Introduction
This topic covers anaerobic gas infections of soft tissues, mainly clostridial gas gangrene (clostridial myonecrosis) and related non-clostridial anaerobic necrotizing infections. It concerns rapidly progressive, toxin-mediated tissue destruction that is a surgical emergency and a classic oral exam subject.
Definition and aetiology
Anaerobic gas infection is an acute, rapidly spreading necrotizing infection of muscle and subcutaneous tissue caused by spore-forming anaerobic bacteria that produce gas and potent exotoxins. The main causative agent is Clostridium perfringens. Other clostridia involved include C. novyi, C. septicum, C. histolyticum and C. sordellii.
- Clostridia are Gram-positive, spore-forming obligate anaerobes present in soil, dust and the intestinal tract.
- Risk factors: deep contaminated wounds, crush injuries, gunshot and open fractures, retained foreign bodies, ischaemic limbs, and surgical or obstetric procedures (including septic abortion).
- Predisposing states: diabetes mellitus, peripheral vascular disease, malignancy and immunosuppression.
Pathogenesis
Spores enter the tissue with contamination. Tissue ischaemia and low oxygen tension allow the spores to germinate and the bacteria to multiply. The organisms then produce toxins and enzymes that cause the damage:
- Alpha-toxin (a lecithinase/phospholipase C), the principal virulence factor, which destroys cell membranes, causes haemolysis and muscle necrosis.
- Collagenases, hyaluronidase and DNase, which break down connective tissue and allow rapid spread along fascial planes.
- Gas production by fermentation of tissue sugars, which causes crepitus and tissue swelling.
- Toxins absorbed into the circulation cause haemolytic anaemia, intravascular haemolysis, jaundice, capillary damage, shock and multi-organ failure.