Mediastinitis

Background

Infection of the structures in the mediastinum
- The mediastinum refers to the space between the lungs which contains the heart, thymus, esophagus, and trachea
Confusing nomenclature, and includes mediastinal infections caused by extension of a cervical infection (necrotizing mediastinitis or descending mediastinitis) and mediastinal infection after sternotomy (sternal infection or deep sternal wound infection)

Post-cardiac surgery: often mixed
- Staphylococcus aureus is by far most common, followed by coagulase-negative staphylococci
- Can also involve other Gram-positive cocci and Gram-negative bacilli (including SPICE organisms and Pseudomonas aeruginosa)
Esophageal rupture: polymicrobial, with oropharyngeal and gastrointestinal flora including anaerobes
Can also occur from contiguous extension of pneumonia, pancreatitis, subphrenic abscess, or epidural abscess, with the microbiology determined by the source of infection

Post-surgical deep sternal wound infections occur after about 1% of cardiac surgeries
- Incidence increases with the complexity of the operation, and is highest with CABG = valve replacement or aortic surgery
- Risk increases with BMI, diabetes, and number of platelet transfusions

For deep sternal wound infections after cardiac surgery
- Mortality is about 15% in the short term, but is also higher than those without infection in the years following surgery
- Mortality is higher when Gram-negatives are isolated

CT chest can show evidence, including sternal wire displacement, sternal disruption, free gas, or fluid collections
Surgical exploration, with fluid sent for culture

One of the following:
- Organisms cultured from mediastinal tissue or fluid
- Gross anatomical or histopathologic evidence of mediastinitis
- Fever, chest pain, or sternal instability
Plus one of the following:
- Purulence from the mediastinal area
- Mediastinal widening on imaging

In general, surgical exploration with debridement should always be performed as quickly as possible
Empiric antibiotics should be broad, including coverage for MRSA and resistant Gram-negatives
- Antimicrobials directed by culture results
Duration of therapy unclear but depends on adequacy of source control, presence of sternal osteitis, and presence of metal or other foreign bodies
- Probably somewhere between 3 and 12 weeks
- Following sternal resection and pectoral flap: maybe 2 to 3 weeks
- After debridement without resection, or with residual bone infection: probably 4 to 6 weeks