Management of small bowel obstruction in adults

INTRODUCTION — Small bowel obstruction (SBO) occurs when the normal flow of intestinal intraluminal contents is interrupted. The management of bowel obstruction depends upon the etiology, severity, and location of the obstruction. The goals of initial management are to relieve discomfort and restore normal fluid volume, acid-base balance, and electrolytes. Bowel compromise (ischemia, necrosis, or perforation) and a surgically correctable cause of SBO (eg, incarcerated hernia) require immediate surgical exploration; other patients may be candidates for a trial of nonoperative management. Although 60 to 85 percent of adhesion-related SBOs resolve without surgery, it is difficult to predict a priori which patients will fail nonoperative management. Non-adhesion-related SBO is usually secondary to another intra-abdominal process (eg, inflammation, infection), the targeted treatment of which will lead to the resolution of SBO symptoms.

This topic review will focus on the management of SBO. The clinical features and diagnosis of SBO are discussed separately. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults".)

Hypertonic water-soluble radiologic contrast (eg, Gastrografin) has been widely used therapeutically to treat adhesion-related SBO. Its use is mentioned here but discussed in depth in another topic. (See "Gastrografin for adhesive small bowel obstruction".)

INITIAL MANAGEMENT — Small bowel obstruction (SBO) is a common disease, accounting for 12 to 16 percent of surgical admissions and more than 300,000 operations annually in the United States [1]. Patients diagnosed with acute SBO should be admitted to the hospital and evaluated by a surgeon.

Admission and surgical consultation — Patients who present with acute SBO should be admitted to the hospital. Some studies have suggested that admission to a surgical service (versus medical service) is associated with improved clinical outcomes and decreased costs [2-4]. At a minimum, prompt surgical consultation should be obtained to determine if immediate surgical intervention is needed. (See 'Indications for immediate surgery' below.)

The use of standardized protocols has been shown to decrease time to surgical consultation and time to operative intervention (if needed) and shorten hospital length of stay (algorithm 1) [5].

Patients with chronic and/or intermittent SBO, such as that caused by Crohn's-related small bowel strictures or radiation enteritis, may be managed expectantly on an outpatient basis by limiting their oral intake to fluids. As long as hydration and normal electrolyte balance can be maintained (which may require outpatient fluid therapy), hospitalization may be avoided. Nevertheless, a structured plan is required to keep these patients engaged until their chronic SBO has resolved.

Fluid therapy — Patients with bowel obstruction can have severe volume depletion, metabolic acidosis or alkalosis, and electrolyte abnormalities. This is particularly true for patients with copious emesis from proximal SBO, those with symptoms lasting several days prior to presentation, or obstruction that causes large-volume intraluminal fluid sequestration. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Pathophysiology'.)

Upon admission, isotonic crystalloid such as Lactated Ringer solution or normal saline may be appropriate for initial intravenous fluid therapy if the patient is dehydrated. Aggressive potassium repletion may be needed, but it is important to be certain the patient does not have acute kidney injury, in which case potassium supplementation should be given cautiously until renal function can be improved. (See "Maintenance and replacement fluid therapy in adults" and "Overview of the management of acute kidney injury (AKI) in adults".)

Even for patients who require immediate surgery, fluid resuscitation, correction of acid-base balance and repletion of electrolytes can generally be completed prior to surgery, which helps minimize complications (eg, hypotension, arrhythmias) related to induction of anesthesia. (See "Induction of general anesthesia: Overview", section on 'Selection of induction technique'.)

Diet — In general, most patients admitted for SBO should be made nil per os (NPO) to limit further bowel distension. However, a small subset of patients with partial bowel obstruction may tolerate a small amount of oral liquids.

Gastrointestinal decompression — The need for gastrointestinal decompression in the setting of SBO may vary from patient to patient and remains a matter of clinical judgment. For patients with SBO that is associated with significant distension, nausea, and/or vomiting, we perform nasogastric tube decompression [6-8]. Such patients likely have complete or high-grade obstruction; decompression of the distended stomach improves patient comfort and also minimizes the passage of swallowed air, which can worsen distension [9]. The placement and management of nasogastric tubes is discussed elsewhere. (See "Inpatient placement and management of nasogastric and nasoenteric tubes in adults".)

For patients with recurrent SBO who have undergone multiple prior operations, and in whom another operation is felt to be particularly risky, one can attempt long tube decompression as a component of conservative management to avoid further surgery. However, there are few data to support this practice over the use of standard nasogastric decompression. Older trials comparing standard nasogastric tubes and long tubes weighted with a mercury-filled balloon (eg, Miller-Abbott tube, Anderson tube, Dennis tube [10,11]) did not show a significant difference in the percentage of patients ultimately requiring surgical intervention [7,12]. However, a later randomized trial comparing 90 patients managed with an endoscopically placed long hydrophilic silicone tube with 96 patients managed with a nasogastric tube found a significantly decreased time to relief of clinical symptoms in the long tube group (4.1 versus 8.5 days) [10]. Overall effectiveness (ie, no need for surgery) was nearly doubled in the long tube group (90 versus 47 percent). The improved outcomes seen in this one study will need to be replicated in future studies before routine implementation; concerns remain over the potential risks of long tubes, such as knot formation. Overall, we do not advocate the routine use of long tubes in patients with SBO.

