Pleural effusions caused by infection.

Diagnostic thoracentesis is imperative when pneumonia is accompanied by an effusion (parapneumonic effusion). Examination of the pleural fluid is the only way to differentiate empyema and complicated parapneumonic effusions from uncomplicated parapneumonic effusions, and this differentiation is vital in deciding whether chest tube drainage is needed. If the aspirated pleural fluid contains pus or bacteria, closed chest tube drainage and antibiotic therapy should be started promptly. The same management approach is indicated if the pleural fluid pH is less than 7.00 or the glucose level is less than 40 mg/ml, since these effusions almost invariably are complicated parapneumonic effusions that do not resolve without fluid drainage. If the pleural fluid pH is greater than 7.20 and glucose level is more than 40 mg/ml, antibiotic therapy alone will suffice. Management of parapneumonic effusions with a pH of 7.00 to 7.20 should be based on serial observations of clinical status and pleural fluid findings.