Necrotizing Soft Tissue Infections
Introduction
Necrotizing soft tissue infections are a spectrum of illnesses characterized by fulminant, extensive soft tissue necrosis, systemic toxicity and mortality rates of up to 35%. Early in their course these infections can seem deceptively benign.
Classification Factors for Necrotizing Soft Tissue Infection
Anatomic Location i.e. Fournier’s Gangrene is a form of necrotizing infection affecting the perineum +/- the scrotum
Depth of infection i.e. Necrotizing adipositis, fasciitis, myositis
Microbial cause
Type 1 = Polymicrobial infections account for 55-75% of all necrotizing soft tissue infections
Type 2 = Monomicrobial - Group A Streptococcus, S.aureues, MRSA, Clostridium sp. causing Gas Gangrene.
Risk Factors
Advanced Age
Diabetes
Obesity
Immunosuppression
Alcoholism
Peripheral Vascular Disease
Chronic Skin Infections/Ulcers
IVDU
Clinical Features
Symptoms
Local
Pain out of proportion to physical finding is probably the most important feature to allow earlier diagnosis
Systemic
Chills, fevers, rigors, anorexia, lethargy
Signs
Local
Rapidly progressive erythema, hard induration and swelling.
Often develop central patches of dusky blue discoloration +/- serosanguineous bullae
Crepitus or surgical emphysema may be palpable due to gas forming organisms
Numbness of involved area is characteristic of advanced necrotizing fasciitis
Systemic
fever, diaphoresis, tachycardia, hypotension, tachypnoea, agitation
Clinical Investigations
Bedside
Venous Blood Gas
Assess lactate and pH balance as part of Sepsis 6
Electrolytes, Blood Sugar
ECG
Sinus Tachycardia
POCUS
Assess cardiac function and IVC collapsibility in shocked patient
Laboratory
Blood Cultures
Bacteraemia is present in 25-30% of cases and is a strong predictor of mortality
FBC
Leucocytosis, Neutrophilia, Thrombocytopaenia, Anaemia
U&E + CK
Acute kidney injury, Hyponatraemia, Myoglobinaemia are common
LFTs + CoAg
? Acute Liver injury and coagulopathy
Radiology
The diagnosis of necrotizing soft tissue infection is primarily a clinical one. Definitive treatment is time critical and should not be delayed for radiology.
Plain x-ray
May reveal subcutaneous gas but it is not a sensitive test
CT
more sensitive (80%) and can demonstrate facial thickening, oedema, deep tissue collections and subcutaneous gas. IV contrast is not necessary.
MRI
more sensitive again but introduces significant delays into treatment.
Management and Disposition
Initial Resuscitation
Attention to airway and breathing as clinically indicated
IV Crystalloid as clinically indicated
Titrate to BP, U/O and lactate
Remeasure lactate post fluid resus
Continuous monitoring of vitals including urine output
MAP < 65 and Lactate > 2 following fluid resuscitation = Septic Shock
Consider vasopressors e.g. Noradrenaline infusion
Specific Treatment
All suspected necrotizing soft tissue infections are a surgical emergency.
Immediate surgical intervention to extensively open and debride the necrotic area is the gold standard for diagnosis and the fundamental therapy.
Broad spectrum intravenous antibiotic therapy should be started concurrently as per local guideline. An example of a regimen is;
Piperacillin-Tazobactam 4.5g IV + Clindamycin 1.2g IV + Vancomycin 25mg/kg IV
Tetanus prophylaxis as indicated
May be a role for post-operative Hyperbaric O2 therapy in specialist centres.
Symptomatic Management
IV opioid analgesia and anti-emetic as required
Disposition
These patients should be transferred from ED to theatre for urgent surgical debridement
Post-operatively patients will require ICU transfer. Most patients require ongoing organ support post-op and they frequently require several more trips to theatre.
References
Tintinalli et al. Tintinalli’s Emergency Medicine. A Comprehensive Study Guide. 7th Edition
Cameron et al. Textbook of Adult Emergency Medicine. 4th Edition
Case courtesy of Dr Ian Bickle, "https://radiopaedia.org/?lang=gb">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/19317?lang=gb" ID: 19317
St James’s Hospital Medicines Guide: Empiric Antimicrobial Guidelines.
This blog post was written by Dr Deirdre Glynn and was last updated on April 12th 2022