Gastroenterology Hepatology

Approach to the patient with intestinal obstruction

Condition:Intestinal obstruction

Are you confident of the diagnosis?

the lumen prevents normal flow of luminal contents. In a simple obstruction there is a single point of obstruction, whereas a closed-loop obstruction is caused by two distinct points of obstruction. A complete obstruction is present if there is no passage of intestinal contents beyond the point of obstruction, whereas a partial obstruction allows for the passage of some contents distal to the obstruction. Compromised blood flow to the bowel causing ischemic necrosis is referred to as strangulated obstruction. This almost always occurs in the setting of complete obstruction and is more frequently seen with closed-loop obstructions. One exception to this is a Richter's hernia, in which strangulation may occur without complete obstruction.

Intestinal pseudo-obstruction, such as Ogilvie's syndrome, or adynamic ileus, may mimic intestinal obstruction clinically, even though there is no distinct physical obstruction.

Also known as:

Small bowel obstruction (SBO), large bowel obstruction

Pathophysiology of intestinal obstruction

Dehydration and its sequelae are the central systemic pathology in intestinal obstruction. As the stomach and small intestine proximal to the obstruction dilate, patients experience nausea and vomiting and cease oral intake. Pain is usually colicky and poorly localized due to visceral distention of the intestine that occurs as it contracts against an obstruction.

As dilation worsens, bowel wall edema develops, leading to deranged absorptive mechanisms, further exacerbating the increased luminal pressure. Emesis causes loss of fluid containing sodium, potassium, hydrogen, and chloride, which may result in metabolic alkalosis. Transudative fluid is lost into the peritoneal cavity. Signs of hypovolemia can develop, including tachycardia, hypotension, acute renal failure, and shock. The proximal small bowel is normally relatively sterile, but with a high grade or complete obstruction, bacterial overgrowth with anaerobes such as Bacteroides may result in feculent vomiting.

In later stages, increased venous pressure in the bowel wall can result in hemorrhage into the lumen, worsening hypovolemia and further increasing intraluminal pressure. Ischemic necrosis of the mucosa may occur, leading to loss of the protective barrier function of the mucosa. If necrosis progresses to all layers of the bowel, perforation is inevitable. Bowel necrosis may also result from direct compression of the blood supply, as can be seen with volvulus or with a tight hernia ring.

What disease states can produce this sign or symptom?

In 1900, Gibson reported that 35% of intestinal obstructions were due to strangulated hernias, while 19% were due to adhesive bands; but currently in the Western world, adhesions have become the most frequent cause of adult small bowel obstruction, accounting for 74% of cases in a series by Miller. The most frequent etiology of bowel obstruction varies by age. (See Table I.)

Table I.

Common causes of intestinal obstruction by age
Middle age/elderly Young adult Infant Neonate
Adhesions Adhesions Inquinal hernia Atresia
Neoplasms: ovarian and colorectal carcinoma Crohn's disease Intussusception Midgut volvulus
Hernia Hernia Meckel's diverticulum Meconium ileus
Crohn's disease Imperforate anus
Diverticulitis
Sigmoid volvulus
Radiation

Adhesions

Overall risk of developing an adhesive SBO after abdominal surgery is approximately 5%, and after major abdominal surgery the risk increases to between 15% and 42%. The most important factor is the type of operation performed. The highest incidence is in patients who undergo open adnexal surgery or ileal pouch-anal anastomosis. The laparoscopic approach results in a lower incidence of adhesive obstruction in many procedures but not in appendectomy and not clearly in colorectal surgery. (See Table II.)

Table II.

Incidence of adhesion-related readmissions according to type of surgery
Surgery Open – incidence Laparoscopic – incidence
Adnexal surgery 23.9% 0.0%
Ileal pouch-anal anastomosis 19.3% N/A
TAH 15.6% 0.0%
Colectomy 9.5% 4.3%
Cholecystectomy 7.1% 0.2%
Trauma laparotomy 2.5% N/A
Appendectomy 1.4% 1.3%
Cesarean section 0.1% N/A

Neoplasms

Malignant tumors are the second-most common cause of SBO, with as many as 42% of women with ovarian carcinoma developing SBO and 28% of patients with advanced colorectal carcinoma. SBO can also be caused by small intestinal tumors such as carcinoid, lymphoma, and small bowel adenocarcinoma. Onset of symptoms is typically slowly progressive.

