II. Epidemiology
- Small Bowel Obstruction accounts 2-4% of Acute Abdominal Pain presentations to the emergency department (and 20% of emergent abdominal surgeries)
- Average age of onset: 64 years old
III. Types
- Simple mechanical obstruction
- Bowel lumen is obstructed
- No vascular compromise
- Strangulated obstruction
- Bowel lumen and vascular supply is compromised
- Closed loop obstruction
- Both ends of a bowel loop are obstructed
- Results in strangulated obstruction if untreated
- Rapid rise in intraluminal pressure
- Contained fluids and gas are trapped without proximal or distal exit
- Causes
- Volvulus (most common)
- Incarcerated Hernia
- Internal Hernia (associated with prior Roux-en-Y Bypass)
- Congenital bands
- Intestinal Malrotation
IV. Pathophysiology: Process (Occurs quickly in closed loop obstruction)
- Obstruction forms in either Small Bowel (much more common) or Large Bowel
- Bowel dilates proximal to obstruction
- Flatus and Bowel Movements cease
- Dehydration and Acute Kidney Injury results from Vomiting, minimal absorption, and bowel edema
- Even without oral intake, gastric, biliary and pancreatic secretions continue to accumulate within the bowel lumen
-
Metabolic Alkalosis and Hypokalemia
- Vomiting: Potassium, chloride and Hydrogen Ion loss
- Proximal renal tube resorbs bicarbonate (contraction alkalosis)
-
Bacterial overgrowth from intestinal stasis
- Stool forms within the Small Bowel (fecalization)
- Foul Emesis (odor of feces)
- Risk of bacteremia from Bacterial translocation across the bowel wall
- Incomplete obstruction (partial Small Bowel Obstruction) may still allow some forward flow of stool
- Intestinal dilation with increased intraluminal pressure
- Luminal pressure greater than venous pressure results in bowel wall edema and hyperemia
- Arterial flow diminishes due to compression and results in bowel ischemia, necrosis and perforation
V. Causes: By Frequency
- Most Common Causes
- Postoperative Adhesions (accounts for 50-60% of cases)
- Hernia (10-25% of cases, especially younger patients)
- Neoplasms (10-20% of cases, esp. older patients)
- Colon Cancer (most common, typically large Bowel Obstruction)
- Ovarian Cancer
- Pancreatic Cancer
- Gastric Cancer
- Less Common Causes (each less than 5% of cases)
- Inflammatory Bowel Disease
- Intussusception
- Volvulus
- Intraabdominal abscess
- Gallstones in the bowel lumen
- Foreign Body Ingestion
VI. Causes: By Type
- Intrinsic bowel lesions
- Congenital anomalies (Pediatric)
- Atresia
- Stenosis
- Bowel duplication
- Strictures
- Colon Cancer
- Peritoneal metastases
- Abdominal Radiation Therapy
- Inflammatory Bowel Disease
- Crohn Disease
- Ulcerative Colitis (10% within 3 years of colectomy, or 25% after restorative proctocolectomy)
- Colon Cancer
- Congenital anomalies (Pediatric)
- Extrinsic bowel lesions
- Adhesion
- Abdominal or pelvic surgery
- Appendectomy
- Colorectal Surgery
- Gynecologic procedures
- Hernia Repairs
- Roux-en-Y Bypass (Internal Hernia risk)
- Surgery in presence of peritonitis or Trauma
- Abdominal or pelvic surgery
- Hernia (higher risk for Strangulation)
- Internal Hernias via mesenteric defects
- External Hernias abdominal wall
- Obturator hernia
- More common in emaciated elderly women
- Small Bowel Volvulus
- Rare compared to colon Volvulus (e.g. Sigmoid Volvulus)
- More common in Africa, Middle East and India
- Occurs in Intestinal Malrotation or adhesions
- Adhesion
- Obturation (Uncommon to Rare)
- Colonic Polyp
- Intussusception
- Presents with Vomiting, Abdominal Pain and sausage-shaped abdominal mass (and a late finding, Currant Jelly Stool)
- Children: Usually idiopathic
- Adults: 95% have underlying mechanical cause
