Severe Soft Tissue Infections: Necrotising Soft Tissue Infections (NSTIs) and Severe Cellulitis

Objectives

This guideline outlines the diagnosis and management of severe soft tissue infections (necrotising soft tissue infections (NSTIs) and severe cellulitis) in the extremities in the deployed environment, with a focus on surgical debridement and appropriate adjunctive therapies.

Scope

This guideline applies to all echelons of deployed surgical care (Role 2 and higher).

Audience

The intended audience is deployed surgical teams and deployed primary care clinicians.

Initial Assessment & Management

Background

Severe soft tissue infections, such as necrotising fasciitis, necrotising myositis, and severe cellulitis, represent life-threatening conditions characterised by rapid progression of infection, tissue destruction, and systemic toxicity. In the deployed setting, delays in diagnosis and treatment significantly increase morbidity and mortality. Early recognition and aggressive management are critical to improving outcomes.

Key Definitions

• Necrotising Fasciitis (NF): A rapidly spreading infection causing extensive necrosis of skin and subcutaneous tissue characteristically in the plane superficial to the deep fascia, with associated sepsis and multi organ failure.
• Necrotising Myositis (NM): A rapidly progressive infection originating within the deep muscle compartment characterised by severe sepsis and multi-organ failure, but often of insidious origin due to the lack / very late presentation of skin changes seen in necrotising fasciitis.
• Severe Cellulitis: A bacterial infection of the dermis and subcutaneous tissues that may progress to systemic involvement or deeper infection.

Diagnosis

Necrotising fasciitis:

• Onset: typically progresses rapidly within minutes / hours with pain that is disproportionate to physical findings.
• Streptococcal-driven NSTIs can be preceded by a minor viral illness and often present in previously fit and well individuals; clostridial and multi-organism NSTIs predominate in the immunocompromised population.
• Skin findings: erythema, oedema, blistering, rapidly progressing to ischaemic then necrotic patches that enlarge and coalesce. Skin changes rapidly progress over the course of minutes, characteristically spreading beyond marked margins at serial review. It is critical to mark the extent of skin changes with date and time to track this progression. Crepitus/ subcutaneous emphysema is present in some cases, though will only present with predominance of gas-forming bacteria (typically clostridium species).
• Sensation: Initially, necrotising infections are very painful, however this develops to numbness due to destruction of cutaneous nerves – Numbness is a late sign and associated with increased morbidity and mortality. Patients with normal sensation over the affected area can still have necrotising fasciitis
• Systemic symptoms: Patients with necrotising fasciitis are likely to have profound septic shock (hypotension, tachycardia, reduced urine output, altered consciousness and multi organ failure), typically they do not respond to antibiotics and IV fluid resuscitation without radical surgical debridement
• Scoring systems can be useful but should not be relied upon to diagnose necrotising fasciitis. The LRINEC scoring system is widely used if somewhat controversial. Whilst very sensitive, the heavy weighting of CRP in the scoring system leads to lack of specificity regarding diagnosis of NSTIs v severe cellulitis. Patients scoring less than 6 are very unlikely to have an NSTI, however patients with a severe cellulitis, as well as those with NSTIs may score over 6.

Necrotising Myositis (NM):

• Onset: typically progresses rapidly within minutes / hours with pain that is disproportionate to physical findings
• Presents in similar populations to NF, though higher risk of NM occurs in patients with deep inoculation injury (blast, fragmentation injury, deep injections, etc).
• NM does not typically present with the same characteristic skin changes as NF due to the plane of infection being deeper, in the intramuscular compartment. As such the perforating blood vessels and nerves often remain intact until later than in NF.
• Pain is often hard to pinpoint, though will often be exacerbated by movement of the joints involved with the affected muscle compartment. Pain is often out of proportion to what one may expect, in a similar fashion to the presentation of septic arthritis.
• Skin changes and loss of sensation are often very late signs, and correlate with pre-terminal progression of the NSTIs
• As with NF, NM patients present with septic As with NF, scoring systems such as LRINEC can be useful in ruling out NM (i.e. if scoring less than 6, NM is unlikely).

In simple terms, any patient presenting with severe soft tissue infection and septic shock should be considered to have NSTI and requires urgent physiological resuscitation, immediate antibiotics, and surgical source control.

Severe cellulitis:

• Onset: Generally slower onset than in NSTI; often from a recognised insult to skin, pain is normally severe but proportional to clinical signs
• Skin findings: erythema, warmth around affected area which is usually well demarcated. Patients may develop lymphangitis with tracking bands of erythema up the limb towards regional lymph nodes – commonly seen in upper limb cellulitis. If left, skin colour may progress from normal erythema to a dark purple or dusky discolouration. In severe infection blistering may also occur
• Absence of crepitus: Cellulitis does not present with surgical emphysema
• Sensation: Normal sensation or painful / allodynic; rarely progresses to numbness.
• Systemic symptoms: moderate systemic dysfunction e.g. fever, tachycardia, and typically responds to antibiotics and fluid resuscitation

Investigations:

Limited laboratory resources in deployed settings may require reliance on clinical diagnosis. If available, basic haematology and biochemistry blood tests (FBC, U+E, CRP) and blood cultures should be taken. Imaging modalities such as X-ray or ultrasound may identify gas in soft tissues or abscesses if available. Delay to these investigations should not delay surgical management if necrotising fasciitis is suspected, nor should it delay delivery of antibiotics in a critically unwell patient.

