Approach to the patient with intestinal obstruction

Table IV.

Condition	Frequency
Trauma (nonoperative)	11%
Infection (pneumonia, sepsis)	10%
Cardiac (MI, heart failure)	10%
Obstetric or gynecologic disease	10%
Abdominal or pelvic surgery	9%
Neurological	9%
Orthopedic surgery	7%
Misc. medical conditions (cancer, metabolic, renal failure, respiratory failure)	32%
Misc. surgical conditions (urologic, thoracic, neurosurgery)	12%

What urgent or emergent measures should be initiated even before the diagnosis is established?

Fluid resuscitation, holding oral intake, and nasogastric decompression should be initiated on presentation for patients with suspected bowel obstruction. Urine output should be monitored closely. As laboratory results are obtained, electrolyte abnormalities should be corrected. Initial treatment should not be delayed for radiologic imaging or laboratory studies.

The most important question to address early in diagnosis is whether strangulated bowel is present. Strangulating groin hernias are usually readily apparent, and imaging studies may not be necessary. Identification of intra-abdominal strangulated hernias may be very difficult. Severe pain early in the patient’s course is concerning for closed-loop obstruction with risk for infarction and perforation. Early involvement of an experienced clinician is critical in cases of suspected strangulated bowel to allow prompt surgical intervention, which can reduce the mortality that is 2 to 10 times higher than with simple obstructions. Identifying the cause and location of obstruction are of secondary importance and rarely affect management decisions.

What is the appropriate initial diagnostic approach to identify the specific underlying disease?

Diagnosis of bowel obstruction is typically made by clinical and radiographic features.

Symptoms

• Crampy, colicky, poorly localized abdominal pain

• Decreased or absent stool and flatus

• Nausea and/or vomiting, which often contains occult blood (‘coffee grounds’ in color) due to bowel distention with mucosal hemorrhage

In general, more proximal obstructions cause more nausea and vomiting but less abdominal distension.

History and physical examination

Important points in the history include:

• Onset and duration of abdominal pain, distention, and vomiting

• Fevers or chills

• Last bowel movement or flatus (note: the colon requires 12-24 hours to empty)

• Previous abdominal operations or obstructive episodes

• History of inflammatory bowel disease

• Known gallstones, diverticular disease, or hernias

• Previous malignancies or abdominal radiation

Physical examination should take note of:

• Tachycardia, hypotension, or fever

• Dehydration: dry mouth and loss of skin turgor

• Colic witnessed at the bedside

• Feculent vomitus, which may suggest high-grade obstruction

• Surgical scars

• Abdominal distension

• Bowel sounds, which are unreliable but may be hyperactive early in an obstruction or hypoactive/absent as the bowel distends

• Abdominal tenderness: mild diffuse tenderness is common, but peritoneal findings raise concern for strangulation

• Hernias (abdominal wall, inguinal, or femoral): note that if hernia contents are soft and reducible, the hernia is unlikely the cause of the obstruction.

• Rectal exam: mass lesions, presence of stool, and guaiac status if stool is present

• Ascites or hepatomegaly, which may raise concern for malignancy

Laboratory tests

Laboratory tests are not particularly helpful in the diagnosis of intestinal obstruction. Common but nonspecific abnormalities include:

• Hemoconcentration, often with both elevated hematocrit and leukocytosis. A WBC >18,000 in an adult should raise concern for strangulation, although one-third of patients with strangulated SBO have a WBC between 10,000 and 14,000.

• Prerenal azotemia

• Acidosis (arterial blood gas or serum lactate measurement) may be seen in strangulation

• Hyperkalemia can be a sign of bowel necrosis

• Serum pancreatic enzymes may be mildly elevated even in simple obstructions

Radiology

Goals of radiologic studies are to confirm the diagnosis of intestinal obstruction, to distinguish between simple and strangulating obstructions, to estimate the degree of obstruction, to determine the cause and location of the obstruction, and to help exclude paralytic ileus as the etiology.

X-ray

Plain radiograph is quick, easily available, and can identify many high-grade or complete obstructions, particularly with distal obstructions. Supine and upright abdominal radiographs provide the most information, but a left lateral decubitus film alone allows visualization of air-fluid levels and also free air against the liver.

Signs of SBO on plain X-ray include dilated loops of small bowel (>2.5 cm) and air-fluid levels with a stepladder appearance on upright film. In a complete SBO of long-standing nature, the colon is empty of air and stool, but in partial obstruction or early complete obstruction, some air and stool may be present in the colon (Figure 3) (Figure 4).

Figure 3.

Figure 4.

