Necrotising Soft Tissue Infection

Necrotising soft tissue infection is a rapidly progressive infection causing necrosis of subcutaneous tissue, fascia or muscle.

It is an umbrella term that includes necrotising fasciitis, Fournier gangrene and necrotising myositis.

The central principle is that suspected necrotising infection is a surgical diagnosis and surgical emergency. Antibiotics cannot penetrate or sterilise devitalised tissue adequately without debridement.

Infection may be polymicrobial or monomicrobial. Important organisms include group A Streptococcus, Staphylococcus aureus, anaerobes, Enterobacterales, Clostridium species, Vibrio vulnificus and Aeromonas species depending on exposure and host factors.

Early disease can resemble cellulitis.

High value warning findings are:

• Severe pain disproportionate to visible skin changes
• Rapid progression over hours
• Oedema or tenderness extending beyond erythema
• Hard or woody subcutaneous induration
• Bullae or ecchymosis
• Skin anaesthesia
• Crepitus
• Skin necrosis
• Severe systemic toxicity or shock

Normal appearing skin does not exclude deep fascial disease.

Diagnosis is primarily clinical and operative.

Laboratory scoring systems such as LRINEC do not reliably exclude disease and should never delay exploration when clinical suspicion is high.

CT: may show fascial oedema or gas and can define disease extent in a stable uncertain case, but imaging must not delay theatre.

Definitive diagnosis is made by surgical exploration showing necrotic fascia, thin abnormal fluid and easy blunt separation of tissue planes.

Obtain deep tissue and fluid cultures at operation. Superficial swabs are inferior.

Call surgery immediately.

Begin sepsis resuscitation and administer broad spectrum antibiotics as soon as possible, but do not delay debridement.

A practical adult empirical regimen is:

Piperacillin tazobactam 4.5 g IV every 8 hours by extended infusion

plus

Vancomycin IV, generally loading 20 to 35 mg/kg using actual body weight in critically ill patients, maximum 3 g, followed by AUC guided maintenance therapy targeting 400 to 600 mg hour/L.

An alternative where vancomycin is unsuitable is linezolid 600 mg IV every 12 hours, depending on microbiology, drug interactions and local protocol.

Emergency radical debridement is the definitive treatment. Excise all necrotic skin, subcutaneous tissue, fascia and muscle until viable bleeding tissue is reached.

Do not perform limited cosmetic debridement in rapidly progressive disease.

Patients usually require planned re exploration. IDSA advises return to theatre approximately 24 to 36 hours after the first debridement and repeatedly thereafter until no additional necrotic tissue remains.

Antibiotics are narrowed when deep operative cultures identify the pathogen.

Critical care management includes haemodynamic support, renal support when required, glycaemic control, aggressive nutrition and repeated assessment for ongoing necrosis.

Hyperbaric oxygen must never delay debridement.