- • Parapneumonic effusions are pleural effusions
that occur in association with pneumonia.
- • If inadequately treated, parapneumonic effusions
progress through the exudative, fibrinopurulent, and organized phases
of empyema formation.
- • All hospitalized patients with pneumonia should
be evaluated by imaging studies for the presence of a parapneumonic
- • Pleural fluid analysis establishes the diagnosis
and aids in determining management.
- • Early diagnosis and prompt thoracentesis decrease
morbidity and mortality for patients with parapneumonic effusions.
Parapneumonic effusions occur in 20–60% of
patients with pneumonia that is sufficiently severe to require hospitalization.
Although most of these effusions are sterile and resolve with antibiotic therapy
for the underlying pneumonia, 5–10% of patients
hospitalized for pneumonia develop intrapleural infection. These
patients require prompt pleural fluid drainage to prevent the formation
of an empyema, which is characterized by the presence of intrapleural
pus. Because of the significant morbidity and mortality associated
with empyema, the primary focus of managing parapneumonic effusions
centers on early detection and urgent evaluation to identify those patients
who require pleural fluid drainage to prevent or treat an empyema.
Heffner JE: Infection of the pleural space. Clin
Chest Med 1999;20:607.
review of parapneumonic effusions and empyema with a discussion
of the value of biochemical tests to guide drainage decisions.)
Parapneumonic effusions occur when regions of pneumonia abut
pleural surfaces and alter pleural membranes. Mesothelial cells
line the visceral pleura and form a semipermeable membrane that prevents
free diffusion of fluid and passage of circulating cells from the
bloodstream into the pleural space. When stimulated by an adjacent
pneumonia, mesothelial cells alter their membrane characteristics
and permit fluid and high-molecular-weight compounds, such as protein
and lactic dehydrogenase (LDH), to enter the pleural space. Activated
mesothelial cells also release cytokines and other proinflammatory
mediators that recruit inflammatory cells and fibroblasts. Progressive
pleural inflammation promotes the deposition of fibrin onto pleural
surfaces, which forms a latticework for fibroblasts to deposit collagen
and form intrapleural loculations and pleural peels. Pleural peels
can encase the lung and prevent lung reexpansion (trapped lung)
when an intrapleural catheter is placed to drain a parapneumonic
The progression of a parapneumonic effusion to an established
empyema has three distinct phases, each of which has therapeutic
implications. Free-flowing nonviscous fluid and the absence of a
pleural peel characterize the exudative phase.
Most but not all exudative effusions respond to antibiotic therapy.
The development of more viscous fluid and the early formation of
intrapleural loculations and pleural peels characterize the fibrinopurulent phase. The organizing phase of empyema formation
is characterized by established fibrotic peels, viscous pleural
pus, and loculations. Management of organized empyema requires thoracotomy
with decortication or other extensive surgical procedures.
Nearly all bacterial and fungal pathogens that cause pneumonia
can also cause parapneumonic effusions and empyemas. The relative
frequency of different pathogens varies by their distribution as
a cause of pneumonia in a community. Streptococcus