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small bowel obstruction


  • SBOs can be partial or complete, simple (ie, non-strangulated) or strangulated (40%)).
  • strangulated obstructions are surgical emergencies. If not diagnosed and properly treated, vascular compromise leads to bowel ischemia and further morbidity and mortality.
  • a closed loop obstruction results from obstruction at two points which may result in strangulation and is a surgical emergency due to high incidence of associated bowel infarction and perforation.
  • after a laparotomy, lifetime risk of SBO is ~5%.
  • after surgery for lysis of adhesions, lifetime risk of subsequent SBO is ~12%.


  • adhesions (40-60%)
  • inguinal herniae (10-40%)
  • neoplasms (7-20%) & rare causes eg. gallstones, FB, diverticulitis
  • paediatric causes also include intussusception, and midgut volvulus (associated with duodenal bands and intestinal malrotation)

clinical features

  • the prime initial symptoms can easily be confused with acute gastroenteritis but there is usually no diarrhoea:
    • colicky central abdominal pain partly relieved by vomiting
    • large volumes frequent bilious green vomiting
  • examination findings
    • abdominal distension with tinkling bowel sounds
    • tenderness tends to be more focal than with large bowel obstruction
    • PR exam may reveal an empty rectum
  • later, obstipation may occur if it is a complete obstruction (ie. no passage or flatus or stools)
  • if not treated, life threatening bowel ischaemia / infarction may occur

Mx of suspected small bowel obstruction in the ED

initial clinical assessment

  • character of abdominal pain - generally central, periumbilical and colicky
  • vomiting - frequent bilious vs less frequent faeculant (suggests LBO)
  • abdominal distension (+/- absolute constipation, no passage of faeces or flatus]]
  • PH of abdominal surgery or small bowel obstruction is a major risk factor
  • look for herniae and check for strangulated or incarcerated herniae
  • assess for abdominal masses
  • PR exam - an empty rectum is supportive of the diagnosis
  • listen for bowel sounds - high-pitched tinkling bowel sounds suggests mechanical obstruction
  • urinalysis

initial Mx of suspected obstruction

  • iv fluids (0.9% saline)
    • initial resuscitative Rx generally 2L over first 2-6 hours, titrated to level of dehydration and cardiac function
  • take bloods for FBE, U&E
    • consider serum lactate and ABG if risk of ischaemic colitis
    • consider HCG if potentially pregnant
    • glucose if diabetic
    • take INR if patient on warfarin
    • consider blood cultures if temp > 38.5degC
  • iv analgesia as indicated (eg. morphine)
  • DO NOT order metoclopramide (Maxolon) prior to resolution of obstruction!
  • erect CXR and erect and supine AXR (consider decubitus film if unable to sit up)
  • consider CT abdomen with oral contrast
  • ECG if over 50 years or at risk of IHD
  • fluid balance chart
  • nil orally

AXR findings in small bowel obstruction

  • free gas under the diaphragm suggests a perforated viscus - contact surg reg ASAP
  • AXR features suggestive of small bowel obstruction:
    • multiple air fluid levels
      • number of loops depends upon level of obstruction
      • may also occur in gastroenteritis or other causes of ileus but in ileus, all parts of the gut are affected equally, and there are generally more fluid levels in ileus with a less orderly pattern
    • absence of colonic distension
    • a “step ladder” orderly appearance of small bowel loops with air fluid levels at unequal heights in the two limbs of each loop of small bowel on the erect view due to hyperperistalsis within the loop
    • “string of pearls or beads” indicating small amount of trapped, residual air in the fluid filled small bowel loops
      • NB. this is NOT pneumatosis (gas in bowel wall) which is a sign of ischaemic colitis
    • NB. if long standing and complete obstruction, no gas will be seen distal to the obstruction
    • NB. compare with large bowel obstruction

the "airless abdomen"

  • NB. the airless abdomen on AXR is abnormal and may be caused by either:
    • excessive vomiting &/or diarrhoea (eg. gastroenteritis)
    • early stages of appendicitis
    • adrenogenital syndrome in young infants
    • Addison's disease
    • conditions with impaired swallowing eg. cerebral depression.

the "sentinel loop"

  • NB. the “sentinel loop” - so called as it may be a sign of local inflammation
    • the loop is regarded as significant rather than a normal finding or just due to gastroenteritis if:
      • it is demonstrable in one general position from film to film - ie. it must persist and remain in the same region
    • a special form is that associated with the colon “cutoff” sign:
      • if occurs on the left transverse colon, then it suggests pancreatitis
      • if occurs on the right side, then it suggests perforated appendicitis
    • potential aetiology:
      • local inflammation:
      • closed loop obstruction - “coffee-bean” loop remains in a fixed position and is associated with evidence of mechanical obstruction +/- ischaemia/infarction
      • early SBO

"rule of threes" concerning normal small bowel on AXR:

  • wall thickness < 3mm
  • valvulae conniventes (normal transverse small bowel folds) less than 3mm thick
  • small bowel diameter < 3cm
  • less than 3 air fluid levels per radiograph


  • NGT removes air which is the intrinsic “contrast” on plain films
  • dilated loops filled only with fluid may not be visible on plain films
  • proximal obstruction may be difficult to diagnose on plain films

ED Mx of confirmed small bowel obstruction

  • notify surgical registrar ASAP and arrange admission
  • nil orally until decision re: surgery is made
  • strict fluid balance chart
  • iv fluids - maintenance plus replacement Rx
  • iv morphine as indicated
  • no metoclopramide prior to resolution
  • mobilise as tolerated
  • nasogastric tube insertion for all patients
    • free drainage with 4hrly aspirations
    • report increasing NG losses
    • if NG losses > 400ml in 4 hours, replace losses ml for ml with iv 0.9% saline in addition to maintenance requirements
  • consider IDC if dehydrated or impaired renal function
  • DVT prophylaxis as per surgical guidelines
  • attend to patient's usual meds

potential indications for emergent surgery

  • signs of peritonitis
  • bowel ischaemia
  • strangulated groin herniae
  • raised WCC or HR, or metabolic acidosis (base excess < -6)
  • colicky pain becomes constant
intraoperative antibiotics
  • single dose iv cephazolin 1g plus iv metronidazole 500mg at induction of anaesthesia - unless already commenced for Mx of peritonitis

non-operative Mx as inpatient

  • continue initial Mx
  • surgical review at least at 4 hours then every 8 hours in the 1st 24 hours
  • remove NGT
  • clear fluids orally then progress to diet
  • cease iv fluids
  • discharge when:
    • tolerating diet
    • has passed flatus or stool
    • home supports are in place
  • discharge planning:
    • outpatient F/U appt in 4 weeks
    • if virgin abdomen book small bowel XR series for prior to OP appt
    • sick certificate
    • provide written and verbal discharge instructions
    • discharge meds
no clinical improvement
  • CT abdomen with iv + oral contrast
    • prior to giving gastrograffin, aspirate NG tube then apply spigot
    • give 100mls gastrograffin orally or via NGT
    • leave NGT spigotted for 2-4 hours prior to performing CT scan BUT do not leave spigot in place > 4 hours even if CT has not been performed.
    • review CT findings and Mx accordingly
    • consider plain AXR the next day
  • consider laparotomy if complete obstruction or adverse features on CT scan
  • otherwise continue conservative Mx
sbo.txt · Last modified: 2021/01/20 10:24 by gary1

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