PARAPNEUMONIC EFFUSION
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.
