Necrotizing Soft Tissue Infections, Emergency Medicine

Basics

Description

Necrotizing soft tissue infections (NSTI) are infections of any layer of the skin associated with necrotizing changes
- Usually spreads rapidly along tissue planes
Characterized by:
- Widespread fascial and muscle necrosis with relative sparing of the skin
- High mortality
- Systemic toxicity
Crepitant anaerobic cellulitis:
- Necrotic soft tissue infection with abundant connective tissue gas
Progressive bacterial gangrene:
- Slowly progressive erosion affecting the total thickness of skin but not involving deep fascia
Nonclostridial myonecrosis (synergistic necrotizing cellulitis):
- Aggressive soft tissue infection of skin, muscle, SC tissue, and fascia
Fournier gangrene:
- Mixed aerobic " anaerobic soft tissue necrotizing fasciitis of the skin of the scrotum and penis in men and the vulvar and perianal skin in women
Necrotizing fasciitis:
- Progressive, rapidly spreading infection with extensive dissection and necrosis of the superficial and deep fascia
Accounts for 500 " 1,500 cases per year in US
Often difficult to recognize
Incidence increases with:
- Age
- Smoking
- Chronic systemic disease:
  - Diabetes
  - Obesity
  - Peripheral vascular disease
  - Alcohol abuse
  - IV drug use
24 " 34% mortality
Also high morbidity:
- Amputations
- Renal failure

Etiology

Conditions that lead to the development of NSTIs:
- Local tissue trauma with bacterial invasion
- Local ischemia and reduced host defenses:
  - More frequently in diabetics, alcoholics, immunosuppressed patients, IV drug users, and patients with peripheral vascular disease
Type I NSTI:
- Polymicrobial
- Anaerobic and aerobic
- Include Fournier gangrene and Ludwig angina
- After surgical procedures
- Existing diabetes, peripheral vascular disease, chronic kidney disease, alcohol abuse
  - Compromised immune system
- Represent 80% of NSTIs
- Strep species are most common aerobes
  - Also staph, enterococci, and gram-negative rods
- Bacteroides are most common anaerobes
Type II NSTI:
- Monomicrobial
- Typically aerobic Streptococcus
- Often young, healthy patients
- Most common cause of "flesh eating " disease
- Methicillin-resistant Staphylococcus aureus (MRSA) species are becoming more common
Type III NSTI
- Least common NSTI (<5%)
- Rapidly progressive
- Clostridial myonecrosis is an example
- Usually following penetrating wounds or crush injuries
- Also can be seen after black tar heroin injection, skin popping, intestinal surgery, obstetrical complications
Bacteria involved include:
- Group A ²2-hemolytic streptococcus (GABHS)
- Group B streptococcus
- Staphylococci
- Enterococci
- Bacillus
- Pseudomonas
- Escherichia coli
- Proteus
- Klebsiella
- Enterobacter
- Bacteroides
- Pasteurella multocida
- Clostridium sp.
- Vibrio sp.
- Aeromonas sp.
- Fungi

Neonates: Omphalitis and circumcision are predisposing factors.
Risk factors for children:
- Chronic illness
- Surgery
- Recent varicella infection (58-fold increased risk of GABHS NSTI)
- Congenital and acquired immunodeficiencies

Diagnosis

Signs and Symptoms

History

Fever
Altered mental status
Chronic medical conditions
IV drug use
Skin:
- Rapid progression of pain and swelling of involved area
- In 1st 24 hr, rapid development of local swelling, heat, erythema, and tenderness
- 24 " 48 hr: Purple and blue discoloration, blisters and bullae develop (often hemorrhagic)
- Foul-smelling thin fluid (from necrosis of fat and fascia)

Physical Exam

Systemic toxicity:
- Fever
- Tachycardia
- Tachypnea
- Hypotension
- Altered mental status
Pain out of proportion to physical findings
Skin:
- Erythema
- Tense edema
- Grayish or other discolored wound drainage
- Vesicles or bullae
- Necrosis
- Ulcers
- Crepitus (pathognomonic but present in only 10 " 37% of cases)
- Pain that extends past margin of infection

Most common presenting symptoms
- Localized pain (97%)
- Rash (73%)
- Hypotension, altered mental status, and other signs of shock are much less common

Essential Workup

Diagnosis can be difficult
Careful exam for the aforementioned signs and symptoms in high-risk patients
NSTIs must be suspected in patients who appear very ill and have pain out of proportion to physical findings
Diagnosis may require incision and probing of tissue

Diagnosis Tests & Interpretation

Lab

CBC with differential
Electrolytes
BUN and creatinine
Disseminated intravascular coagulation panel
Calcium level: Hypocalcemia can develop from extensive fat necrosis
Gram stain and aerobic/anaerobic cultures of wound or tissue biopsy

Imaging

X-rays to detect soft tissue gas: Pathognomonic, but present in only 39 " 57% of cases
CT scan:
- May be more helpful than plain x-rays in detecting SC air
- May also identify deep abscess or other cause of infection
MRI:
- Can delineate extent of spread of the infection
US:
- Fascial thickening
- Fluid in the fascial plane
- SC soft tissue edema

Imaging of any kind should never delay surgical debridement
Diagnostic Procedures/Surgery

All patients with suspected NSTI must undergo surgical debridement
Deep incisional biopsy and cultures are the gold standard for diagnosis

Differential Diagnosis

Cellulitis
Gas gangrene

Treatment

Pre-Hospital

IV fluid resuscitation
Manage airway as necessary.