- AIDS may predispose to Intussusception
- GallstoneIleus
- Gallstones that have entered the bowel lumen
- More common in those over age 65 years
- Bezoar
- Barium
- Ascaris infection
- Tuberculosis
- Actinomycosis
- Diverticulitis
- Lumphoma
- Idiopathic Intestinal Obstruction
VII. Symptoms: Classic presentation
- Colicky Abdominal Pain
- Nausea and Vomiting
- Abdominal Distention
- Cessation of Flatus and Bowel Movements
VIII. Symptoms: General
- Frequent and recurrent Generalized Abdominal Pain
- Duration: Seconds to minutes
- Character: Spasms of crampy Abdominal Pain (colicky pain)
- Frequency
- Intermittent pain initially
- Every few minutes in proximal obstruction
- Constant pain suggests ischemia or perforation
- Associated Symptoms
- Symptoms more severe in proximal obstruction
- Proximal obstruction
- Severe, Colicky Abdominal Pain
- Develops over hours and occurs every few minutes
- Bilious Emesis
- Mild Abdominal Distention
- Distal obstruction
- Develops over days and becomes progressively worse
- Emesis may occur and is brown and feculent
- Significant Abdominal Distention
- Proximal obstruction
IX. Signs
- Vital Signs: Dehydration vs SIRS Criteria (Sepsis with peritonitis)
-
Bowel sounds
- Initial, Early: High pitched, hyperactive bowel sounds
- Later (after several hours): Hypoactive or absent bowel sounds
- Tender abdominal mass
- Closed loop Bowel Obstruction may be palpable
-
Abdominal Distention and tympany on percussion
- Indicates distal obstruction
- Abdominal Distention and tympany has greatest Positive Predictive Value for Small Bowel Obstruction
-
Rectal Examination
- Blood
- Fecal Impaction or rectal mass
- Clues to underlying etiology
- Abdominal wall or Inguinal Hernias
- Surgical scars
X. Diagnosis: Factors predicting Bowel Obstruction
- History of prior surgery
- Constipation history
- Age over 50 years
- Vomiting
- Abdominal Distention
- Hyperactive bowel sounds
XI. Labs
-
Complete Blood Count
- Leukocytosis may be significant (e.g. >20k) in bacteremia and intestinal perforation
- Comprehensive Metabolic Panel or Basic Metabolic Panel
- Hypokalemia
- Contraction Alkalosis (Dehydration)
- Acute Kidney Injury (increased Serum Creatinine)
- Serum Lactic Acid
- Increased with bowel ischemia, Sepsis and Dehydration
XII. Imaging: Flat and upright (or decubitus) abdominal XRay
- Indications
- CT Abdomen has largely replaced abdominal XRay when there are no delays (e.g. ED)
- Abdominal XRay has previously been a first-line test in suspected Small Bowel Obstruction
- However, it has poor accuracy (low Test Sensitivity and Test Specificity)
- Abdominal XRay is most useful in excluding abdominal free air (upright view)
- Efficacy
- Test Specificity: 50%
- Test Sensitivity: 60% (up to 80-90% in high grade obstruction)
- False Negative in early obstruction and high jejunal or duodenal obstruction
- Typical findings of Bowel Obstruction
- Bowel distention proximal to obstruction
- Bowel collapsed distal to obstruction (<6 cm colon, <9 cm cecum)
- Minimal colonic gas
- Upright or decubitus view
- Multiple air fluid levels
- Air-fluid levels >2.5 cm
- Supine view findings in Small Bowel Obstruction
- Sharply angulated distended bowel loops
- Step-ladder arrangement or parallel bowel loops
- Large Bowel with minimal air
- Stomach dilated
- Smal bowel dilated >2.5 cm
- Findings on upright or decubitus films
- String of pearls sign (specific for obstruction)
- Series of small pockets of gas in a row (gas trapped in the superior Small Bowel wall)
- Coffee-bean sign
- Bowel loops are distended and air filled
- U-Shaped bowel loop divided by edematous bowel wall
- Pseudotumor Sign
- Bowel loop filled with fluid (resembles mass)
- Signs of perforation
