Characterization of a pleural effusion in patients with pneumonia

* Thoracentesis is typically ultrasound-guided and can be performed at the bedside or in a radiology suite. Computed tomography-guided thoracentesis may be needed when access is difficult or ultrasound fails.
¶ Uncomplicated parapneumonic effusions are free-flowing (ie, no loculations), small to moderate size (eg, costophrenic angle blunting only, <10 mm on lateral decubitus or estimated volume <100 mL on imaging and, if sampled, have no evidence of bacterial involvement on culture/chemistry. They generally resolve with antibiotics alone and typically do not need drainage, unless the effusion is symptomatic, the patient has poor respiratory reserve, and/or the effusion is the suspected source of infection. Please refer to the UTD topic for further details.
Δ An empyema is defined by the presence of pus in the pleural space and requires immediate drainage and antibiotics.
◊ Complicated parapneumonic effusions are often loculated, are typically large (ie, >half the hemithorax, estimated volume >1000 mL) and have evidence of infection by culture or chemistry. They generally do not resolve with antibiotics alone but, rather, need both antibiotics and drainage. Please refer to the UTD topic for further details.
§ While evidence of pleural space infection by culture or chemistry is preferred for the diagnosis of complicated parapneumonic effusion, in some cases, pleural fluid cannot be obtained, sampling is inadequate, or patients have been pre-treated with antibiotics, thereby limiting pleural fluid analysis for evidence of infection. In such cases, clinical findings (eg, history of probable pneumonia) and radiographic imaging is used to make a diagnosis of "probable" or "likely" complicated parapneumonic effusion and are generally treated as such.