Initial Stabilization/Therapy

Manage airway and resuscitate as indicated:

Rapid-sequence intubation as needed
Supplemental oxygen, monitor, evaluate for acid " base disturbances
IV access, CVP line may be needed
Aggressive volume expansion including crystalloid, plasma, packed RBCs, and albumin

Ed Treatment/Procedures

Antibiotics: Broad coverage of aerobic gram-positive and gram-negative organisms and anaerobes
Acceptable combination therapy:
- Penicillin or cephalosporin + an aminoglycoside or fluoroquinolone + anaerobic coverage with either clindamycin or metronidazole
Treat methicillin-resistant Staphylococcus aureus (MRSA) until excluded:
- Vancomycin
- Linezolid
- Daptomycin
Surgical consultation:
- Early debridement of all necrotic tissue with fasciotomy and drainage of fascial planes is paramount
Hyperbaric oxygen as an adjunct:
- Early transfer to hyperbaric facility may result in greater tissue salvage
IV immunoglobulin (IVIG):
- Controversial
- May be beneficial in NSTI caused by group A streptococcal infection
Observe for major complications including acute respiratory distress syndrome, renal failure, myocardial irritability, and DIC

Clindamycin therapy should be initiated as soon as possible when group A strep infection is suspected

Medication

Ceftriaxone: 2 g (peds: 100 mg/kg/24 h; max. 4 g) IV q24h
Ciprofloxacin: 400 mg IV q12h
Clindamycin: 900 mg (peds: 40 mg/kg/d q6h) IV q8h
Daptomycin: 4 mg/kg IV q24h
Gentamicin: 2 mg/kg (peds: 2 mg/kg IV q8h) IV q8h
Doxycycline: 100 mg IV q12h
Imipenem/cilastatin: 250 " 1,000 mg IV q6 " 8h
Levofloxacin: 750 mg IV q24h
Linezolid: 600 mg PO/IV q12h (peds: 30 mg/kg/d PO/IV div. q8h)
Meropenem: 1 g (peds: 20 " 40 mg/kg up to 2 g/dose) IV q8h
Metronidazole: 500 mg (peds: Safety not established) IV q8h
Penicillin G: 24 million U q24h (peds: 250,000 IU/kg/24h) IV q4 " 6h
Piperacillin/tazobactam 3.375 " 4.5 g (peds: 240 mg/kg/d of piperacillin div. q8h) IV q6h
Tigecycline: Start 100 mg IV 1; 50 mg IV q12h
Vancomycin: 10 " 15 mg/kg IV q12h (peds: 10 " 15 mg/kg IV q6 " 8h)

First Line

Type I infections:
- Piperacillin/tazobactam + clindamycin + ciprofloxacin/levofloxacin
- Imipenem/cilastatin
- Meropenem
Type II infections:
- Clindamycin + penicillin (or linezolid or vancomycin)
Type III infections:
- Clindamycin + penicillin
Type IV infections:
- Doxycycline

Follow-Up

Disposition

Admission Criteria

All patients with an NSTI must be admitted for surgical debridement and IV antibiotics
Early hyperbaric oxygen therapy may be an important adjunct

Discharge Criteria
No patient with NSTI should be discharged
Issues for Referral
After stabilization with antibiotics and surgical debridement, consider referral for hyperbaric oxygen treatment as an adjunct.

Pearls and Pitfalls

The clinician must have a high index of suspicion for NSTI, as initial skin findings may be unimpressive
Pain out of proportion to exam may be a key finding
Mortality will be near 100% if treatment is ONLY with antimicrobials
Scoring systems for NSTI have limited utility
4 tenets of treating NSTI:
- Fluid resuscitation and management of metabolic disturbances
- Early antimicrobial therapy
- Surgical debridement
- Treating organ failure

Additional Reading

Anaya DA, Bulger EM, Kwon YS, et al. Predictingdeath in necrotizing soft tissue infections: A clinical score. Surg Infect(Larchmt). 2009;10:517 " 522.
Anaya DA, Dellinger EP. Necrotizing soft-tissue infection: Diagnosis and management. Clin Infect Dis. 2007;44:705 " 710.
Cainzos M, Gonzalez-Rodriguez FJ. Necrotizing soft tissue infections. Curr Opin Crit Care. 2007;13:433 " 439.
Jamal N, Teach SJ. Necrotizing fasciitis. Pediatr Emer Care. 2011;27:1195 " 1199.
Lancerotto L, Tocco I, Salmaso R, et al. Necrotizingfasciitis: Classification, diagnosis, and management. J Trauma Acute CareSurg. 2012;72:560 " 566.
Ustin JS, Malangoni MA. Necrotizing soft-tissue infections. Crit Care Med. 2011;39:2156 " 2162.

Codes

ICD9

608.83 Vascular disorders of male genital organs
728.86 Necrotizing fasciitis
785.4 Gangrene
729.99 Other disorders of soft tissue
616.89 Other inflammatory disease of cervix, vagina and vulva

ICD10

I96 Gangrene, not elsewhere classified
N49.3 Fournier gangrene
M72.6 Necrotizing fasciitis
M79.89 Other specified soft tissue disorders
N76.89 Other specified inflammation of vagina and vulva

SNOMED

52486002 Necrotizing fasciitis (disorder)
398318005 Fourniers gangrene
372070002 Gangrenous disorder (disorder)
443928008 Necrotizing soft tissue infection

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