A parapneumonic effusion is deﬁned as pleural ﬂuid that develops from pneumonia. Parapneumonic effusion is the most common cause of an exudative effusion. A practical, clinical classiﬁcation of a parapneumonic effusion is as follows: (1) an uncomplicated parapneumonic effusion resolves with antibiotic therapy alone without pleural space sequelae; (2) a complicated para-pneumonic effusion requires pleural space drainage to resolve pleural sepsis and prevent progression to an empyema; and (3) empyema is the end-stage of a para-pneumonic effusion. Empyema is deﬁned by its appearance, which is an opaque, whitish-yellow, viscous ﬂuid (pus) that is generated from serum coagulation proteins, cellular debris, and ﬁbrin deposition.
An empyema develops primarily because of delayed patient presentation and less often from inappropriate clinical management. Early antibiotic treatment prevents progression of the pneumonia, the development of a parapneumonic effusion, and the progression to an empyema. Risk factors for empyema include extremes of age, debilitation, male gender, pneumonia requiring hospitalization, and comorbidities (e.g., bronchiectasis, chronic obstructive pulmonary disease, rheumatoid arthritis, alcoholism, diabetes, gastroesophageal reﬂux disease).
Pleural ﬂuid analysis allows the clinician to stage the parapneumonic effusion and to guide initial management, with complicated effusions tending to be more cloudy, with pH below 7.20, glucose level below 40 mg/dL, lactate dehydrogenase (LDH) level above 1000 U/L, and neutrophils above 25,000 cells per microliter. Early and appropriate antibiotic treatment prevents the development of a parapneumonic effusion and its progression. A parapneumonic effusion is one of the few clinical situations in which a diagnostic thoracentesis should be performed as soon as possible. There should be timely escalation of treatment if the parapneumonic effusion progresses with continued pleural sepsis. Early pleural space drainage with a small-bore catheter promoting expansion of the lung prevents the development of a complicated parapneumonic effusion and empyema in the majority of patients. Clinical features that suggest the need for surgical drainage include prolonged pneumonia symptoms, comorbid disease, failure to respond to antibiotic therapy, and the presence of anaerobic organisms. Chest radiographic ﬁndings that suggest the need for pleural space drainage include an effusion larger than 50% of the hemithorax, loculation, or an air-ﬂuid level. Stranding or septation noted on ultrasonography suggests the need for pleural space drainage; and marked pleural enhancement, pleural thickening, and the split pleura sign on contrast chest computed tomography indicate the need for pleural space drainage. Aspiration of pus is a clear indication for drainage; however, a positive Gram stain or culture, pH below 7.20, glucose level below 40 mg/dL or LDH level above 1000 IU/L all support the need for pleural space drainage. If pleural sepsis persists, video-assisted thoracoscopic surgery is usually successful in resolving the infection and promoting lung expansion.