Small bowel obstruction: Difference between revisions

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(Major update: CT transition point, strangulation signs, Gastrografin challenge evidence, closed-loop obstruction, nonoperative management criteria, classification, references with PMIDs)
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==Background==
==Background==
*Mechanical obstruction of the small intestine preventing normal passage of intestinal contents
*'''Adhesions from prior surgery''' are the most common cause ('''60-75%''' of all SBO)
*Second most common cause: '''incarcerated [[hernia]]''' (~15%)
*Other causes: malignancy, [[Crohn's disease]], [[intussusception]], volvulus, gallstone ileus, foreign body, stricture
*'''Closed-loop obstruction''': segment of bowel obstructed at two points → rapid progression to '''strangulation and ischemia'''
*SBO accounts for ~15% of ED visits for acute abdominal pain
*Mortality: <5% for simple SBO; '''up to 25% for strangulated SBO'''


[[File:Blausen 0817 SmallIntestine Anatomy.png|thumb|Small bowel anatomy with surrounding structures.]]
===Classification===
*Small bowel obstruction without history of surgery or hernia is malignancy until proven otherwise
*'''Partial''': some gas/fluid passes through → flatus may be present
*"Never let the sun rise or set on a small bowel obstruction"
*'''Complete''': no passage of gas or stool
 
*'''Simple''': obstruction without vascular compromise
 
*'''Strangulated''': obstruction with compromised blood supply → '''ischemia → necrosis → perforation'''
===Causes===
 
*Adhesions (history of previous abdominal surgeries +LR 3.86 and -LR 0.19)
**Most common cause in developed countries
*Hernia
**Port hernias can occur after laparoscopic surgery
*Malignancy
*Intraluminal strictures
**[[Special:MyLanguage/Crohn's disease|Crohn's disease]]
**Radiation therapy
**[[Special:MyLanguage/Mesenteric ischemia|Mesenteric ischemia]]
*[[Special:MyLanguage/Intussusception|Intussusception]] (due to [[Special:MyLanguage/lymphoma|lymphoma]] as lead point)
*[[Special:MyLanguage/ingested foreign body|Foreign body]] ([[Special:MyLanguage/bezoar|bezoar]]s)
*[[Special:MyLanguage/abdominal trauma|Trauma]] ([[Special:MyLanguage/duodenal hematoma|duodenal hematoma]])
*Gallstone [[Special:MyLanguage/ileus|ileus]]
*Small bowel [[Special:MyLanguage/volvulus|volvulus]] (3-6% of causes of SBO)<ref>Roline CE and Reardon RF.  Disorders of the Small Intestine.  Rosen's.  Edition 8.  Chapter 92.  2014.  1216-1224.</ref>
 


==Clinical Features==
==Clinical Features==
*'''Crampy, intermittent abdominal pain''' (colicky; occurs in waves)
*'''Nausea and vomiting''' (the more proximal the obstruction, the earlier and more prominent the vomiting)
*'''Obstipation''' (absence of flatus and stool) — '''complete obstruction'''
*'''Abdominal distension''' (more prominent with distal obstruction)
*'''High-pitched, hyperactive bowel sounds''' → late: absent bowel sounds (ileus from ischemia)
*'''Prior surgical history''' — ask about ALL prior abdominal/pelvic operations
*Tachycardia, dehydration from third-spacing and vomiting


*[[Special:MyLanguage/Abdominal pain|Abdominal pain]]
===Signs of Strangulation (Surgical Emergency)===
**Colicky
*'''Constant, severe pain''' (no longer colicky)
**Periumbilical or diffuse
*'''Fever'''
**Paroxysms of pain occur q5min
*'''Peritoneal signs''' (rebound, guarding)
*[[Special:MyLanguage/Vomiting|Vomiting]]
*'''Tachycardia, hypotension'''
**More common in proximal than distal obstruction
*'''Leukocytosis with left shift'''
**Bilious (proximal) or feculent (distal ileal)
*'''Elevated lactate'''
***Abdominal pain relieved with vomiting positively predictive +LR (4.50-2.82) -LR (0.78-0.35)
*'''No single clinical or lab finding reliably rules out strangulation'''
*Abdominal distention
**Seen more in distal than proximal obstruction
**+LR (16.8-5.64) -LR (0.43-0.34)
*Inability to pass flatus
**May pass flatus/stool initially
***Takes 12-24hrs for colon to empty
***History of constipation +LR 8.8 and -LR 0.59
*[[Special:MyLanguage/Dehydration|Dehydration]]
*Anorexia
*[[Special:MyLanguage/ischemic bowel|Ischemia]] (increased intraluminal pressure initially leads to venous obstruction, progresses to frank arterial ischemia)
**[[Special:MyLanguage/Fever|Fever]]
**[[Special:MyLanguage/Leukocytosis|Leukocytosis]]
*Abnormal bowel sounds
**Studies suggest that auscultating bowel sounds is not clinically useful to differentiate between normal and pathologic<ref>Felder S, Margel D, Murrell Z, et al. Usefulness of Bowel Sound Auscultation: A Prospective Evaluation. J Surg. 2014; 71(5):768–773.</ref>
 


