What causes Gangrene ?

Written by Christian Nordqvist
Copyright: Medical News Today

Gangrene occurs when tissue dies (necrosis) because its blood supply is interrupted. Gangrene may be caused by an infection, injury, or a complication of a long-term condition that restricts blood circulation. It most commonly occurs in the extremities - the toes, fingers, arms and legs - but internal organs and muscles may also become gangrenous.

There are five main types of gangrene :
1. Dry gangrene.
2. Wet gangrene.
3. Gas gangrene.
4. Internal gangrene.
5. Fournier's gangrene.


What are the causes of gangrene ?

Our cells require nutrients and oxygen to survive and they get this from our blood. If their blood supply goes down below a certain level, the cells will become damaged and will eventually die.

Tissues and cells are also attacked by organisms such as bacteria, viruses, parasites and fungi. Our white blood cells and the Thymus cells (T-cells) form part of our immune system and fight germs. If the blood supply is cut there will be no white cells or T-cells to stop the organisms from multiplying and causing an infection.

What are the risk factors for gangrene ?

• Age - gangrene is much more common in older people.


• Diabetes - the high blood sugar levels, which are common in diabetes, may eventually damage the nerves, especially in the feet. When the nerves are damaged the patient does not feel pain and will not know if he/she has an injury. The patient may continue walking without protecting the wound. The wound may get worse and develop into a foot ulcer. High blood sugar levels may also damage blood vessels, resulting in poor blood supply to the area. Less blood means less nutrients and oxygen for the tissue cells, and fewer white blood cells and T-cells to fight off infection. The ulcer becomes infected; the infection grows rapidly and gangrene develops. The oxygen/nutrient deprived cells are weak and rapidly die.


• Vascular diseases - diseases of the blood vessels, such as atherosclerosis (narrowed arteries) and blood clots can result in poor blood flow to various parts of the body.


• Injury or surgery - anything which wounds the skin and tissues below it will raise the risk of gangrene. People with underlying conditions which may affect blood flow who also wound their skin run an even higher risk. Approximately 40% of wet gangrenes are caused by infections that occur during surgery and about 50% are caused by serious traumatic injuries. Gangrene from frostbite and gunshot wounds are less common than from automobile accidents, crush injuries, burns and industrial accidents.


• Weakened immune system - people with weakened immune systems, such as those with AIDS/HIV, patients receiving chemotherapy or radiotherapy, as well as organ transplant recipients who are on immunosuppressants, are more susceptible to the complications of infection, which include gangrene.


• Smoking - smoking causes the blood vessels to narrow, resulting in less blood flow.
  
  

What are the symptoms of gangrene ?

Symptoms of dry gangrene

Generally, dry gangrene develops slowly. It is the most common gangrene for patients with atherosclerosis and other vascular diseases.

• A red line appears on the skin which surrounds the affected tissue.
• The area will gradually become numb and cold.
• When necrosis (tissue death) occurs there may be some pain.
• Some patients, especially older ones, may feel nothing at all.
• The area will change from red, to brown, to black.
• The necrotized tissue then shrivels up and eventually falls off.
  
  

Symptoms of wet gangrene

Wet gangrene is much more painful than dry gangrene. The term 'wet' is used to refer to a bacterial infection in the affected tissue. It can develop as a result of an injury, a severe burn, or frostbite. This type of gangrene is common with diabetes patients who unwittingly injure a toe or foot. As it spreads rapidly and can be fatal it needs to be treated urgently.

• The affected area swells before any tissue dies.
• The skin will change color from red, to brown, to black.
• There will be pus and a foul smell.
• Fever (temperature).
  
  

Gas gangrene

Usually deep muscle tissue is affected. The surface of the skin may appear normal, but as the condition advances the skin may become pale, and then turn grey or purplish-red. Gas gangrene is usually caused by Clostridium perfringens bacteria. The bacteria multiply when the blood supply is depleted. The bacterial infection produces toxins that release a gas. Gas gangrene can become life-threatening.

• The affected area feels heavy and painful. The pain is caused by the infection which produces a gas.
• The skin may appear to bubble.
• A crackling sound when area is pressed. This sound is caused by the gas.
• Sometimes there may be a watery discharge which does not usually have a foul smell.
  
  

Internal gangrene

The most common organs to be affected are the intestines, gallbladder, or the appendix. An infected person may have more than one affected organ. Gangrene in the intestine may be the result of a hernia; when a part of the intestine bulges through a weakened area of muscle and becomes twisted.

