Gas Gangrene

Definition

 

Clostridial Myonecrosis

- necrotizing, gas producing infection of skeletal muscle 2° Clostridia

- life threatening & rapidly progressive

 

Classification

 

There are 3 types of bacterial gas-forming infections

 

1. Classical clostridial gas gangrene

- rapid onset of sepsis / couple of days

- muscle nearly always involved

- critically ill immediately following an open injury 

- typically > 40° C

- pain & disorientation 

- extensive myonecrosis

- brownish discharge 

- extensive crepitus along the tissue planes

- requires amputation 1 joint above all involved muscle compartments & high dose penicillin

 

2. Streptococcal myonecrosis 

- tissue-plane infection

- clinical evolution is slower / 3 - 4 days

- patients are not as critically ill as those with clostridial infection

- requires excision of all involved muscle compartments combined with open wound management and penicillin therapy

 

3. Anaerobic Gram negative gas gangrene 

- necrotizing fasciitis

- common in diabetics with open ulcers

- usually polymicrobial

- requires open debridement combined with broad-spectrum antibiotics

 

Epidemiology

 

Open Fractures

Penetrating wounds

War & Farmyard wounds

Surgical wounds - Bowel / Poor technique

Hypovascular limbs - DM / PVD

 

USA 1000 / year 

- 0.05% of open fractures

 

Pathology

 

Need 3 things

 

1. Necrotic tissue - especially buttock & thigh

2  Ischaemia with low PO2

3. Contamination with Clostridium

 

Greatly increased by

- poor debridement

- poor antibiotics

- 1° wound closure

 

Clostridium perfringens

 

Large gram positive rod

- does not produce spores 

- obligate anaerobe

 

Ubiquitous (present in several places simultaneously)

- 20% of patient's skin

- commensal of GIT

- faeces in high concentrations

- coil 

- common in hospitals

 

Saprophytic

- nutrition involving uptake of organic materials obtained from dead or decaying plant or animal matter

 

Exotoxins 

- proteolytic or sacrolytic

- most important is A-Toxin (Lecithinase) 

- + Haemolysin, Collagenase, Hyaluronidase, Leukocidin, Deoxyribonuclease, Protease & Lipase

 

Vicious cycle

- necrotic closed wound is contaminated with clostridium

- low PO2

- production of Histotoxins

- destruction of cell wall / local tissue death

- overwhelms WBC 

 

Pathology

 

Necrotic muscle

- reddish purple & friable

- becomes greenish purple

- gas in tissue

 

Clinical Features

 

History

- develops within 24 hours of closure of a deep contaminated wound

- muscle penetrating injury

 

Pain out of proportion to injury or procedure

- alert & anxious

- patient in fear of death

 

Septic shock

- pale & sweaty

- moderate fever 

- tachycardia + shock

- Delerium » Coma » Death

 

Wound

 

Early

- skin swollen & white 

- tense oedema & local tenderness 

- serosanguineous & brown discharge

- foul or sweet odour

- ± crepitus secondary to gas 

 

Rapid progression

- bronze discolouration

- blebs containing dark fluid 

- areas of green-black cutaneous necrosis 

 

Investigations

 

Clinical diagnosis

- positive blood culture in 15%

- gram-stain of exudate not helpful

- positive Nagler's test (Lecithinase turns egg yolk opaque in agar)

 

X-ray

 

Gaseous distension of muscle & fascial planes

 

DDx

 

1.  Anaerobic clostridial cellulitis

- clostridial infection of necrotic soft tissue 

- poorly debrided wound

- gradual onset / slight toxaemia & no pain

- slight brown, seropurulent exudate

- foul gas +++

- no muscle invasion

 

2.  Strept. myonecrosis

- group A ß haemolytic Strep pyogenes

- " Flesh-eating bug"

- similar to Cl myonecrosis / muscle dead

- patient not as critically ill

- minimal gas

- muscle debridement / open wound management / penicillin

 

3.  Anaerobic cellulitis / necrotizing fasciitis

- subcutaneous emphysema

- pain, swelling, and toxemia usually remain minimal

- gas production may be abundant with a foul smell

- muscle compartments are not involved

- multiple Causative organisms 

- Clostridia / anaerobic streptococci / Bacteroides / gram-negative rods

- debridement / broad-spectrum antibiotics

 

Prophylaxis

 

Awareness 

- early meticulous debridement

- leave wound open

 

Appropriate antibiotics

- Kefazol

- + Gentamicin if extensive contamination

- + Penicillin if farmyard 

 

Management

 

1. Surgery

 

Most important 

- Delay = Death

 

Emergency exploration

- examine muscles directly

- differentiate Myonecrosis from Anaerobic cellulitis from Necrotising Fasciitis

 

Appropriate debridement

- radical myoexcision

- fasciotomies

- ± amputation

 

2. Antibiotics

 

Penicillin high dose

- allergies - clindamycin

- beware penicillin resistance

- gentamycin for co-infection

 

High dose clindamycin

- may block Clostridial exotoxin

 

3.  Resuscitate

 

Fluid loss +++

- prompt replacement 

- monitor fluid balance 

 

4. Hyperbaric O2

 

Controversial

- bacteriostatic 

- bactericidal

 

Hazards

- barotrauma

- decompression sickness

- convulsions

- otitis media

 

Useful where trunk involved 

- may decrease margin needed

- 3 ATM for 1hr TDS for 2/7

- don't delay debridement to transfer to hyperbaric chamber

 

Prognosis

 

Mortality 

- WWI = 50% 

- WWII = 25%

 

Now lower

- 50% if reaches trunk