Role of antibiotics — For most patients with uncomplicated SBO, we suggest not administering prophylactic antibiotics. Although administering broad-spectrum antibiotics is practiced because of concerns for bacterial translocation, data are inadequate to support or refute such a practice [13].

However, antibiotics are warranted for patients with suspected bowel compromise (ie, ischemia, necrosis, or perforation), and standard perioperative prophylactic antibiotics should be administered to those who undergo operative exploration, depending upon the expected wound classification (table 1) [14-16]. (See "Overview of gastrointestinal tract perforation", section on 'Antibiotics'.)

Antibiotic therapy is also warranted to treat infectious causes of nonadhesive SBO (eg, infectious small bowel disease or colonic diverticulitis). Targeting the underlying causes in such patients is the key to the resolution of their bowel obstruction. (See 'Nonadhesive small bowel obstruction' below.)

INDICATIONS FOR IMMEDIATE SURGERY — Immediate surgical exploration is indicated for either suspected bowel compromise (ie, perforation, necrosis, or ischemia) or treating a surgically correctable cause of small bowel obstruction (SBO), except adhesions.

Bowel compromise — All patients suspected of having bowel compromise (ischemia, necrosis, or perforation) based upon clinical and radiologic examination should be taken to the operating room for abdominal exploration [6,8]. SBO with associated bowel compromise is sometimes referred to as complicated SBO.

Clinical signs — Clinical signs and symptoms that are associated with bowel ischemia include the following, but each of these clinical signs is nonspecific, cannot be used in isolation, and does not always indicate ischemia [17-21]:

●Fever

●Leukocytosis

●Tachycardia that does not respond to fluid resuscitation

●Continuous or worsening abdominal pain, sometimes out of proportion to examination

●Metabolic and lactic acidosis

●Tachypnea

●Peritonitis

●Systemic inflammatory response syndrome (SIRS)

It is difficult to accurately predict bowel ischemia based upon clinical parameters alone [22,23]. In one study, experienced clinicians were wrong in their preoperative assessment more than half the time in patients eventually found to have gangrenous bowel [23].

Radiologic signs — Abdominal computed tomography (CT) should be performed in all stable patients with suspected acute SBO since it is difficult to accurately predict bowel ischemia based on clinical parameters alone [24]. Oral and intravenous contrast can be helpful but are not always feasible depending on the clinical scenario (eg, acute kidney injury or complete obstruction). In addition to laboratory and clinical signs, the following radiologic signs will identify 70 to 96 percent of patients who will benefit from immediate surgery [22,23,25-29]:

●Free air on plain radiographs or abdominal CT indicating bowel perforation.

●Signs of intestinal ischemia. Although advanced ischemia is usually obvious (eg, pneumatosis intestinalis, portal venous gas), it remains difficult to identify early and intermediate stages of bowel ischemia. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Exclude bowel compromise'.)

●Closed-loop obstruction (eg, U-shaped, distended, fluid-filled loops; triangular loop; beak sign; two loops of collapsed bowel adjacent to the obstruction site) [17,30]. While true closed-loop obstructions are associated with bowel ischemia, they are often "overcalled" in radiology reports; clinical correlation is required. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Complete obstruction and closed-loop obstruction'.)

●Other CT scan findings that are sometimes predictive of the need for surgery include findings of an abnormal course of a mesenteric vessel, a high-grade obstruction, a transition zone/point, a "whirl sign" [31], a "venous cut-off sign" [32], a "small bowel feces sign" [26], and high-density free peritoneal fluid [33-35]. However, these signs are also nonspecific. In one study that included 145 patients with high-grade obstruction on CT, 46 percent were successfully managed nonoperatively [20].

Surgical causes of small bowel obstruction — By convention, timely surgery following adequate resuscitation is generally also offered to patients with SBO caused by one of the surgically correctable causes (eg, closed-loop obstruction, volvulus, intussusception, incarcerated hernia, gallstone ileus, foreign body ingestion, small bowel tumor). For these conditions, although surgical exploration does not need to be "immediate" as it is for bowel compromise, it should happen as soon as is practical, since the SBO is not likely to resolve without surgery.

