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gas gangrene

Sunday 15 March 2009

Gas gangrene is a bacterial infection that produces gas within tissues in gangrene. It is a deadly form of gangrene usually caused by Clostridium bacteria (e.g. Clostridium perfringens). It is a medical emergency.

Gas gangrene can cause myonecrosis, gas production, and sepsis. Progression to toxemia and shock is often very rapid.

Clostridial gas gangrene is life threatening and is characterized by marked edema and enzymatic necrosis of involved muscle cells 1 to 3 days after injury.

An extensive fluid exudate, which is lacking in inflammatory cells, causes swelling of the affected region and the overlying skin, forming large, bullous vesicles that rupture.

Gas bubbles caused by bacterial fermentation appear within the gangrenous tissues. As the infection progresses, the inflamed muscles become soft, blue-black, friable, and semifluid as a result of the massive proteolytic action of the released bacterial enzymes.

On microscopic examination, there is severe myonecrosis, extensive hemolysis, and marked vascular injury, with thrombosis. C. perfringens is also associated with dusk-colored, wedge-shaped infarcts in the small bowel, particularly in neutropenic patients.

Regardless of the site of entry, when C. perfringens disseminates hematogenously, there is widespread formation of gas bubbles.

Pathophysiology

Gas gangrene is caused by exotoxin-producing Clostridial species (most often Clostridium perfringens, but less commonly C. septicum or C. ramnosum), which are mostly found in soil but also found as normal gut flora, and other anaerobes (e.g. Bacteroides and anaerobic streptococci).

The exotoxin is commonly found in C. perfringens type A strain and is known as alpha toxin. These environmental bacteria may enter the muscle through a wound and go on to proliferate in necrotic tissue and secrete powerful toxins. These toxins destroy nearby tissue, generating gas at the same time.

Other organisms may rarely cause gas gangrene (for example, Klebsiella pneumoniae in the context of diabetes).

A gas composition of 5.9% hydrogen, 3.4% carbon dioxide, 74.5% nitrogen and 16.1% oxygen was reported in one clinical case.

Treatment

Treatment is usually debridement and excision with amputation necessary in many cases.

Antibiotics alone are not effective because they do not penetrate ischaemic muscles enough to be effective. However, penicillin is given as an adjuvant treatment to surgery.

In addition to surgery and antibiotics, hyperbaric oxygen therapy (HBOT) is used and acts to inhibit the growth of and kill the anaerobic C. perfringens.

See also

- Clostridium perfringens