==Differential Diagnosis==
==Differential Diagnosis==
*[[Large bowel obstruction]]
*Paralytic [[ileus]] (postoperative, metabolic, medication-related)
*[[Mesenteric ischemia]]
*[[Volvulus]]
*[[Incarcerated hernia]]
*[[Appendicitis]]
*[[Pancreatitis]]
*Pseudo-obstruction (Ogilvie syndrome — large bowel)
*[[Crohn's disease]] flare


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{{Abdominal pain DDX}}
{{Abdominal Pain DDX Diffuse}}
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{{Constipation DDX}}
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==Evaluation==
==Evaluation==
[[File:Upright X-ray demonstrating small bowel obstruction.jpg|thumb|Upright abdominal X-ray demonstrating a small bowel obstruction. Note multiple air fluid levels.]]
[[File:SBO plain.png|thumb|Small bowel obstruction]]
[[File:SBO_Cai_Maurelus.gif|thumbnail|Ultrasound shows dilated, non-compressible loops of bowel with characteristic to-and-fro motion of bowel contents<ref>http://www.thepocusatlas.com/bowel/</ref>]]
[[File:SBO.gif|thumbnail|Ultrasound shows dilated loops of bowel steep precipice and tumbling feces<ref>http://www.thepocusatlas.com/bowel/</ref>]]
[[File:PSBOCT.png|thumb|A small bowel obstruction as seen on CT.]]
===Labs===
===Labs===
 
*'''BMP''': electrolytes (hypokalemia, metabolic alkalosis from vomiting), BUN/Cr (dehydration), bicarbonate
*CBC
*'''CBC''': leukocytosis (consider strangulation if WBC >15,000)
**WBC >20K suggests bowel gangrene, abscess, or peritonitis
*'''Lactate''': elevated suggests bowel ischemia (but '''normal lactate does NOT exclude strangulation''')
**WBC >40K suggests mesenteric vascular occlusion
*'''Lipase''': rule out [[pancreatitis]]
*Chemistry - degree of dehydration, evidence of ischemia ([[Special:MyLanguage/acidosis|acidosis]])
*'''Type and screen''' if surgery likely
*[[Special:MyLanguage/Lactate|Lactate]] - sensitive (90-100%), though not specific marker of strangulation
 


===Imaging===
===Imaging===
====Abdominal X-ray====
*'''Sensitivity ~60-70%''' for SBO
*Findings: dilated small bowel loops ('''> 3 cm'''), air-fluid levels on upright, '''absence of colonic gas'''
*'''Three film series''' (supine, upright, CXR): may show free air if perforated
*'''Normal X-ray does NOT exclude SBO'''