Although adhesive SBO is also technically surgically correctable (by lysis of adhesion), data suggest that most patients resolve without surgery [36]. Thus, in the absence of suspected bowel compromise, adhesive SBO should be initially managed nonoperatively [1,36,37]. (See 'Adhesive small bowel obstruction' below.)

●Closed-loop obstruction – Closed-loop obstruction can rapidly lead to bowel complications (ischemia, necrosis, perforation); thus, early identification and prompt surgical treatment are important to restore perfusion to the affected segment of bowel. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Complete obstruction and closed-loop obstruction'.)

●Hernia – Among patients who present with SBO, acutely incarcerated hernias (abdominal or groin) cause the majority of complications [38]. Any acutely incarcerated hernia that is causing SBO but without signs of strangulation could undergo attempted manual reduction; a safe technique of manual reduction of an acute inguinal hernia, called GPS (Gentle, Prepared and Safe) Taxis approach, has been adopted by a group of surgeons [39]. Hernias that fail to reduce require immediate surgical repair [40].

By contrast, chronically incarcerated hernias are usually not the cause of an acute SBO, especially when they are associated with loss of domain (greater than 50 percent of viscera outside the abdominopelvic cavity). Thus, unless there are clinical or radiological signs mandating immediate surgical exploration, patients may undergo initial nonoperative management. Such patients should be followed closely by a surgeon, both for the acute SBO and for potential hernia repair following the resolution of the SBO. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Complicated hernia'.)

●Volvulus – SBO can be caused by small bowel (midgut) volvulus or cecal volvulus. Volvulus is technically a subset of closed-loop obstruction. Timely surgical correction is the only solution to avoid bowel loss and other complications. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Volvulus' and "Intestinal malrotation in adults" and "Cecal volvulus".)

●Intussusception – Intussusception is uncommon in adults but would require surgery if it causes SBO. Because intussusception is caused by a lead point or structural abnormality (eg, tumor) in up to 90 percent of adult cases [41], resection of the involved bowel segment is recommended over simple reduction [42]. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Intussusception'.)

●Gallstone ileus or foreign body ingestion – The treatment for gallstone ileus is primarily surgical. All patients with gallstone ileus who are surgical candidates should undergo an enterolithotomy with the goal of relieving intestinal obstruction. (See "Gallstone ileus".)

Patients with a gallstone impacted in the duodenum (Bouveret syndrome) may benefit from a period of nonoperative management that will allow the stone to pass into the small bowel, where surgical retrieval is less likely to cause complications. Endoscopic fragmentation of stone can also be attempted in this location, with the goal of sparing the patient a duodenotomy should they need ultimate surgery [43]. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Gallstones or foreign body'.)

●Small bowel tumor – For patients who present with SBO due to a nonmetastatic or locally advanced primary small bowel tumor, operative intervention with curative intent should be pursued [40]. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Tumor' and "Treatment of small bowel neoplasms".)

Bowel obstruction from incurable advanced malignant disease, commonly referred to as malignant bowel obstruction, is much more difficult to manage and is discussed elsewhere. (See "Palliative care of bowel obstruction in cancer patients".)

NONOPERATIVE MANAGEMENT — Most patients with small bowel obstruction (SBO) but no indication for immediate surgery can safely undergo an initial trial of nonoperative management [44]. Nonoperative management resolves symptoms in many patients with SBO, but success rates depend upon the etiology [7,45,46].

It is pertinent to distinguish adhesive from nonadhesive SBO as the components of nonoperative management may differ between the two. Adhesive SBO is caused by intra-abdominal adhesions most commonly brought on by prior abdominal surgeries or previous episodes of abdominal inflammation (eg, pelvic inflammatory disease). Because adhesions cannot be directly seen on any imaging modalities, adhesive SBO is usually a diagnosis of exclusion made by combining a known history of prior abdominal surgery with a lack of other discernable causes of SBO on imaging studies [36]. By contrast, nonadhesive SBO is typically diagnosed by imaging studies (eg, the presence of inflammation or abscess). In industrialized nations, adhesive SBO is more prevalent than nonadhesive SBO [47].

Adhesive small bowel obstruction — In the setting of adhesive SBO, nonoperative management is overall successful in 65 to 83 percent of patients [48-52]. However, nonoperative management of adhesive SBO is associated with higher recurrence rates and lower disease-free intervals compared with operative management [53-55].

Water-soluble contrast — For patients with adhesive SBO, hypertonic water-soluble gastrointestinal contrast agents (eg, Gastrografin) may be therapeutic [8,56-62]. Gastrografin draws fluid into the lumen of the bowel due to its hypertonicity, decreasing intestinal wall edema and stimulating intestinal peristalsis. Evidence from randomized trials suggests that a Gastrografin challenge can predict clinical resolution of SBO without surgery, reduce the length of hospital stay, and accelerate the resolution of SBO in patients who would have resolved without surgery, but it does not reduce the need for surgical intervention [56,57,61,63-65]. (See "Gastrografin for adhesive small bowel obstruction".)