- Free air above the liver on upright or left lateral decubitus films
- Consider upright Chest XRay which may best demonstrate free air
- String of pearls sign (specific for obstruction)
XIII. Imaging: CT Abdomen and Pelvis
- Obtain with Intravenous Contrast
- Contrast identifies Small Bowel ischemia findings
- Indications
- First-line study for high suspicion of Small Bowel Obstruction
- Replaces plain Abdominal XRay as it identifies obstruction site and cause
- Identifies emergent Bowel Obstruction causes (e.g. Volvulus)
- Pre-surgical planning to identify obstruction site
- Definitive diagnosis of Bowel Obstruction is not clear from Abdominal XRay and clinical exam
- Distinguishes partial from complete obstruction
- No Contrast Material seen distal to obstruction site
- Avoid use of rectal contrast to allow differentiation of partial from complete obstruction
- First-line study for high suspicion of Small Bowel Obstruction
- Efficacy
- Test Sensitivity: 90-93% for high grade Small Bowel Obstruction
- However, much less sensitive in partial Small Bowel Obstruction
- Consider Oral Contrast in low grade, partial obstruction
- Test Specificity: 100%
- Test Sensitivity: 90-93% for high grade Small Bowel Obstruction
- Findings: Diagnosis
- Dilated bowel loops proximal to obstruction
- Decompressed bowel distal to obstruction
- Findings: Causes and complications
- Intussusception
- Volvulus
- C loop of distended bowel with radial mesenteric vessels and medial conversion
- Ischemia
- Thickened bowel walls and poor flow of Contrast Material
- Bowel perforation
- Pneumatosis Intestinalis, peritoneal free-air, and mesenteric fat stranding
- Extraluminal mass (e.g. abscess, neoplasm)
- Closed loop obstruction
- Strangulated bowel
XIV. Imaging: Contrast Fluoroscopy
- Indications
- Partial Intestinal Obstruction
- Refractory but stable cases of Intestinal Obstruction
- Protocols
- Water-soluble Contrast Material such as gastrograffin (may also be therapeutic in up to 74% of SBO patients)
- Small-bowel follow through
- Serial XRays after Oral Contrast (or NG instilled contrast)
- Contrast Material passing to Rectum within 24 hours of oral intake
- Associated with a 97% chance of spontaneous resolution
- Rectal fluoroscopy
- Demonstrates obstruction site in Large Bowel
XV. Imaging: Other advanced imaging
-
Ultrasound
Abdomen
- Consider in pregnancy, Unstable Patients or when Bedside Ultrasound is available
- Unable to identify transition point
- Efficacy (operator dependent)
- Test Specificity: 100%
- Test Sensitivity: 85% (however CT is typically performed instead in most cases)
- However, intraluminal gas and increasing mean BMI/Body habitus results in decreasing efficacy
- References
- MRI Abdomen (93% Test Sensitivity for SBO cause)
- CT Abdomen is typically preferred due to its lower cost and more rapid imaging
- Consider in pregnancy and adolescents
- May be performed with enteroclysis (Nasogastric Tube instills contrast directly into duodenum)
XVI. Differential Diagnosis (Abdominal Pain, distention, Nausea, cessation of Flatus/stool)
-
Adynamic Ileus or postoperative Paralytic Ileus
- Transient intestinal dysfunction and dysmotility without a physical blockage, anywhere along the Small Bowel or colon
- Similar presentation to SBO (Nausea, Vomiting, obstipation, crampy Abdominal Pain)
- Causes include recent surgery, medication-induced ileus (e.g. Opioids, Tricyclic Antidepressants)
-
Bowel Pseudoobstruction (Ogilvie Syndrome)
- Acute Large Bowel dilation with risk of dysmotility (e.g. Diabetes Mellitus, Scleroderma)
- Constipation
- Ascites
- Bowel Perforation
- Ischemic Bowel (superior mesenteric syndrome or Mesenteric Ischemia)
- Gastroenteritis
