Gas Gangrene

  • AKA Clostridial Myonecrosis

Definition

  • Life threatening, rapidly progressive, necrotizing, gas-producing infection of skeletal muscle due to Clostridia
  • Characterised by
    • Massive muscle necrosis
    • Gas production
    • Due to invasive anaerobic Clostridial infection
  • Clostridial infections are
    • Cl perfringens (welchii)
      • gas gangrene
    • Cl tetani
      • tetanus
    • Cl botulinum
      • botulism
    • Cl difficile
      • pseudomembranous colitis

Epidemiology

  • Seen with
    • Open fractures
    • Penetrating wounds
    • War & farmyard wounds
    • Arterial insufficiency in an extremity
    • Surgical wounds
      • Bowel & Biliary surgery
      • Poor technique
  • USA 1000 cases/ year
  • 0.05% of open fractures
  • Need 3 things
    • Necrotic tissue
    • Especially buttock & thigh
      • Ischaemia with low PO2
    • Contamination with Clostridium perfringens or other histotoxic Clostridia
  • Greatly ↑ by
    • Poor debridement
    • Poor antibiotics
    • Primary wound closure

Aetiology

  • Clostridium perfringens (welchii) 80%
  • Clostridium novyi 15%
  • Clostridium septicum 5%

Clostridium perfringens

  • Large gram positive bacillus
  • Non-motile
  • Encapsulated
  • Obligate anaerobe
  • Produces spores
  • Found in soil & faeces
  • Ubiquitous
    • 20% of patients skin
    • Saprophytic commensal of GIT
    • Theatres & A&E

Exotoxins (histotoxins)

  • Production of large variety of toxins/ enzymes that result in myofascial spread
  • Necrotising & Haemolysing nature
  • Proteolytic or Sacrolytic
    • Based on Nagler reaction
  • Sweet or foul odour
  • 9 types
    • Most important is Alpha Toxin (Lecithinase)
    • Others include
      • Haemolysin
      • Collagenase
      • Hyaluronidase
      • Leucocidin
      • Deoxyribonuclease
      • Protease
      • Lipase

Vicious Cycle

  • Necrotic closed wound is contaminated
  • Clostridium colonization
  • Low PO2
  • Production of histotoxins
  • Destruction of cell wall
  • Local tissue death
  • Further colonization
  • Overwhelms WBC
  • Further tissue destruction

Pathology

  • Involved muscle rapidly undergoes disintegration & necrosis
  • Initially pale, swollen & inelastic
  • Later becomes discoloured & friable
    • Reddish purple then
    • Greenish purple & gangrenous
  • Gas in tissues
  • Histology shows coagulation necrosis

Clinical Features

  • Incubation
  • Usually ~ 2-3/7
  • Can be as short as 6/24

Symptoms

  • History muscle penetrating injury
  • Earliest & most sensitive symptom is pain
    • Pain/ heaviness out of proportion to injury or procedure
  • Initially alert & anxious
  • Later fearful of death

Signs

  • General
    • Pale & sweaty
    • Moderate fever
    • Marked tachycardia
    • Hypotension & shock follows
    • Delirium » Stupor » Coma » Death
  • Wound
    • Early
      • Skin swollen & white
      • Tense oedema & local tenderness
      • Serosanguinous & brown discharge
      • Foul or Sweet odour
      • ± Crepitus due to gas
      • Progress over 2-4 hours with advancing crepitus & oedema
    • Later
      • Bronze discolouration
      • Blebs containing dark fluid
      • Areas of green-black cutaneous necrosis

Investigations

  • Clinical diagnosis only

Laboratory

  • Positive blood culture in 15%
  • Gram-stain of exudate
    • Not diagnostic
    • Many organisms » Large gram positive rods
    • But few leukocytes & no spores
  • Positive Nagler’s test
    • Lecithinase turns egg yolk opaque in agar

XRay

  • Gaseous distension of muscle & fascial planes

Differential Diagnosis

  • Pain with myonecrosis is the key

Anaerobic Clostridial Cellulitis

  • Clostridial infection of necrotic soft tissue
    • Onset > 3/7
    • Poorly debrided wound
  • Gradual onset
  • Slight toxaemia & no pain
  • Slight brown, seropurulent exudate
  • No skin lesions
  • Foul gas +++
    • More than Clostridium myonecrosis
  • No muscle invasion

Streptococcal Myonecrosis

  • Group A ß Haemolytic Streptococcus
    • S pyogenes
    • “Flesh-eating bug”
  • Similar to Clostridium myonecrosis
    • Longer incubation period (> 3/7)
    • Characteristic pain not present
    • Little gas formation & profuse seropurulent discharge

Infected Vascular Gangrene

  • Due to saprophytic Clostridia
  • Proliferates & produces gas
  • Gangrenous muscle
  • Line of demarcation
  • No acute toxaemia
  • Can develop into Clostridial myonecrosis

Other Gas-Producing Organisms

  • Coliform Bacteria
  • Anaerobic Streptococcus
  • Anaerobic Bacteroids

Prophylaxis

  • Awareness
    • Open fractures
    • Deep penetrating injuries – buttock / thigh
  • Early meticulous surgical debridement
  • Leave wound open with no pack
  • Appropriate AB
    • Cephalothin
    • + Gentamicin if extensive
    • + Penicillin if farmyard, crush or vascular injury

Management

Surgery

  • Most important
  • Delay » Death
  • Emergency exploration
  • Examine muscles directly
    • Differentiate Myonecrosis from anaerobic Cellulitis (creputant cellulitis)
  • Appropriate debridement
    • Radical myoexcision
    • Fasciotomies
    • ± Amputation

Antibiotics

  • Penicillin G 3MU (1.8mg) q3h IVI
    • If allergic to penicillin
      • Metronidazole
      • Chloramphenicol
      • Tetracycline 2-4g/ day
    • Beware penicillin resistance (developing recently)
  • Gentamicin for co-infection with other organisms
  • Cephalosporins less effective

Resuscitation

  • Fluid loss +++
  • Prompt replacement
  • Monitor fluid balance

Hyperbaric O2

  • Controversial
  • 3 atmospheres for 60-90 minutes every 8-12 hours for 4-6 sessions
  • Appears to allow peroxides to develop & so destroy organism
    • Bacterostatic
    • Bacterocidal
  • Also appears to neutralise clostridial toxin
  • May reduce extent of debridement required
  • Hazards
    • Barotrauma
    • Decompression sickness
    • Convulsions
    • Otitis media
    • Lung damage
  • Useful where trunk involved
  • Don’t delay debridement to transfer to hyperbaric chamber

Prognosis

  • Mortality
    • WWI – 50%
    • WWII – 25%
    • 50% if reaches trunk