2. Soft Tissue Infections, Wound Infections, NPWT, and Antibiotic Prophylaxis

I. Soft Tissue Infections

Basic Logic

• Soft tissue infection: infection of skin, subcutis, fascia or muscle
• Key questions: pus? necrosis? systemic toxicity?
• Spectrum: folliculitis → furuncle/carbuncle → erysipelas/phlegmon → abscess → necrotizing infection

Folliculitis

• Folliculitis: infection of hair follicle
• Etiology: usually Staphylococcus aureus; also fungi/viruses
• Clinical features: tender red follicular spot, often surface pustule
• Treatment: hygiene, local treatment; oral antibiotics/antifungals if extensive or high-risk

Furuncle and Carbuncle

• Furuncle: deep bacterial folliculitis with small abscess
• Carbuncle: cluster of connected furuncles
• Etiology: usually Staphylococcus aureus
• Clinical features: painful deep nodule/abscess; carbuncle may have fever and multiple draining points
• Treatment: drainage if fluctuant; antibiotics if cellulitis, systemic signs or immunosuppression

Abscess

• Abscess: encapsulated pus-filled lesion
• Etiology: usually Staphylococcus aureus; mixed flora/anaerobes depending on site
• Clinical features: calor, rubor, tumor, dolor, functio laesa + fluctuation
• Diagnosis: clinical; ultrasound if deep/uncertain
• Treatment: incision and drainage = key treatment
• Antibiotics: if large/deep, surrounding cellulitis, systemic signs, diabetes/immunosuppression, recurrent/high-risk site

Empyema

• Empyema: collection of pus within a natural anatomical cavity
• Examples: pleural cavity, gallbladder, joint
• Treatment: drainage + antibiotics + source control

Phlegmon / Cellulitis

• Phlegmon: diffuse acute purulent soft tissue inflammation without defined capsule
• Cellulitis: diffuse dermis/subcutis infection with ill-defined border
• Etiology: streptococci, Staphylococcus aureus, anaerobes/mixed flora depending on site
• Clinical features: redness, warmth, swelling, tenderness, ill-defined margins
• Systemic symptoms more common than abscess: fever, chills, fatigue, headache
• Can progress → abscess or necrotizing infection
• Treatment: elevation/rest + empirical antibiotics; drainage if abscess forms

Erysipelas

• Erysipelas: acute infection of upper dermis and lymphatics
• Etiology: mainly beta-hemolytic streptococci / Streptococcus pyogenes
• Clinical features: sharply demarcated raised hot tender erythema, usually unilateral + fever/chills
• Complications: lymphangitis, abscess, recurrence, sepsis
• Treatment: anti-streptococcal antibiotics + elevation + treat entry lesion

Gangrene

• Dry gangrene: ischemia without infection → dry black mummified tissue
• Treatment: assess revascularization possibility + remove/amputate necrotic tissue when demarcated or infected
• Wet gangrene: bacterial infection in ischemic tissue → foul soft necrosis, rapid spread
• Treatment: emergency debridement/amputation + broad-spectrum IV antibiotics
• Gas gangrene / clostridial myonecrosis: Clostridium perfringens → gas, crepitus, severe toxicity
• Treatment: emergency radical debridement + high-dose IV antibiotics; hyperbaric oxygen is adjunct only

Necrotizing Fasciitis

• Necrotizing fasciitis: rapidly progressive infection with subcutaneous/fascial necrosis
• Warning signs: pain out of proportion, rapid spread, bullae, skin anesthesia, crepitus, shock
• Treatment: emergency radical debridement or amputation + broad-spectrum IV antibiotics + ICU resuscitation

II. Wound Infections

Definition and Types

• Wound infection: bacterial invasion of surgical/traumatic/chronic/burn wound with tissue inflammation
• Colonization alone is not infection
• Antibiotics do not replace drainage, debridement and source control

1. Surgical site infection (SSI)

• Occurs within 30 days after operation at operated site
• Superficial incisional SSI: skin + subcutaneous tissue
• Deep incisional SSI: fascia + muscle
• Organ/space SSI: deeper manipulated organ/space

