Surgery Book

Stomach Disorders


Small Bowel Obstruction

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

Small bowel obstruction (C0235329)

Definition (NCI_CTCAE) A disorder characterized by blockage of the normal flow of the intestinal contents.
Definition (NCI) Blockage of the normal flow of the small intestinal contents.
Concepts Disease or Syndrome (T047)
SnomedCT 235802005, 197080000, 281255004
English SMALL BOWEL OBSTRUCTION, SMALL INTESTINE OBSTRUCTION, Small bowel obstruction NOS, Small bowel obstruction, Small intestinal obstruction NOS, Obstruction small intestine, Small Intestinal Obstruction, bowel obstructions small, intestines obstruction small, obstruction small intestine, small intestine obstruction, bowel obstruction small, small bowel obstruction, small intestinal obstruction, Small bowel obstruction NOS (disorder), Small intestine obstruction, Small intestinal obstruction, SBO - Small bowel obstruction, Small bowel obstruction (disorder)
Italian Ostruzione dell'intestino tenue, Ostruzione dell'intestino tenue NAS
Dutch dunne darmobstructie NAO, obstructie dunne darm, dunne darmobstructie
French Occlusion de l'intestin grêle SAI, Occlusion de l'intestin grêle, OBSTRUCTION DE L'INTESTIN GRELE, Obstruction de l'intestin grêle
German Duenndarmobstruktion NNB, Obstruktion des Duenndarms, DUENNDARMVERSCHLUSS, Duenndarmobstruktion
Portuguese Obstrução do intestino delgado NE, OCLUSAO DO INTESTINO DELGADO, Obstrução do intestino delgado
Spanish Obstrucción del intestino delgado, Obstrucción del intestino delgado NEOM, INTESTINO DELGADO, OBSTRUCCION, obstrucción del intestino delgado, SAI (trastorno), obstrucción del intestino delgado, SAI, obstrucción del intestino delgado (trastorno), obstrucción del intestino delgado, Obstrucción de intestino delgado
Japanese 小腸閉塞NOS, 小腸閉塞, ショウチョウヘイソクNOS, ショウチョウヘイソク
Czech Obstrukce tenkého střeva NOS, Obstrukce tenkého střeva
Hungarian Vékonybél obstructio, Vékonybél elzáródás, Vékonybél elzáródása, Vékonybél obstructiója, Vékonybél obstructio k.m.n.
Derived from the NIH UMLS (Unified Medical Language System)

Mechanical ileus (C0400843)

Concepts Acquired Abnormality (T020)
SnomedCT 46420000
English Mechanical intestinal obstruct, Mechanical ileus, Mechanical intestinal obstruction, Mechanical ileus (disorder), ileus; mechanical, mechanical; ileus
Italian Ileo meccanico
Japanese 機械的イレウス, キカイテキイレウス
Czech Mechanický ileus
Hungarian Mechanikus ileus
Dutch ileus; mechanisch, mechanisch; ileus, mechanisch ileus
Spanish íleo mecánico (trastorno), íleo mecánico, Ileo mecánico
Portuguese Íleo mecânico
French Iléus mécanique
German Mechanischer Ileus
Derived from the NIH UMLS (Unified Medical Language System)

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