Hernias

Hernias now account for approximately 10% of all cases of intestinal obstruction. Most common are ventral and inguinal hernias, but internal hernias, parastomal, femoral, and obturator hernias may cause obstruction as well. See Figure 1.

Figure 1.

Contrast-enhanced coronal CT image of incarcerated femoral hernia: F, right-sided femoral hernia passing below the inguinal ligament (IL); dilated proximal small bowel (PS) is seen entering the femoral canal, and collapsed distal small bowel (DS) exits; S, distended stomach; incidental ventral hernia (V) containing dilated small bowel is seen exterior to rectus abdominis muscle (RA) and is not the cause of obstruction. (Image courtesy of Mukesh Harisinghani.)

Hernias through the obturator canal are difficult to diagnose and most often occur in thin elderly women. Mortality due to obturator hernias is 25% due to the affected patient population and the difficulty in diagnosis. Closure of the obturator canal after reduction of hernia contents is of debatable value, as approximation of the tissues is difficult and recurrence rates are low even with a patent canal.

An internal hernia occurs when an intraperitoneal structure protrudes through a compartment within the abdominal cavity, either an anatomic foramen or space, a congenital defect, or a surgically created space. Surgically created defects occur alongside end stomas or through spaces left open in the mesentery after intestinal anastomoses. Approximately 75% of iatrogenic hernias occur within the first year after surgery, and their subsequent discovery on laparotomy warrants repair.

The special case of internal herniation and volvulus after Roux-en-Y gastric bypass surgery is increasing in frequency as the preferred approach becomes laparoscopic, which results in fewer adhesions to anchor the new anatomy. Diagnosis of internal herniation after gastric bypass surgery can be difficult, with patients often reporting intermittent abdominal pain and obstructive symptoms but showing no radiological abnormalities.

Hernias can occur through the transverse mesocolon, through Petersen's space, and through a jejunojejunostomy mesenteric defect. Retrocolic, retrogastric placement of the Roux limb has the highest risk of herniation, with the worst case being herniation of the entire small intestine with ischemic necrosis and perforation of the gastric remnant, which is almost universally fatal. See Figure 2.

Figure 2.

Barium study after gastric bypass showing internal hernia through Petersen's space with dilated proximal Roux limb (RL) reflecting obstruction. (Image courtesy of Mukesh Harisinghani.)

Special forms of obstruction

Crohn's disease and other causes of strictures

Obstructive symptoms due to strictures are usually chronic and progressive. Although Crohn's disease is the most common culprit, other conditions can also lead to stricture formation (Table III).

Table III.

Etiologies of intestinal strictures
Crohn's disease
Drugs (enteric-coated potassium chloride, NSAIDs)
Radiation (worse when post-surgical adhesions fix bowel in place)
Mesenteric ischemia (distal ileum is at highest risk)
Neoplasms (carcinoma, carcinoid, lymphoma, etc.)
Anastomotic
Trauma
Infectious (e.g., tuberculosis)
Cystic fibrosis (most commonly esophageal strictures)
Postinflammatory (e.g., after diverticulitis)

Strictures are one of the most common reasons for surgery in patients with Crohn's disease and usually result from food impacted at a site of narrowing. Indications for surgery include recurrent obstructions and obstructions that fail to resolve with nonoperative management. Ileo-colic anastomotic strictures may be treated by colonoscopic balloon dilatation, but this procedure carries a significant risk of perforation and has a high recurrence rate.

Strictureplasty rather than segmental small bowel resection may be performed in many cases to relieve a luminal narrowing. Several large series have shown very low rates of recurrence at the site of strictureplasty and few complications, although occurrence of new strictures remote from the prior strictureplasty often necessitates subsequent operation, similar to what is seen after resectional surgery for Crohn's.

Early postoperative obstruction

By definition, early postoperative SBO occurs within 30 days of an abdominal surgery. The incidence is estimated at 1% to 5%. Early postoperative SBO should be suspected in patients whose bowel function returns but subsequently develop obstructive symptoms, whereas patients with adynamic ileus do not experience return of bowel function after surgery. Abdominal imaging of patients with early postoperative SBO shows gaseous distention of the bowel and a paucity of air in the colon.

