Practice Essentials
Small-bowel obstruction (SBO) is caused by a variety of pathologic processes. The most common cause of SBO in developed countries is intra-abdominal adhesions, accounting for approximately 65% to 75% of cases, followed by hernias, Crohn disease, malignancy, and volvulus. [1] In contrast, SBO in developing countries is primary caused by hernias (30-40%), adhesions (about 30%), and tuberculosis (about 10%), along with malignancy, Crohn disease, volvulus, and parasitic infections. [2] The general trend in developing countries is an increased incidence of SBO from adhesions, with a higher incidence of laparotomies. See the image below.
See Can't-Miss Gastrointestinal Diagnoses, a Critical Images slideshow, to help diagnose the potentially life-threatening conditions that present with gastrointestinal symptoms.
Signs and symptoms
Symptoms of SBO can be characterized as either partial or complete versus simple or strangulated. The classic symptoms of nausea, vomiting, abdominal pain, and constipation are rarely present in all cases of SBO. Abdominal pain associated with SBO is often described as crampy and intermittent. Without treatment, the abdominal pain can increase as a result of bowel perforation and ischemia. Therefore, having a clinical suspicion for the condition is paramount to early identification and intervention. Furthermore, the clinical presentation of the patients varies and no one clinical symptom on its own identifies the majority of patients with SBO.
Background
In the United States, 15 of every 100 admissions for abominal pain are due to small-bowel obstruction (SBO), with 300,000 admissions annually. [8] An SBO is caused by a variety of pathologic processes. The leading cause of SBO in industrialized countries is postoperative adhesions (65-75%), followed by malignancy, Crohn disease, and hernias, although some studies have reported Crohn disease as a greater etiologic factor than neoplasia. Surgeries most closely associated with SBO are appendectomy, colorectal surgery, and gynecologic and upper gastrointestinal (GI) procedures (see the image below). (See Etiology.)
One study from Canada reported a higher frequency of SBO after colorectal surgery, followed by gynecologic surgery, hernia repair, and appendectomy. Lower abdominal and pelvic surgeries lead to obstruction more often than upper GI surgeries. (See Etiology.)
SBOs can be partial or complete, simple (ie, nonstrangulated) or strangulated. Strangulated obstructions are surgical emergencies. If not diagnosed and properly treated, vascular compromise leads to bowel ischemia and further morbidity and mortality. Differentiating the characteristics and etiologies of obstruction is critical to proper patient treatment because as many as 40% of patients have strangulated obstructions. SBO accounts for 20% of all acute surgical admissions. (See Presentation, Workup, and Treatment.)
Pathophysiology
Small-bowel obstruction (SBO) leads to proximal dilatation of the intestine due to accumulation of gastrointestinal (GI) secretions and swallowed air. Bowel dilatation stimulates cell secretory activity, resulting in more fluid accumulation. This, in turn, leads to increased peristalsis above and below the obstruction, with frequent loose stools and flatus early in its course.
Vomiting occurs if the level of obstruction is proximal. Increasing small-bowel distention leads to increased intraluminal pressures. This can cause compression of mucosal lymphatics, leading to bowel wall lymphedema. With even higher intraluminal hydrostatic pressures, increased hydrostatic pressure in the capillary beds results in massive third spacing of fluid, electrolytes, and proteins into the intestinal lumen. The fluid loss and dehydration that ensue may be severe and contribute to increased morbidity and mortality.
Strangulated SBOs are most commonly associated with adhesions and occur when a loop of distended bowel twists on its mesenteric pedicle. The arterial occlusion leads to bowel ischemia and necrosis. If left untreated, this progresses to perforation, peritonitis, and death.
Bacteria in the gut proliferate proximal to the obstruction. Microvascular changes in the bowel wall allow translocation to the mesenteric lymph nodes. This is associated with an increase in the incidence of bacteremia due to Escherichia coli, but the clinical significance is unclear.
