Surgical site infection (SSI) is an infection that occurs at or near a surgical incision or deep to it within 30 days of the procedure or within 90 days if prosthetic material is implanted.
Classification of surgical site infections
- Superficial: involves skin and subcutaneous tissue
- Deep: involves fascial and/or muscle layers
- Organ/space: involves organs or spaces deep to the incision (e.g., intraabdominal abscess)
Classification of surgical wounds
Surgical wounds are classified from clean to dirty on the basis of the increasing risk of infection.
Contamination of surgical wounds occurs to some degree in all surgical procedures. However, in most cases, the infecting agents do not overcome host defenses. For SSI to occur, the bacterial colonization must trigger an immune response.
- Violations of sterile technique (i.e., poor skin preparation, contamination of instruments, inadequate handwashing/scrubbing)
- Inadequate or ill-timed antibiotic prophylaxis
- Prolonged procedure time
- Local tissue necrosis
- Hematoma formation
- Use of foreign material in wounds (e.g., drains, mesh)
- Preoperative shaving
- Prolonged preoperative hospital stay (↑ nosocomial infection)
- Contamination with bowel contents
- Advanced age (> 65 years)
- Prior surgical infection
- Diabetes mellitus
- Therapy with corticosteroids
- Chronic inflammation
- Renal failure
- Peripheral vascular disease (PVD)
- Previous radiation of surgical site
- Chronic skin disease
- Carrier state (e.g., chronic Staphylococcus carriage)
When the virulence factors of a microorganism are sufficient to overcome the innate and adaptive immune responses, a clinically important infection occurs in the following manner:
- Once microbes enter, host defenses (i.e., tissue barriers, iron-sequestering lactoferrin and transferrin, and fibrinogen) act to limit and/or eliminate all pathogens.
- Resident macrophages secrete cytokines (tumor necrosis factor α (TNF-α); IL-1β, 6, and 8; and interferon (IFN-γ)) within the tissue milieu and the systemic circulation.
- Microbial opsonization, phagocytosis, and extracellular and intracellular microbial destruction occur via cellular ingestion.
- At the same time, the classical and alternative complement pathways are activated and vascular permeability increases.
- Inflammatory fluid and neutrophils flow into the area of infection.
- Possible outcomes:
- The microorganism is eradicated.
- Containment in the parenchyma (i.e., abscess)
- Localized infection, displaying local symptoms (i.e., cellulitis)
- Systemic infection (bacteremia or fungemia) with its accompanying presentation (i.e., fever, tachycardia)
- Local erythema
- Purulent discharge
- Peritoneal signs in organ/space abdominal infections
- Abscesses close to the skin are painful, and the overlying skin is swollen, erythematous, and warm.
- Confusion (altered mental status)
The diagnosis of SSI relies primarily on clinical findings. Diagnostic imaging and laboratory studies are helpful for identifying deep tissue and organ/space infections.
Clinical findings (local):
- Purulent exudate draining from the surgical site
- A surgical site that has reopened in the setting of ≥ 1 clinical sign of infection (pain, swelling, erythema, warmth)
- Erythema, swelling, fluctuance, and/or induration around the incision
- Organ/space infections:
- Fever/chills/signs of sepsis
- Localized abdominal tenderness with peritoneal signs
Sepsis findings (systemic):
- Criteria for systemic inflammatory response syndrome (SIRS):
- Temperature > 38°C (100.4°F) or < 35°C (95°F)
- HR > 90/minute
- RR > 20 or partial pressure of carbon dioxide (PaCO2) < 35 mm Hg
- WBC > 12,000 (leukocytosis) or < 4000 (leukopenia)
- Sequential Organ Failure Assessment (SOFA):
- Mortality prediction score
- Used to track a person’s status during the stay in an ICU
- Based on an assessment of the degree of dysfunction of 6 organ systems.
- The score is calculated at admission and every 24 hours until discharge.
- Quick SOFA (qSOFA) is an abbreviated assessment tool (poorly sensitive, but decently specific for the risk of death):
- RR ≥ 22/minute
- Altered mentation
- Systolic BP ≤ 100 mm Hg
- CBC: WBC > 10,000 (leukocytosis)
- Serum creatinine
- Gram staining and culture of a wound or aspiration
- Blood cultures in patients who are febrile or have suspected sepsis
- Deep tissue or organ/space SSIs may require radiologic imaging for definitive diagnosis.
- Prosthetic infection (e.g., hernia mesh) may also require imaging to support the diagnosis.
- CT, MRI, or ultrasonography can identify abdominal, pelvic, and soft tissue abscesses.
- Imaging is needed for percutaneous or surgical drainage planning.
The management of SSIs may include antibiotics, abscess drainage (open or percutaneous), and removal of infected prosthetic material.
- Reserved for patients with significant cellulitis, SIRS, or organ/space or prosthetic infections
- Antibiotic choice depends on the procedure performed/type of wound:
- Infections associated with skin flora mostly require gram-positive coverage as well consideration for possible methicillin resistance.
- Contamination with intestinal flora requires gram-negative and anaerobic coverage.
|Methicillin-sensitive Staphylococcus aureus||Cefazolin||Clarithromycin|
|Methicillin-resistant Staphylococcus aureus||Vancomycin||Linezolid or daptomycin|
|Coagulase-negative staphylococci||Vancomycin||Linezolid or daptomycin|
|Streptococcus pyogenes (group A β-hemolytic streptococcus)||Benzylpenicillin, clindamycin||Clarithromycin|
|Clostridium spp.||Benzylpenicillin, metronidazole||Metronidazole|
- Superficial wound infection/abscess:
- Opening the wound
- Allowing the wound to heal by secondary intention with daily packing/dressing changes
- Deep wound infection with fascia/muscle involvement:
- Opening the wound
- Debridement of infected/ devitalized tissue may be needed.
- Daily packing/dressing changes for the wound; may benefit from vacuum wound therapy
- Organ/space infection:
- Very small abscesses (< 3 cm) may resolve with antibiotic therapy alone.
- Larger abscesses usually require either percutaneous or operative drainage.
- Infections involving prosthetic materials:
- Initial therapy is antibiotics with drainage of all associated abscesses.
- Salvage may be attempted if there is good clinical response to antibiotics and drainage, but most of the time, removal of the prosthetic material is required.
- Adherence to sterile technique
- Appropriate antibiotic prophylaxis
- Bowel preparation (cleansing) when feasible in cases involving bowel resection/anastomosis
- Optimizing patient’s condition (smoking cessation, adequate nutrition, blood glucose control, avoiding hypothermia in the OR)
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