Indications for draining a parapneumonic effusion: an evidence-based approach.

A patient with pneumonia who develops a parapneumonic effusion challenges the physician to determine the need for pleural fluid drainage. This determination is influenced by multiple factors including the patient's general state of health, the existence of comorbidities, the virulence of the underlying pathogen, and the extent of the pneumonia that dictate clinical outcome and the relative risks and benefits of drainage. The presence of intrapleural pus represents the only factor that clearly establishes the need for drainage, although most experts recommend draining pleural fluid that is positive by Gram's stain or culture for a pathogen. Other factors such as the extent of the patient's pneumonia, severity of systemic signs of inflammation, radiographic features of the effusion, and pleural fluid chemical profile assist clinical decision making. The fundamental principle that guides therapy is the need to promptly and effectively drain pleural fluid whenever it appears likely that it will progress to a frank empyema with antibiotic therapy alone.