GenSurg.nz

Necrotising faѕciitiѕ

Definition

  • A life threatening clinical syndrome of aggressive bacterial infection of soft tissues with progressive tissue necrosis
  • Predominantly affecting deep fascia & subcutaneous tissue layers
  • a.k.a. “Flesh-eating bacteria”, suppurative fasciitis, hospital gangrene, necrotizing erysipelas, haemolytic streptococcus gangrene

Incidence

  • 0.4 cases per 100,000
  • Increasing incidence
  • M > F 2-3:1
  • Mean age 38-44
  • Rare in children

Classification

  • Type 1 – Polymicrobial
  • Type 2 – Monomicrobial

Type 1

  • Polymicrobial
    • Average 4 micro-organisms
  • Anaerobes and Aerobes work synergistically
    • Anaerobic species
      • Most commonly Bacteroides, Clostridium, or Peptostreptococcus
    • Enterobacteriaceae
      •  Escherichia coli, Enterobacter, Klebsiella, Proteus
    • Facultative anaerobic
      • Streptococci - other than group A Streptococcus 
  • More common in trunk & perineum
  • More common in
    • Immunocompromised
    • T2DM
    • PVD

Type 2

  • Monomicrobial:
    • Gram positive Cocci
      • Group A Strep (S. pyogenes – Beta- hemolytic)
        • Group A strep is associated with higher rate of bacteremia & TSS
          • Hence more rapid progression
      • Staphylococcus aureus
    • Gram negative rods
      • Aeromonas species (Aeromonas hydrophila)
        • Freshwater exposure
      • Vibrio species (Vibrio vulnificus)
        • Salt water exposure

Risk Factors

  • DM
  • PVD
  • Immunosuppression
  • Smoking
  • IVDU
  • Obesity
  • Chronic renal failure
  • Alcohol abuse
  • Trauma
  • Insect bites/animal bites
  • Surgical incision
  • Chickenpox
  • Indwelling catheters
  • Perforation of GI Tract

Clinical Presentation

  • HIGH INDEX OF SUSPICION = KEY TO DIAGNOSIS
    • Erythema 66-100%
    • Pain or tenderness beyond margin of erythema 73-98%
    • Swelling 75-92%
    • Crepitus or skin necrosis 13-31%
    • Bullae 23-42%
    • Fever 32-53%
    • Hypotension 11-18%
    • 10-40% - Hx of trauma or break in skin
  • May present as fulminant, acute or sub-acute
    • Patients with fulminant disease progress to shock
  • Earliest clues
    • Local pain out of proportion to the apparent severity of cellulitis
    • Erythema and oedema - spreading diffuse inflammatory reaction, that blends into the surrounding tissue
    • Overlying skin is shiny & tense, without sharply demarcated borders
    • Speed of spread
    • Skin may be anaesthetic
    • Crepitus may be present (late)
      • Gas: Clostridium, E. coli, Peptostreptococcus, Bacteroides
  • Low grade fever, tachycardia = Common
  • Patients anxious & sweaty
  • In later stages: Skin necrosis may become evident → Skin turns purple / black
    • Manifests sooner in areas of thinner skin (perineum)
  • In adults: limbs most commonly affected
  • 14-35% initially diagnosed as simple cellulitis or abscess

Pathology

  • Infection usually begins through a break in the skin
    • Bacteria spread through tissue
    • Aided by Endotoxin (components of bacterial cell membranes that illicit an inflammatory response), Exotoxin (compounds secreted by bacteria) & enzymes
      • Hyaluronidase, Collagenase, Streptokinase, Lipase
      • Enable horizontal extension through fascial planes
    • Get necrosis & thrombosis of vasculature
    • Further spread, facilitated by ischaemic microcirculation
      • Develop ischaemic necrosis
    • Disturbance of host humoral and cellular immune response
      • There is systemic response with an exaggerated inflammatory response caused by cytokines TNFa and IL-1, IL-6
    •  Infection spreads along the muscle fascia due to its relatively poor blood supply
    • This results in multi-organ dysfunction, shock, DIC, Death.
  • Clostridium
    • Releases α toxin
  • Group A Streptococcus
    • Surface M proteins
      • Inhibits phagocytosis/opsonization by complement
    • Many Exotoxin including Spe A, C, G, Streptolysin O, Streptococcus Superantigen (TSS)
      • Trigger cascade of cytokines by activating T-Cells and Macrophages
      • Strep toxins trigger profound cellular/tissue damage
  • Staphylococcus
    • Toxic shock syndrome toxin-1
      • superantigen
    • Staphylococcal enterotoxins A, B, C, D, E, G, H
    • Staphylococcal hemolysins

