Gangrene

What is gangrene?

Gangrene occurs when there is death and decay of body tissue. It is caused by a lack of blood supply and is most common in the lower limbs, but can occur in the upper limbs and intestine. Lack of blood supply is caused by three major mechanisms: infection, vascular or trauma.

Types of gangrene

There are two broad types. Wet gangrene is gangrene due to necrotising bacterial infections, including necrotising fasciitis. Wet gangrene should be distinguished from 'dry' gangrene, which is due to ischaemia.

Dry gangrene¹

• Results from diminished blood supply due to vascular problems - eg, peripheral arterial disease (especially consider if cardiac risk factors are present, such as smoking and diabetes mellitus).

• Other causes can be associated with vasculitis - eg, autoimmune conditions such as Raynaud's phenomenon or scleroderma. The area involved will become cold, dry and black and will eventually slough off.

Wet gangrene²

Necrotising bacterial infections are caused by three main bacterial subgroups:

• Polymicrobial necrotising infections often involve a mix of Gram-positive cocci, Gram-negative rods, and anaerobes, including clostridial species. They tend to affect the trunk and perineum, usually on a background of other medical problems, especially diabetes, and likely to be older adults. The initial injury to the skin may have been unnoticed.

• Group A beta-haemolytic streptococci (alone or associated with staphylococcal species). These tend to be locally aggressive and can lead to sepsis or toxic shock syndrome. generally occur in younger age grouped in better general health than those with polymicrobial infections. Entry of infection usually follows trauma, including surgery and intravenous drug use.

• Gram-negative marine organisms, such as Vibrio vulnificus. Rare causes of gangrene and mostly reported in warm coastal regions. Route of infection can be through an open wound exposed to water, or via ingestion of infected oysters. Systemic toxicity tends to occur early.

Gas gangrene is a particular subtype of wet gangrene.

Other specific types of gangrene³

• Cancrum oris (noma) is a rapidly progressive opportunistic infection most often affecting the mouth and face that occurs during periods of immune compromise. Noma can also cause tissue damage to the genitals.⁴

• Symmetrical peripheral gangrene occurs in a wide variety of medical conditions and presents as symmetrical gangrene of two or more extremities without large vessel obstruction or vasculitis.⁵

• Fournier's gangrene is a severe necrotising fasciitis of the external genitalia.^{6 7}

• Other forms of necrotising fasciitis.⁸

How common is gangrene? (Epidemiology)

There are few data, if any, on the prevalence or incidence of gangrene, which may reflect the fact that it occurs with accompanying conditions.

Gangrene symptoms (presentation)^{1 2}

Gangrene can affect any part of the body but most often affects the extremities, ie the fingers and toes. Gangrene can also affect the internal body organs, particularly the gastrointestinal tract.

• Fever.

• Loss of appetite.

• Tachycardia.

• Hypotension.

• Tachypnoea.

Symptoms/signs relating to area of involvement

Wet gangrene

• Swelling.

• Erythema in early stages.

• Pain.

• Discharge - may be frank pus.

• Foul-smelling odour.

• The area becomes black.

Dry gangrene

• Erythema may be present.

• Coldness and pallor in the affected region.

• Numbness.

• No discharge.

• The affected area may become brown and then black.

Investigations

• Blood tests: FBC, LFTs and renal function. Clotting screen and fibrinogen may be required in more severely ill patients. Blood glucose should also be measured.

• Microbiology samples: these may include swabs of the infected area in wet gangrene and also peripheral blood cultures (multiple samples are preferable).

• Imaging: local radiographs of the affected area may help detect the presence of gas, as seen in gas gangrene. CT or MRI scans may also be performed to determine the extent of involvement of the local area (especially if surgery is being considered).

• Specific tests: these are usually aimed at investigating the underlying cause. For example, an arteriogram is likely in dry gangrene.

Associated diseases

There are underlying diseases which can be associated with gangrene, and which should be looked for, especially if the cause of gangrene is unclear. They include:

• Atherosclerosis.

• Diabetes mellitus.

• Raynaud's disease.

• Peripheral arterial disease.

Gangrene treatment and management^{1 2}

This initially involves resuscitation with attention to airways, breathing and circulation. Once patients are stable they need to receive therapy for the gangrene, which can involve the use of antibiotics and surgical debridement. It is important to note that antibiotics may not penetrate the tissue involved but will help prevent spread of infection.

Wet gangrene

• Analgesia.

• Broad-spectrum intravenous antibiotics - eg, antipseudomonal penicillin, metronidazole and possibly aminoglycosides (check with local microbiologist).

• Surgical debridement.

• Amputation may be required if wet gangrene cannot be controlled.

Dry gangrene

• Requires restoration of blood supply to the gangrenous area.

• Amputation may be required if blood supply cannot be restored (although, if a small area is involved, auto-amputation may take place).

Other therapies

Hyperbaric oxygen therapy - this provides the patient with higher-than-normal levels of oxygen which will then pass to the gangrenous area and lead to faster wound healing. Hyperbaric oxygen therapy has been used successfully as adjunctive therapy for wound healing.^{9 10}

It is also important to assess cardiovascular risk (if appropriate) and institute risk-reducing measures.

Complications

These include sepsis and amputation.

Prognosis

Prognosis depends on the presence of other morbidity, the area of the body affected and the extent of gangrene. One quarter of patients will develop septic shock which has a high fatality rate. Early recognition and institution of treatment are associated with a relatively good outcome.

Prevention

Meticulous attention to care in patients at risk is needed. Thus, people with diabetes and those known to have peripheral vascular disease must be educated on watching for signs of infection and/or dry gangrene. These patients also need education about proper foot care.