A thumbprint appearance, resulting from edema of the bowel, may be present with strangulation. The presence of a single loop of dilated bowel in a patient with acute severe abdominal pain is concerning for a closed-loop obstruction. However, plain X-rays are diagnostic in only 46% to 80% of SBO cases, and normal X-rays can be seen in as many as 20% of patients with strangulation.

In acute large bowel obstruction, dilation of the entire colon (>5-6 cm) up to the point of obstruction may be seen. The cecum is always the most dilated (abnormal if >9 cm) as predicted by Laplace’s law, and risk of perforation is high when the cecum is larger than 12 cm.

CT scans

CT imaging has become the primary radiologic tool in diagnosing bowel obstructions. If patient condition allows, both intravenous and oral or nasogastric contrast should be given prior to imaging. CT allows visualization of dilated proximal loops and collapsed distal bowel, often identifying the precise site of obstruction. In some cases, an obstructing lesion can be seen, but adhesions are presumed to be the culprit when a transition point is seen without apparent cause.

CT scans have about 60% sensitivity for detecting closed-loop obstructions. Signs of a closed-loop obstruction include:

• Marked distention of a segment of small bowel

• Radial distribution of C- or U-shaped small bowel loops

• Two adjacent collapsed loops of bowel

• the beak sign

• the whirl sign

The greatest challenge in diagnosis of intestinal obstruction is identifying strangulation and need for an urgent operation. Imaging criteria for ischemia are nonspecific for strangulation and lead to many false positive readings of strangulation.

Classical signs of bowel ischemia include:

• Thickening of the bowel wall with or without the target sign

• Pneumatosis

• Portal venous gas

• Increased density of bowel wall on CT without intravenous contrast

• Nonenhancement of bowel wall on CT with intravenous contrast (or, rarely, increased enhancement due to decreased outflow)

• Mesenteric haziness, fluid, or hemorrhage

• Free peritoneal fluid.

See Figure 5 for a CT image of a strangulated closed-loop obstruction.

Figure 5.

Recently, Zielinski et al. (2011) prospectively tested a model based on three clinical and CT features (history of obstipation, mesenteric edema, and lack of small-bowel fecalization) that, when all present, predicted a high risk of ischemia (29%) and a 90% chance of requiring exploration before hospital discharge, suggesting that patients with all three features should undergo urgent exploration.

Diagnosis of strangulation remains a major challenge, as none of the imaging findings of strangulation are sensitive or specific and should not be relied upon in isolation

Ultrasound

Abdominal ultrasonography is more sensitive and specific than plain X-ray for diagnosis of SBO but less so than CT scan. Ultrasound has the ability to detect peristaltic activity as well as fluid-filled, dilated small bowel proximal to collapsed distal bowel, but it is not as helpful as CT scan in identifying the precise location, cause, and possible strangulation, and its usefulness is limited if gaseous distention predominates. It is highly operator-dependent, but it can be useful in diagnosing pregnant patients or in bedside assessment of critically ill patients.

An algorithm for managing the patient with bowel obstruction is shown in Figure 6.

Figure 6.

What is the diagnostic approach if this initial evaluation fails to identify the cause?

If other studies are indeterminate and symptoms persist, enteroclysis is sometimes helpful. The volume challenge of the barium and the time-lapse imaging allow for enhanced visualization of the lumen of the bowel, especially in the case of a low-grade or intermittent obstruction.

Drawbacks of enteroclysis include:

• Risk of inspissation or impaction of barium

• Inability to do subsequent CT scans due to retained barium

• Inability to examine anatomy outside of the intestinal lumen

• Amount of radiation delivered to the patient

• Operator-dependent and time-consuming study

To overcome some of these limitations, some centers now use CT enteroclysis.

Treatment options

General considerations

Adequate intravenous access should be ensured for fluid resuscitation, typically with Lactated Ringer’s, until the patient is clinically euvolemic. A foley catheter should be placed to closely monitor urine output. In patients with cardiopulmonary disease, a central venous catheter or Swan-Ganz catheter may be helpful to aid in fluid management.

Urgent surgical intervention is warranted in cases where strangulation or closed-loop obstruction is suspected, whether due to clinical presentation or radiologic imaging, or in patients with no prior history of abdominal surgery or hernia. If a patient is felt to be safe for nonoperative management, the cardinal rule of general surgeons to “never let the sun rise or set on a small bowel obstruction” should be kept in mind, and if the obstructed patient does not improve in 24 to 48 hours, the patient should be explored.

Nonoperative treatment

Correction of fluid deficits, acid-base disorders, and electrolyte abnormalities are paramount and should be not be delayed by radiological imaging or laboratory studies. Normal saline or Lactated Ringer’s solution with additional potassium supplementation can be given. Acid-base disorders are usually corrected by adequate fluid resuscitation, and persistent acidosis should raise concern for bowel ischemia or necrosis. Urinary flow rates should be monitored closely as a measure of hydration status. The patient should take no food or drink by mouth and should undergo placement of a nasogastric tube to decompress the stomach, which provides symptomatic relief and decreases risk of aspiration.