Therapeutic use of water-soluble contrast is contraindicated in the presence of bowel compromise (ischemia, necrosis, or perforation) and has only been studied in patients with adhesive SBO. Therefore, Gastrografin challenge should not be administered to patients with a known nonadhesive cause of SBO (see 'Nonadhesive small bowel obstruction' below). Additionally, Gastrografin has not been found to be effective for treating postoperative SBO, and the agent is contraindicated during pregnancy. (See 'Special cases' below.)

Unless contraindicated, we suggest giving a challenge of hypertonic water-soluble contrast agent (eg, Gastrografin) as part of the nonoperative treatment of adhesive SBO (algorithm 1). In order to maximize the benefit, Gastrografin should be administered as soon as possible once nasogastric decompression is performed. Implementation of an evidence-based SBO pathway incorporating Gastrografin is associated with reduced length of stay without any difference in rates of readmission, surgery, or need for bowel resection (in those requiring surgery) [66].

In most clinical situations, an abdominal computed tomography (CT) scan has been performed and a nasogastric tube has been inserted once the diagnosis of SBO is made. The stomach should be aspirated to dryness before Gastrografin is administered via the nasogastric tube. Although practices may vary [44,67], 100 mL of undiluted Gastrografin is most often given as a one-time dose [63], and the nasogastric tube is clamped for the next two to four hours. If a nasogastric tube is not placed, the same volume of Gastrografin can be administered orally [44]. It is essential that the nursing staff understands the purpose of using undiluted Gastrografin in this setting as it is far more common in nursing practice that Gastrografin is diluted in water before use as an oral contrast agent for CT. Reasonable precautions are also required to prevent aspiration as Gastrografin can cause pneumonitis when aspirated.

After Gastrografin is administered, a plain abdominal radiograph (ie, Kidney-Ureter-Bladder [KUB]) should be obtained in 6 to 24 hours. Within that window of time, the radiograph can be taken at a time that is convenient for both the patient and surgical team caring for them. Evidence of Gastrografin reaching the colon is highly predictive of the resolution of SBO without surgical intervention [68-70] and should inform the clinical decision to advance the patient's diet (algorithm 1). Failure of the contrast to reach the colon 24 hours later should influence, but not dictate, the decision to operate. A significant percentage of patients may require longer duration of nonoperative management for successful SBO resolution [71]. The time allowed for nonoperative resolution following instillation of Gastrografin is a matter of clinical judgment in these patients. (See 'Duration of observation' below.)

Serial monitoring — Although the incidence of bowel ischemia during nonoperative management of SBO is low at 3 to 6 percent [17], and the incidence of complications with adhesive obstruction is low overall [23,72-81], the patient still needs to be carefully monitored with serial abdominal examination and laboratory studies; some will benefit from follow-up imaging. Frequent clinical reassessments of the patient are necessary to ensure that complications are not developing.

Clinical assessment — Patients should be regularly assessed clinically with one of three possible outcomes:

●Resolution of SBO is generally accompanied by a decrease in abdominal distension, the passage of flatus and/or stool per rectum, and a decrease in the volume of nasogastric tube output. In cases where the obstruction has clearly resolved, the nasogastric tube can be removed and diet initiated and advanced as tolerated.

●The patient remains stable but signs and symptoms of SBO persist. For such patients, surgery may eventually be required. The optimal duration of nonoperative management is debated, but most surgeons would wait for up to three to five days before operating. In this setting, operating too soon may submit patients to an unnecessary operation, while waiting too long to operate is associated with increased complication rates and hospital length of stay. A three- to five-day trial of nonoperative management is a reasonable compromise that has been endorsed by multiple authorities. (See 'Duration of observation' below.)

●Patients who deteriorate should undergo immediate surgical exploration. Clinical deterioration (eg, fever, tachycardia, increasing pain or distension, acidosis, leukocytosis) is usually caused by bowel compromise, for which urgent surgical attention is required. (See 'Failure of nonoperative management' below.)

The volume of output from the nasogastric tube should be carefully documented to help with clinical judgments regarding the progression or resolution of the obstruction and the requirement for intravenous fluid therapy. Nasogastric losses can be replaced with normal saline plus potassium chloride (30 to 40 mEq/L). (See "Maintenance and replacement fluid therapy in adults".)

Laboratory studies — Laboratory tests should be repeated only as indicated by clinical parameters. As examples, in patients with severe electrolyte or acid-base disturbances, particularly those with renal dysfunction, blood chemistries should be repeated to ensure that replacement therapy is effective. Repeat assay of white blood cell counts may be helpful if there is concern for bowel ischemia and/or strangulation.