- Cholecystitis or Biliary Colic
- Pancreatitis
- Peptic Ulcer Disease or Dyspepsia
- Appendicitis
- Myocardial Infarction
- Pregnancy
XVII. Management: Conservative Therapy
- Surgical Consultation
- Admit all patients with complete Small Bowel Obstruction
-
Fluid Replacement
- Intravenous Fluid Replacement and maintenance
- Electrolyte replacement (e.g. Potassium Replacement)
- Consider monitoring fluid output with urine catheter
-
Bowel decompression
- Keep patient NPO without food or drink
- Nasogastric Tube
- No evidence for routine use in Small Bowel Obstruction
- Typically recommended for refractory Vomiting and Stomach distention
- Paradis (2014) Emerg Med J 31(3): 248-9 +PMID:24532357 [PubMed]
- Witting (2007) J Emerg Med 33(1):61-4 +PMID: 17630077 [PubMed]
- Long intestinal tube (eg. Cantor) offers no advantage
- Water soluble contrast trial
- Indicated in adhesion related Small Bowel Obstruction
- Contraindicated in pregnancy and non-adhesion SBO
- Technique
- Give Diatrizoate (e.g. Gastrografin) water soluble undiluted contrast 100 ml
- Clamp Nasogastric Tube for 2 to 4 hours
- Obtain KUB XRay at 6-24 hours to evaluate progression of contrast
- Progression of contrast to colon is predictive of Small Bowel Obstruction spontaneous resolution
- Lack of contrast in colon at 24 hours may indicate need for surgical intervention
-
Antibiotic
- Indications (Not for routine use)
- Surgery planned
- Bowel ischemia or infarction
- Bowel perforation
- Fever and Leukocytosis at presentation
- Cover Gram Negative Bacteria and Anaerobes
- Ciprofloxacin and Metronidazole OR
- Piperacillin-Tazobactam (Zosyn)
- Indications (Not for routine use)
- Possible benefit: Magnesium, Acidophilus, Simethicone
- Avoid in complete Bowel Obstruction due to bowel ischemia and perforation risk
- Give orally, then clamp NG tube x1 hour; Repeat tid
- Magnesium Oxide 500 mg
- L. acidophilus 0.3 grams
- Simethicone 40 mg
- Studied in partial Small Bowel Obstruction
- Unblinded trial
- Reduced length of stay and number needing surgery
- Chen (2005) CMAJ 173:1165-9 [PubMed]
XVIII. Management: Surgical Intervention
- Spontaneous resolution often occurs without surgery within 48 hours
- Partial Small Bowel Obstruction: 75%
- Complete Small Bowel Obstruction: Up to 50%
- Predictors of resolution without surgery
- Early postoperative Bowel Obstruction
- Adhesive obstruction (prior laparotomy)
- Crohn's Disease
- Indications for Surgery
- Inadequate relief with Nasogastric Tube placement
- Persistant symptoms >3-5 days without resolution with conservative management
- Acute management of surgically reversible cause
- Strangulated Hernia
- Volvulus
- Intra-abdominal malignancy
- Signs of abdominal Sepsis, bowel ischemia or bowel perforation
- Peritonitis
- Clinical instability
- Unexplained Leukocytosis or Metabolic Acidosis
XIX. Complications
- Intestinal Ischemia or infarction
- Bowel necrosis, bowel perforation and Bacterial peritonitis
- Hypovolemia
- Complications of surgical intervention if needed
- Fluid and Electrolyte imbalance
XX. Prognosis: Recurrence of obstruction due to adhesions
- Risk after first episode: 53%
- Risk after more than one episode: 83%
- Surgical Consultation to review elective surgery for reversible causes (e.g. Hernia Repair)
- However risk of additional postoperative intestinal adhesions
XXI. References
- Han (2022) Crit Dec Emerg Med 36(12): 4-10
- Torrey in Marx (2002) Rosen's Emergency Med, p. 1283-7
- Townsend (2001) Sabiston Surgery, p. 883-8
- Turnage in Feldman (1998) Sleisenger GI, p. 1799-804
- Jackson (2018) Am Fam Physician 98(6): 362-7 [PubMed]
- Jackson (2011) Am Fam Physician 83(2): 159-5 [PubMed]
- Matsuoka (2002) Am J Surg 183:614-7 [PubMed]