Pathogenesis of posttraumatic empyema: the impact of pneumonia on pleural space infections.

BACKGROUND: Thoracic empyema may result either from primary pneumonic sources or intraabdominal sources of infection that seed the pleural space secondarily. In patients with thoracostomy tubes, empyema may result when blood in the pleural space becomes contaminated during tube insertion. To elucidate the cause of posttraumatic empyema, preoperative bronchoalveolar lavage (BAL)/sputum cultures obtained from patients with posttraumatic empyema were compared with cultures obtained at the time of decortication.
MATERIALS AND METHODS: A retrospective study was conducted of trauma patients who developed empyema and underwent either video-assisted thoracoscopy or thoracotomy with decortication following blunt or penetrating trauma. At our level I trauma center, we studied all empyema cases diagnosed from November, 1998 to July, 2001. Data collection included patient demographics, injuries sustained, preoperative BAL/sputum cultures, and culture data obtained at the time of decortication. All BAL/sputum cultures were performed no more than 5 days prior to decortication.
RESULTS: Thirty-seven patients (26 blunt/11 penetrating) were identified. No patients had concurrent intra-abdominal sources of infection. All patients had at least one chest tube placed prior to decortication. Preoperative respiratory cultures (BAL/sputum) were obtained in 34 patients. The most common organisms isolated were Staphylococcus aureus in six patients (18%) and Hemophilus influenzae in six patients (18%). Intraoperative cultures were obtained in all 37 patients, with the most common organism being S. aureus isolated in 22 patients (60%). Interestingly, a correlation between preoperative BAL/sputum and intraoperative cultures was found in only seven of the 34 patients (21%) who had concomitant respiratory and pleural cultures. Cultures positive for S. aureus were isolated from five patients, Streptococcus pneumoniae from one patient, and Pseudomonas aeruginosa from one patient.
CONCLUSION: Little correlation existed between preoperative BAL/sputum cultures and intraoperative cultures in this series of patients with posttraumatic empyema. This suggests that the causation is most often not a parapneumonic process. Furthermore, since S. aureus was the most common organism recovered from empyema, the source was more likely from inoculation of the pleural space by the injury itself or by tube thoracostomy.