Serum procalcitonin (PCT), which is a marker of inflammation, is a promising prognostic biomarker for predicting failure of nonoperative management of SBO [8,82,83]. In the Acute Bowel Obstruction Diagnostic (ABOD) study, for example, PCT levels were significantly higher in the surgery group compared with the nonoperatively managed group (0.53 versus 0.14 ng/mL) and significantly higher in those managed surgically who had ischemia compared with those who did not (1.16 versus 0.21 ng/mL) [82]. However, additional prospective studies are required to validate the use of PCT for routine clinical use.

Follow-up imaging — Aside from abdominal plain radiographs performed as a part of the water-soluble contrast challenge, we do not recommend routine serial imaging studies without clinical indication.

Although abdominal plain radiographs may be useful for assessing whether or not the patient has clearly resolved their obstruction by demonstrating that gas or oral contrast has passed from the small bowel into the colon, they are otherwise insensitive for all but the most advanced stages of bowel obstruction (eg, free air indicating perforation). Therefore, we do not recommend routine serial abdominal radiographs for SBO.

If the patient deteriorates or fails to improve after an adequate trial of nonoperative management for adhesive SBO (typically three to five days, depending on clinical situation), patients may undergo a repeat abdominal CT [59,84]. However, many surgeons would perform surgical exploration on clinical grounds at this point without further imaging (algorithm 1). (See 'Failure of nonoperative management' below.)

Failure of nonoperative management — Approximately a quarter of patients admitted for SBO will eventually require surgery [55].

The decision to proceed with surgical exploration or continue nonoperative management is based primarily on the clinical status of the patient. Clinical deterioration or developing a complicated obstruction during a trial of nonoperative management should lead to prompt surgical exploration [8]. In the absence of clinical deterioration, failure to regain bowel function after three to five days of nonoperative management may also suggest the need for an operation. Several studies have reported that delay in operation intervention greater than three [85] to five days [86,87] was associated with higher morbidity [88], higher mortality, and longer hospital stay [86].

However, stable patients with known "frozen" abdomens, recent abdominal surgery, presence of enterocutaneous fistula, or other complicating factors may be observed for a longer period of time with possible institution of parenteral nutrition. Clinical judgment of the surgeon is required to weigh the benefit and harm of surgical exploration against further observation. (See 'Special cases' below.)

Duration of observation — In contemporary practice, it is widely accepted that stable patients with SBO may undergo initial nonoperative management as long as there is no complication (eg, bowel ischemia, necrosis, or perforation) or deterioration. The point of contention, however, is how long one can wait before surgical exploration becomes mandatory. The challenge to clinicians is that earlier operations may be unnecessary, whereas delayed operation may be associated with worse patient outcomes [89].

The World Society of Emergency Surgery (Bologna) guidelines (2017) recommended waiting for up to three days before surgical exploration [7,90]. The Eastern Association for the Surgery of Trauma (EAST) guidelines (2012) recommended waiting for up to five days before surgical exploration [6,8]. We suggest that in the absence of clinical deterioration, most patients with adhesive SBO should undergo surgery after up to three to five days of unsuccessful nonoperative management, depending on the clinical situation (algorithm 1).

Earlier or later surgery may be warranted in certain patient populations, although disease distribution and location need to be carefully considered and the decision to operate or not individualized accordingly. As an example, early postoperative SBO can be managed nonoperatively for a longer period of time (eg, up to six weeks) in the absence of clinical deterioration. (See 'Special cases' below and "Palliative care of bowel obstruction in cancer patients", section on 'Surgical candidates'.)

With nonoperative management, appropriately selected patients usually improve within two to five days [17,51]. However, it should be noted that for patients who ultimately require an operation, a delay of more than one day has been identified as a risk factor for requiring bowel resection [91]. In other studies, nonoperative management for uncomplicated adhesive bowel obstruction exceeding three to five days was associated with increased morbidity and mortality [85,86].

Predicting requirement for surgery — For surgeons, the "holy grail" of SBO management is to predict who will and will not fail nonoperative management. Logic stands that operating on the former early improves patient outcomes, reduces complications, and saves resources. However, it proves quite difficult to prospectively identify the patients who are destined for surgery with accuracy.

In a multivariate analysis, six clinical and radiographic values correlated with the need for bowel resection [92]. A scoring system was developed that assigned one point to each of these variables, which are listed below. Among 233 consecutive patients with bowel obstruction, 11 patients with a total score ≥4 points required bowel resection. A total score ≥3 points predicted the need for resection with a specificity of 90.8 percent. The variables include:

●History of pain lasting greater than four days

●Abdominal guarding on physical examination

●Elevated C-reactive protein (CRP) above 75 mg/L

●Elevated white blood cell (WBC) count above 10

●Presence of >500 mL of free intra-abdominal fluid on CT

●Reduced wall contrast enhancement on CT  

Another group of investigators identified the presence of free fluid and high-grade obstruction on CT scan as strong predictors for early surgery [93].