Management Principles

NSTIs:

Immediate surgical excision of necrotic tissue is mandatory. Repeat excision and/or relook will be required. See the CGO “Wound Excision” for guidance on timings of return to theatre. Broad-spectrum antibiotics should be commenced immediately on diagnosis of NSTI including broad spectrum cover of gram positive and negative organisms as well as clindamycin for its membrane-stabilising properties. Refer to the Deployed Antimicrobial Guidelines (LINK) for details of choice and duration of antibiotic therapy.

Surgical Considerations:

The principles of excising necrotic tissue due to NSTI are the same as for traumatic wound excision (See CGO: “Wound Excision” for further details LINK). The key differences for NSTIs are: 1. The tissues may look normal on the surface even though the infection is well established and spreading in deeper layers. 2. This is a time critical condition, and delay can be fatal.

Further Principles:

• Surgical excision must aim to remove all necrotic and non-viable tissue
• Margins of excision should extend into visibly healthy tissue
• Use copious irrigation – low pressure not pulsed lavage
• Tissue samples should be sent for urgent Gram stain, and formal microbiological culture (if available).
• Avoid delay in debridement; diagnosis is primarily clinical
• Wounds should be dressed with non-adherent dressing, wrapped in wool or velban and crepe – if negative pressure dressings are available, they may be utilised to manage complex or high-exudate wounds.

Severe Cellulitis:

• Empirical antibiotics covering likely pathogens with adjustments based on clinical response and if available, microbiological data. Follow the Deployed Antimicrobial Guidelines. Seek microbiological / infection service reachback via available communication means if patient is not improving.
• Mark the advancing edge of the erythematous area with a skin marker (time and date at time of marking) to monitor response to antibiotics.
• If cellulitis crosses a joint, splinting of the joint may offer pain relief

Elevation of the affected limb +/- application of splint immobilisation is a critical part of treatment to manage swelling and pain.

Advanced Assessment & Management

Equipment Required

Surgical Instruments / Equipment / Drugs:

• Scalpel
• McIndoe scissors
• Mayo scissors
• Forceps, toothed, large and small
• Gigli Saw if considering amputation (note that through-joint amputation (e.g. through elbow or knee) may be faster and cause less bleeding than other options in the setting of life threatening soft-tissue amputation).
• Artery clips
• Vascular Ties
• Diathermy for haemostasis
• Blood products
• TXA
• Adrenaline-soaked swabs can help to control vascular ooze from large areas of debrided tissue

Dressing Materials:

• Non-adherent dressings
• Wool/velband
• Crepe
• Negative pressure wound therapy (if available)

Patient Positioning and Preparation:

• Position the patient to maximise surgical access to affected areas - utilisation of arm boards if required
• Prepare the entire limb or affected region with betadine (chlorhexidine should be avoided if surgical field includes mucosal membranes – such as genital or perineal areas), draping should extend beyond the margins of infection

Post-Operative Management

Wound Care:

• Dressings should be left undisturbed unless they become saturated or compromised
• Monitor for signs of recurrent infection or systemic instability
• Negative pressure wound therapy may be utilised to manage exudate if available

Monitoring and Follow-Up:

• post operative bloods (FBC, U+E, blood gas if available)
• Strict fluid monitoring following debridement (3^rd space loss) and continued fluid resuscitation
  • Will require catheterisation for accurate fluid balance
• Continue IV Abx
• Regular surgical re-reviews for recurrence of infection, ongoing necrosis, or systemic deterioration in necrotising fasciitis patients
  • Relook at 24-48 hours depending on clinical response to first debridement
• Plan for urgent post-operative evacuation to Role 3 or Role 4

Pain Management:

• Multimodal analgesia, including paracetamol, NSAIDs, and opioids, should be used as appropriate

Evacuation:

• Patients requiring ongoing surgical intervention or advanced wound care should be prioritised for evacuation to a Role 3 or higher facility

Special Considerations

Multiple Cases:

Where there are a cluster of cases, or a single case due to an organism prone to spread in deployed settings (such as a PVL Staph aureus, or Streptococcus infection), then Defence Public Health should be informed immediately, either by a FMed 85 or via appropriate reachback communications.

Delayed Presentation:

Late presentation with extensive tissue necrosis may necessitate amputation or palliation if further surgical intervention is unlikely to benefit

Prolonged Casualty Care

In scenarios where evacuation is delayed, focus on wound care, infection control, and supportive measures

Paediatric Considerations

Management principles are the same as in adults, though recognition of infection may be more challenging due to more non-specific symptoms

Paediatric patients with necrotising fasciitis symptoms progress more rapidly than in adults, therefore morbidity and mortality is typically worse in children