London Hyperbaric Medicine

Necrotizing (anaerobic) Soft Tissue Infections

Anaerobic soft tissue infections are life-threatening infections. Although they are uncommon nowadays, they remain severe conditions because often associated with major organ failure leading to patient death if not promptly recognised and aggressively treated. Their origins are often traumatic or surgical but they can also develop from an ulcer or small wound in patients at risk. Such patients can include diabetics, patients with peripheral vascular disease.

Infections which may be treated with Hyperbaric Oxygen include:

Necrotizing fasciitis
Progressive bacterial gangrene
Non-clostridial myonecrosis
Fournier's gangrene
Crepitant anaerobic cellulites

Anaerobic soft tissue infection of right arm (after initial aggressive surgery)

Gangrenous leg

Anaerobic soft tissue infection of left leg (before surgery)

Causes	Tissue hypoxia, traumatic muscle injury and bacterial contamination are major causes. These infection can affect widespread areas involving various parts of the body and is mainly caused by Clostridial bacteria
Clostridial myonecrosis	Clostridial myonecrosis (‘gas gangrene’) is caused by anaerobic bacteria, which thrive in low oxygen levels. This occurs in: Direct injury to an artery Arterial obstruction by foreign body Haemorrhage Micro vascular disease (atheromatous plaques) Often, there is also reduced immunity, from chronic illness or malnutrition. The bacteria include clostridium perfringens (‘welchii’) in 80-95% of these infections, although there are often other clostridial bacteria, as well as non-anaerobic bacteria mixed with them. Clostridium perfringens functions at different levels, depending on oxygen availability.
Symptoms	After the initial trauma, a short period of incubation usually follows. Local signs include: Pale and non-healing wound Sharp local pain Local paresthesias A feeling of fullness in the area. The area soon becomes swollen and painful. The infection develops rapidly. The alpha-exotoxin, produced by the clostridial bacterium, causes local toxicity, including tissue necrosis and haemolysis. It also affects other organs of the body, causing: Renal failure Cardiotoxicity Cerebral toxicity Adult Respiratory Distress Syndrome (ARDS) Haemolysis Coagulopathy Other toxins (q,k,µ) are produced by the bacteria: these may cause local and distant harm. When incised during surgery, the tissue is pale, necrotic and there is little bleeding. A cloudy exudates is normally present. Multiple thromboses cause extensive oedema and severe local hypoxia. Radiography of the soft tissue can show gas bubbles or ‘feathering’ tissue
Necrotizing faciitis	Necrotizing faciitis sometimes called Fourniers gangrene (for scrotum and penis). Subcutaneous (anaerobic) infection spreading along the deep fascia (layer covering the muscles), causing secondary skin lesions and sparing muscles until the late stages of the infection.Symptoms as described above.
Treatment	Septic shock, acute kidney, or respiratory failures sometimes associated with these conditions require conventional intensive care treatment. Antibiotic Therapy - Penecillin is the antibiotic of choice for treating and preventing anaerobic infections. Surgery - Before antibiotics, mutilating surgery, involving amputation at the root of the limb, could save a patient's life if carried out early on before the infection spread. With the development of antibiotics and HBO therapies, surgery is now used to eliminate necrotic tissue and reduce oedema related compression. Hyperbaric Oxygen Therapy - The management of these infections includes Hyperbaric Oxygen, adjunctive to general resuscitation, intensive care, surgery and antibiotics. The order in which they are given is dictated by the patient’s condition; however, if Hyperbaric Oxygen can be given before or during surgery, the patient’s general condition can be improved by reducing the level of exotoxin. The use of Hyperbaric Oxygen is determined by the patient’s general condition rather than the local infection. Hyperbaric Oxygen: Directly inhibits action of a-toxin Inhibits the secretion of exotoxin Directly damages anaerobic bacteria Promotes white-cell (leukocyte) activity Decreases oedema, by causing constriction of arterioles Promotes the formation of new blood vessels into the recovering tissues Promotes the action of aminogycoside antibiotics (such as gentamicin)
Duration of HBO treatment	Standard treatment at LHM involves 2-4 sessions of Hyperbaric Oxygen Therapy administered on a daily basis, before and after surgery. Individual sessions last approximately 2 hrs 45 minutes with patient breathing oxygen for 150 minutes at 3.0 atmospheres.
Evidence/References for HBO	1.Bakker D.J. ‘Pure and mixed aerobic and anaerobic soft tissue infections. Classification and role of Hyperbaric oxygen treatment. HBO Rev., 1985, 6, 65-96 2. Mathieu D. (Ed.) Handbook on Hyperbaric Medicine, 263-289. Springer 2006