Residency · Residency · Cardiothoracic Surgery
Sternal Wound Complications and Mediastinitis
Introduction
Sternal wound complications range from superficial wound infections to deep sternal wound infections (DSWI) and mediastinitis, a life-threatening condition affecting 1-5% of patients following median sternotomy. Despite advances in perioperative care, mediastinitis remains associated with significant morbidity, prolonged hospitalization, and mortality rates of 10-25%. Early recognition and aggressive surgical management are essential for optimal outcomes.
Classification
El Oakley and Wright Classification
| Type | Timing | Risk Factors | Special Features |
|---|---|---|---|
| I | <2 weeks post-surgery | None | Early presentation |
| II | 2-6 weeks post-surgery | None | Delayed presentation |
| IIIA | <2 weeks post-surgery | One or more present | Early + risk factors |
| IIIB | 2-6 weeks post-surgery | One or more present | Delayed + risk factors |
| IVA | Any | Any | Failed prior treatment attempt |
| IVB | Any | Any | Failed treatment + osteomyelitis |
| V | >6 weeks post-surgery | Any | Late presentation |
Type I mediastinitis presents within 2 weeks of surgery without risk factors. Type II presents within 2-6 weeks without risk factors. Type IIIA is Type I with one or more risk factors, and Type IIIB is Type II with one or more risk factors. Type IVA involves Type I or II with failed prior treatment, while Type IVB adds bone involvement (osteomyelitis). Type V is the first presentation more than 6 weeks after surgery.
Depth of Infection
Superficial wound infection involves skin and subcutaneous tissue only with preserved sternal stability. Deep sternal wound infection (DSWI) involves sternal bone with or without mediastinal extension. Mediastinitis involves infection extending to the mediastinal space with sternal instability and systemic sepsis.
Risk Factors
Patient Factors
Patient risk factors include diabetes mellitus (especially poorly controlled with HbA1c above 7%), obesity (BMI above 30 kg/m2), chronic obstructive pulmonary disease, immunosuppression (steroids, chemotherapy, transplant), peripheral vascular disease and renal insufficiency, and tobacco use (active or recent cessation less than 30 days).
Surgical Factors
Surgical risk factors include bilateral internal mammary artery (BIMA) harvesting (though the skeletonized technique reduces risk), prolonged operative time and CPB duration, re-exploration for bleeding, use of bone wax (which impairs sternal healing), and off-midline sternotomy with excessive electrocautery.
Microbiology
Staphylococcus aureus is the most common pathogen (40-50% of cases, including MRSA). Coagulase-negative staphylococci (Staphylococcus epidermidis), gram-negative organisms (Pseudomonas, Enterobacter, Klebsiella), polymicrobial infections (up to 20% of cases), and fungal infections (Candida species in immunocompromised or prolonged ICU patients) account for the remainder.
Diagnosis
Clinical signs include wound erythema, drainage (purulent or serosanguinous), sternal instability ("clicking"), fever, and leukocytosis. CT chest demonstrates sternal dehiscence, retrosternal fluid collections, and air in the mediastinum beyond 14 days postoperatively. Deep tissue cultures are more reliable than superficial swabs. Blood cultures should be obtained before initiating antibiotics. Inflammatory markers including CRP and procalcitonin trends aid in diagnosis and monitoring treatment response.
Prevention Strategies
Preoperative nasal mupirocin and chlorhexidine bathing (decolonization protocol) reduce infection rates. Tight perioperative glycemic control targeting blood glucose below 180 mg/dL is essential. Weight-based cefazolin prophylaxis (2g for patients under 120 kg, 3g for those over 120 kg) with timely redosing is standard, with vancomycin added for MRSA-colonized patients. Rigid sternal fixation techniques including sternal plating benefit high-risk patients. Bone wax should be avoided in favor of hemostatic agents that allow bone healing.
Surgical Management
Wound Exploration and Debridement
Aggressive debridement of all necrotic tissue, infected bone, and devitalized cartilage is performed. Deep tissue cultures from multiple sites are obtained before antibiotic escalation. All foreign material (wires, wax, sutures) in the infected field is removed, and sternal viability and structural integrity are assessed.
Negative Pressure Wound Therapy (NPWT)
Vacuum-assisted closure (VAC) serves as a bridge to definitive closure. It is applied at -75 to -125 mmHg with continuous or intermittent suction, promoting granulation tissue formation, reducing bacterial load, and stabilizing the chest wall. Dressing changes occur every 48-72 hours with serial debridements as needed. Mediastinal structures must be protected with non-adherent interface layers.
Definitive Closure Options
Primary sternal rewiring is reserved for early, clean infections with viable bone and no tissue loss. Pectoralis major flap reconstruction uses bilateral advancement or turnover flaps and is the most commonly used muscle flap for sternal defects. The rectus abdominis flap, based on the superior epigastric artery, provides well-vascularized tissue for inferior sternal defects. The omental flap, transposed through the diaphragm, offers excellent dead-space filling and highly vascularized coverage. Rigid sternal fixation with titanium plates may be combined with muscle flaps for structural support.
Antibiotic Therapy
Empiric broad-spectrum coverage with vancomycin plus piperacillin-tazobactam is initiated until culture-directed therapy becomes available. Duration is typically 4-6 weeks of IV antibiotics for mediastinitis with osteomyelitis. Infectious disease consultation is recommended for complex or resistant organisms. Transition to oral suppressive therapy may be considered for chronic infections.
Outcomes
Flap reconstruction achieves wound healing in 85-95% of cases. Recurrence rates range from 5-15% depending on severity and adequacy of debridement. Mortality from mediastinitis has improved significantly with modern VAC therapy and muscle flaps. Long-term sternal instability may persist, affecting respiratory mechanics and quality of life.
Key Clinical Pearls
Sternal instability or "clicking" in a postoperative patient with fever should be considered mediastinitis until proven otherwise. CT imaging beyond postoperative day 14 showing persistent retrosternal air is highly suggestive of mediastinitis. VAC therapy has revolutionized management by stabilizing the chest, controlling sepsis, and bridging to definitive flap closure. Skeletonized IMA harvesting significantly reduces DSWI risk in diabetic patients who require BIMA grafting. A multidisciplinary approach involving cardiac surgery, plastic surgery, and infectious disease optimizes outcomes.
References
- El Oakley RM, Wright JE. Postoperative mediastinitis: classification and management. Annals of Thoracic Surgery. 1996;61(3):1030-1036.
- Lazar HL, Salm TV, Engelman R, et al. Prevention and management of sternal wound infections. Journal of Thoracic and Cardiovascular Surgery. 2016;152(4):962-972.
- Baillot R, Cloutier D, Montalin L, et al. Impact of deep sternal wound infection management with vacuum-assisted closure therapy followed by sternal osteosynthesis. Journal of Thoracic and Cardiovascular Surgery. 2010;139(6):1286-1293.
- Abu-Omar Y, Kocher GJ, Bosco P, et al. European Association for Cardio-Thoracic Surgery expert consensus statement on the prevention and management of mediastinitis. European Journal of Cardio-Thoracic Surgery. 2017;51(1):10-29.