Soft Tissue Infection

Nashrul Hadi

GAS GANGRENE

• Gas gangrene also known as "Clostridial myonecrosis", and "Myonecrosis"

• It is a bacterial infection that produces gas in tissues in gangrene.

Epidemiology•demographics– Male : female ratio• no sexual predilection

•location– buttocks, thigh, perineum

• risk factors– Posttraumatic (associated with C perfringens)

• MVA (most common)• crush injuries• gunshot wounds with foreign bodies• burns and frostbite• IV drug abuse

– Postoperative• bowel resection or perforation• biliary surgery• premature wound closure

– Spontaneous• colon cancer (associated with C. septicum)• neutropenia

• Pathophysiology– Clostridial species

• Clostidium perfringens (most common), Clostridium novyi, Clostridium septicum

• found in soil and gut flora• gram-positive obligate anaerobic spore-

forming rods that produce exotoxins (e.g. C. perfringens alpha toxin) – causes muscle necrosis and vessel

thrombosis – can cause hemolysis and shock

• incubation period <24h• gas produced by fermentation of glucose

– main component is nitrogen

– other bacteria include E. coli, Pseudomonas aeruginosa, Proteus species, Klebsiella pneumoniae

• Prognosis– overall 25% mortality – 50% mortality if bacteremic– 100% mortality if treatment is delayed– poorer prognosis for older patients with

comorbidities.

Clinical Features

• History– recent surgery to GI or biliary tract

• Symptoms– Triad • suddent progressive pain out of proportion to injury

– from thrombotic occlusion of large vessels

• tachycardia not explained by fever• feeling of impending doom

• Physical exam– sweet smelling odor– swelling, edema, discoloration and ecchymosis– blebs and hemorrhagic bullae– "dishwater pus" discharge– crepitus– altered mental status

Investigation

Radiographs•Findings– linear streaks of gas in soft tissues

• Labs– Elevated LDH– Elevated WBC– Metabolic acidosis and renal failure

• Histology– Gram stain reveals Gram-positive bacilli – absence of neutrophils

• lack of acute inflammatory response is hallmark of gas gangrene

• Culture– blood culture rarely grows Clostridial species

• DDx– Necrotizing Fasciitis

Treatment• Nonoperative– high dose IV antibiotics

• 1st line is penicillin G and clindamycin • alternative treatment is erythromycin, tetracycline or ceftriaxone

– clindamycin and tetracycline inhibit toxin synthesis– hyperbaric O2

• indications– useful adjunct

• outcomes– effectiveness of HBO2 is inconclusive

• Operative– radical surgical debridement with fasciotomies

• indications– 1st line treatment is surgical

Complication

• Shock• Renal failure– both mediated by TNF alpha, IL-1, IL-6

NECROTIZING FASCIITIS

INTRODUCTION:•Necrotizing fasciitis is a rapidly progressive inflammatory infection of the fascia, with secondary necrosis of the sub cutaneous tissue.

•It is a life threatening infection that spreads along soft tissue planes.

• Risk factors– immune suppression

• diabetes• AIDS• cancer

– bacterial introduction• IV drug use• hypodermic therapeutic injections• insect bites• skin abrasions• abdominal and perineal surgery

– other host factors• obesity

• Associated conditions– cellulitis

• overlying cellulitis may or may not be present

• Prognosis– life threatening infection• mortality rate of 32%• mortality correlates with time to surgical intervention

Necrotizing Fasciitis Classification

Type Organism Characteristics

Type 1 Polymicrobial Typical 4-5 aerobic and

anerobic species cultured: • non-Group A Strep

• anaerobes including Clostridia• facultative anaerobes

• enterobacteria• Synergistic virulence between

organisms

• Most common (80-90%) • Seen in immunosuppressed (diabetics and cancer patients) • Postop abdominal and perineal infections

Type 2 Monomicrobial • Group A β-hemolytic Streptococci is

most common organism isolated

• 5% of cases • Seen in healthy patients • Extremities

Type 3 Marine Vibrio vulnificus(gram negative rods)

• Marine exposure

Type 4 MRSA

Clinical Features

• Symptoms– early• localized abscess or cellulitis with

rapid progression• minimal swelling• no trauma or discoloration

– late findings• severe pain• high fever, chills and rigors• tachycardia

• Physical exam– skin bullae– discoloration • ischemic patches• cutaneous gangrene

– swelling, edema– dermal induration and erythema– subcutaneous emphysema (gas producing

organisms)

• DDx– Gas Gangrene

Investigation

• Radiographs– not required for diagnosis or treatment

• Biopsy – only method of definitive diagnosis– surgical intervention should not be delayed to

obtain

• LRINEC Score– score > 6 has PPV of 92% of having necrotizing fasciitis– CRP (mg/L) ≥150: 4 points– WBC count (×103/mm3)

• <15: 0 points• 15–25: 1 point• >25: 2 points

– Hemoglobin (g/dL)• >13.5: 0 points• 11–13.5: 1 point• <11: 2 points

– Sodium (mmol/L) <135: 2 points– Creatinine (umol/L) >141: 2 points– Glucose (mmol/L) >10: 1 point

Management• Operative– Emergency radical debridement with broad-

spectrum IV antibiotics • indications

– whenever suspicion for necrotizing fascitis• operative findings

– liquified subcutaneous fat– dishwater pus– muscle necrosis– venous thrombosis

• technique– hemodynamic monitoring with systemic resuscitation is

critical– hyperbaric oxygen chamber if anaerobic organism identified

– antibiotics• initial antibiotics

– start empirically with penicillin, clindamycin, metronidazole, and an aminoglycoside

• definitive antibiotics– penicillin G

» for strep or clostridium– imipenem or doripenem or meropenem

» for polymicrobial– add vancomycin or daptomycin

» if MRSA suspected

04/12/23

– Amputation• indications

– low threshold for amputation when life threatening

Reference

• Orthobullet

04/12/23