*Use the 3/6/9 rule for bowel imaging
====CT Abdomen/Pelvis with IV Contrast (Test of Choice)====
**Upper limit of 3cm for small bowel, 6cm for colon, and 9cm for cecum
*'''Sensitivity 90-95%''' for SBO
*'''Xray'''
*Identifies:
**[[Special:MyLanguage/Acute Abdominal Series|Acute Abdominal Series]]
**'''Transition point''' (dilated proximal → decompressed distal bowel)
**Upright chest film: rule out free air
**Cause of obstruction (adhesion, hernia, mass, volvulus)
**Upright abdominal film: air-fluid levels:
**'''Signs of strangulation''': bowel wall thickening, mesenteric haziness/fluid, '''decreased/absent bowel wall enhancement''', pneumatosis intestinalis, portal venous gas
**Supine abdominal film: width of bowel loops most visible (estimate of amount of distention)
*'''Oral contrast NOT needed''' (pooled intraluminal fluid serves as natural contrast)
**String of pearls sign (small pockets of gas along the small bowel that are trapped between the valvulae conniventes) is virtually diagnostic<ref>Maglinte DDT, Reyes BL, Harmon BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR 1996; 167:1451-1455</ref>
*'''Small bowel feces sign''': particulate material in dilated SB (distal/complete obstruction)
**Small bowel diameter ≥3cm is associated with obstruction
***Sen 75% Spec 66% +LR 1.6 -LR 0.43
***Air in colon or rectum makes complete obstruction less likely (esp if symptoms >24hr)
***If patient does not tolerate upright position left lateral decub abdominal film can substitute
*'''CT A/P with IV contrast'''
**Consider if plain films are non-diagnostic
**Can show closed-loop obstruction, evidence of ischemia
**Per American College of Radiology PO contrast is no longer indicated
***Modern CT Scanner (0.75mm slices): Sen 96%, Spec 100%, +LR infinity -LR 0.04
***Historical CT scanner meta-analysis: Sen 87%  Spec 81%, +LR 3.6  -LR 0.18
*[[Ultrasound: Abdomen|Ultrasound for SBO]]
**Sen 97%, Spec 90%, +LR 9.5, -LR 0.04 (four studies, 2 done by EM residents and 2 by radiology residents)
*'''MRI for SBO''' - Sen 92%, Spec 89% +LR 6.7 -LR 0.11
 


==Management==
==Management==
===Initial Resuscitation===
*'''NPO'''
*'''Aggressive IV fluid resuscitation''' (NS or LR) — patients are often significantly volume depleted
*'''Electrolyte correction''' (K, Mg replacement)
*'''NG tube decompression''': for persistent vomiting, significant distension
*'''Pain control''': IV opioids as needed; ketorolac
*'''Antiemetics''': ondansetron 4 mg IV


===Nonoperative Management (Adhesive SBO without Strangulation)===
*'''Trial of nonoperative management''' for '''partial, adhesive SBO without signs of strangulation'''
*NG decompression + IV fluids + bowel rest
*'''Water-soluble contrast challenge''' (Gastrografin):
**100 mL PO/via NGT
**If contrast reaches '''colon by 24 hours''' → predicts resolution with nonoperative management (sensitivity ~97%)<ref>Abbas S, et al. Water-soluble contrast in management of adhesive small bowel obstruction. ''Cochrane Database Syst Rev''. 2007;(3):CD005598. PMID 17636810</ref>
**May also have therapeutic effect (osmotic — draws fluid into lumen, stimulates peristalsis)
*'''~70-80% of adhesive SBO resolves with conservative management'''
*'''Failure of nonoperative trial''': no improvement in 24-72 hours → surgery


===[[Special:MyLanguage/Volume resuscitation|Volume resuscitation]]===
===Surgical Management===
 
*'''Indications for emergent surgery''':
*IV fluid resuscitation with [[Special:MyLanguage/electrolyte repletion|electrolyte repletion]]
**'''Complete obstruction'''
*Assessment of need for operative vs nonoperative management
**'''Signs of strangulation/peritonitis'''
 
**'''Incarcerated/strangulated hernia'''
 
**'''Closed-loop obstruction on CT'''
===[[Special:MyLanguage/Nasogastric tube|Nasogastric tube]]===
**'''Hemodynamic instability not responding to resuscitation'''
 
**'''Failure of nonoperative management'''
*14 French
*Surgical consult '''early''' for all cases (even if initially managed conservatively)
**Intermittent low wall suction
*Nasogastric fluid losses can be replaced with NS + KCL (30-40 meq)
*There is some evidence to suggest nasogastric tube decompression was not associated with decreased bowel ischemia or need for surgery<ref>Berman, DJ et al. Nasogastric decompression not associated with a reduction in surgery or bowel ischemia for acute small bowel obstruction. Am J Emerg Med. 2017 Dec;35(12):1919-1921.PMID: 28912083</ref>
 
 
===Oral Contrast===
 
*Both diagnostic and therapeutic (draws water into the bowel stimulating peristalsis)
*Associated with decreased hospital stay, more rapid resolution of symptoms
*Repeat CT scan may be helpful to detect early signs of bowel ischemia
**Repeat plain films are not helpful (only detect perforation)
 
