# Small Bowel Obstruction ## Overview Small bowel obstruction (SBO) is one of the most common surgical emergencies, accounting for approximately 15% of emergency department visits for abdominal pain and 20% of surgical admissions. The general surgeon must differentiate partial from complete obstruction, identify strangulation, and determine the appropriate timing of operative intervention. ## Etiology ### Most Common Causes **Adhesions** from prior abdominal surgery are the most common cause of SBO in developed countries, responsible for 65 to 75% of cases. **Hernias** are the second most common cause at 10 to 15%, including inguinal, incisional, and internal hernias (the last being particularly important after bariatric surgery). **Neoplasm** accounts for 5 to 10% of cases, whether from primary small bowel tumors or extrinsic compression by peritoneal carcinomatosis. **Crohn disease** causes SBO through both inflammatory and fibrotic strictures. ### Less Common Causes Less frequent etiologies include gallstone ileus (1 to 3%), in which a cholecystoduodenal fistula allows a stone to pass into the bowel and typically lodge at the ileocecal valve -- the Rigler triad of pneumobilia, SBO, and ectopic gallstone on imaging is characteristic. Intussusception in adults usually has a pathologic lead point such as a tumor or Meckel diverticulum. Other causes include small bowel volvulus, foreign bodies, bezoars, radiation enteritis, superior mesenteric artery syndrome, Meckel band, and early postoperative SBO occurring within 30 days of surgery. ## Pathophysiology Obstruction leads to progressive proximal bowel dilation with gas and fluid accumulation, intestinal wall edema, increased intraluminal pressure, and third-spacing of fluid into the bowel wall and peritoneal cavity. Bacterial overgrowth develops proximal to the obstruction. **Closed-loop obstruction** -- in which two points of obstruction exist, as with an adhesive band or hernia -- carries a high risk of rapid progression to strangulation. **Strangulation** involves compromised blood supply leading to bowel ischemia, necrosis, and perforation, occurring in approximately 10 to 15% of SBO cases. The risk of strangulation is highest with complete obstruction, closed-loop configurations, and incarcerated hernias. ## Clinical Presentation The four cardinal symptoms of SBO are crampy or colicky abdominal pain, nausea and vomiting, abdominal distension, and obstipation (failure to pass flatus or stool). The clinical picture varies with the level of obstruction. **Proximal (high) SBO** produces early, profuse bilious vomiting with less distension and less pain. **Distal (low) SBO** causes more distension, feculent vomiting (a late finding), and more pronounced colicky pain. **Complete obstruction** manifests as absolute constipation with no passage of flatus or stool and more severe symptoms overall. **Partial obstruction** allows passage of some flatus or stool with intermittent symptoms. ### Signs of Strangulation Signs of strangulation require urgent surgical intervention and include a shift from colicky to continuous pain, fever, tachycardia, peritoneal signs (localized or diffuse tenderness, guarding, or rigidity), leukocytosis with a left shift, elevated lactate (though this is a late finding), and metabolic acidosis. CT findings suggestive of strangulation include mesenteric haziness, reduced bowel wall enhancement, pneumatosis intestinalis, and portal venous gas. ## Diagnostic Workup ### Laboratory Studies The complete blood count may show leukocytosis, suggesting strangulation or ischemia. The basic metabolic panel often reveals electrolyte derangements from vomiting (hypokalemia, hypochloremic metabolic alkalosis) and elevated BUN and creatinine from dehydration. Serum lactate is elevated in bowel ischemia with a sensitivity of 90% and specificity of 87% for strangulation, but it may be normal early in the course. Liver function tests are obtained when gallstone ileus is suspected. ### Imaging **CT abdomen/pelvis with IV contrast** is the gold standard, with sensitivity of 94 to 100% and specificity of 90 to 95% for SBO. CT identifies the site, cause, and degree of obstruction, including the transition point. The small bowel feces sign proximal to the obstruction is a helpful finding. Signs of strangulation include mesenteric haziness, reduced wall enhancement, ascites, and pneumatosis. Closed-loop obstruction appears as C-shaped or U-shaped loops with convergent mesenteric vessels forming a "beak sign." Specific etiologies such as hernias, masses, and gallstone ileus can be identified. **Abdominal radiographs** are less sensitive than CT but useful as an initial screening tool. Findings include dilated small bowel loops (greater than 3 cm), air-fluid levels on upright film, and paucity of gas in the colon. Three or more air-fluid levels with loops greater than 2.5 cm is suggestive. However, radiographs may be normal in 20 to 30% of SBO cases, particularly when the obstruction is proximal or early. ### Water-Soluble Contrast Study The **Gastrografin (water-soluble contrast) study** serves both a diagnostic and therapeutic role. Administered orally or via nasogastric tube at a volume of 50 to 100 mL, the presence of contrast reaching the colon or cecum on abdominal X-ray at 4 to 24 hours reliably predicts resolution with non-operative management, with a sensitivity of 96% and specificity of 98%. The hyperosmolar properties of the contrast may have a therapeutic effect by drawing fluid into the intestinal lumen and promoting peristalsis. This study reduces both the need for surgery and the length of hospital stay. ## Management ### Initial Management All patients receive initial supportive care: NPO status, IV fluid resuscitation with electrolyte correction, nasogastric tube decompression (if the patient is vomiting or significantly distended), a Foley catheter for urine output monitoring, serial abdominal examinations every 4 to 8 hours, and DVT prophylaxis. ### Indications for