Necrotising fasciitis is a rapidly spreading infection of the deep fascia that kills tissue faster than it declares itself on the skin, and at the CST management and clinical station the answer is suspicion, resuscitation, antibiotics and the consultant, in that order and within the hour. According to the NHS, it gets worse quickly and can be fatal, and symptoms can develop within hours. The LRINEC score can support the diagnosis at a cut-off of 6, but a surgeon who waits for a score is already late.

Key takeaways

  • Necrotising fasciitis is a clinical diagnosis made on pain out of proportion to the skin findings, rapid spread and systemic toxicity; the NHS lists intense pain or loss of feeling, redness and swelling as early signs
  • Later signs are vomiting, diarrhoea, confusion, and blisters or black, purple or grey blotches on the skin
  • The LRINEC score uses white cell count, haemoglobin, sodium, glucose, creatinine and C-reactive protein; a score of 6 or more had a positive predictive value of 92.0% and a negative predictive value of 96.0% in the original study
  • LRINEC was derived retrospectively in 454 patients, so it supports the decision and cannot exclude the diagnosis
  • Treatment is immediate broad-spectrum intravenous antibiotics and surgical debridement, and sometimes amputation, with re-look surgery planned from the start
  • Manage the patient as sepsis from the first minute: this is a critical care admission, not a ward patient

How do I recognise necrotising fasciitis early?

Recognise necrotising fasciitis by pain out of proportion to what you can see, an area of erythema that is spreading while you watch, and a patient who is systemically far sicker than a cellulitis should make them.

The NHS describes the early symptoms as intense pain or loss of feeling and redness and swelling around the affected area, followed later by vomiting, diarrhoea, confusion, and blisters or black, purple or grey blotches.

The trap is the early case that looks like cellulitis. Ask about diabetes, immunosuppression, intravenous drug use, a recent wound or injection, and mark the edge of the erythema with a pen and the time.

How do I assess a patient with a suspected necrotising infection?

Assess a suspected necrotising infection with the CCrISP three stages, treating the patient as septic from the outset: immediate ABCDE management, then a full assessment, then a plan that ends in theatre.

In the immediate stage give high-flow oxygen, secure two wide-bore cannulae, take blood cultures and a venous gas with lactate, start intravenous fluid resuscitation and a catheter, and give broad-spectrum antibiotics at once.

In the full assessment, examine the whole limb and the perineum, feel for crepitus, note any anaesthesia over the erythema, and look at the trend of observations. Then call the consultant, because the plan is debridement.

What is the LRINEC score and what does it add?

The LRINEC score is the Laboratory Risk Indicator for Necrotising Fasciitis, built from six routine admission bloods, and it adds support to a clinical suspicion rather than a rule-out.

According to Wong and colleagues, writing in Critical Care Medicine in 2004, the variables are total white cell count, haemoglobin, sodium, glucose, serum creatinine and C-reactive protein, weighted from a logistic regression model.

The cut-off was 6 points, with a positive predictive value of 92.0% and a negative predictive value of 96.0%, and the authors concluded that patients scoring 6 or more should be carefully evaluated for necrotising fasciitis.

Say its limits: the score was derived retrospectively in 454 patients, 145 of whom had necrotising fasciitis, at two hospitals. A low score in a patient with pain out of proportion still goes to theatre.

Which investigations help, and which must not delay surgery?

The investigations that help are the LRINEC bloods, a lactate, blood cultures, clotting and a group and save; imaging may show gas in the soft tissues, but no investigation should delay surgical exploration when suspicion is high.

A plain radiograph or CT can show subcutaneous gas, and CT can define the extent, but a normal scan does not exclude the disease. The definitive test is the finger test at the bedside or in theatre: dishwater fluid, and fascia that separates without resistance.

What is the management of necrotising fasciitis?

The management of necrotising fasciitis is sepsis resuscitation, immediate broad-spectrum intravenous antibiotics, and urgent surgical debridement of all necrotic tissue, with a planned return to theatre for a second look.

The NHS states that treatment will usually include antibiotics and surgery to remove the damaged tissue, and that sometimes amputation of affected limbs is needed. Antibiotic choice follows the local microbiology guideline and covers streptococci, anaerobes and gram-negatives.

Debridement is radical and repeated until the margins are healthy, and the wound is left open. The patient goes to critical care afterwards, and the plastic surgeons are involved for reconstruction once the infection is controlled.

Who do I escalate necrotising fasciitis to, and how fast?

Escalate necrotising fasciitis to the on-call consultant surgeon directly and immediately, alongside the anaesthetist and the critical care team, because the decision to operate is a consultant's and the operation cannot wait for the morning.

Say that you would speak to the consultant yourself rather than relay through a registrar who is scrubbed, book the emergency theatre, alert microbiology, and involve plastic surgery early if the limb or perineum is affected.

What are the pitfalls the panel wants you to name?

The pitfalls in necrotising fasciitis are treating it as cellulitis, waiting for imaging or a score, under-resuscitating a septic patient, and an inadequate first debridement.

  • Analgesia that does not work is a sign, not a nursing problem
  • A normal-looking skin surface can overlie dead fascia
  • Non-steroidal anti-inflammatories and diabetes can blunt the systemic picture
  • Perineal disease, Fournier's gangrene, is easy to miss under a blanket

How this comes up at the CST interview

Necrotising fasciitis is set as a diabetic patient with a red, exquisitely painful calf that has spread past the pen line in two hours, and the panel wants the diagnosis said, the consultant called and the antibiotics given before any test is named.

Follow-ups ask what the LRINEC score is and whether a low score reassures you, what you would say to the consultant, and how you would consent a patient who may lose the limb.

The coresurgeryinterview bank has a scored necrotising fasciitis scenario with AI-marked spoken practice: /Question-Bank/Sample-Questions.