Necrotizing infections

Necrotizing soft-tissue infections (NSTIs) are life-threatening, invasive, soft-tissue infections with a necrotizing component involving any or all layers of the soft-tissue compartment, from the superficial dermis and subcutaneous tissue to the deeper fascia and muscle. The latter is most commonly called “necrotizing fasciitis”

DIAGNOSIS

Delay in diagnosis and delay in treatment of these infections increase the risk of mortality.
Local signs
• Edema
• Erythema
• Severe and crescendo pain out of proportion
• Skin bullae or necrosis (at later stage)
• Swelling or tenderness
• Crepitus

Systemic signs:
• Fever
• Tachycardia
• Hypotension
• Shock

A rapidly progressive soft-tissue infection should be treated as a necrotizing infection, from the beginning. The clinical picture may worsen very quickly, sometimes during a few hours.

Lrinec score. Laboratory Risk Indicator for Necrotizing Fasciitis

Variable (units)Score points
C-Reactive Protein (CRP) (mg/L)
<1500
≥1504
White blood cell count (per mm3)
<150
15-251
>252
Hemoglobin (g/dl)
>13.60
11-13.51
<10.92
Serum Sodium (mmol/L)
≥1350
<1352
Serum Creatinine (mg/dl)0
≤1.60
>1.62
Serum Glucose (mg/dl)
≤1800
>1801

With a score of 8 or higher, there is a 75% risk of a necrotizing infection.

Imaging
• CT
• MRI
• US

Computed tomography (CT) has a higher sensitivity than plain radiography in identifying early necrotizing infections. Findings consistent with necrotizing infections are fat stranding, fluid and gas collections that dissect along fascial planes, and gas in the involved soft tissues. Additionally, fascial thickening and non-enhancing fascia on contrast CT suggests fascial necrosis.
Magnetic resonance imaging (MRI) has been the imaging modality of choice for necrotizing fasciitis. However, MRI may be difficult to perform under emergency conditions and is not recommended as the first-choice imaging technique.
Ultrasound has the advantage of being rapidly performed at bedside and may be helpful in differentiating simple cellulitis from necrotizing infections.

TREATMENT

Surgical source control as soon as possible, but at least within the first 12 h after admission
and
Antibiotic therapy

Empiric antibiotic regimens. Normal renal function
The initial empirical antibiotic regimen should comprise broad-spectrum drugs including anti-MRSA and anti-Gram-negative coverage. Antitoxin active antibiotics such as clindamycin or linezolid should be included in the empirical antibiotic regimen of necroticzing infections.

In stable patients

Amoxicillin/Clavulanate 1,2-2,2 g 6-hourly

+

Clindamycin 600 mg 6-hourly

In unstable patients

One of the following antibiotics

Piperacillin/tazobactam 4.5 g 6-hourly

Meropenem 1 g 8-hourly

Imipenem/Cilastatin500 mg 6-hourly

+

One of the following antibiotics

Linezolid 600 mg 12-hourly

Tedizolid 200 mg 24-hourly

or

another anti MRSA-antibiotic as

Vancomycin 25–30 mg/kg loading dose then 15–20 mg/kg/dose 8-hourly

Teicoplanin LD 12 mg/kg 12-hourly for 3 doses, then 6 mg/kg 12-hourly

Daptomycin 6-8 mg/kg 24-hourly*

Televancin 10 mg/kg 24-hourly

+

Clindamycin 600 mg 6-hourly

*Approved at the dosage of 4 mg/kg/24 h, it is currently used at higher dosages