Necrotizing Soft Tissue Infection
You should remove the dressing and examine the wound for any signs of necrotizing fasciitis.
The term necrotizing fasciitis was coined in 1951 to describe all gas-forming and non–gas-forming necrotizing infections, both of which shared the common feature of fascial necrosis. Recently, the term necrotizing soft tissue infection (NSTI) has replaced the older terminology, as this encompasses all infections regardless of the depth of tissue involved.
Patients who are most at risk for NSTIs include individuals with diabetes mellitus, obesity, peripheral vascular disease, chronic kidney disease, and alcohol abuse. NSTIs present with pain out of proportion to the physical exam, anxiety, and diaphoresis within 48 hours of bacterial inoculation in a wound. Other classic findings include erythema, pain or tenderness beyond the margins of erythema, woody edema, crepitus, bronzing of the skin, grayish, or “dishwater” discharge from the wound, skin necrosis, bullae formation, induration, fluctuance, fever, and hypotension. For examples of these skin findings, see Figure 40-1. Unfortunately, many of these distinctive features are late findings that are indicative of severe, life-threatening infection. You should therefore have a high index of suspicion for this type of infection, especially in a patient who has an otherwise unexplained fever in the acute postoperative period. In those cases it is incumbent on you to take down the dressing and, using sterile technique, examine the wound and surrounding skin.
Images of several examples of characteristic physical exam findings of NSTI. Variations in the appearance of bullae overlying NSTIs. (Reproduced with permission from Knoop K, Stack L, Storrow A, et al. Atlas of Emergency Medicine. 3rd ed. New York: McGraw-Hill Education; 2010. Figure 12.8. Photo contributed by Lawrence B. Stack, MD.)
One of the hallmarks of NSTIs is a rapid progression of symptoms that can lead to death within hours. Delays in diagnosis and debridement are associated with a nine times greater mortality rate. It should be clear that any consult for a potential NSTI must be seen quickly, taken seriously, and be escalated to more senior residents or attendings should any suspicion of NSTI exist.
When evaluating a patient for an NSTI, it is essential to remember that the more dramatic physical exam findings associated with NSTIs are often not seen at the time of presentation, which can make differentiating them from non-necrotizing infections difficult. Edema and erythema are almost always present, but are very nonspecific. You should at a minimum mark out the boundaries of the erythema in order to characterize the rate of spread of the infection.
While the physical exam can be nonspecific or even misleading, there are other features characteristic of NSTIs that can aid in making an early and potentially life-saving diagnosis. A basic set of labs can be key and should not be overlooked. A white blood cell count of >15,400 cells/mm3 or a sodium level <135 mmol/L on admission to the hospital has an 80% positive predictive value and, if not present, an 80% negative predictive value, respectively, for NSTI.
Imaging studies may be useful but only in those instances where the patient is not decompensating and the diagnosis remains equivocal. Plain radiographs may show gas within soft tissues, although this is only present in one third of patients and a negative study cannot rule out NSTI. There are some data that suggest CT scans, with or without contrast, may be helpful in identifying characteristic features of NSTIs such as soft tissue gas and inflammatory changes. Although CT scans may have a role in diagnosing NSTIs, this has not yet been adequately studied. MRI has been shown to have a sensitivity of 90% to 100% in diagnosing NSTIs, but a specificity of only 50% to 80%. Because MRIs take such a considerable amount of time to obtain, the risks associated with delaying treatment drastically limit the utility of MRI in the evaluation of NSTIs. For examples of imaging studies that demonstrate NSTIs, see Figure 40-2.
Radiographic evidence of necrotizing soft tissue infections. (A) Plain radiograph that demonstrates gas in the soft tissue of the right lower extremity. (Courtesy of Susan Dufel, MD.) (B) CT scan demonstrating gas within the soft tissue of the neck as well as fat stranding that crosses fascial planes. (Reproduced, with permission, from Tintinalli JE, Stapczynski JS, Ma OJ, et al. Tintinalli’s Emergency Medicine. 7th ed. New York: McGraw-Hill; 2011. Figure 241-5.)
The gold standard in the diagnosis of NSTI is operative exploration. Operative findings consistent with necrotizing infection include tissue necrosis, lack of bleeding, foul-smelling discharge, and loss of normal fascial resistance to finger dissection. When there is any level of concern for NSTI and especially if a patient is showing signs of rapid clinical deterioration, the patient should be emergently taken to the operating room for exploration. The consequences of not doing so are far more severe than those associated with a negative exploration.
The treatment of NSTIs is based on four key principles: (1) immediate surgical debridement; (2) fluid resuscitation and correction of electrolyte and acid–base abnormalities; (3) antimicrobial therapy; and (4) support of failing organ systems. Early surgical debridement, as previously discussed, is the mainstay of treatment and has been shown to increase survival. Fluid resuscitation with crystalloids is necessary, as nearly all patients with NSTIs have intravascular volume depletion. Lactated Ringer’s solution is the crystalloid of choice since it is common for these patients to be acidotic. Electrolyte abnormalities should be corrected in the usual fashion. Antimicrobial therapy should be started immediately in cases of NSTI. Although they do not penetrate necrotic tissue and thus are not curative, they do decrease the systemic symptoms of infection and are an important adjuvant therapy. Given the rapid progression and extremely high morbidity and mortality associated with NSTIs, initial antibiotic coverage should be broad until culture results are available. Clindamycin should also be included in the initial antibiotic regimen, as it decreases the toxin production by Staphylococcus aureus, hemolytic Streptococcus, and Clostridium infections. Lastly, providing support for failing organ systems is essential in the ICU setting.
In summary, if you have any suspicion that a wound infection might be an NSTI, you should examine the wound closely, removing the original operative dressing if necessary. If you remain concerned about an NSTI, you must immediately notify your senior resident or attending in order to expedite the diagnostic workup and/or the possible emergency operation. While you wait for the resident or attending to call you back, you should start IV fluids and a broad-spectrum empiric antibiotic regimen that includes clindamycin.