Ch08: Surgical Infection（外科感染）

Preparatory Mindset

Surgical infection = infection requiring operative intervention or arising from trauma/operation/burns/catheters — accounting for 30-50% of surgical disease. The exam tests: definition, SIRS/sepsis spectrum, surgical site infection (SSI) prevention, abscess principles ("where there is pus, let it out"), and the specific surgical infections (cellulitis, necrotizing fasciitis, gas gangrene, tetanus, peritonitis).

Exam mindset: the lecture emphasizes the definition (pneumonia is NOT a surgical infection per se, but postop pneumonia is a surgical complication) and the SSI classification. The prep PDFs add the classic treatment principles (切开引流 for abscess, 破伤风 prophylaxis, 气性坏疽 = 彻底清创+高压氧).

Core Concepts

1. Definitions (MUST KNOW)

• Infection: microorganisms in host tissue/bloodstream + inflammatory response to their presence (bacteria, viruses, fungi)
• Surgical infection: infection that requires operative intervention (abscess drainage, debridement) OR arises from surgery/trauma/burns/catheters; accounts for 30-50% of surgical disease
• Examples: peritonitis & intra-abdominal abscesses, surgical site infections, infected wounds, necrotizing fasciitis, gas gangrene, breast abscess, pilonidal abscess
• Pneumonia itself is not a surgical infection, but postoperative pneumonia is a surgical complication

2. SIRS, sepsis & the sepsis spectrum (MUST KNOW)

1. Temp > 38°C or < 36°C 2. HR > 90/min 3. RR > 20/min or PaCO2 < 32 mmHg 4. WBC > 12,000 or < 4,000 or >10% bands

• SIRS (systemic inflammatory response syndrome): ≥2 of:
• Sepsis (Sepsis-3): infection + organ dysfunction (SOFA ≥2)
• Septic shock: sepsis + vasopressors needed + lactate > 2 mmol/L
• Progression: infection → SIRS → sepsis → severe sepsis → septic shock → MODS

3. Surgical site infection (SSI) (MUST KNOW)

- Antibiotic prophylaxis within 60 min before incision; redose intraoperatively (every 3-4 h / major blood loss); stop within 24 h - Hair removal by clipping (NOT shaving) immediately before surgery (razor causes micro-abrasions) - Skin prep with alcohol-based antiseptic (chlorhexidine-alcohol); maintain normothermia, normoglycemia, oxygenation - Aseptic technique, careful tissue handling, minimize dead space

• Types: superficial incisional, deep incisional, organ/space
• Risk factors: patient (diabetes, obesity, smoking, malnutrition, immunosuppression), procedure (duration, contamination class, hair removal method), environment
• Prevention (bundles):
• Management: open the wound, culture, drainage; antibiotics for cellulitis/systemic infection

4. Abscess — the core surgical principle (MUST KNOW)

• Definition: localized collection of pus (dead neutrophils, bacteria, debris) walled off by inflammation
• Clinical: local pain, swelling, erythema, heat, fluctuance (mature); systemic fever
• Management: "Ubi pus, ibi evacua" — where there is pus, drain it. Incision & drainage (I&D) is the definitive treatment; antibiotics alone do NOT penetrate/clear an abscess
• Common abscesses: skin/soft tissue (boil/furuncle, carbuncle), breast abscess (lactation), perianal abscess, intra-abdominal (appendiceal, subphrenic, pelvic), liver abscess, psoas abscess
• Post-drainage: packing, regular dressing changes, culture, antibiotics for surrounding cellulitis/sepsis

