Complicated parapneumonic effusions frequently represent pleural space infections. Approximately 1 in 7 cases of pneumonia have an associated parapneumonic effusion (PPE) on chest x-ray. Most of these effusions are small and usually resolve spontaneously with prompt antibiotic administration. However, moderate-to-large PPEs should always be aspirated to check for a pleural space infection.
A thoracentesis should be performed for all moderate to large parapneumonic effusions to determine if the patient has a complicated parapneumonic effusion (PPE). A complicated PPE has at least one of the following pleural fluid or radiographic characteristics: pleural fluid pH<7.20, pleural fluid glucose <35 mg/dL, pleural fluid LDH >1000 IU/L, positive pleural fluid gram stain/culture or an effusion with loculations or septations. A recent systematic review demonstrated that only 56% of pleural fluid cultures in a complicated PPE will be positive. The most common isolates are Staph aureus, Strep pneumoniae, Strep viridans and gram-negative aerobes. The yield can be improved by about 50% by inoculating aerobic and anaerobic blood culture bottles at the bedside vs sending pleural fluid to the lab prior to inoculating culture bottles. With the advent of RNA sequencing techniques, the culture yield may significantly improve.
All complicated PPEs should be treated as if they represent a pleural space infection and require pleural space drainage. This can initially be accomplished by placement of a chest tube. A small-bore chest tube (<14 Fr) has been shown to be equally effective compared with a large-bore chest tube (>14 Fr) for pleural space drainage. Additionally, the British Thoracic Society and the American Association of Thoracic Surgery recommend initiation of empiric broad-spectrum antibiotics including anaerobic coverage until culture identification and sensitivities are known. The evidence to inform the duration of antibiotics for pleural space infections is sorely lacking. Most experts recommend 4-6 weeks of therapy (IV + PO).
Intrapleural fibrinolytic therapy with DNase can increase the success rate of eradicating complicated pleural space infections compared with tube thoracostomy drainage and antibiotics alone. The usual combination is intrapleural TPA and DNase given through the chest tube. Surgical intervention is now reserved for the treatment of Stage III empyema or infections refractory to medical therapy. Unfortunately, there is only weak evidence to inform when a thoracotomy is indicated over tube thoracostomy drainage alone. It is recommended that a chest surgeon should be consulted for all complicated PPEs if readily available.
Exciting therapeutic options that are under development is the use of local anaesthetic thoracoscopy (LAT) in the management of pleural space infections. This is being studied in the ongoing SPIRIT trial due to conclude at the end of this year. In addition, the use of intrapleural antibiotics or antibiotic-coated chest tubes is being studied. How these advances change our management of pleural infections is still to be determined.