Surgical infections remain a major source of post-operative complications and morbidity. These infections can arise due to various factors like a high bacterial load, poor immune defense, contaminated environments, or lack of aseptic measures. This guide offers an in-depth exploration of the causes, natural history, prevention, and management strategies of surgical infections, aligned with evidence-based surgical best practices.
What is a Surgical Infection?
A surgical infection is an infection that occurs in a patient who has recently undergone a surgical procedure, usually within 30 days post-op. These infections may occur at the site of incision or in deeper tissues and organs, depending on the type of surgery.
Infection occurs when pathogenic organisms (bacteria, fungi, or viruses) gain access to body tissues, overpower local immunity, and initiate a destructive inflammatory process.
Pathophysiology of Bacterial Infections in Surgery
Establishment of Infection Requires:
- A bacteria-friendly environment (warmth, moisture, nutrients).
- High inoculum load (>100,000 bacteria/ml).
- Reduced host resistance, such as impaired immunity or physical barriers.
Bacterial Secretions:
- Enzymes: e.g., hyaluronidase, streptokinase.
- Exotoxins: Produced by gram-positive bacteria, e.g., diphtheria toxin.
- Endotoxins (LPS): Released from gram-negative cell walls; these can cause severe systemic effects including fever, hypotension, and disseminated intravascular coagulation (DIC).
Natural History of Surgical Infections
Once the infection is established, the body responds with an inflammatory cascade:
1. Inflammatory Response
- Clinical signs: Rubor (redness), Tumor (swelling), Calor (heat), Dolor (pain)
- May resolve or progress
2. Resolution
- Healing with granulation tissue, fibrosis, and possible scarring
3. Spreading Infection
- Tissue planes (cellulitis)
- Lymphatic system (lymphangitis)
- Bloodstream (septicemia)
4. Abscess Formation
- Localized pus surrounded by inflamed tissue
- May lead to necrosis or systemic spread if untreated
5. Chronic Infection
- Organism persists in tissue causing ongoing inflammation
Koch’s Postulates – Proving Causality in Infection
To attribute disease to a specific microbe:
- Organism must be found in all diseased individuals
- Must be isolated and grown in culture
- Should reproduce disease in animals
- Must be re-isolated from experimentally infected animals
Prevention of Surgical Infections
1. Operating Theatre Measures
- Filtered air systems
- Sterile surgical attire (masks, gowns)
- Clean skin with antibacterial cleansing agents
2. Surgical Protocols
- Shorter operation durations are safer
- Avoid excessive tissue trauma
- Minimal foreign body placement
- Ensure good hemostasis
3. Prophylactic Antibiotics
- Administer 1 hour before incision
- Ensure bactericidal levels at the time of incision
- Higher doses in patients with prostheses or immunosuppression
- Avoid unnecessary broad-spectrum usage
Management of Established Infections
Diagnosis:
Based on clinical signs and cultures from:
- Pus, urine, blood, sputum, CSF, stool
Antibiotic Guidelines:
Use culture sensitivity reports to guide therapy
Empirical treatment should consider:
- Hospital antibiogram
- Site and severity of infection
- Patient’s comorbidities
Narrow-spectrum antibiotics preferred to reduce resistance
Monitor therapeutic levels (e.g., aminoglycosides)
Use combination therapy when needed (e.g., metronidazole + cephalosporins)
Special Cases:
- MRSA or VRE: Requires barrier nursing and strict isolation
Drainage of Infections
Surgical or radiological drainage is crucial for:
- Abscesses
- Collections of pus
Antibiotics alone are ineffective without drainage
Wound Classification and Infection Risk
| Wound Type | Definition | Example | Infection Rate |
|---|---|---|---|
| Clean | No contamination from GI, GU, RT | Thyroidectomy, hernia repair | 1–5% |
| Clean-Contaminated | Minimal contamination from GI, GU, RT | Cholecystectomy, TURP | 7–10% |
| Contaminated | Significant contamination from GI, GU, RT | Elective colon surgery, appendicitis | 15–20% |
| Dirty | Active infection or perforation present | Bowel perforation, abscess drainage | 30–40% |
Common Types of Surgical Infections
1. Cellulitis
- Spreading infection of soft tissue
- Often presents as red, warm, painful swelling
2. Abscess
- Localized pus-filled cavity
- Needs drainage, not just antibiotics
3. Necrotizing Fasciitis
- Rapidly progressive infection of deep fascia
- Requires emergency debridement
4. Septicemia
- Systemic infection due to bloodstream spread
- May lead to multi-organ failure
Key Points Summary
- >100,000 bacteria/ml needed for infection to occur
- Endotoxins from gram-negative organisms cause major systemic effects
- Drainage is the cornerstone of abscess management
- Antibiotic stewardship is essential to prevent resistance
- Prophylactic measures greatly reduce infection risk
Frequently Asked Questions (FAQs)
Q1. What is the most important step in treating a surgical abscess?
A: Drainage, either surgical or radiological, is essential. Antibiotics alone are often insufficient.
Q2. When should prophylactic antibiotics be given before surgery?
A: Ideally, 1 hour before the incision to achieve effective tissue concentration during surgery.
Q3. What is the difference between clean and dirty wounds?
A: Clean wounds have no contamination; dirty wounds have existing infection or gross contamination.
Q4. Why are narrow-spectrum antibiotics preferred?
A: They are less likely to cause resistance and target the causative organism more precisely.
Q5. How does the body react to bacterial infection initially?
A: With inflammation: redness (rubor), swelling (tumor), heat (calor), and pain (dolor).
