Gangrene is caused due to tissue death that results from stoppage of blood supply to the affected organ.
Blood vessels carry red blood cells that in turn carry life giving oxygen to all tissues. Blood also carries nutrients, such as glucose, amino acids, and fatty acids essential for the normal functioning of the tissues. The white blood cells in addition are fighters that fight against the invading bacteria.
Obstruction in blood flow thus results in deprivation of all these components necessary for normal functioning. As the blood supply is blocked the cells lose the ability to function and die. (1-5)
Blockage of blood supply
This blockage of blood supply may occur in three different ways –
- Damage to the blood vessels due to an underlying condition like diabetes, arteriosclerosis or peripheral artery disease.
While diabetes damages the smaller blood vessels, due to high blood sugar and resultant chemical reactions at the molecular level, both arteriosclerosis and peripheral artery disease lead to narrowing of the arteries.
- Infections leading to swelling of the affected organ and stoppage of blood flow. This is commonly seen in wet gangrene.
- Injury to the blood vessels coupled with infections. This is seen in traumatic gas gangrene.
Diabetes and gangrene
Diabetes further raises the risk of gangrene since gangrene develops as a complication of an open wound or sore.
Diabetics in addition have damaged small nerves of the hands and especially feet and toes called peripheral neuropathy. This makes them less sensitive to small injuries that may leave open sores prone to infections. Due to high blood sugar these infections refuse to heal and may lead to gangrene.
Causes of wet gangrene
Wet gangrene often develops as a result of a traumatic injury like an automobile accident, gunshot wound, burns or wound due to a sharp instrument.
The injury causes a sudden loss of blood to the affected area due to damage to blood vessels. This leads to infection and invasion by bacteria. Infections may also develop after a surgery. This is rare.
Gangrene and people with weak immune systems
People with a weak immune system are also prone to infections that may lead to gangrene. These people include:
- those with HIV AIDS
- those with cancer and on chemotherapy and radiotherapy
- long term alcoholics
- long term drug abusers
- those with severe malnutrition or deficient diets
- the overweight
- those with long term end stage kidney disease
Causes of gas gangrene
Gas gangrene was a common occurrence until the middle of the 20th century when war injuries were exposed to spores containing the causative bacteria present in soil. During the Civil War in the USA nearly half of the soldiers receiving gunshot wounds developed infection with many progressing to gas gangrene.
The primary organism causing gas gangrene is Clostridium perfringens. The spores of the bacteria are carried in animal feces and are present in the soil.
Other organisms that lead to gangrene in these conditions include Group A Streptococci and Staphylococci, C. histolyticum or other Clostridium spp. Gas gangrene has become uncommon in modern warfare due to better surgical management and treatment.
Traumatic gas gangrene is caused after a deep, penetrating injury like a knife or a gunshot wound or a car crash. This type of trauma accounts for about 70% of cases of gas gangrene and Clostridium perfringens is found in about 80% of such infections. Other organisms are:
- C. septicum,
- C. novyi,
- C. histolyticum,
- C. bifermentans,
- C. tertium
- C. fallax.
Necrotizing fasciitis (Type II) is also called streprtococcal gas gangrene and is caused due to group A streptococci. This is seen in those who have sustained an injury with a blunt instrument, after child birth, long term intravenous drug abuse or penetrating injury such as caused by a laceration or a surgical procedure.
Fournier’s gangrene is caused in the genitalia. It is caused by the Bacteroides spp. and peptostreptococci.
The spread of the infection is via gastrointestinal tract or via urinary tract. This type of gangrene is seen in diabetics.