Placement of a nasogastric tube: Supplies needed include a 14 French or larger soft nasogastric tube, lubrication, a cup of water and a straw, and tape. Seat the patient upright with his or her head tilted slightly forward. Approximate the length of tube needed to reach the stomach by measuring the distance from the ear to the nose and adding the distance from the ear to the xiphoid process. Insert the well-lubricated tube into one nare and direct it straight back along the floor of the nose. If significant resistance is met, the contralateral nare can be tried. After insertion of 3 to 4 inches of tube, have the patient sip water through the straw to allow the patient’s swallowing mechanism to guide the tube into the esophagus and then the stomach. If the patient is unable to speak or has excessive gagging, the tube should be removed as it may have passed into the trachea.

Aspiration of gastric contents suggests the tip of the tube is in the intestinal tract. Instillation of air while listening over the left upper quadrant signifies that the tube is in the intestinal tract, but air may be heard if the tip of the tube is just proximal or distal to the stomach, so position of the tube should be confirmed with X-ray. Alternatively, about 20 cc of water can be instilled into the tube then withdrawn. If the tube is in the correct position, at least half of the instilled volume should be able to be withdrawn. If not, the tube should be repositioned.

Tape the tube securely to the nose, taking care to prevent pressure necrosis of the nares. Place the tube to intermittent low wall suction or, if a Salem sump nasogastric tube was placed, low continuous wall suction. Discomfort from the tube usually lasts for 1 to 2 days and may be improved with topical anesthetic sprays.

Nasogastric tube output should be carefully monitored and losses replaced with IV fluid. Thick intestinal secretions often clog the tube, so patency should be checked frequently.

Several trials using a variety of long intestinal tubes placed in attempts to optimize decompression have shown no benefit of long tubes over standard nasogastric tubes.

Resolution of the obstruction and avoidance of an operation may occur after fluid resuscitation and decompression of the stomach. Factors that favor nonoperative resolution include a history of multiple prior obstructive episodes that resolved with nonoperative treatment, a partial obstruction due to adhesions, carcinomatosis, a history of extensive radiation, or impaction of food particles at strictures. Signs of resolution usually include decreased abdominal distention, passage of flatus or stool, and a decrease in nasogastric tube output. When it is clear that the obstruction has resolved, remove the nasogastric tube and slowly advance the patient’s diet. When it is less clear that the obstruction has resolved, intermittent clamping of the tube for several hours followed by checking residuals can be helpful. Residuals less than 100 cc in 4 hours usually indicate that the obstruction has resolved.

Water soluble contrast as therapy: In the setting of a partial SBO, hypertonic, water-soluble contrast agents such as Gastrografin can be used for both diagnostic and therapeutic purposes. Because Gastrografin is hypertonic, it draws fluid from the bowel wall into the lumen, decreasing bowel wall edema and stimulating peristalsis. Several studies have shown it to be safe and effective at improving bowel function, decreasing length of stay, and decreasing the need for operative intervention.

Operative treatment

Approximately one-quarter of patients admitted with small bowel obstruction require an operation prior to discharge. Exploration is warranted in patients suspected of having strangulation or for nonresolution of simple obstruction after 24 to 48 hours of nonoperative therapy.

Prior to surgery, fluid deficits and electrolyte derangements should be corrected. Preoperative antibiotics should be given to cover skin pathogens, and in cases of suspected strangulation, patients may benefit from antibiotic coverage of enteric bacteria. A nasogastric tube should be in place to decrease the risk of aspiration during induction of anesthesia.

Operative Approach: The goals of an operation for bowel obstruction include:

• Identification of the cause of obstruction

• Relief of obstruction

• Resection of nonviable bowel

• Avoidance of inadvertent enterotomy

When planning an abdominal wall incision, it is ideal to enter the peritoneum in a “virgin” area to avoid bowel loops that may be adherent to the abdominal wall. This may be accomplished by using a new incision or extending a prior incision. Typically a midline incision affords the best exposure to all quadrants of the abdomen. An inguinal incision may be used for incarcerated inguinal hernias even if bowel resection may be required.

Upon entering the peritoneal cavity, any cloudy fluid should be sent for culture. If the point of obstruction is not obvious, collapsed loops of bowel may be followed proximally toward the obstruction while taking care to identify anatomical structures and avoid iatrogenic injury of the fragile and thin-walled bowel. Adhesions should be gently retracted and cut with cautery or scissors while protecting surrounding bowel. Rarely, a scalpel may be necessary to separate dense adhesions. After the obstruction is resolved, all remaining adhesions should be lysed unless doing so puts bowel at risk for injury. Any identified internal hernias should be closed. The bowel should be carefully inspected for viability and for possible iatrogenic injury.

