What are the symptoms and treatment of sternum (sternal) infection post-valve repair?

Sternal Infection After Valve Repair: Clinical Presentation and Management

Sternal wound infection following valve surgery presents with wound drainage, erythema, sternal instability or dehiscence, fever, and elevated inflammatory markers, requiring immediate surgical debridement combined with prolonged intravenous antibiotics for 4-6 weeks. 1, 2

Clinical Presentation and Symptoms

Sternal infection (mediastinitis/sternal osteomyelitis) manifests with the following key features:

• Local wound signs: Purulent drainage from the sternal incision, erythema, warmth, swelling, and tenderness over the sternum 2
• Sternal instability: Palpable movement or "clicking" of the sternum with respiration or palpation, indicating dehiscence of the sternal wires 2
• Systemic signs: Persistent or recurrent fever, often with persistently elevated or rising inflammatory markers (CRP, white blood cell count) 1
• Timing: Most commonly occurs within the first 20 days post-operatively, though delayed presentations can occur months later 2, 3

Critical pitfall: Mediastinal infection can progress despite a normal external wound appearance, with manifestations potentially delayed for months and extending to involve the aorta and prosthetic valve 3. Maintain high clinical suspicion even with seemingly healed wounds.

Risk Factors

Patients at highest risk include those with:

• Diabetes mellitus, obesity, smoking history 1
• Combined valve replacement and coronary revascularization procedures 2
• Early re-exploration for bleeding 2
• Prolonged low cardiac output syndrome or ventilatory support >24 hours 2
• Immunosuppressive therapy or prior radiation 1
• Elevated BUN >40 mg/dL at presentation (predicts treatment failure) 2

Diagnostic Approach

Immediate evaluation must include:

• Multiple blood cultures before antibiotics to identify causative organisms 1
• Wound cultures from any drainage 2
• Inflammatory markers (CRP, ESR, white blood cell count) 1
• CT imaging to assess extent of mediastinal involvement and abscess formation 1
• Transoesophageal echocardiography to evaluate for concurrent prosthetic valve endocarditis, which occurs in 42% of sternal infections 2, 1

Common organisms: Staphylococcus aureus (including MRSA), coagulase-negative staphylococci, gram-negative organisms including Pseudomonas aeruginosa, and rarely atypical organisms like Mycobacterium fortuitum or Aspergillus fumigatus 4, 3, 5

Treatment Algorithm

Immediate Management (Within 20 Days of Surgery)

For early diagnosis (<20 days post-op) with BUN <40 mg/dL:

1. Surgical debridement with complete removal of infected and devitalized tissue, including removal of sternal wires 2, 1
2. Closed antibiotic irrigation following debridement achieves 76-90% success rate in this timeframe 2
3. Intravenous antibiotics for 4-6 weeks minimum, continuing at least 2-3 weeks after fever resolution 1

Delayed Presentation (>20 Days Post-Op)

For late diagnosis or BUN ≥40 mg/dL:

1. Radical surgical debridement 2, 6
2. Negative pressure wound therapy (strongly associated with improved survival) 6
3. Muscle flap reconstruction (pectoralis major or rectus abdominis) or omental flap for definitive closure 2, 6
4. Prolonged IV antibiotics for 6 weeks post-operatively 1

Evidence note: Open granulation alone, while 74% successful, unnecessarily prolongs hospitalization by an average of 10 days compared to closed irrigation 2. However, when diagnosis is delayed beyond 20 days, 81% of patients require open treatment approaches 2.

Antibiotic Selection

• Empiric therapy: Vancomycin plus anti-pseudomonal coverage (piperacillin-tazobactam or ceftazidime) pending cultures 1
• Targeted therapy: Adjust based on culture results and sensitivities 1
• Multidrug-resistant organisms: May require combination therapy (e.g., ceftazidime-avibactam plus aztreonam plus amikacin for metallo-beta-lactamase producers) 5
• Fungal infections: Require prolonged antifungal therapy, potentially lifelong for certain organisms 1, 4

Surgical Considerations for Concurrent Valve Involvement

If prosthetic valve endocarditis is confirmed:

• Urgent valve re-operation is required, particularly for staphylococcal infections which are highly destructive 1
• Complete removal of infected prosthesis with extensive debridement of annular tissue and abscesses 1
• Autologous or heterologous pericardium preferred over synthetic materials for reconstruction due to greater resistance to bacterial colonization 1
• Homograft root replacement is treatment of choice for extensive aortic root destruction 1

Prognosis and Outcomes

• In-hospital mortality: 15.7% for mediastinitis, with higher rates (10-20%) when emergency valve re-operation is required 6, 1
• Independent mortality predictors: Heart failure, sepsis, advanced age, vascular disease, and elevated BUN 6, 2
• Recurrent wound complications: More common with muscle flap repair (though survival is unaffected by reconstruction method) 6
• Long-term survival: Primarily determined by underlying cardiac function and comorbidities rather than reconstruction technique 6

Key principle: Early diagnosis within 20 days allows simpler treatment with 76-90% success using debridement and closed irrigation, while delayed diagnosis necessitates more complex reconstruction but still achieves acceptable outcomes with aggressive management 2.