Necrotizing soft tissue infections

Background

Fasciitis

1. does not involve muscle- but can spread to muscle
2. syst toxicity
3. skin c blebs, crepitus, necrosis
4. risks- dm, pvd, trauma or recent surg
5. pain varies since nerve endings damaged- cessation or absence of pain may indicate worsening sxs
6. necrosis of fat can lead to soapanification and hypocalemia
7. pcn/gent/clinda

Myositis

1. myonecrosis- deep soft- tissue infection with death of muscle
2. often with little skin changes but does have gas formation
3. result of trauma or surgical wounds
4. exotoxin of clostridia damages and kills muscle, setting up anaerobic environment that promotes further bacterial growth
5. odor described as "sickly sweet:
6. pt usually anuric
7. muscle appears cooked or dead, does not bleed when cut or retract when pinched

Necrotizing Fasciitis

1. can occur p minor trauma
2. mortality 20- 50%

Microorganisms

1. Type I Polymicrobrial- Anaerboic (mixed) staph, proteus, pseudomonas
2. Type 2 Streptococcal (toxin-generating)
3. Type 3 Clostridium Perfringens (gas gangrene)
4. Grp A beta hemolytic strep pyogenes releases substance in cell wall that causes separation of the dermal connective tissue resulting in continued inflammation and necrosis

Diagnosis

"Hard Signs"

1. Hypotension
2. Gas on XR
3. Skin necrosis
4. Bullae
5. Crepitance

Other common signs/symptoms

1. Systemic toxicity
2. Numbness or deep pain out of proportion to exam
3. Violaceous or hemorrhagic appearance
4. Pain beyond margins of cellulitis
5. Skip lesions

Other

1. Meleney's synergistic gangrene- (progressive bacterial synergistic gangrene) involves superficial and deep fascial planes with thrombosis of subQ vessels and gangrene of tissue
2. Clostridial cellulitis- healthy muscle not invovled
3. Fournier's syndrome- necrotizing subq infection of perineum- risk factors include infection or trauma to the perineal area,, anal intercourse, scratches, chemical or thermal burns or diabetes. Obliteration of small branches of pudendal arteries results in dermal gangrene of perineal and scrotal skin.
4. Necrotizing Otitis Externa (Malignant Otitis Externa) - deep infection of cartillaginous-bony junction. Risk factors -Elderly, diabetics, immunocomprised. Clinically severe pain and signs of mastoditis. IV antibiotics against pseudomonas, aspergillus, mucorales. ENT consult stat. Complications- Basal skull infection with Cranial Nerves 8, 7, 10(vagus) initially.

Labs

1. Hyponatremia, Na<135
2. Leukocytosis

Imaging

1. XR- gas
2. CT- most commonly used, up to 80% sensitive
3. UTZ- operator dependent
4. MRI- overly sensitive

Treatment

1. wide surgical debridement and excision
2. IV ABX
3. Resuscitate as in sepsis

Unclear benefit

1. hyperbaric O2
2. IVIG

Antibiotic Regimens

1. Harbor:
   1. community-acquired- Ceftriaxone/vanc/clinda +/- gent
   2. hospital-acquired- Zosyn/vanc/clinda
   3. pcn allergic- Cipro/vanc/clinda/gent
2. Other common regimens:
   1. pen/ ox/ gent/ clinda- and also use vanco

Source

6/06 PANI