Distinguishing between these two entities is not usually of major management significance, as initial treatment is nonoperative for both conditions. About 90% of cases of early postoperative SBO spontaneously resolve with cessation of oral intake and nasogastric decompression. The immature, filmy adhesions present low risk for strangulation. Long periods of nonoperative therapy (up to 2-3 weeks) may be tried before considering surgery, given that there is no concern for strangulation or inclusion of the bowel in the abdominal closure.

Almost all patients with early postoperative obstruction after laparoscopic surgery require surgery. The most common cause of obstruction in these cases is trocar site herniation, but internal hernias must be considered as well.

Gallstone ileus

Gallstones cause 1% to 2% of cases of intestinal obstruction, usually in patients older than 60 years. Obstructive symptoms are acute, and diagnosis is made by the presence of air in the biliary tree accompanied by the usual radiological features of intestinal obstruction, usually with a transition point in the distal ileum. Stones must be large (>2.5 cm) to cause an obstruction and therefore enter the intestine by ulceration and fistulization, most commonly via a cholecystoduodenal fistula, although stones may erode into the stomach, jejunum, ileum, colon, or through the common bile duct into the duodenum. Mortality ranges from 12% to 27%.

Surgical treatment consists of laparoscopic or open enterolithotomy. An impacted stone may require limited bowel resection. Cholecystectomy and fistula takedown should follow after recovery from the acute episode. Only low-risk, young, healthy patients should be considered for one-stage procedures. In elderly patients with significant comorbidities, the gallbladder can be left in situ, assuming it contains no remaining stones.

A similar presentation of bowel obstruction may be seen with other intraluminal foreign bodies, including worms, bezoars, and other swallowed objects.

Volvulus

Volvulusoccurs most often in the sigmoid colon or cecum and accounts for approximately 5% of adult obstructions in the United States. Most patients present with colicky abdominal pain and a distended abdomen, which may be asymmetric. Loops of bowel with a long mesentery are at higher risk for twisting, and volvulus frequently results in a closed-loop obstruction with impingement of the blood supply. Small intestine volvulus most often occurs in newborns and can be associated with congenital anomalies.

Radiological studies are very helpful in diagnosis. Cecal volvulus shows a greatly distended cecum, which may be located in the left upper quadrant, and small bowel obstruction. The classic sign of sigmoid volvulus is the "bent inner-tube sign" (also known as the coffee-bean sign and the kidney-bean sign) with a very distended sigmoid loop arising from the pelvis and often taking up the entire abdomen. Barium enema often shows the sigmoid twist at the base of the mesocolon with the loops of distended sigmoid colon above.

Treatment of cecal volvulus involves operative reduction of the twist and cecopexy or right colon resection. Sigmoid volvulus can often be relieved by colonoscopic placement of a rectal tube beyond the point of volvulus. This should only be performed if the patient has no clinical features of intestinal gangrene or perforation, and if the mucosa appears gangrenous the procedure should be aborted. Sigmoid volvulus recurs in approximately 60% of patients after colonoscopic decompression, so unless the patient is considered a prohibitive surgical risk, it is recommended to follow colonoscopic decompression with mechanical bowel preparation and sigmoid resection with primary anastomosis.

Intussusception

Intussusception ccurs when peristalsis pulls a segment of proximal bowel and its mesentery, known as the intussusceptum, inside the intussuscipiens, or the distal segment of involved bowel. Clinical presentation is similar to other causes of obstruction, although symptoms may be more intermittent and chronic. Abdominal X-ray may show signs of bowel obstruction, the target sign, the crescent sign, or absence of the subhepatic angle. The diagnosis is usually confirmed by CT scan or, in children, by ultrasound.

Intussusception is the most common cause of bowel obstruction in childhood, but it rarely occurs in adults. Intussusception in children can usually be managed by nonoperative reduction using hydrostatic pressure or air enema. Intussusception in an adult raises concern for an intrinsic bowel lesion, such as a small bowel tumor, a submucosal lipoma, a Meckel's diverticulum, or a parasite. Intussusception is also increasingly being recognized as a cause of obstruction after Roux-en-Y gastrc bypass, occurring at the site of the jejuno-jejunal anastomosis.

