Small bowel obstruction

Section: Small bowel Curriculum: Curriculum, page 58

General

• Most common surgical disorder of the SB
• Mechanical obstruction:
  • Physical obstruction to the progress of bowel contents
  • Complete or partial
• Non-strangulating:
  • 2% mortality
  • Mostly in elderly
• Strangulation:
  • 8% mortality if surgery within 36 hours
  • Thereafter 25% mortality
• Recurrent obstruction is uncommon after adhesiolysis

Aetiology

Extra-luminal

• Adhesions > 60% (1st)
• Congenital bands in children
• Post-op / post-inflammatory adults
• Neoplasm – 20% (2nd)
• Peritoneal Carcinomatosis
• Extrinsic neoplasms (17%)
• Hernias – 10% (3rd)
  • Internal
  • External
• Intra-abdominal abscess
• Endometriosis

Intra-Mural

• Inflammation
  • Crohn’s 5% (4th most common).
  • Infective: TB, Actinomycosis, Diverticulitis
• NSAID related strictures
• Neoplasm (intrinsic 3%)
• Ischaemic stricture
• Haematoma
• Intussusception
• Radiation enteropathy / strictures
• Congenital duplications/cysts

Intra-Luminal

• Foreign body/Bezoars
• Gallstone ileus
• Enterolith
• Cystic Fibrosis:
  • Chronic Partial Distal Intestinal Obstruction Syndrome (DIOS)

Pathophysiology

• Overview
  • Overview
  • Initial Insult
    • Increase motility and contractility, pain
    • Fatigued bowel - dilation
  • Downstream Effects
    • Electrolyte Disturbances
    • Hypovolaemia
    • Ventilation difficulty
    • Bowel ischaemia
    • Bacterial Translocation
• Breakdown
  • Initial Insult
    • Initial increase in intestinal motility and contractility
      • Accounts for initial diarrhoea of contents below the lesion
    • Later, intestine becomes fatigued and dilates with less frequent and intense contractions
    • Bowel dilates
      • Swallowed air is the major source of gaseous distention
      • Water and electrolytes accumulate intra-luminally and in bowel wall
      • Bidirectional salt flux is disrupted, net secretion is increased
      • Dehydration / Hypovolaemia
  • Electrolyte Disturbances
    • Depends on location of obstruction
      • Proximal Gastric Outlet Obstruction
        • Dehydration, low Cl-, low K+
        • Hypochloraemic, hypokalaemia, metabolic alkalosis
        • Due to excessive vomiting of acid rich gastric contents
          • Paradoxical acid urine due to preservation of K+ over H+ in renal tubules, further worsens alkalosis
      • Distal obstruction
        • Less dramatic electrolyte disturbance
        • Reflexive vomiting accentuates fluid and electrolyte disturbance
  • Hypovolaemia
    • Fluid filled small bowel leads to
    • Oliguria
    • Azotemia (hyperurea)
    • Haemoconcentration
    • Progression to hypotension/shock
  • Ventilation Problems
    • Ventilation impaired by
      • Increased intra-abdominal pressure
      • Decreased venous return
      • Elevation of the diaphragm
      • Respiratory complications are common
  • Ischaemia
    • Increased intraluminal pressure from distension
    • Eventually surpasses venous pressure causing oedema and congestion
    • Get decreased mucosal blood flow
    • Further increases parenchymal pressure until arterial pressure no longer sufficient to provide oxygen
    • Subsequent ischaemia ⇒ ATP pumps at the cell membrane fail
    • Necrosis and release of inflammatory mediators and toxins
    • Perforation and peritonitis
  • Bacterial Translocation
    • With ischaemia, the integrity of the enteroluminal barrier is compromised
    • Get a significant change in bacterial flora
      • NB: Usually almost sterile in jejunum and proximal ileum
    • Increased E. coli, Streptococcus faecalis and Klebsiella
    • Change the colour and odour of vomitus

Clinical Presentation

• Colicky abdo pain
• Lasts few seconds to minutes, typically 4-5mins
  • Less if distal
• Nausea and vomiting
  • More pronounced proximally
  • Faeculent in more distal complete obstruction with bacterial overgrowth
• Abdominal distension
• Obstipation
  • May be preceded by diarrhoea

History and Exam

• Vitals, hydration status
• Systemic signs of disease
• Crohn’s, malignancy etc
• Abdominal exam
  • Scars, distention, bowel sounds, peritonitis, hernias
  • Hyperactive bowel sounds early sign

Investigations

• Baseline bloods:
  • FBC (haemoconcentration, leukocytosis)
  • Hypochloraemic hypokalaemic metabolic alkalosis
• Plain x-ray: 60% accuracy
  • Ladder-like pattern of dilated small bowel loops with air-fluid levels
  • Colon devoid of gas unless enema, sigmoidoscopy, partial obstruction
  • Look for gallstones and gas in biliary tree
• CT: esp. for complete/high-grade obstruction
  • History of abdominal malignancy
  • Post surgical patients
  • Virgin abdomen
• Contrast series
  • More useful in recurrent obstructions to define obstructed segment and completeness
• Others
  • USS in pregnant patients
  • MRE useful in Crohn’s disease, radiation enteritis and NSAID related enteritis to identify degree and number of strictured areas
  • NB: No reliable distinction from simple obstruction and vascular compromise on clinical, lab or radiological grounds
    • 1/3 vascular compromise unsuspected on clinical grounds
    • Be concerned if fever, increased pain, bloody vomitus, abdominal tenderness and rigidity, leucocytosis, intraperitoneal fluid widens interloop spaces

Initial Management

• Aggressive fluid resuscitation and IV electrolyte replacement
• Sodium and potassium replacement (Hartmann’s)
• IDC
• May require HDU/ICU monitoring if large volumes
• Analgesia
• NG decompression (14F)
  • 90% successful at decompressing
• Consider Gastrograffin as an adjunct for decompression

Concerning Features/Indications for Surgery

• Fever
• Increased pain
• Bloody vomitus
• Abdominal tenderness and rigidity
• Peritonitis
• Leucocytosis
• Closed loop on CT
• Intraperitoneal fluid widens interloop spaces
• No improvement after 48hrs
• Virgin Abdomen

Operative Management

• Depends on pathology
  • Peritonitis requires an operation!
• Consider laparoscopy
• Assessing viability:
  • Completely release bowel segment
  • Warm wet pack for 15-20 minutes
  • Normal colour, peristalsis, pink (clinical judgement is 90% accurate)
  • May need a planned re-look at 24 hours
• Limiting Adhesions:
  • Good surgical technique
    • Gentle handling
    • Avoiding unnecessary dissection
    • Exclusion of foreign material
    • Removal of infectious and ischaemic debris
• Metastatic obstruction:
  • Bypass or resection
  • Long segments bypass may lead to functional short gut