Necrotising Fasciitis

Necrotising fasciitis is a necrotising soft tissue infection predominantly involving the superficial fascial planes and adjacent subcutaneous tissue.

It may be polymicrobial or monomicrobial. Group A Streptococcus is particularly important because toxin mediated shock can progress rapidly despite initially limited skin changes.

Risk factors include diabetes, obesity, peripheral vascular disease, immunosuppression, recent surgery, penetrating injury and injection drug use, although healthy patients can develop fulminant streptococcal disease.

Pain out of proportion to superficial findings is the most important early clue.

Progression may produce:

• Rapidly expanding oedema and erythema
• Woody induration beyond the visible margin
• Bullae
• Ecchymosis
• Skin anaesthesia
• Dusky or necrotic skin
• Crepitus
• Fever, delirium and septic shock

Crepitus is not required. Streptococcal necrotising fasciitis frequently produces no visible gas.

Failure of presumed cellulitis to respond as expected should increase suspicion.

Do not wait for a scoring system or imaging if clinical suspicion is high.

CT or MRI: can demonstrate fascial oedema, fluid or gas when diagnosis remains uncertain in a stable patient, but operative findings are definitive and imaging must not delay exploration.

At surgery, grey necrotic fascia, little resistance to blunt dissection, lack of normal fascial bleeding and thin abnormal fluid are characteristic.

Send multiple deep tissue specimens for Gram stain, aerobic and anaerobic cultures.

Immediate surgical exploration and aggressive debridement are mandatory.

Start broad empirical coverage before culture results:

Piperacillin tazobactam 4.5 g IV every 8 hours by extended infusion

plus

Vancomycin IV, weight based and AUC guided for MRSA coverage.

For serious infection, vancomycin AUC should be targeted at 400 to 600 mg hour/L.

Where group A streptococcal or clostridial toxin mediated disease is strongly suspected, add:

Clindamycin 900 mg IV every 8 hours

because protein synthesis inhibition suppresses toxin production.

Once group A Streptococcus is confirmed, narrow to:

Penicillin G 4 million units IV every 4 hours

plus

Clindamycin 900 mg IV every 8 hours.

IDSA specifically recommends penicillin plus clindamycin for documented group A streptococcal necrotising fasciitis.

Debride all necrotic tissue during the first operation. Inadequate first debridement worsens outcome.

Return to theatre approximately 24 hours later, or sooner if physiological deterioration suggests continuing necrosis. Serial debridement continues until the wound is unequivocally viable.

Antibiotic duration is guided by operative source control and clinical response. IDSA recommends continuing treatment until no further debridement is required, the patient has clinically improved and fever has been absent for approximately 48 to 72 hours.

Do not delay surgery for transfer to imaging, hyperbaric therapy or laboratory confirmation. In necrotising fasciitis, time to definitive debridement is more important than diagnostic elegance.