Necrotising Faciitis

Question 1

Define necrotising faciitis

Answer 1

Necrotising fasciitis is a life-threatening subcutaneous soft-tissue infection that may extend to the deep fascia, but not into the underlying muscle. It is rapidly progressive and causes necrosis to the underlying soft tissue.

• Type I necrotising fasciitis is a polymicrobial infection with an anaerobe such as Bacteroides or Peptostreptococcus and a facultative anaerobe such as an Enterobacteriaceae or non-group A streptococcus.
• Type II necrotising fasciitis is most commonly a monomicrobial infection with Streptococcus pyogenes (group A streptococci).

Question 2

What are the causes/risk factors of necrotising faciitis?

Answer 2

• Bacteria are introduced into the skin and soft tissue from minor trauma, puncture wounds, or surgery.
• However, in up to 20% of cases no primary site of infection is identified –microtrauma to the skin.
• Infection extends through the fascia but not into the underlying muscle, and tracks along fascial planes extending beyond the area of overlying cellulitis.
• Systemic signs of necrotising fasciitis, such as fever, tachycardia, and hypotension, are primarily due to the action of bacterial toxins.

Question 3

What are the signs and symptoms of necrotising faciitis?

Answer 3

• Patient may be septic/ present with SIRS -2 of:
- T> 38°C or T< 36°C
- HR > 90 bpm
- RR > 20 bpm
- WBC > 12 x 109/L or WBC< 4 x 109/L; or >10% immature neutrophils/ band form.
• Fever, tachycardia, tachypnoea and hypotension.
• Cellulitis or red/ erythematous skin.
• Pain in affected area.
• Fournier’s Gangrene: Necrotising Fasciitis localised to the scrotum and perineum

Question 4

What investigations are carried out for necrotising faciitis?

Answer 4

• FBC -
WBC > 12 x 109/L or WBC< 4 x 109/L; or >10% immature neutrophils/ band form.
• U&Es - elevation due to AKI, secondary to sepsis.
• CRP - elevated
• CK - elevated, suggestive of systemic infection or circulatory collapse.
• Blood Cultures - positive; may indicate polymicrobial or monomicrobial aetiology.
- Gram Stain may identify the causative organism
• ABG - hypoxaemia and metabolic acidosis
• Imaging - may reveal oedema of underlying tissue. X-ray and CT can be done, as well as MRI.
• Surgical Exploration - a surgical consultation for inspection, exploration, and drainage of infected tissue should be obtained in every case of suspected necrotising fasciitis.