Patients will experience fever and pain in the affected area. Internal gangrene can be fatal if left untreated.


Fournier's gangrene

This type is very uncommon. It affects the male genital organs. It is usually the result of a urinary tract infection or an infection in the genital area. The patient will feel pain, tenderness, and swelling in the affected area. Women can also develop Fournier's gangrene, but much less so than men. Approximately half of all people who develop this type of gangrene have diabetes.

Septic shock - if bacteria get into the bloodstream the patient may go into septic shock - the bacteria multiply in the blood and release a toxin which harms the organs and cells. Septic shock always results in a severe drop in blood pressure. The symptoms of septic shock include:

• Weak and rapid pulse
• Less urine flow
• Confusion
• Pale-looking skin (pallor)
• Cold and clammy skin (during the later stages)
  
  

How is gangrene diagnosed ?

For a proper diagnosis of gangrene the doctor will need to carry out a physical examination, study the patient's medical history, and order some clinical tests.

The GP (general practitioner, primary care physician) will firstly need to establish whether the patient has a chronic health condition, and whether any injuries may have caused the condition.

The doctor will check the affected area for skin coloration, any foul smell, and symptoms of pain.

The following tests may also be ordered :

• Blood test - if the number of white blood cells are high it could indicate that there is gangrene.


• Tissue/fluid culture - a sample of tissue or fluid from the affected area will be taken and tested for infection. When the test identifies the type of bacteria the doctor can better choose which antibiotic to use. The doctor may also look at a piece of tissue culture to determine the extent of tissue death.


• Imaging scans - MRI, CT, scans as well as X-rays may help to confirm not only the presence of gangrene, but also how much it has spread. An arteriogram can visualize the arteries and determine how well blood is flowing through the arteries - this helps the doctor identify any blockages.


• Surgery - in suspected cases of internal or gas gangrene surgery may be required to confirm a diagnosis.
  
  

What is the treatment for gangrene ?

Necrotized (dead) tissue cannot be saved, but a lot can be done to stop the gangrene from spreading.

• Surgery (Debridement)
  
  The surgical removal of dead tissue (debridement) helps prevent the gangrene from spreading, and allows healthy tissue to recover.
  
  Damaged or diseased blood vessels might also be repaired during surgery so that blood flow is restored to the affected area.
  
  Skin graft - if damage is extensive the surgeon may remove some healthy skin from one part of the patient's body and spread it over the affected area. Sacrificed skin is usually taken from a part of the body that is hidden by clothing. Skin grafts are only possible if the blood supply to the affected area is adequate.
  
  Amputation - if the gangrene is severe it is sometimes necessary to amputate the affected body part, for example a finger, toe, or limb.


• Imaging techniques
  
  Interventional radiologists can use angiography, an X-ray exam of the arteries and veins, to confirm loss of blood flow to a patient's hand or toes, then intra-arterial catheters to directly deliver drugs to dissolve the blood clots and relax the arteries' muscular walls resulting in better blood flow to the affected area. Radiologists in St. Paul Radiology in St. Paul, Minnesota say this technique is very effective.


• Antibiotics
  
  Antibiotics are administered to fight infection - these will usually be given intravenously.


• Hyperbaric oxygen therapy
  
  The patient will be placed on a padded table which slides into a special chamber. The chamber is pressurized with oxygen to about 2.5 times normal sea level atmospheric pressure. If the air pressure is high and oxygen rich more oxygen can be carried in the blood to the affected area. Bacteria require environments that lack oxygen to thrive. The oxygen chamber helps fight the bacteria and heal the wounds.


• Maggot therapy
  
  Maggot therapy is a non-surgical way of removing dead tissue. A type of maggot from fly larvae feeds on dead and infected tissue, but does not eat healthy tissue. They also release a substance which destroys bacteria. The maggots are specially bred in the laboratory. They are placed over the wound and covered with gauze and left there for a few days. Many studies have found that this therapy is often more effective than surgery. Sometimes doctors find it difficult to persuade patients to try it.


• Blood transfusions
  
  These may help reduce the infection and speed up the healing process.

Prevention

• Foot care - if you have diabetes regularly examine your hands and feet for cuts, sores and signs of infections. Get your doctor to examine you at least once a year.


• Smoking - don't smoke. Smoking damages the blood vessels, raising the risk.


• Treat cuts promptly - if you cut or graze your skin wash it with warm water and a mild soap and keep it clean and dry until it heals.


• Frostbite - if you have been out in the cold for a long time and your skin becomes pale, cold, and numb see a doctor.