When a benign-appearing obstructing lesion is identified, resection with primary anastomosis can be performed. If a primary tumor of the small intestines is found, the segment of small intestines containing the lesion as well as the associated mesenteric lymph nodes should be resected, and the rest of the small intestines should be inspected for a possible second primary tumor. If a metastatic lesion to the small bowel is identified, the lesion may be resected or bypassed.

Assessment of bowel viability: Bowel viability is typically determined by color and the presence of normal motility and mesenteric arterial pulses. If viability of a segment is questionable, the bowel may be wrapped in warm saline-soaked laparotomy pads for 10 to 15 minutes and then reexamined. Doppler examination of mesenteric vessels can also be helpful in determining the extent of resection. A refinement of this technique, laser Doppler flowmetry, has been shown to be superior to clinical judgment and standard Doppler examination, but this requires equipment and skills that are not commonplace.

An alternative technique involves intravenous injection of 1000 mg of fluorescein followed by illumination of the intestine by fluorescent light. Areas of nonfluorescence or patchy fluorescence indicate nonviability. This technique has been shown to be superior to clinical judgment and Doppler examination in preventing unnecessary resection of viable intestine.

Because segments of questionable viability may initially survive but later develop strictures, it is prudent to remove most questionable areas. In patients with limited small bowel length (less than two-thirds of their original length), a second look operation in 24 hours should be considered.

Laparoscopic versus open approach: A laparoscopic approach can be considered in selective patients with bowel obstructions. Laparoscopic lysis of adhesions has a reported success rate between 46% and 87%, whereas the remainder required conversion to laparotomy. It is generally recommended that the initial trocar be placed via the open technique in an area of the abdomen that has no scars, often the left upper quadrant, and that the remaining trocars be placed under direct vision. Atraumatic grasping instruments should be used to handle the fragile bowel. Tilting of the operating table to allow distended bowel to fall away from the area of interest is helpful.

Several predictors of successful laparoscopic lysis of adhesions have been reported:

• Two or fewer prior abdominal operations

• Previous upper abdominal incision

• Appendectomy as only prior operation

• Transition point outside of the pelvis

• Bowel dilation of less than 4 cm

• Partial bowel obstruction

• Surgeon training in advanced laparoscopic techniques

Contraindications to the laparoscopic approach include:

• Massive abdominal distension that prevents safe entry into the peritoneal space and limits working space

• Peritonitis with the need for bowel resection

• Hemodynamic instability

• Inability to tolerate pneumoperitoneum due to comorbid disease

Several retrospective analyses have reported benefits of the laparoscopic approach over laparotomy, including a shorter length of postoperative stay due to earlier return of bowel function and fewer days spent in the intensive care unit, but a randomized trial is still needed to assess the true patient and/or cost benefits.

Malignant bowel obstruction

Decisions about management of obstruction in patients due to primary intra-abdominal malignancy are difficult and need to be highly individualized due to the high recurrence rate and morbidity, which is approximately 50% at 6 months. Palliative operative management may be appropriate in some cases, with Chi et al. (2009) reporting successful relief of the obstruction in 71% of patients with recurrent ovarian cancer. Other patients may benefit from placement of a percutaneous endoscopic gastrostomy for symptom relief.

It is important to consider that in patients with known recurrence of malignancy, about one-third of bowel obstructions is due to benign adhesions. Obstructions due to recurrent cancer tend to occur earlier after operation for intra-abdominal malignancy than adhesive obstructions.

Prevention

It is anticipated that as more procedures are performed laparoscopically, the frequency of postoperative adhesions will decrease.

Efforts in prevention of intestinal obstruction have mostly aimed at minimizing postoperative adhesions. The most effective method involves application of bioresorbable barrier membranes. Currently there are two commercially available products: Seprafilm (sodium hyaluronate-based carboxymethylcellulose, Genzyme Corp, Cambridge, Massachusetts) and Intercede (oxygenated regenerated cellulose, Ethicon Inc., Somerville, NJ). Both have been shown to be safe and effective at decreasing adhesion formation at the site of application, although they do not affect adhesion formation in distant sites and do not decrease incidence of postoperative small bowel obstruction. These materials should not be used to wrap intestinal anastomosis because this practice causes increased rates of leak, fistula formation, peritonitis, abscess, and sepsis.

In patients that will receive postoperative pelvic radiation therapy, placement of a pelvic “sling” at the time of laparotomy may hold the small bowel in the upper abdomen and out of the radiation field, decreasing the risk for radiation-induced small-bowel strictures.

What's the evidence?

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