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Parapneumonic Pleural Effusions and Empyema Thoracis Workup

  • Author: Atikun Limsukon, MD; Chief Editor: Ryland P Byrd, Jr, MD  more...
 
Updated: Mar 12, 2014
 

Laboratory Studies

No specific laboratory studies of the serum suggest the presence of a parapneumonic effusion or empyema. However, the possibility of a parapneumonic effusion and empyema should be a consideration for every patient with pneumonia. The presence of pleural fluid may be suggested based on physical examination findings; however, small pleural effusions may not be detected during the physical examination. In this case, any significant effusion can be visualized using 2-view (ie, posteroanterior, lateral) chest radiography.

Sputum should be submitted for culture, especially if purulent (see Sputum Culture). The infecting organism may be suggested based on Gram stain results. Mixed florae are often seen in anaerobic infections.

As with any infection, leukocytosis may be present (>12,000/µL) (see Leukocyte Count); however, it should decrease with adequate antibiotic therapy. Persistent fever and leukocytosis despite adequate antibiotic therapy may signal a persistent focus of infection, such as a complicated parapneumonic effusion or empyema, with subsequent evaluation as outlined in the following sections. Diagnosing a complicated parapneumonic effusion and/or empyema is crucial for optimal management because a delay in drainage of the pleural fluid substantially increases morbidity.

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Imaging Studies

See the list below:

  • Chest radiography
    • Lateral chest radiography usually demonstrates the presence of a significant amount of pleural fluid, as shown in the image below.
      Left lateral chest radiograph shows a large, left Left lateral chest radiograph shows a large, left pleural effusion.
    • If either of the diaphragms is not visible throughout its entire length, the posterior costophrenic angles are blunted, or a lateral meniscus is visible, then bilateral decubitus chest radiographs should be obtained.
    • Free pleural fluid is seen as a dense linear shadow layering between the chest wall and the lung parenchyma.
    • Unchanging pleural-based linear densities, pleural-based mass-liked densities, or collections with obtuse angles suggest the presence of loculated fluid, especially if the differences in the fluid or the appearance between upright and lateral views are minimal.
    • If the pleural fluid distance measures more than 10 mm from the chest wall, sufficient free-flowing fluid is present to perform a diagnostic thoracentesis.
  • Ultrasonography
    • Ultrasonography can be used to localize fluid for a thoracentesis. Fluid appears dark or black on ultrasound images, and most bedside ultrasonography devices permit measurement of the depth of location from the chest wall.
    • Complex fluid (purulent or viscous) may have more density or shadows within in the pleural fluid collection. Sometimes, fibrinous strands can be seen floating in the pleural fluid.
    • Other structures such as the diaphragm or lung parenchyma can provide landmarks to assist in needle placement for thoracentesis.
    • Loculated pleural effusions may be difficult to localize during physical examination, but they can usually be identified with ultrasonography.
    • Ultrasonography can effectively distinguish loculated pleural fluid from an infiltrate. The latter may have air bronchograms visible, but the distinction may be difficult if a dense consolidation is present. If a loculated pleural effusion is suspected, an ultrasonographic examination is recommended for diagnosis and marking the area for thoracentesis.
  • CT scanning of the thorax
    • CT scanning of the chest with contrast, as shown in the image below, enhances the pleural surface and assists in delineating the pleural fluid loculations.
      CT scan of thorax shows loculated pleural effusion CT scan of thorax shows loculated pleural effusion on left and contrast enhancement of visceral pleura, indicating the etiology is likely an empyema.
      Chest CT scan with intravenous contrast in a patie Chest CT scan with intravenous contrast in a patient with mixed Streptococcus milleri and anaerobic empyema following aspiration pneumonia, showing a thickened contrast-enhanced pleural rind, high-density pleural effusion, loculation, and septation. Thoracentesis yielded foul-smelling pus.
    • Pleural enhancement can be seen in patients with active inflammation and severe pleuropulmonary infections, which provides another sign of the possibility of a complicated pleural effusion or empyema.
    • CT scanning of the chest may also help detect airway or parenchymal abnormalities such as endobronchial obstruction or the presence of lung abscesses.
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Other Tests

While no diagnostic serum laboratory tests are available for a parapneumonic effusion, serum total protein and lactic dehydrogenase (LDH) levels should be obtained to help characterize whether the pleural fluid is an exudate or transudate. The ratio of pleural fluid/serum protein and LDH is used to distinguish between these two entities.

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Procedures

Thoracentesis is recommended when the suspected parapneumonic pleural effusion is greater than or equal to 10 mm thick on a lateral decubitus chest radiograph.[8] See the image below.

A right lateral decubitus chest radiograph shows a A right lateral decubitus chest radiograph shows a free-flowing pleural effusion, which should be sampled with thoracentesis for pH determination, Gram stain, and culture.

Pleural fluid appearance may vary from a clear yellow liquid to an opaque turbid fluid to grossly purulent thick, viscous, foul-smelling pus. Foul-smelling fluid indicates an anaerobic infection.