Abnormal initial laboratory values in sodium, creatinine, and hematocrit are not predictive of the need for operative intervention [91].

Nonadhesive small bowel obstruction — A trial of nonoperative management is warranted in patients with one of the following etiologies for their bowel obstruction who do not otherwise have indications for surgical exploration (see 'Indications for immediate surgery' above). Because the SBO in these patients is not caused by adhesions, a Gastrografin challenge is not indicated, as the efficacy and safety of the therapeutic use of Gastrografin has only been demonstrated in adhesive SBO. Instead, targeted therapy for the underlying cause (eg, antibiotics for infection), if available, is paramount to the resolution of SBO in these patients.

Inflammatory bowel disease — Patients who do not have fulminant disease causing complete bowel obstruction may respond to medical therapy. The medical management of inflammatory bowel disease is discussed in other topics. (See "Overview of the medical management of mild (low risk) Crohn disease in adults" and "Medical management of low-risk adult patients with mild to moderate ulcerative colitis".)

However, refractory strictures due to repeated episodes of inflammation usually require eventual resection and/or stricturoplasty to relieve obstruction. (See "Surgical management of Crohn disease".)

Infectious small bowel disease — Patients who present with a partial SBO due to tuberculosis may improve with medical management, although, similar to Crohn disease, delayed diagnosis is more likely to require surgery [94]. (See "Abdominal tuberculosis".)

In some countries, parasites can also cause SBO, which should be treated with anthelminthic therapy. (See "Ascariasis".)

Colonic diverticular disease causing small bowel obstruction — Here, the small bowel is obstructed secondarily by the pelvic inflammation or abscess caused by acute colonic diverticulitis. Antibiotic therapy reduces peridiverticular inflammation and may relieve obstructive symptoms. (See "Acute colonic diverticulitis: Medical management".)

Radiation enteritis — Small bowel damage (radiation enteritis) can be caused by radiation therapy for cancer of the cervix, endometrium, ovary, bladder, or prostate. It results in an obliterative arteritis that leads to intestinal ischemia or stricture, followed by SBO. Partial SBO is the most common clinical manifestation. Because of a higher risk of anastomotic leak, surgical intervention for SBO due to radiation enteritis is best avoided [95]. When an operation is absolutely necessary, an intestinal bypass is preferred to resection [96]. Specific approaches to radiation enteritis are discussed separately. (See "Surgical approach to radiation enteritis".)

Malignant obstruction — Primary or secondary tumor involvement can lead to SBO due to intrinsic or extrinsic compression; in addition, bowel obstruction may be due to adhesions or postradiation fibrosis. Tumors can also impair bowel motility by infiltrating the mesentery, nerves (eg, celiac plexus), or bowel wall. Some cancers (eg, colonic, ovarian, pancreatic, and gastric) have a particular propensity for peritoneal dissemination [97].

Although some surgeons may be reluctant to operate on patients with a history of prior surgery for intra-abdominal malignancy because they believe that obstruction due to metastatic cancer is not likely to be relieved by surgery, this is not necessarily the case, as many are due to adhesions. Radiological evaluations with CT scans can potentially differentiate peritoneal carcinomatosis from adhesive small bowel obstruction. Nonoperative therapy for malignant obstruction is associated with a high failure rate and high mortality, but on the other hand, palliative surgery for those in whom the obstruction cannot be relieved is also associated with overall poor outcomes [98-102].

There is no consensus regarding the optimal treatment strategy for management of malignant bowel obstruction and no strong evidence addressing the relative value of palliative surgery versus medical management, or for supporting the efficacy of any specific treatment for improving quality of life or prolonging survival. A decision to proceed to surgical intervention requires careful weighing of risks and benefits, including an assessment of the estimated life expectancy and goals of care (algorithm 2).

Management strategies for SBO in patients with intra-abdominal malignancy are discussed in a separate dedicated topic. (See "Palliative care of bowel obstruction in cancer patients".)

SPECIAL CASES

Complete bowel obstruction — The management of patients with complete small bowel obstruction (SBO) due to adhesions is controversial. Although complete adhesive SBO is associated with a higher failure rate of nonoperative management and a higher requirement for small bowel resection (31 percent) in some series [103], others have demonstrated that nonoperative management is still successful in 41 to 73 percent of patients [48,53]. Thus, patients with a complete bowel obstruction can be treated nonoperatively unless there is an indication for immediate surgery. (See 'Indications for immediate surgery' above.)

