נמק גז

Synonym: clostridial myonecrosis

זהו life-threatening bacterial infection with gangrene which has the following three features:

• Muscle necrosis

• אלח דם

• Gas production - usually a mixture of hydrogen, carbon dioxide, nitrogen and oxygen

These can rapidly lead to ספטיסמיה, septic shock and death.

Types of gas gangrene

Gas gangrene can be broadly grouped into:

Traumatic or surgical

Usually caused by direct inoculation with clostridia (especially Clostridium perfringens) but there are other causes too (see 'Pathogens', below).

Non-traumatic or spontaneous

• More rare and most often caused by Clostridium septicum.

• Seen in the setting of colonic neoplasms, immunosuppression or neutropenia.¹

• C. septicum from the gastrointestinal (GI) tract can pass via the blood to muscles (associated with a very poor prognosis). C. septicum is aerotolerant and can infect normal tissue.

אפידמיולוגיה

ה Clostridium species C. perfringens, C. septicum ו C. histolyticum are the principal causes of trauma-associated gas gangrene and their incidence increases dramatically in times of war, hurricanes, earthquakes and other mass casualty conditions.²

Pathogens

The vast majority of cases are caused by clostridia, especially C. perfringens.

• Clostridium spp. (found in soil and normal GI tract flora of humans and animals) - eg, C. perfringens, C. septicum, C. novyi , C. histolyticum

• Bacteroides spp.

• Anaerobic streptococci

The Infectious Disease Society of America has defined gas gangrene as an infection caused by Clostridium species. However soft tissue infections that produce subcutaneous gas have often been diagnosed as gas gangrene without identification of the presence of Clostridium species. The diagnosis has instead been based on clinical and radiological findings.³

פתופיזיולוגיה

In traumatic or surgical gas gangrene the pathogens enter through wounds, usually after contact with soil - eg, soil contaminated with faeces (not always so). The development of gas gangrene does not simply occur with the presence of Clostridium spp. - the environment has to have enough devitalised tissue present to support anaerobic metabolism.

The destruction caused by the pathogen is caused by the release of exotoxins. C. perfringens releases alpha toxin - which requires anaerobic surroundings to survive and thrive, and also theta toxin. This explains why hypoxic or poorly perfused tissue is attractive to these organisms.

The powerful toxins lead to breakdown of cells, coagulation and microvascular thrombosis and these can consequently add or contribute to rhabdomyolysis and acute kidney injury. The toxins also lead to haemolysis of red blood cells, cardiac depression and shock through vasodilatation.

Risk factors for gas gangrene

כוללים:

• כרוני alcohol abuse.

• תת תזונה.

• Trauma (eg, burns, crush injuries, open fractures), and large muscle involvement (eg, thigh).

• סוכרת.⁴

• Corticosteroid use.

• GI tract malignancy - eg, infection of perineum or scrotum from colonic seeding.

• Haematological disease with immunosuppression.

• Has been reported to follow intramuscular injections.⁵

• Features relating to the wound - eg. contamination with dirt or shrapnel.

• Abortion (especially criminal abortion).

הצגה

The incubation period varies from one to several days but symptoms may progress within hours.

• Initially - no skin changes - just pain.

• Systemic symptoms - eg, fever, dehydration.

• Once nerves are damaged, anaesthesia occurs.

• Paralysis.

• Skin changes - cellulitic progressing to dark purple; vesicles and bullae develop.⁶

• Subcutaneous air on palpation (may not be present early on).

• Foul-smelling discharge.

• Oedema.

• Necrotic or haemorrhagic tissue.

• Patients may also present in septicaemic shock with tachycardia, hypotension, fever, and stupor.

אבחנה מבדלת

זה כולל:

• פאשיאיטיס נמקית, in the early stages.

• Anaerobic צלוליטיס with myonecrosis.

חקירות

• FBC

• Renal function

• LFTs

• Creatine kinase

• Specimens from skin for culture - eg, vesicle exudate

• Immunological methods - provide more rapid diagnosis

• תרביות דם

• Arterial blood gas - patients may be acidotic

• Urine dipstick - query myoglobinuria

• Plain X-rays - will show gas in soft tissues⁶

ניהול

Gas gangrene is a rare and deadly infection that progresses very rapidly. Prompt diagnosis and treatment is therefore vital.⁷

• Supportive therapy - for example, analgesia, oxygen, intravenous fluids and good nourishment.

• Surgical - radical debridement of necrotic tissue (may require amputation if a limb is involved).

• Antibiotics - these do not work alone, as they are unable to penetrate the necrotic tissue. Cover Gram-negative, Gram-positive and anaerobes - eg, combination of penicillin, gentamicin and metronidazole.

• Hyperbaric oxygen therapy - kills anaerobic C. perfringens; however, efficacy has not been proven.⁸

• Tetanus toxoid may also be indicated.⁹

סיבוכים

• Multi-organ failure

• Spread to involve bone marrow¹⁰

• קרישת דם תוך-כלית מפושטת

תחזית

Mortality rates for patients with gas gangrene from trauma or surgery are as high as 25%, but increase to 50-80% for patients injured in natural hazards. This can be improved with better and more rapid recognition of the disease followed by early treatment of gas gangrene.¹¹