Necrotizing Soft Tissue Infections (NSTI) Flashcards
What are Necrotizing Soft Tissue Infections (NSTI)?
Subset of STIs involving skin, subcutaneous tissue, muscle, and fascia leading to vascular occlusion, ischemia, and necrosis
NSTIs are characterized by their progressive and rapidly spreading nature.
Which areas of the body are most susceptible to NSTI? and why?
Limbs and neck. Fibrous attachments between SQ and fascia can form a boundary to limit spread however not in extremities or truncal regions
Fibrous attachments between subcutaneous tissue and fascia can limit spread, but this is not effective in extremities or truncal regions.
A 6-year-old Labrador Retriever presents with rapidly progressing necrotizing fasciitis (NF) involving the hind limb. The dog had a recent minor cut on the limb. Culture results reveal β-hemolytic Streptococcus. Based on the microorganism identified, what type of NF is this?
type 2
These syndromes are associated with virulent bacterial and fungal organisms.
What are the four categories of NSTI?
- Type 1: Polymicrobial (usually <4 organisms)
- Type 2: Monomicrobial (usually beta-hemolytic Streptococcus)
- Type 3: Gram-negative mono (Clostridia, marine-related)
- Type 4: Fungal (Candida)
Type 2 is the most common and associated with minor trauma.
What is Toxic Shock Syndrome (TSS) and when can you see it?
Subset of Type 2 NSTI, characterized by severe acute circulatory shock and multiple organ dysfunction syndrome (MODS)
TSS is often linked to beta-hemolytic Streptococcus.
What are the key pathophysiological mechanisms involved in NSTI?
o Strepto= release of exotoxin superantigens, cell envelope proteinases, hyaluronidase, complement inhibitor, protein M, streptolysin O, prot F-> cytokine release, SIRS, septic shock
o Clostridial toxins= hemolysis, platelet aggregation, leukocyte destruction, histamine release, damage to vascular endothelium, collagen, and hyaluronic acid
o Microbial invasion-> localized thrombosis-> liquefactive necrosis
These mechanisms lead to cytokine release, systemic inflammatory response syndrome (SIRS), and septic shock.
What is required for a definitive diagnosis of NSTI?
Tissue sampling showing fascial necrosis and myonecrosis
Preliminary diagnosis is based on clinical suspicion.
What are the recommended antibiotics for NSTI treatment? and what are not?
- Penicillins
- Clindamycin
- Aminoglycosides
Not recomm: fluoro
Clindamycin is effective against stationary phase bacteria and inhibits exotoxin production.
Why is enro not recommended?
has limited activity vs strepto + cause lysis of S. canis= enhancing pathogenicity
Fluoroquinolones have limited activity against Streptococcus and may enhance pathogenicity.
What is the recommended timeframe for sx intervention?
Necrosis creates an anaerobic environment; intervention within 4-6 hours after stabilization is crucial
Early intervention may prevent the need for extensive surgery.
What indicates a need for muscle debridement during surgery?
Muscle does not contract upon stimulation from an electrocautery device
This indicates a lack of viability in the muscle tissue.
what antimicrobial combination is recommended for tx?
Clinda + 3rd generation cephalo or aminoglycosides
Name 3 gram +ve and 3 gram -ve bacteria
+ve aerobic: strep, staph, enterococcus, bacillus, listeria, nocardia, cornebacterium. +ve anerobic: clostridium, lactobacillus, actinomyces, pseudostrepto.
-ve aerobic: enterobacteriacee, pseudomonas, hemophilus. -ve anerobic: pastorella
MOA of clinda?
inhibiting bacterial protein synthesis.
binds to the 50S ribosomal subunit of ribosome, preventing formation of peptide bonds during protein synthesis-> bacteriostatic effects. In certain situations, such as with high concentrations or highly susceptible organisms, it can also exhibit bactericidal activity. Clindamycin is particularly effective against Gram +ve bacteria and anaerobes.