Postoperative bowel obstruction — SBO that occurs within four to six weeks of an abdominal surgery is called postoperative SBO. Adhesions associated with early postoperative bowel obstruction rarely lead to strangulation. Meanwhile, after 10 to 14 days postoperatively, adhesions are dense and hypervascular, making reoperation difficult. Consequently, postoperative SBO should not only be treated nonoperatively but also for a duration longer than non-postoperative SBO, in the absence of clinical deterioration. Some have suggested withholding repeat surgery until after six weeks, when adhesions mature, so it would be safer to operate [40].

In a retrospective study of postoperative SBO, 91 percent of 34 patients who were treated with home parenteral nutrition recovered bowel function without an operation after a median of 60 days (range 17 to 244 days) [104]. By contrast, early reoperation in 27 patients at a mean of 17 days after the index operation was complicated by 12 bowel resections, 5 incidental enterotomies, 3 new stomas, 2 enterocutaneous fistulas, 1 anastomotic leak, and 1 fascial dehiscence.

Although Gastrografin challenge has been tried and is safe for postoperative SBO, it has not produced any positive effect [105,106]. Therefore, it should be not administered to postoperative patients with SBO. (See "Measures to prevent prolonged postoperative ileus", section on 'Other pharmacologic treatments'.)

Patients without prior abdominal surgery — Although adhesions are most commonly formed as a response to prior abdominal surgery, they can develop in the absence of prior surgery. One prospective clinical study reported that 10 percent of first-time laparotomies had adhesions [107]. A study of 752 consecutive autopsies reported adhesions in 28 percent of those who had never undergone laparotomy [108]. In several single-center observational studies, 5 to 16 percent of SBO occurred in patients who had no prior surgery, radiotherapy, or known peritoneal inflammatory disease [109].

Although SBO is most often caused by acquired adhesions from previous abdominal surgery, it can also be caused by congenital or inflammatory adhesions. In five series, 100, 76, 62, 35, 30, and 26 percent of patients operated for SBO in patients without prior abdominal surgery were found to have adhesion as the etiology; the average was 48 percent [110-115].

Alternatively, SBO can also be caused by a mechanical etiology such as a tumor. In several series, 3 [116] to 13 percent of SBOs were caused by a malignancy in the small bowel, mesentery, or retroperitoneum [111-113,116]. Abdominal computed tomography (CT) imaging can help elucidate the exact etiology of the obstruction. (See "Etiologies, clinical manifestations, and diagnosis of mechanical small bowel obstruction in adults", section on 'Abdominal CT'.)

In the absence of another indication for immediate surgery, patients with SBO but no prior abdominal surgery can still be managed nonoperatively, including therapeutic Gastrografin challenge [115,117], but there is a greater chance that the SBO will not resolve without surgery [110,111]. If surgery is required, laparoscopic exploration is ideal in this patient population [90].

In a systematic review and meta-analysis of six studies with SBO in the absence of prior abdominopelvic surgery, more than half of the patients underwent a trial of nonoperative management, which often failed [118]. The most common etiology was de novo adhesion (54 percent), whereas malignancy was found in 7.7 to 13.4 percent of patients, most not suspected before surgery. However, if nonoperative management is successful, the prognosis is good. One study reported that of 63 SBOs in patients lacking prior abdominal surgery who were successfully managed with nonoperative management, 58 (92 percent) did not experience a recurrence during a mean 4.5 years of follow-up [110].

Older adults — Approximately 10 to 12 percent of patients above 65 years presenting with abdominal pain are diagnosed with SBO [119]. Older adult patients often present with atypical symptoms [120]; therefore, abdominal CT is important for a correct diagnosis. Although emergency surgery in older adults can cause significant morbidity and mortality, delaying necessary surgery may lead to negative consequences as well. In one retrospective study, the mortality in older patients undergoing delayed surgery was much higher than older patients undergoing early surgery (14 versus 3 percent) [121]. Thus, experts advocate early operative intervention for management of SBO in older adults if they do not resolve quickly with nonoperative management [40,122].

Pregnancy — SBO in pregnant women is rare; one-half of reported cases are due to adhesions and the other half due to nonadhesive causes (eg, internal hernia, volvulus). Magnetic resonance imaging (MRI) should be used in lieu of CT for the initial diagnosis. Indications for immediate surgery are the same as for nonpregnant patients. Patients with adhesive SBO may undergo a trial of nonoperative management with a low threshold for operation. Due to a lack of safety data of the contrast agent, Gastrografin challenge should not be administered to pregnant patients [123]. (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients", section on 'Bowel obstruction'.)