 
====Gastrografin PO====
 
*Alternative to operative management if early obstructive process
*Gastrografin through NG or OG decreases bowel wall edema and increases bowel motility<ref>Assalia A, Schein M, Kopelman D, et al. Therapeutic effect of oral Gastrografin in adhesive, partial small-bowel obstruction: A prospective randomized trial. Surgery 1994; 115: 433-437.</ref>
**Diagnostic and therapeutic<ref>Chen SC, Lin FY, Lee PH, et al. Water-soluble contrast study predicts the need for early surgery in adhesive small bowel obstruction. Br J Surg 1998; 85: 1692-1694.</ref>
**100 cc of gastrografin through NG tube
**Transit may be observed through serial radiographs
***Contrast within the large bowel within 24 hrs suggest partial SBO
***Contrast failing to reach large bowel within 24-48 hrs suggests complete obstruction, requiring laparotomy
**Therapeutic, may reduce necessary operative rate by ~75%<ref>Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).</ref>
*Avoid barium as it becomes inspissated in bowel, causing complete obstruction<ref>Choi HK et al. Therapeutic Value of Gastrografin in Adhesive Small Bowel Obstruction After Unsuccessful Conservative Treatment: A Prospective Randomized Trial. Annals of Surgery. 2002;236(1).</ref>
**Gastrografin is water-soluble and relatively safer if perforation occurs
 
 
===Non-operative Management vs. Operative===
 
*75% of patients are amenable to non-operative management
 
 
====Operative Management====
 
*25% of patients admitted for SBO require surgery
*Surgery is indicated for patients with:
**Increasing pain, distention, or peristent high NGT output
**Necrotic bowel
**Closed-loop obstruction (incarcerated hernia, small bowel volvulus, cecal volvulus)
**[[Special:MyLanguage/Fever|Fever]], leukocytosis, peritonitis
 
 
===[[Special:MyLanguage/Antibiotics|Antibiotics]]===
 
*Not typically indicated, unless evidence of concurrent ischemia or infection
*See [[Special:MyLanguage/Peritonitis#Management|peritonitis antibiotics]]
 


==Disposition==
==Disposition==
 
*'''Admit all patients with SBO'''
*Admit
*'''Surgical consultation''' in ED for all patients
 
*'''ICU''' if septic, hemodynamically unstable, or peritonitic
 
*Serial abdominal exams every 4-8 hours
==Prognosis==
*Repeat imaging if clinical deterioration
 
*In the context of advancing malignancy with widespread peritoneal metastases, bowel obstruction is common and often indicates a poor prognosis
*A less interventional and more comfort based approach to treatment may be appropriate
*See [[Special:MyLanguage/Malignant bowel obstruction|Malignant bowel obstruction]] for details
 


==See Also==
==See Also==
 
*[[Large bowel obstruction]]
*[[Special:MyLanguage/Malignant bowel obstruction|Malignant bowel obstruction]]
*[[Ileus]]
*[[Special:MyLanguage/Small Bowel Obstruction (SBO)|Small Bowel Obstruction (SBO)]]
*[[Volvulus]]
*[[Special:MyLanguage/Volvulus (Adults)|Volvulus (Adults)]]
*[[Incarcerated hernia]]
*[[Special:MyLanguage/Volvulus (Peds)|Volvulus (Peds)]]
*[[Mesenteric ischemia]]
 
*[[Abdominal pain]]


==References==
==References==
<references/>
<references/>
*Maung AA, 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):S362-369. PMID 23114494
*Defined by ten Broek RP, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction. ''World J Emerg Surg''. 2018;13:24. PMID 29946347
*Taylor MR, Lalani N. Adult small bowel obstruction. ''Acad Emerg Med''. 2013;20(6):528-544. PMID 23758299


[[Category:GI]]  
[[Category:GI]]
[[Category:Surgery]]
[[Category:Surgery]]
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Revision as of 19:53, 21 March 2026

Background

  • Mechanical obstruction of the small intestine preventing normal passage of intestinal contents
  • Adhesions from prior surgery are the most common cause (60-75% of all SBO)
  • Second most common cause: incarcerated hernia (~15%)
  • Other causes: malignancy, Crohn's disease, intussusception, volvulus, gallstone ileus, foreign body, stricture
  • Closed-loop obstruction: segment of bowel obstructed at two points → rapid progression to strangulation and ischemia
  • SBO accounts for ~15% of ED visits for acute abdominal pain
  • Mortality: <5% for simple SBO; up to 25% for strangulated SBO

Classification

  • Partial: some gas/fluid passes through → flatus may be present
  • Complete: no passage of gas or stool
  • Simple: obstruction without vascular compromise
  • Strangulated: obstruction with compromised blood supply → ischemia → necrosis → perforation