  • Pleural fluid studies
    • Blood cell count (WBC count) and differential: Results generally are not diagnostic, but most transudates are associated with a WBC counts of less than 1000 cells/µL and empyemas are exudates, with WBC counts generally greater than 50,000 cells/µL.
    • Pleural fluid total protein, LDH, and glucose (corresponding serum protein and LDH): Exudates are defined by pleural/serum total protein ratio of greater than 0.5 and a pleural/serum LDH ratio of greater than 0.6 or a pleural fluid LDH value greater than two thirds the upper limit of normal. One criterion is sufficient to classify fluid as an exudate.
    • Pleural fluid pH (iced blood gas syringe): Values of less than 7.20 are suggestive of a complicated pleural effusion.
    • Other laboratories suggestive of complicated pleural effusion or empyema: These include (1) an LDH value of greater than 1000 U/L, (2) a pH of less than 7.00, and (3) a glucose level of less than 40 mg/dL.
  • Microbiology (Gram stain, bacterial culture): Acid-fast bacilli and fungal infections may cause pleural effusions or empyema, but these organisms are more difficult to culture from pleural fluid.
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Histologic Findings

Multiple granulocytes are typically identified on histologic examination. Necrotic debris may be present. Bacteria are seen in the pleural fluid in severe infections.

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Staging

The following classification and treatment scheme has been used to characterize parapneumonic effusions and empyema.

  • Category 1 (parapneumonic effusion)
    • Minimal free-flowing fluid, smaller than 10 mm on decubitus films
    • Culture, Gram stain, and pH unknown
    • No thoracentesis needed; treatment with antibiotics alone
  • Category 2 (uncomplicated parapneumonic effusion)
    • Larger than 10 mm fluid and less than half the hemithorax on decubitus films
    • Gram stain and culture negative
    • pH higher than 7.20
    • Treatment with antibiotics alone
  • Category 3 (complicated parapneumonic effusion)
    • Large free-flowing effusion, more than half the hemithorax
    • pH lower than 7.20, LDH level greater than 1000 U/L and glucose level greater than 40 mg/dL
    • Gram stain or culture positive
    • Treatment with tube thoracostomy and antibiotics
    • Multiloculated effusions may require multiple tubes
    • Thrombolytics may help resolution
  • Category 4 (empyema)
    • Large free-flowing effusion, greater than equal to half the hemithorax
    • Loculated effusion or effusion with thickened pleura
    • Gross pus on aspiration
    • Treatment with tube thoracostomy
    • Thrombolytics may help resolution
    • May require decortication
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Contributor Information and Disclosures
Author

Atikun Limsukon, MD Instructor, Department of Pulmonary, Allergy and Critical Care Medicine, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, Thailand

Disclosure: Nothing to disclose.

Coauthor(s)

Guy W Soo Hoo, MD, MPH Clinical Professor of Medicine, University of California, Los Angeles, David Geffen School of Medicine; Director, Medical Intensive Care Unit, Pulmonary and Critical Care Section, West Los Angeles Healthcare Center, Veteran Affairs Greater Los Angeles Healthcare System

Guy W Soo Hoo, MD, MPH is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Thoracic Society, Society of Critical Care Medicine, California Thoracic Society, American Association for Respiratory Care

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Ryland P Byrd, Jr, MD Professor of Medicine, Division of Pulmonary Disease and Critical Care Medicine, James H Quillen College of Medicine, East Tennessee State University

Ryland P Byrd, Jr, MD is a member of the following medical societies: American College of Chest Physicians, American Thoracic Society

Disclosure: Nothing to disclose.

Additional Contributors

Michael Peterson, MD Chief of Medicine, Vice-Chair of Medicine, University of California, San Francisco, School of Medicine; Endowed Professor of Medicine, University of California, San Francisco-Fresno, School of Medicine

Michael Peterson, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, American Thoracic Society

Disclosure: Nothing to disclose.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author, Sat Sharma, MD, FRCPC, to the development and writing of this article.

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Left pleural effusion developed 4 days after antibiotic treatment for pneumococcal pneumonia. Patient developed fever, left-sided chest pain, and increasing dyspnea. During thoracentesis, purulent pleural fluid was removed, and the Gram stain showed gram-positive diplococci. The culture confirmed this to be Streptococcus pneumoniae.
Left lateral chest radiograph shows a large, left pleural effusion.
A right lateral decubitus chest radiograph shows a free-flowing pleural effusion, which should be sampled with thoracentesis for pH determination, Gram stain, and culture.
CT scan of thorax shows loculated pleural effusion on left and contrast enhancement of visceral pleura, indicating the etiology is likely an empyema.
Chest CT scan with intravenous contrast in a patient with mixed Streptococcus milleri and anaerobic empyema following aspiration pneumonia, showing a thickened contrast-enhanced pleural rind, high-density pleural effusion, loculation, and septation. Thoracentesis yielded foul-smelling pus.
Chest CT scan with intravenous contrast in a patient with mixed Streptococcus milleri and anaerobic empyema following aspiration pneumonia, 3 days following thoracostomy and intrapleural fibrinolysis (Reteplase).
 
 
 
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