When a patient is found to have a pleural effusion, it is important to determine whether this is a transudate or an exudate. You can read more about that here.
When dealing with a parapnumonic effusion, it is important to categorize it into one of three types:
- Uncomplicated Parapneumonic Effusions: These resolve on their own with antibiotic therapy.
- Complicated Parapneumonic Effusions: This will require drainage to prevent progression to an empyema.
- Empyema: pus in the pleural space, with cellular debris and fibrin deposition. This certainly requires drainage.
Managment issues: Complicated parapneumonic effusions should be drained to prevent conversion to an empmyema. A pig-tail catheter may suffice, but sometimes something larger like a chest tube may be necessary. An empyema may be difficult to drain even with chest tubes/empyema tubes in place. Sometimes thrombolytic therapy is given through the tube to help break up the contents and ease drainage. Other times, Video-assisted thoracoscopic surgery is used. In a recent trial published in NEJM , it was found that "intrapleural administration of streptokinase does not improve mortality, the rate of surgery, or the length of the hospital stay among patients with pleural infection".
Here is a link to a good review on the diagnosis and management of parapneumonic effusions from Clinical Infectious Diseases.