Necrotizing soft tissue infection is any infection of the soft tissue that is associated with necrosis requiring operative intervention. This usually occurs in the context of a critically ill patient. Necrotizing soft tissue infection is really a spectrum of disease, depending upon the level of the skin and subcutaneous tissue that is involved. There are various terms used including necrotizing cellulitis, which is generally a more superficial infection but still can cause significant necrosis. The traditional term, necrotizing fascitis, really refers to tracking in either the superficial or the deep fascial planes and often involves the subcutaneous fat, which is a relatively avascular area and therefor at high risk, particularly in the very obese patient. Even deeper infections can cause myonecrosis with significant destruction of the muscle.
The diagnosis is based on a constellation of symptoms, physical signs, and laboratory assessment. Pain out of proportion to the physical findings is the major symptom. This can sometimes be difficult to interpret,especially if the patient is already far down the course of their illness and does not have a clear mental status. Other signs include: an x-ray with a huge amount of gas in the soft tissue, tense edema, purple discoloration, and cutaneous gangrene. There may be blistering of the skin. Late signs include a patient in shock or with sever organ dysfunction. The laboratory signs to look at include: admission WBC (white blood count) greater than 15.4 or Na (sodium) level less than 135.
If you (the surgeon) are doubt, take the patient to the operating room for exploration down to the fascia level. Look for the ominous signs, such as some thrombosis of the microvasculature, dishwater fluid; or being able to push your finger along the deep fascial planes with no resistance. It has been shown that if you diagnose and treat the patient early (getting the patient to the operating room withing 24 hours), the mortality is about 30-36%. If diagnosis and treatment is delayed, the mortality rate nearly doubles (70%). Sometimes amputation of the infected arm or leg will be necessary.
The major principle in the management of these diseases, in any necrotizing process, is surgical management. The goal here is early intervention. The principle is wide debridement of all necrotic tissue. That often involves decompression of fascial planes and may require an amputation, which is a difficult decision to make at the first operation, but in many circumstances can be lifesaving. It is recommended that you should schedule a return to the operating room within 12 to 24 hours for repeat debridement, careful inspection of the wound, and evaluation for progression of necrosis. If the patient is clinically deteriorating, then take them back sooner than that. It is important to remember that you're going to create large wounds in these patients in order to get an adequate debridement. The subcutaneous necrosis often extends well beyond the skin changes, and really it cannot be appreciated until you are in the operating room. These wounds may require reconstruction later.
The second principle, after wide and frequent surgical debridement, is antimicrobial therapy. Empiric broad spectrum coverage is certainly warranted for these critically ill patients. You want to cover streptococci and clostridia, which are the most rapidly progressive of these organisms that are associated with necrotizing infections. It should be remembered that this is often a mixed infection, so it's important to cover the gram-negatives as well. Penicillin in high doses provides excellent coverage for streptococci and clostridia. Clindamycin is suggested for clostridia coverage. As a protein-synthesis inhibitor, clindamycin may both reduce toxin production and may also bind the toxin produced by clostridia which is thought to be responsible for the rapid decline of many of these patients. Gentamicin is usually added as the gram-negative coverage unless there is significant renal dysfunction, in which case a fluoroquinolone is used. Because of the emergent resistance pattern to MRSA, particularly in intravenous drug users, vancomycin may be warrented in these patients until culture results return.
These patients end up in the intensive care unit (ICU). There has to be good glycemic control and nutritional support. These patients are very hypermetabolic and have large wounds and high-protein needs (similar to burn patients). All these issues must be addressed.
Once the infection is controlled and the patient begins to stabilize and heal, then the issue of wound closure can be addressed. The clean wound really needs to 5-10 days old with appearance of clean granulation tissue. Then a skin graft, a flap, or wound suture can be done. If the patient continues to be unstable, alternative wound treatment such as continued wound dressings or the use of the a wound vac may be the best option.
Treating Severe Soft Tissue Infections: How and What I Do by Eileen M. Bulger, MD, FACS (Medscape article well worth reading)
Necrotizing Fascitis by Robert A Schwartz, MD--an eMedicine article
Necrotizing Fascitis--Wikipedia Article