Clinical Features

  • Crampy, intermittent abdominal pain (colicky; occurs in waves)
  • Nausea and vomiting (the more proximal the obstruction, the earlier and more prominent the vomiting)
  • Obstipation (absence of flatus and stool) — complete obstruction
  • Abdominal distension (more prominent with distal obstruction)
  • High-pitched, hyperactive bowel sounds → late: absent bowel sounds (ileus from ischemia)
  • Prior surgical history — ask about ALL prior abdominal/pelvic operations
  • Tachycardia, dehydration from third-spacing and vomiting

Signs of Strangulation (Surgical Emergency)

  • Constant, severe pain (no longer colicky)
  • Fever
  • Peritoneal signs (rebound, guarding)
  • Tachycardia, hypotension
  • Leukocytosis with left shift
  • Elevated lactate
  • No single clinical or lab finding reliably rules out strangulation

Differential Diagnosis

Template:Abdominal pain DDX

Evaluation

Labs

  • BMP: electrolytes (hypokalemia, metabolic alkalosis from vomiting), BUN/Cr (dehydration), bicarbonate
  • CBC: leukocytosis (consider strangulation if WBC >15,000)
  • Lactate: elevated suggests bowel ischemia (but normal lactate does NOT exclude strangulation)
  • Lipase: rule out pancreatitis
  • Type and screen if surgery likely

Imaging

Abdominal X-ray

  • Sensitivity ~60-70% for SBO
  • Findings: dilated small bowel loops (> 3 cm), air-fluid levels on upright, absence of colonic gas
  • Three film series (supine, upright, CXR): may show free air if perforated
  • Normal X-ray does NOT exclude SBO

CT Abdomen/Pelvis with IV Contrast (Test of Choice)

  • Sensitivity 90-95% for SBO
  • Identifies:
    • Transition point (dilated proximal → decompressed distal bowel)
    • Cause of obstruction (adhesion, hernia, mass, volvulus)
    • Signs of strangulation: bowel wall thickening, mesenteric haziness/fluid, decreased/absent bowel wall enhancement, pneumatosis intestinalis, portal venous gas
  • Oral contrast NOT needed (pooled intraluminal fluid serves as natural contrast)
  • Small bowel feces sign: particulate material in dilated SB (distal/complete obstruction)

Management

Initial Resuscitation

  • NPO
  • Aggressive IV fluid resuscitation (NS or LR) — patients are often significantly volume depleted
  • Electrolyte correction (K, Mg replacement)
  • NG tube decompression: for persistent vomiting, significant distension
  • Pain control: IV opioids as needed; ketorolac
  • Antiemetics: ondansetron 4 mg IV

Nonoperative Management (Adhesive SBO without Strangulation)

  • Trial of nonoperative management for partial, adhesive SBO without signs of strangulation
  • NG decompression + IV fluids + bowel rest
  • Water-soluble contrast challenge (Gastrografin):
    • 100 mL PO/via NGT
    • If contrast reaches colon by 24 hours → predicts resolution with nonoperative management (sensitivity ~97%)[1]
    • May also have therapeutic effect (osmotic — draws fluid into lumen, stimulates peristalsis)
  • ~70-80% of adhesive SBO resolves with conservative management
  • Failure of nonoperative trial: no improvement in 24-72 hours → surgery

Surgical Management

  • Indications for emergent surgery:
    • Complete obstruction
    • Signs of strangulation/peritonitis
    • Incarcerated/strangulated hernia
    • Closed-loop obstruction on CT
    • Hemodynamic instability not responding to resuscitation
    • Failure of nonoperative management
  • Surgical consult early for all cases (even if initially managed conservatively)

Disposition

  • Admit all patients with SBO
  • Surgical consultation in ED for all patients
  • ICU if septic, hemodynamically unstable, or peritonitic
  • Serial abdominal exams every 4-8 hours
  • Repeat imaging if clinical deterioration

See Also

References

  1. ↑ Abbas S, et al. Water-soluble contrast in management of adhesive small bowel obstruction. Cochrane Database Syst Rev. 2007;(3):CD005598. PMID 17636810
  • Maung AA, 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):S362-369. PMID 23114494
  • Defined by ten Broek RP, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction. World J Emerg Surg. 2018;13:24. PMID 29946347
  • Taylor MR, Lalani N. Adult small bowel obstruction. Acad Emerg Med. 2013;20(6):528-544. PMID 23758299
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