Etiology
Adhesions, hernias, and malignancy are the predominant causes of SBO. [9]
The most common cause of SBO in developed countries is intra-abdominal adhesions, accounting for approximately 65% to 75% of cases. [1] Postoperative adhesions can be the cause of acute obstruction within 4 weeks of surgery or of chronic obstruction decades later. The incidence of SBO parallels the increasing number of laparotomies performed in developing countries.
Prevention of SBO may be essentially limited to decreasing the risk of adhesion formation by decreasing the number of intra-abdominal procedures (ie, laparotomies) and resultant scar formation. In a study by Van Der Wal et al, the incidence of chronic abdominal symptoms was significantly reduced after the use of a hyaluronic acid ̶ carboxymethylcellulose membrane (Seprafilm). However, Seprafilm placement did not provide protection against SBO. [10]
Following adhesions, the most common causes of SBO in developed regions are hernias (incarcerated groin hernias) (10-20%), malignancy (10-20%), inflammatory bowel disease (5%), volvulus (3%), and miscellaneous causes (2%). [1] The causes of SBO in pediatric patients include congenital atresia, pyloric stenosis, and intussusception.
In a 2024 Danish nationwide cohort study that analyzed whether the risk of ileus or intestinal obstruction in patients with inflammatory bowel disease is elevated with the use of glucagon-like peptide 1 (GLP-1) receptor agonists (RAs), which are increasingly used to treat patients with diabetes and/or obesity and which have associated concerns regarding retained gastric contents and delayed gastric empyting and motility, Nielsen et al did not find an increase in the risks of ileus or intestinal obstruction in individuals with inflammatory disease. [11] However, in a 2024 review of the literature, Jalleh et al found there was only limited evidence to determine whether current recommendations for periprocedural withholding of GLP-1 RAs, among other suggestions, are justified. [12] The investigators did note that patients on these agents more often are found to have retained gastric contents at the time of upper gastrointestinal endoscopy, but it is rare for them to be associated with pulmonary aspiration.
In contrast, SBO in developing countries is primarily caused by hernias (30-40%), adhesions (about 30%), and tuberculosis (about 10%), along with malignancy, Crohn disease, volvulus, and parasitic infections. [2]
Prognosis
With proper diagnosis and treatment of the obstruction, prognosis in small-bowel obstruction (SBO) is good. Complete obstructions treated successfully nonoperatively have a higher incidence of recurrence than do those treated surgically.
Morbidity/mortality
Morbidity and mortality are dependent on the early recognition and correct diagnosis of obstruction. [9] In general, there is a 10% mortality. [9] If untreated, strangulated obstructions cause death in 100% of patients. If surgery is performed within 36 hours, the mortality rate decreases to 8%. The mortality rate is 25% if the surgery is postponed beyond 36 hours in these patients.
Some factors associated with death and postoperative complications include age, comorbidity, and treatment delay. According to one Norwegian group, morbidity and mortality from SBO decreased from 1961 to 1995; the mortality was reported to be about 5%. [13]
Complications
Complications of SBO also depend on the severity of the condition, the patient's age, the presence of comorbities and, often, the duration of symptoms/signs, and include the following:
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Sepsis: Due to translocation of intestinal bacteria from tissue breakdown
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Intra-abdominal abscess
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Wound dehiscence
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Aspiration
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Short-bowel syndrome (as a result of multiple surgeries)
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Disability and death (secondary to delayed treatment)
Cardiac and pulmonary complications may result from procedures and hospitalization, neurologic complications, thrombosis/embolism, major hemorrhage, incision infection or rupture, and abdominal abscess or fistula formation. They include the following [3, 13] :
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Pneumonia: Including aspiration, ventilator associated, and/or hospital acquired
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Bowel ischemia/perforation
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Peritonitis
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Acute kidney injury/acute renal failure
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Surgical complications
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Small bowel obstruction. Image courtesy of Ademola Adewale, MD.
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Small bowel obstruction. Image courtesy of Ademola Adewale, MD.
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Small bowel obstruction. Image courtesy of Ademola Adewale, MD.
