the bowel wall. The bowel motility decreases. If pressure becomes high enough, there will be decrease in microcirculation and resultant ischemia.

Epidemiology

In one recent study, 16% of patients developed ileus while in the ICU. Approximately 300,000 patients undergo surgery for small bowel obstruction each year, most being secondary to adhesive disease. Hernia, malignancy and Crohn's disease also are major causes.

Prognosis

Prognosis for ileus in the critically ill is based on underlying cause. However, delay in enteral nutrition has been shown to increase morbidity and trend to mortality.

The mortality rate for small bowel obstruction is dependent on co-morbidities and cause of obstruction. Without ischemia, the mortality has been quoted at 5%; however this markedly rises for ischemic or necrotic bowel.

Special considerations for nursing and allied health professionals.

NA

What's the evidence?

Dries, DJ. "Abdominal Problems in the ICU: Acute Abdomen/Pancreatitis/Biliary Infection and Injury". ACCP Crit Care Med Brd Rev. vol. 20. 2009. pp. 301-20.

(Dr. Dries provides a detailed and useful overview of acute abdominal processes in the critically ill, including bowel obstruction and ileus.)

Tavakkolizadeh, A, Whang, EE, Ashley, SW, Zinner, MJ, Brunicardi, FC, Anderson, DK, Billiar, TR, Dunn, DL, Hunter, JG, Matthews, JB, Pollock, RE. "Chapter 28. Small Intestine". Schwartz's Principles of Surgery. McGraw-Hill. 2010. http://accesssurgery.com/content.aspx?aID=5017621.

(The authors of this chapter of this standard surgical textbook provide an excellent overview of the pathophysiology of both small bowel obstruction and ileus.)

Houghton, SG, Medina, AR, Sarr, MG, Ashley, SW, Zinner, MJ. "Chapter 17. Bowel Obstruction". Maingot's Abdominal Operations. McGraw-Hill. 2007. http://www.accesssurgery.com/content.aspx?aID=128405.

(This chapter reviews the treatment of bowel obstruction is a systematic and thorough manner.)
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