GI
Small Bowel Obstruction
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Small Bowel Obstruction
, Mechanical Ileus, Mechanical Bowel Obstruction
See Also
Bowel Obstruction in Terminally Ill Patient
Intestinal Obstruction
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
Causes
Volvulus
(most common)
Internal Hernia
(associated with prior Roux-en-Y bypass)
Congenital bands
Intestinal Malrotation
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 Movement
s cease
Dehydration results from
Vomiting
, minimal absorption, and bowel edema
Metabolic Alkalosis
and
Hypokalemia
Vomiting
:
Potassium
, chloride and
Hydrogen Ion
loss
Proximal renal tube resorbs bicarbonate (contraction alkalosis)
Bacteria
l overgrowth from intestinal stasis
Stool
forms within the
Small Bowel
(fecalization)
Foul
Emesis
(odor of feces)
Risk of bacteremia from
Bacteria
l 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
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
Gallstone
s in the bowel lumen
Foreign Body Ingestion
Causes
By Type
Obturation
Colonic Polyp
Intussusception
Children: Usually idiopathic
Adults: 95% have underlying mechanical cause
AIDS
may predispose to
Intussusception
Gallstone
s that have entered the bowel lumen
More common in those over age 65 years
Bezoar
Barium
Ascaris
infection
Tuberculosis
Actinomycosis
Diverticulitis
Intrinsic bowel lesions
Congenital anomalies (Pediatric)
Atresia
Stenosis
Bowel
duplication
Strictures
Inflammatory Bowel Disease
(e.g.
Crohn's Disease
)
Colon Cancer
Extrinsic bowel lesions
Adhesion
Abdominal or pelvic surgery
Appendectomy
Colorectal Surgery
Gynecologic procedures
Hernia Repair
s
Surgery in presence of peritonitis or
Trauma
Hernia
(higher risk for
Strangulation
)
Internal Hernia
s via mesenteric defects
External
Hernia
s abdominal wall
Obturator hernia
More common in emaciated elderly women
Small Bowel Volvulus
Rare compared to colon
Volvulus
More common in Africa, Middle East and India
Occurs in
Intestinal Malrotation
or adhesions
Idiopathic
Intestinal Obstruction
See
Bowel Pseudoobstruction
)
Symptoms
Classic presentation
Colicky Abdominal Pain
Nausea
and
Vomiting
Abdominal Distention
Cessation of
Flatus
and
Bowel Movement
s
Symptoms
Gene
ral
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
Nausea
and
Vomiting
Stool
passage
Initially may be present despite complete obstruction
Later, obstipation (no stool) in complete obstruction
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
Signs
Vital Sign
s: Dehydration vs
SIRS
Criteria (
Sepsis
)
Sinus Tachycardia
Hypotension
Bowel
sounds
Initial: High pitched, hyperactive bowel sounds
Later: 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
has greatest PPV
Rectal examination for blood
Diagnosis
Factors predicting
Bowel Obstruction
History of prior surgery
Constipation
history
Age over 50 years
Vomiting
Abdominal Distention
Hyperactive bowel sounds
Labs
Complete Blood Count
Leukocytosis
may be significant in bacteremia and intestinal perforation
Comprehensive Metabolic Panel
Hypokalemia
Contraction Alkalosis (dehydration)
Acute Kidney Injury
(increased
Serum Creatinine
)
Serum
Lactic Acid
Increased with bowel ischemia,
Sepsis
and dehydration
Imaging
Flat and upright (or decubitus) abdominal XRay
Indications
Consider abdominal XRay as first-line test in suspected Small Bowel Obstruction
However,
CT Abdomen
has largely replaced abdominal XRay when there are no delays (e.g. ED)
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
Upright or decubitus view: Air-fluid levels
Supine view findings in Small Bowel Obstruction
Sharply angulated distended bowel loops
Step-ladder arrangement or parallel bowel loops
Large Bowel
with minimal air
String of pearls sign (specific for obstruction)
Series of small pockets of gas in a row
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
Imaging
CT Abdomen
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
Test Sensitivity
: 90% for high grade SBO
However, much less sensitive in partial 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
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
Imaging
Other advanced imaging
Ultrasound
Abdomen
Consider in pregnancy, unstable patients or when
Bedside Ultrasound
is available
Unable to identify transition point
Test Sensitivity
previously approached 85% (however CT is typically performed instead in most cases)
However, intraluminal gas and increasing mean BMI/Body habitus results in decreasing efficacy
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)
Differential Diagnosis (Abdominal Pain, distention, Nausea, cessation of Flatus/stool)
Adynamic Ileus
(e.g. medication-induced such as
Opioid
s,
Tricyclic Antidepressant
s)
Ascites
Bowel Pseudoobstruction
(Ogilvie Syndrome)
Acute
Large Bowel
dilation with risk of dysmotility (e.g.
Diabetes Mellitus
,
Scleroderma
)
Bowel
Perforation
Ischemic bowel (superior mesenteric syndrome or
Mesenteric Ischemia
)
Gastroenteritis
Cholelithiasis
Cholecystitis
Pancreatitis
Peptic Ulcer Disease
Postoperative
Paralytic Ileus
Appendicitis
Myocardial Infarction
Pregnancy
Management
Conservative Therapy
Fluid Replacement
Intravenous Fluid Replacement
and maintenance
Electrolyte
replacement (e.g.
Potassium Replacement
)
Consider monitoring fluid output with urine catheter
Bowel
decompression
Nasogastric Tube
Long intestinal tube (eg. Cantor) offers no advantage
Surgical
Consultation
Antibiotic
Indications (Not for routine use)
Surgery planned
Bowel
ischemia or infarction
Bowel
perforation
Fever
and
Leukocytosis
at presentation
Cover
Gram Negative Bacteria
and
Anaerobe
s
Ciprofloxacin
and
Metronidazole
OR
Piperacillin
-Tazobactam (Zosyn)
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]
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 >48 hours despite treatment
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
Complications
Intestinal Ischemia
or infarction
Bowel
necrosis, bowel perforation and
Bacteria
l peritonitis
Hypovolemia
Complications of surgical intervention if needed
Fluid and
Electrolyte
imbalance
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
References
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]
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