5. Specific surgical infections (MUST KNOW)

• Cellulitis (蜂窝织炎): diffuse spreading infection of subcutaneous tissue — erythema, pain, swelling, no clear border, no pus collection; treat with antibiotics (may progress to abscess/fasciitis)
• Furuncle (疖) & carbuncle (痈): hair-follicle infection (Staph aureus); furuncle = single, carbuncle = multiple follicles (diabetes!); central face (danger triangle) — don't squeeze (cavernous sinus); treat warm compresses/antibiotics; I&D if fluctuant
• Necrotizing fasciitis (坏死性筋膜炎): surgical EMERGENCY — rapidly spreading infection along fascial planes, pain out of proportion, skin necrosis, crepitus (gas), systemic toxicity; "flesh-eating" (Group A Strep, mixed, gas formers) — treatment: urgent radical debridement (all necrotic fascia), broad-spectrum antibiotics, ICU, repeated debridements; high mortality
• Gas gangrene / clostridial myonecrosis (气性坏疽): Clostridium perfringens in contaminated wounds — crepitus, severe pain, bronze skin, bullae, myonecrosis, systemic toxicity; treatment: urgent wide debridement/amputation, high-dose penicillin, hyperbaric oxygen (adjunct)
• Tetanus (破伤风): Clostridium tetani (anaerobe, contaminated wounds) → tetanospasmin toxin → generalized muscle spasms, trismus (lockjaw), risus sardonicus, opisthotonos; prophylaxis: TIG (tetanus immune globulin) + tetanus toxoid booster + wound debridement; treatment: wound care, TIG, metronidazole/penicillin, sedation/muscle relaxants, supportive
• Peritonitis (腹膜炎): see Y4S2 chapter — primary (spontaneous), secondary (perforation — appendicitis, ulcer, diverticulitis), tertiary
• Catheter-related infection (CRBSI): central line sepsis — remove the catheter, culture, antibiotics
• Surgical infections of specific organs: breast abscess, acute cholecystitis, appendicitis, diverticulitis, liver abscess — covered in organ chapters

6. Antimicrobial therapy principles

• Empiric → directed: start broad-spectrum (cover likely organisms) then narrow per culture
• Common surgical pathogens: skin = Staph aureus/Strep; abdomen = enteric gram-negatives (E. coli), anaerobes (Bacteroides); wounds = mixed
• Antibiotic choices: cefazolin (prophylaxis/SSI), piperacillin-tazobactam/carbapenem (severe intra-abdominal), metronidazole (anaerobes), vancomycin (MRSA), fluconazole (Candida)
• Duration: short for prophylaxis (≤24 h); longer for established infection (source control + clinical response)

High-Yield Points

• Surgical infection = requires operation OR arises from surgery/trauma/burns/catheters; 30-50% of surgical disease
• SIRS: ≥2 of (T >38/<36, HR >90, RR >20, WBC >12k/<4k)
• Sepsis = infection + organ dysfunction (SOFA); septic shock = vasopressors + lactate >2
• Abscess: "where there is pus, drain it" — I&D is definitive; antibiotics don't penetrate pus
• SSI prevention: antibiotics ≤60 min pre-incision, clip not shave, chlorhexidine-alcohol, normothermia/glycemia
• Necrotizing fasciitis & gas gangrene = surgical emergencies — urgent radical debridement + antibiotics (+ HBO for gas gangrene)
• Tetanus: trismus, risus sardonicus, opisthotonos; prophylaxis = TIG + toxoid + debridement
• Furuncle/carbuncle: Staph, diabetes association; central face danger
• Cellulitis: diffuse, no pus — antibiotics

Topic Summary

Surgical infection requires operative intervention or arises from surgery/trauma/burns/catheters (30-50% of surgical disease). The sepsis spectrum runs SIRS (≥2 criteria) → sepsis (infection + organ dysfunction) → septic shock (vasopressors + lactate >2). SSI prevention bundles: prophylactic antibiotics ≤60 min pre-incision (stop ≤24 h), clipping not shaving, chlorhexidine-alcohol prep, normothermia/normoglycemia (CM exam tested — NOT on PPT). The core principle: abscess = drain it (I&D definitive). Specific infections: cellulitis (antibiotics), furuncle/carbuncle (Staph, diabetes), necrotizing fasciitis & gas gangrene (emergencies — radical debridement ± HBO), tetanus (trismus; TIG + toxoid + debridement), peritonitis, CRBSI. Antibiotics: empiric broad → directed narrow.