Viva - Nec Fasc

Question 1

What is necrotising fasciitis

Answer 1

Fulminant bacterial infection of the deep fascia and subcut fat.

Different from cellulitis as that is at the superficial fascia and dermis

Question 2

How is it different from cellulitis

Answer 2

Different from cellulitis as that is at the superficial fascia and dermis

Question 3

Describe the pathophysiology

Answer 3

The organisms release exo and enotoxins and enzymes that cause rapid infection through fascial planes

extensive tissue damage

Subsequent interuption of microcirculation
–> vascular thrombossi and local necrosis/ischaemia of skin

Loss of sensation from superficial nerve destruction

Question 4

Types

Answer 4

1 - polymicrobial
2 - Group A strep +/- S.aureus
3 - Gram neg monomicrobial (Vibrio)
4 - Fungal Candida

Question 5

Describe the polymicrobial

Answer 5

Grm pos cocci and bacilli, gram neg and anaerobes

Usually more than 1 anaeoribc specia (clostridium, bacterioides)

Risk - DM, HIV, IVDU, alcohol

Assoc with chicken pox

Question 6

Describe class 4

Answer 6

Fungal mostly in trauam patients, wounds and burns, and immnocomprimsed

Mortality 47%

Question 7

Presentation of NG

Answer 7

Severe pain out of proprotion with the findings
PRECEDES the skin changes by 48 hours

Skin may loo normal

Progression - haeorrhagic bullae
Ulceraction
Nectrosis of skin

Thrombosis of capilary beds BEFORE skin changes

Latter - fulminant sepsis, shock, TSS (partiular in Group A strep) and MOF

Question 8

Skin features

Answer 8

3 stages

1) Erythema wth tenderness extending beyond swelling
2) Formationof bullae and blisters, fluctuant skin
3) Haemorahhagiv bullae, crepitus, necrosis, gancrene

Question 9

Ix of NF

Answer 9

Largely clincal.

Do not delay surery for radiology

Surgery - fascial necrosis with or without dead muscle

No resistnce to blunt disessection, no bleeding

Foul dishwater pus

Question 10

Tests

Answer 10

Bloods - FBC, U&E, raised CK, low Ca. Coag (DIC)

Micro - bloood cultures in 20% of type 1, and 11-60% of type 2
Tissue samples and aspirates
Fungal culture in high risk

Histology to cofnrim fascial involvement

Radiology - MRI differentiates oedema from necrosis (T2)
USCT

Question 11

Scoring system

Answer 11

Laboaratory Risk Indicator for NF (LRINEC)

> 6 PPV 92% NPV 96%.
8 PPV 93.4%

Features
CRP >150 (4)
WCC  15-25 (1), >25 (2)
Hb 110-135 (1) < 110 (2)
Na <135 (2)
Cr >141 (2)
Glucose >10 1

Question 12

Tx

Answer 12

resus, supportive care
early exploration and debridements; delay is bad
Regular re-looks

empirical Abx - ben pen and clindoamycin (turns off toxin production)

If mixed - ceftriaxone

MRSA with vancomicin

IvIG

HBOT swith off toxin production in clostridal infection. Weak evidence in non-clostrial

Question 13

How does IvIG work

Answer 13

Indixated in strep/staph NF

Induces antibody against exotoxin
Neutralises superantigens
Inhibits Membrane attack complex and complemetn
Opsoniation of GAS organsism