21. Anaerobic gas infection

1. Definition

• Anaerobic gas infection (gas gangrene, clostridial myonecrosis) → rapidly spreading infection of muscle by toxin-producing clostridia, with gas formation, oedema, necrosis and severe toxaemia
• Non-clostridial anaerobic infection → mixed anaerobes with aerobes (Bacteroides, Peptostreptococcus); synergistic gangrene, necrotising fasciitis

2. Aetiology

• Clostridium perfringens (welchii) → 80–90% of cases
• C. novyi (oedematiens), C. septicum, C. histolyticum
• Gram-positive, spore-forming, obligate anaerobic rods
• Spores → soil, dust, human and animal intestine
• C. septicum → spontaneous (non-traumatic) gas gangrene in colorectal cancer and neutropenia

3. Conditions for development

• Devitalised muscle, low oxygen tension
• Deep, contaminated wounds → war wounds, gunshot, crush injuries, open fractures
• Soil, clothing, foreign bodies in the wound
• Ischaemia → arterial injury, tight plaster, tourniquet
• Delayed or incomplete primary surgical treatment
• Surgery on bowel, biliary tract, amputation for ischaemia
• Diabetes, peripheral arterial disease, intramuscular injections (adrenaline)
• Septic abortion
• Incubation period → 6 h to 3 days (usually < 24 h)

4. Pathogenesis: tissue processes

Toxins

• Alpha toxin (lecithinase, phospholipase C) → destroys cell membranes, haemolysis, myonecrosis, cardiac depression
• Theta toxin → endothelial damage, leucocyte destruction
• Collagenase, hyaluronidase → spread along tissue planes

Microscopic changes

• Muscle fibre necrosis with few neutrophils (toxins destroy leucocytes)
• Gas bubbles between fibres
• Large Gram-positive rods without spores in tissue
• Thrombosis of small vessels

Macroscopic changes

• Muscle → pale, then brick-red, then grey-green or black, does not contract or bleed when cut
• Gas and oedema → raise compartment pressure → further ischaemia (vicious circle)
• Spread along muscle groups, faster along the length of the limb
• Sweetish, mousy foul smell

5. Classification

By clinical form

1. Emphysematous (classical) → gas predominates
2. Oedematous (toxic) → oedema predominates, little gas; C. novyi
3. Mixed
4. Putrefactive → tissue liquefaction, foul smell
5. Phlegmonous → with pus; mixed flora

By depth

• Epifascial → clostridial cellulitis (anaerobic cellulitis); muscle spared, better prognosis
• Subfascial → myonecrosis, most dangerous

By spread

• Localised
• Spreading
• Fulminant

6. Clinical picture

Local manifestations

• Sudden severe bursting pain in the wound, out of proportion to signs
• Tense, swollen limb; tight dressing, bandage cutting into the skin (thread sign)
• Skin → pale and shiny, then bronze, then dark with haemorrhagic blisters
• Crepitus on palpation; tympanic note on percussion
• Scanty thin brown, foul-smelling discharge (dishwater fluid)
• Muscle bulging out of the wound, dull, not bleeding
• Shaving sign → crackling under a razor

Systemic manifestations

• Tachycardia out of proportion to fever → early sign
• Low-grade fever, then hypothermia in shock
• Apathy or euphoria, anxiety, then confusion
• Pallor, jaundice (haemolysis)
• Hypotension, oliguria → septic shock
• Multi-organ failure

7. Diagnosis

Laboratory

• Gram stain of exudate → large Gram-positive rods, few leucocytes
• Anaerobic culture
• Anaemia (haemolysis), leucocytosis
• Raised creatine kinase, myoglobinuria
• Metabolic acidosis, lactate

Imaging

• X-ray → gas in muscle (feathery pattern)
• CT → gas and fluid along tissue planes
• Surgical exploration → definitive diagnosis

8. Differential diagnosis

• Necrotising fasciitis → fascia and fat; muscle spared
• Clostridial cellulitis
• Gas from wound air or hydrogen peroxide (no toxaemia)
• Erysipelas, phlegmon
• Deep vein thrombosis

9. Treatment

Surgical

• Emergency radical debridement → excision of all dead muscle until it bleeds and contracts
• Wide longitudinal incisions (lampas incisions) through skin and fascia
• Fasciotomy → release compartment pressure
• Wounds left open; irrigation with hydrogen peroxide, oxidising agents
• Repeat inspection and debridement every 12–24 h (second look)
• Amputation → whole limb involved, extensive myonecrosis, fulminant course
  • Guillotine (open) amputation through healthy tissue, no sutures

Antibiotics

• Benzylpenicillin high dose intravenously + clindamycin (stops toxin synthesis)
• Add metronidazole or broad-spectrum cover for mixed infection

Supportive

• Intensive care → fluids, blood transfusion, vasopressors
• Correct acidosis, renal support
• Hyperbaric oxygen → adjunct after surgery where available; never delays surgery
• Polyvalent anti-gangrenous serum → historical, little evidence
• Tetanus prophylaxis

Prevention

• Early, complete primary surgical treatment of contaminated wounds
• Leave war and contaminated wounds open
• Prophylactic penicillin in high-risk wounds and amputations for ischaemia
• Isolate patients; sterilise instruments by autoclaving (spores)

10. Complications

• Septic shock, multi-organ failure
• Acute kidney injury, haemolysis
• Loss of limb
• Mortality → 20–30% with treatment, almost 100% without