2. Other wound infections

• Traumatic wound infection
• Chronic wound infection: diabetic foot, pressure ulcer, venous/arterial ulcer
• Burn wound infection

Surgical Wound Contamination

• Clean: no tract entered, no inflammation → lowest risk; no routine prophylaxis unless implant/high-risk
• Clean-contaminated: GI/respiratory/GU tract entered in controlled manner → prophylactic antibiotics
• Contaminated: fresh open trauma, gross spillage, acute inflammation → antibiotics + debridement/source control
• Dirty/infected: old trauma, devitalized tissue, fecal contamination, pus/perforation → therapeutic antibiotics + aggressive debridement/source control

Pathogens and Risk Factors

• Most common pathogen: Staphylococcus aureus
• Skin/clean wounds: staphylococci, streptococci
• GI/perineal wounds: Gram-negative rods + anaerobes ± enterococci
• Burn/chronic/hospital wounds: consider Pseudomonas, resistant organisms, mixed flora
• Local risk factors: poor perfusion, necrosis, foreign body, hematoma/seroma, contamination
• Systemic risk factors: age, obesity, malnutrition, diabetes, anemia, malignancy, sepsis, immunosuppression, smoking
• Surgical risk factors: poor tissue handling, dead space, prolonged operation, contamination, implant/drain/foreign material

Diagnosis

• Signs: erythema, warmth, swelling, increasing pain, pus/odor, induration, delayed healing, dehiscence, fever/chills
• Assess: depth, pus/collection, necrosis, foreign body, hematoma, systemic severity
• Culture: pus/deep tissue if severe, recurrent, chronic, failed treatment or resistant pathogen risk
• Imaging: ultrasound for collection; CT/MRI for deep infection, gas or organ/space abscess

Treatment

1. Open wound if pus/collection or SSI under tension
2. Drain abscess/hematoma/seroma
3. Irrigate and mechanically clean
4. Debride necrotic/devitalized tissue
5. Empirical antibiotics if systemic signs, cellulitis, deep/dirty infection, immunosuppression or necrotizing infection
6. Adjust antibiotics after culture
7. Closure: clean → primary; contaminated/high-risk → delayed primary; infected/pus/necrosis → leave open
8. Tetanus prophylaxis for traumatic/dirty wounds

III. Negative Pressure Wound Therapy (NPWT / VAC)

Definition and Mechanism

• NPWT / VAC: sealed wound dressing applying continuous or intermittent subatmospheric pressure
• System: foam/gauze dressing + occlusive film + tubing + vacuum pump
• Mechanism: removes exudate, decreases edema, improves perfusion, promotes granulation, helps approximate wound edges

Indications and Contraindications

• Indications: chronic non-healing wounds, post-debridement wounds, contaminated/infected wounds after source control, trauma/fasciotomy wounds, soft tissue loss, dehisced wounds, graft fixation
• Open abdomen/laparostomy: selected use with visceral protection to control fluid and facilitate staged closure
• Contraindications/caution: active bleeding, necrotic eschar before debridement, untreated osteomyelitis, malignant wound, unexplored fistula, unprotected exposed vessels/organs/nerves

IV. Antibiotic Prophylaxis in Surgery

Indications

• Goal: prevent SSI by adequate tissue antibiotic level at incision
• Clean surgery with prosthesis/implant/foreign material
• Most clean-contaminated operations
• Selected contaminated operations / fresh trauma
• High-risk patient or high-consequence infection

• Ex: diabetes, immunosuppression, prolonged surgery

• Dirty/infected wound → therapeutic antibiotics, not prophylaxis alone

Principles

1. Choose site-appropriate narrow spectrum according to expected flora and local guideline
2. Tailor to surgical site, local microbiology and allergy history
3. Cefazolin: common prophylaxis for skin flora (Staphylococcus/Streptococcus)
4. Cefazolin + metronidazole: GI/colorectal surgery → anaerobic coverage
5. Vancomycin: MRSA colonization/risk or selected beta-lactam allergy situations according to local protocol
6. Give IV before incision, usually 30-60 min before surgery
7. Re-dose during long operation or major blood loss
8. Stop within 24 h postoperatively in most procedures
9. Do not prolong prophylaxis just because a drain is present