Nagorney reported a series of adult intussusceptions in which half involved the small bowel and half involved the colon. Of the small bowel intussusceptions, one-third was due to malignancy, and 70% of these malignancies were metastatic. Two-thirds of the large bowel intussusceptions were due to primary colon cancer.

Colonic intussusception should be resected using appropriate oncologic techniques without initial reduction of the intussusception to minimize manipulation of a potential primary malignancy. Small bowel intussusceptions are at low risk for containing a primary malignancy, and if the patient is at risk for short bowel syndrome or a benign diagnosis has already been established, they may be reduced prior to limited resection of small bowel lesions. If a primary small bowel malignancy is suspected, surgical resection without reduction is favored

Trauma

Intramural hematoma may result from blunt abdominal trauma, such as when a lap-belt forcefully compresses the abdomen and crushes the duodenum, which is fixed in the retroperitoneum, against the thoracic vertebral column. The relatively weak abdominal musculature of children places them at higher risk for these injuries.

Symptoms are nausea, vomiting, and upper abdominal tenderness, and diagnosis is made by upper gastrointestinal series. In the absence of peritonitis, initial management is conservative with nasogastric decompression and total parenteral nutrition, but obstruction lasting more than 2 weeks raises concern for the development of intestinal fibrosis. If early laparotomy is performed for other reasons, a duodenal hematoma may be treated by incision and drainage. If surgery is later performed for concern of intestinal fibrosis, resection or bypass may be required

Ogilvie's syndrome

Ogilvie's syndromeresults in massive colonic dilatation without a mechanical obstruction, often associated with an underlying disease. Treatment is aimed at the underlying cause, with important measures including mobilization of the patient, correction of electrolyte abnormalities, holding oral intake, nasogastric decompression, and avoidance of opioids and psychiatric medications. Administration of intravenous neostigminecan aid in colonic decompression. A rapidly expanding colon or a cecum larger than 12 cm is high risk for perforation or ischemia, which more than doubles mortality rates. Decompression is performed either by colonoscopic placement of a decompression catheter, or when endoscopic management fails, surgical decompression via cecostomy or proximal stoma creation.

See Table IV.

Table IV.

Conditions commonly associated with acute colonic pseudo-obstruction
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.

Supine plain abdominal X-ray showing multiple loops of dilated small bowel consistent with small bowel obstruction. (Image courtesy of Mukesh Harisinghani.)

Figure 4.

Plain upright abdominal X-ray showing dilated loops of small bowel and multiple air-fluid levels, characteristic of small bowel obstruction. (Image courtesy of Mukesh Harisinghani.)

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.

Coronal image of contrast-enhanced CT scan showing strangulated closed-loop obstruction: C, dilated C-shaped, nonfilling closed loop; V, two adjacent pairs of mesenteric vessels in swirl pattern; P, dilated contrast-filled proximal small bowel loops; S, contrast-filled distended stomach; M, fluid in mesentery of closed loop; F, free peritoneal fluid in perihepatic space and right lower quadrant. (Image courtesy of Mukesh Harisinghani.)

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.

Algorithm for managing the patient with bowel obstruction.

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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(Retrospective review of 410 patients with SBO and analysis of the factors contributing to adhesive SBO.)

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(Meta-analysis of 446,331 abdominal operations and assessment of incidence and risk factors for adhesive SBO following laparotomy.)

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(A detailed discussion of CT findings associated with closed-loop and strangulating obstructions.)

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(Thorough review of the attributes and limitations of CT scan in diagnosing intestinal obstruction with sample images highlighting CT features of particular conditions.)

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(Thorough and updated evaluation of the efficacy of techniques to prevent formation of postoperative adhesions.)

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(Reviewed 339 patients who underwent open colectomy and 448 who underwent laparoscopic colectomy and found no difference in incidence of SBO within 1 year of surgery.)

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Frager, D. "Intestinal obstruction: role of CT". Gastroenterol Clin North Am. vol. 31. 2002. pp. 777-99.

(Thorough review of the attributes and limitations of CT scan in diagnosing intestinal obstruction with sample images highlighting CT features of particular conditions.)

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