Urgent/Emergent Surgery Immediate operative intervention is indicated for peritonitis or signs of strangulation, closed-loop obstruction identified on CT, an incarcerated hernia that cannot be reduced, pneumatosis intestinalis or portal venous gas, hemodynamic instability despite resuscitation, and free air indicating perforation. ### Non-Operative Management Non-operative management is appropriate for partial SBO and adhesive SBO without signs of strangulation. It consists of nasogastric tube decompression, IV fluids, serial examinations, and the Gastrografin challenge. Traditional teaching allows 48 to 72 hours for non-operative management, but the water-soluble contrast study can guide earlier decision-making: if Gastrografin reaches the colon within 24 hours, non-operative management should continue with a high likelihood of resolution; if no contrast reaches the colon by 24 to 36 hours, operative intervention should be considered. The success rate for non-operative management of adhesive partial SBO is 65 to 80%. ### Operative Management Delayed intervention beyond 24 to 48 hours in complete SBO is associated with increased bowel resection rates, underscoring the importance of timely surgical decision-making. The **approach** depends on clinical factors: laparoscopy is feasible for first episodes, suspected single-band adhesions, and limited prior surgery, while laparotomy is preferred for dense adhesions, multiple prior operations, and distended bowel that limits laparoscopic visualization. **Procedures** include adhesiolysis (the most common), hernia reduction and repair, bowel resection with anastomosis for necrotic or non-viable bowel, strictureplasty for Crohn disease, and enterotomy with stone extraction for gallstone ileus (with or without fistula repair). **Bowel viability assessment** considers color (pink indicates viable tissue; purple or black indicates necrosis), peristalsis, and mesenteric pulsation. When viability is equivocal, adjuncts such as IV fluorescein with a Wood lamp, Doppler evaluation, or ICG fluorescence angiography can help. A second-look laparotomy at 24 to 48 hours is appropriate when viability remains uncertain. ### Early Postoperative SBO SBO occurring within 30 days of surgery is usually managed non-operatively, as most cases resolve spontaneously. CT is essential to rule out internal hernia, abscess, or other correctable causes. Re-operation is indicated if peritoneal signs develop or if there is no resolution after prolonged non-operative management. ## Adhesion Prevention Strategies to prevent adhesive SBO include barrier products such as Seprafilm (hyaluronic acid/carboxymethylcellulose) and Adept (icodextrin 4%), as well as meticulous surgical technique with minimal tissue handling and use of laparoscopy when appropriate. No single strategy has eliminated adhesive SBO. CT scan illustration of small bowel obstruction showing the key diagnostic features: dilated proximal small bowel loops greater than 3cm, a clear transition point with decompressed distal bowel, the small bowel feces sign proximal to the transition point, and mesenteric haziness suggesting early ischemic changes. Include an annotation showing the beak sign of a closed-loop obstruction in a separate panel. Abdominal radiograph findings in small bowel obstruction showing multiple dilated loops of small bowel with valvulae conniventes (plicae circulares) visible, multiple air-fluid levels on upright film at different heights within the same loop (differential air-fluid levels), and paucity of colonic gas. Label the key features distinguishing SBO from large bowel obstruction (haustra vs. valvulae conniventes, distribution pattern). Clinical algorithm flowchart for management of adhesive small bowel obstruction: starting with initial resuscitation and CT scan, branching into complete vs. partial obstruction, signs of strangulation vs. no strangulation, water-soluble contrast challenge with decision points at 24 hours, and endpoints of operative intervention vs. continued non-operative management with criteria for each pathway. ## Clinical Pearls Adhesions from prior surgery are the most common cause of SBO, but all hernia orifices must be examined on physical exam before attributing the obstruction to adhesions. A CT scan with IV contrast is the single most valuable imaging study, as it identifies the site, cause, and presence of complications. Gastrografin reaching the colon within 24 hours on plain X-ray reliably predicts resolution with non-operative management. The classic teaching of "never let the sun set on a bowel obstruction" applies to complete SBO with signs of strangulation -- partial SBO without strangulation can be safely managed non-operatively. Signs of strangulation on CT, including reduced wall enhancement, mesenteric haziness, and ascites, mandate urgent surgical exploration. Gallstone ileus should be suspected in elderly patients with SBO and pneumobilia on CT, which constitutes the Rigler triad. Early postoperative SBO occurring within 30 days is usually managed non-operatively unless peritoneal signs develop. A normal serum lactate does not exclude bowel strangulation, and clinical judgment combined with CT findings is more reliable. ## References - Maung AA, Johnson DC, Piper GL, et al. Evaluation and management of small-bowel obstruction: an Eastern Association for the Surgery of Trauma practice management guideline. *J Trauma Acute Care Surg*. 2012;73(5 Suppl 4):S362-S369. - Catena F, Di Saverio S, Coccolini F, et al. Adhesive small bowel adhesions obstruction: evolutions in diagnosis, management and prevention. *World J Gastrointest Surg*. 2016;8(3):222-231. - Ceresoli M, Coccolini F, Catena F, et al. Water-soluble contrast agent in adhesive small bowel obstruction: a systematic review and meta-analysis of diagnostic and therapeutic value. *Am J Surg*. 2016;211(6):1114-1125. - Ten Broek RPG, Krielen P, Di Saverio S, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO): 2017 update. *World J Emerg Surg*. 2018;13:24.