necrotising fasciitis Flashcards
what is it?
Necrotising fasciitis is a severe infection characterised by rapidly progressing inflammation and necrosis of the subcutaneous tissues. While it spreads along the fascial planes, it typically spares the underlying muscle
what areas are usually affected?
legs, trunk + perineum
what is the aetiology?
Invasion of subcutaneous tissues by virulent bacteria occurs initially - there may be an identifiable source e.g. an insect bite or wound
Bacteria proliferate and release enzymes and toxins that destroy tissues, allowing the infection to spread rapidly along fascial planes
Tissue destruction and inflammation leads to thrombosis in the microcirculation, causing ischaemia of the skin which then becomes necrotic
what are the RF?
Immunocompromise e.g. due to immunosuppressant medications
DM - SGLT2i
Chronic medical conditions (e.g. peripheral vascular disease, cirrhosis, obesity, malnutrition)
Recent trauma or surgery
IV drug or alcohol abuse
Elderly patients
how many types?
1-4
fournier’s gangrene refers to rapidly progressive necrotising fasciitis of the perineum.
what is type 1?
(70-80% of cases): polymicrobial, frequently involving anaerobes and bowel flora. Usually patients have multiple comorbidities and the trunk and perianal regions are most commonly affected.
what is type 2?
monomicrobial, usually caused by Group A Streptococcus +/- Staphylococcus aureus. Limbs are most often affected, and a toxic shock syndrome may occur due to massive cytokine release, causing multi-organ failure.
what is type 3?
(rare): gram-negative monomicrobial infection with marine bacteria e.g. Vibrio species, Aeromonas hydrophila. Occur if seawater contaminates wounds or after eating contaminated seafood.
what is type 4?
(rare): fungal rather than bacterial infection, e.g. Zygomycetes or Candida species. Patients are usually immunocompromised and have suffered recent trauma or burns.
what re the features?
acute onset
pain, swelling, erythema at the affected site
often presents as rapidly worsening cellulitis with pain out of keeping with physical features
extremely tender over infected tissue with hypoaesthesia to light touch
skin necrosis and crepitus/gas gangrene are late signs
fever and tachycardia may be absent or occur late in the presentation
differentials?
DVT
cellulitis
osteomyelitis
gas gangrene
compartment syndrome
what are the bedside ix?
Wound swab to identify causative pathogens
Blood gas which may show a metabolic acidosis; hyperglycaemia and a raised lactate are common
what are the bloods done?
FBC + CRP - inflammatory markers
U&Es and LFTs to assess for organ dysfunction, hyponatraemia and AKI may be seen
Clotting screen
Group and save
CK may be raised due to muscle damage
Blood cultures t
what imaging done?
X-ray, CT or ultrasound of the affected area may show gas in the soft tissues, supporting a diagnosis
what is the mx?
Resuscitation with IV fluids and inotropes to optimise haemodynamic stability and tissues perfusion prior to surgery
Commonly used antibiotics include tazocin, meropenem, clindamycin and linezolid (with the latter two being particularly useful in inhibiting bacterial toxin production)
Urgent surgical debridement is the essential treatment - this is critical so that the spread of infection can be controlled and necrotic tissue removed