Bariatric patients — Patients may be susceptible to developing SBO after certain bariatric procedures (eg, Roux-en-Y gastric bypass) because of a variety of reasons, including adhesions, internal hernias, intussusception, and closed loop obstruction due to mesenteric defects [124]. In one large series of >800 consecutive cases of laparoscopic Roux-en-Y gastric bypass, internal hernia was the most common etiology and was frequently missed on CT scan [125]. Once SBO is suspected, early operative intervention is recommended for bariatric patients. Contrary to recommendations for nonbariatric patients, early postoperative SBO should undergo prompt surgical exploration to avoid anastomotic leak or bowel ischemia [126]. The type of surgical intervention depends on operative findings and may require lysis of adhesions, reduction of internal hernia, and repair of abdominal wall defect or mesenteric defect. Depending on surgeon expertise, surgery can be performed open or laparoscopically. (See "Late complications of bariatric surgical operations", section on 'Small bowel obstruction'.)

OUTCOMES

Mortality and morbidity — In a retrospective National Inpatient Sample database study of close to two million patients diagnosed with adhesive small bowel obstruction (SBO) between 2003 and 2013, the rate of operative intervention declined from 46 to 42 percent, while the delay between admission and operative intervention shortened from 5.29 to 3.77 days [127]. Meanwhile, the in-hospital mortality rate decreased from 5 to 4 percent (or by 6 percent per year), and the hospital length of stay decreased from 10 to 9 days.

Recurrence — In a longitudinal, propensity-matched, administrative database study of nearly 28,000 patients with adhesive SBO, those who underwent operative intervention (22 percent) had a lower risk of recurrence (13 versus 21 percent) [55]. The five-year probability of recurrence increased with each episode of SBO until surgical intervention, at which point the risk of subsequent recurrence decreased by approximately half.

In another administrative database study, among the nearly 16,000 patients with adhesive SBO who were managed nonoperatively during the index admission, 19 percent were readmitted, and 35 percent of those readmitted required an operation [128]. Operations during the first readmission conferred a greater risk of death (5 versus 1 percent) than no operation but a longer time to a second readmission among the survivors.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Bowel obstruction".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Small bowel obstruction (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Definition – Small bowel obstruction (SBO) occurs when the normal flow of intestinal contents is interrupted. (See 'Introduction' above.)

●Initial management – Patients diagnosed with acute SBO should be admitted to the hospital and evaluated by a surgeon. The initial management includes volume resuscitation, correction of metabolic abnormalities, bowel rest, and gastrointestinal decompression (with a nasogastric tube) for those with significant abdominal distension, nausea, or vomiting (algorithm 1). (See 'Initial management' above.)

For most patients with uncomplicated SBO, we suggest not administering prophylactic antibiotics (Grade 2C). However, we administer standard perioperative prophylactic antibiotics to patients with suspected bowel compromise (ie, ischemia, necrosis, or perforation) undergoing operative exploration, depending upon the expected wound classification. (See 'Role of antibiotics' above and "Overview of gastrointestinal tract perforation", section on 'Antibiotics'.)

●Definitive management

•Indications for immediate surgery – Patients with clinical (fever, persistent tachycardia, focal or generalized peritonitis) or radiologic signs of bowel compromise (ischemia, necrosis, perforation) require immediate surgical exploration. By convention, timely surgery is generally also offered to patients with SBO caused by one of the surgically correctable causes, except adhesions. (See 'Indications for immediate surgery' above.)

•Patients without an indication for immediate surgery – These patients are managed nonoperatively with serial abdominal examinations and laboratory and/or imaging studies as indicated by clinical parameters. In industrialized nations, adhesive SBO is more prevalent than nonadhesive SBO. In the setting of adhesive SBO, nonoperative management is overall successful in 65 to 80 percent of patients. (See 'Nonoperative management' above.)

For patients with adhesive SBO, we suggest giving a hypertonic water-soluble contrast agent (eg, Gastrografin) as a part of nonoperative treatment (Grade 2C). Limited data suggest that a Gastrografin challenge can accelerate the resolution of SBO and reduce the length of hospital stay. However, there is also evidence to suggest that it does not reduce the need for future surgical intervention. Therapeutic use of Gastrografin has not been studied for nonadhesive SBO, is not effective against postoperative SBO, and may not be safe for pregnant patients. (See 'Water-soluble contrast' above and "Gastrografin for adhesive small bowel obstruction".)

The optimal duration of nonoperative management is uncertain and largely depends on the patient's clinical status and situation. For most clinically stable patients with SBO, we suggest that nonoperative management not be extended beyond three to five days given the increased morbidity and mortality associated with this approach (Grade 2C). However, there are some clinical scenarios in which prolonging nonoperative management may be appropriate. As an example, those with early postoperative SBO can be managed for a longer period of time (eg, up to six weeks) in the absence of clinical deterioration. (See 'Duration of observation' above and 'Special cases' above.)

●Nonadhesive SBO – SBO can also be caused by nonadhesive etiologies (eg, inflammatory bowel disease, infection, radiation, malignancy), against which targeted therapies are paramount for the resolution of the bowel obstruction. (See 'Nonadhesive small bowel obstruction' above.)