Gangrene

Gangrene is necrosis and subsequent decay of body tissues caused by infection or thrombosis or lack of blood flow. It is usually the result of critically insufficient blood supply sometimes caused by injury and subsequent contamination with bacteria. This condition is most common in the extremities. The best of all possible treatments is revascularization (restoration) of the affected organ, which can reverse some of the effects of necrosis and allow healing. Depending on the extent of tissue loss and location, treatment other than revascularization runs the gamut from allowing digits to auto-amputate (fall off), debridement and local care, to amputation, the removal of infected necrotic tissues.

Types

Gangrene caused by a serious bacterial infection is called wet gangrene.
Gangrene caused by lack of circulation in an injured or diseased area is called dry gangrene.

One specific example of gangrene is so called diabetic foot that can be seen in long-standing complicated diabetes. It is caused by a combination of arterial ischemia, injury and poor healing that is rather common in diabetics. It often combines poor healing with a superimposed infection. The picture here is of a foot with a recent amputation of a great toe and yet increasing loss of circulation (the bluish area) with subsequent tissue loss to come. The most common surgical treatment for irreversible gangrene is immediate amputation, as the infection grows 2 to 3 cm per hour.

History

In the years before antibiotics, fly maggots were commonly used to treat chronic wounds or ulcers to prevent or stop necrotic spread. Some species of maggots consume only dead flesh, leaving nearby living tissue unaffected. Their use largely died out after the introduction of antibiotics and enzyme treatments for wounds. In recent years, however, maggot therapy has regained some credibility and is sometimes employed to great effect in cases of chronic tissue necrosis. See maggot therapy for more information.

Pathophysiology

Dry gangrene

If the blood flow is interrupted for a reason other than severe bacterial infection, the result is a dry gangrene. Persons with impaired peripheral blood flow, such as diabetics, are at greater risk for dry gangrene.

The early signs of dry gangrene are a dull ache and sensation of coldness in the area, along with pallor of the flesh. If caught early, the process can sometimes be reversed by vascular surgery. However, if necrosis sets in, the affected tissue must be removed just as with wet gangrene.

Gas gangrene

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

Gas gangrene is caused by exotoxin-producing clostridial species, which is mostly found in soil, and other anaerobes (e.g. Bacteroides and anaerobic streptococci). 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. A gas composition of 5.9% hydrogen, 3.4% carbon dioxide, 74.5% nitrogen and 16.1% oxygen was reported in one clinical case.^*

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

Treatment

Treatment is usually surgical debridement and excision with amputation necessary in many cases. Antibiotics alone are not effective because they do not penetrate ischemic muscles sufficiently. 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.