Investigations

  • Clinical diagnosis
  • Bloods: FBC, UEC, CRP
    • If both WCC & serum Na are normal, necrotising fasciitis is unlikely
      • (NPV = 99%)
  • X-ray: May demonstrate air (?50% sensitive)
  • CT: 80% sensitivity (even without IV contrast)
  • MRI more sensitive but less specific – fascial enhancement
  • USS no good
  • Bedside FNA, incisional biopsy for culture – high false –ve rate
  • LRINEC score
  • At operation – “the finger test”

LRINEC Score

  • Biochemical scoring system based on a retrospective observational study
    • Gives probability of necrotizing soft tissue infection
  • Points for
    • CRP
    • WCC
    • Hb
    • Na+
    • Creatinine
    • Glucose
  • Score of ≥ 6 used as a cut-off for nec fasc
    • PPV 92%, NPV 96%
    • Note 10% of patients with nec fasc had LRINEC <6!
  • Must use with caution
    • No prospective trials validating LRINEC
    • Validation studies have not replicated same results as original study

Operative Test

  • “Finger Test”
  • 2cm incision in skin, to deep fascia
  • Lack of bleeding / exudate
  • Insert index finger, if subcutaneous tissue is easily dissected off the fascia (to which it is normally densely adherent), the test is +ve
    • Pathognomonic for necrotizing fasciitis
  • Liquefactive necrotic tissue or pus (“dishwater”) can also be found in between the fascial planes

Management

  • Resuscitation
  • Broad spectrum antibiotics (as per local guidelines)
    • UTD recommends
      • Carbapenem (Meropenem 1g IV Q8hrs), or Tazocin
      • anti-MRSA – Vancomycin
      • Clindamycin (antitoxin effects)
  • Te Whatu Ora Waitemata Guidelines:
    • Benzylpenicillin 2.4g (4MU) IV Q4Hly
    • Clindamycin 600mg IV Q8H
    • Gentamicin as per dose guidelines
    • Can tailor further therapy to culture sensitivities
      • e.g. Penicillin + Clindamycin/Metronidazole
      • +/- Gentamicin for gram negatives
  • Surgical debridement
  • ICU care

Surgical Debridement

  • Beyond margins of infection
    • Boundary should be as wide as rim of cellulitis, back to healthy bleeding tissue
    • Most important determinant of mortality is time & adequacy of debridement
  • x 9 increase in MR if delayed > 24 hours
  • x 7 increase in MR if debridement incomplete
  • ± Relook / serial debridement
    • Average of three needed – 12-36 hours apart
  • ± Fasciotomy
  • Amputations needed in 20%
  • Staged reconstruction of defects
  • Vac dressing
  • May require grafting

ICU Care

  • Fluids (aggressive)
    • Avoidance of vasopressors if possible
  • Nutritional support
  • ± Hyperbaric Oxygen
    • ?↓ mortality (conflicting reports in literature, data limited)
    • 100% oxygen at 2.8x atmospheric pressure for 95mins up to 3x/day for 6 days
    • Arterial oxygen 2000mmHg (versus 300mmHg in normobaric)
    • Tissue oxygen 300mmHg versus 75mmHg
    • Used to target anaerobes (Clostridium etc.)
    • In theory inhibits anaerobic growth & exotoxin production & enhance killing abilities of leucocytes

Prognosis/Natural History

  • Mortality rates: 30-50%
    • Higher mortality if head, neck, chest or abdo are involved
  • Predictors of Mortality
    • Time to operative intervention
    • Age > 60
    • WCC > 30
    • Creatinine > 200
    • Shock
    • DM

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