eMedicine Specialties > Pulmonology > Pleural Disorders
Empyema, Pleuropulmonary
Updated: Jun 23, 2006
Introduction
Background
For centuries, empyema has been recognized as a serious problem. Around 500 BC, Hippocrates recommended treating empyema with open drainage. Since then, the treatment of empyema remained essentially unchanged until the middle of the 19th century. In 1876, Hewitt described a method of closed drainage of the chest in which a rubber tube was placed into the empyema cavity and drained via the water seal drainage. In the early 20th century, surgical therapies for empyema (eg, thoracoplasty, decortication) were introduced.
Parapneumonic pleural effusions are divided into 3 groups or stages based on pathogenesis: uncomplicated parapneumonic effusion, complicated parapneumonic effusion, and thoracic empyema.
Uncomplicated parapneumonic effusion is an exudative predominantly neutrophilic effusion that occurs as the lung interstitial fluid increases during pneumonia. These effusions are resolved with appropriate antibiotic treatment of pneumonia.
Complicated parapneumonic effusion is a bacterial invasion of the pleural space that leads to an increased number of neutrophils, pleural fluid acidosis, and elevated lactic dehydrogenase (LDH) concentration. These effusions often are sterile because bacteria are usually cleared rapidly from the pleural space.
Thoracic empyema is characterized by either aspiration of pus on thoracentesis or the presence of bacterial organisms on Gram stain. A positive culture is not required for diagnosis.
Pathophysiology
The evolution of a parapneumonic pleural effusion (see Image 1) can be divided into 3 stages, including exudative, fibropurulent, and organization stages.
During the exudative stage, sterile pleural fluid rapidly accumulates in the pleural space. The pleural fluid originates in the interstitial spaces of the lung and in the capillaries of the visceral pleura because of increased permeability. The pleural fluid has a low WBC and LDH level, and the glucose and pH levels are within the reference range. These effusions resolve with antibiotic therapy, and chest tube insertion is not required.
During the fibropurulent stage, bacterial invasion of the pleural space occurs, with accumulation of polymorphonuclear leucocytes, bacteria, and cellular debris. A tendency toward loculation exists, pleural fluid pH and glucose levels are lower, and the LDH level increases.
During the organization stage, fibroblasts grow into the exudates from both the visceral and parietal pleural surfaces, and they produce an inelastic membrane called pleural peel. Pleural fluid is thick. In an untreated patient, pleural fluid may drain spontaneously through the chest wall (ie, empyema necessitatis). Empyema may arise without an associated pneumonic process. The most common causes are esophageal perforation, trauma, surgical procedure on pleural space, and septicemia.
Bacteriologic features of culture-positive parapneumonic effusions have changed over time. Prior to the antibiotic era, Streptococcus pneumoniae and hemolytic streptococci were common. Presently, aerobic organisms are isolated slightly more frequently than anaerobic organisms. Staphylococcus aureus and S pneumoniae account for approximately 70% of aerobic gram-positive cultures.
Bacteriology of parapneumonic effusions is closely related to the bacteriology of a pneumonic process. Gram-positive aerobic organisms are isolated twice as frequently as gram-negative aerobic organisms. Klebsiella, Pseudomonas, and Haemophilus species are the 3 most commonly isolated aerobic gram-negative organisms. Bacteroides and Peptostreptococcus species are the 2 most commonly isolated anaerobic organisms. A mixed bacterial flora containing aerobes and anaerobes is more likely to produce an empyema than a single-organism infection. Anaerobic bacteria have been cultured in 36-76% of empyemas.
Frequency
United States
Incidence of pleural effusion with various pneumonias depends on the infecting organism. The pleural space is commonly infected in patients with anaerobic pneumonia. In one series of patients with anaerobic infections of the lung, 35% had pleural effusions, and 94% of these were positive for organisms. Aerobic organisms were cultured from the pleural fluid in 40% of patients. Generally speaking, pleural effusions occur in 40% of bacterial pneumonias.
Mortality/Morbidity
Mortality rates associated with empyema depend upon severity of the underlying disease and prompt therapy. A mortality rate of 11-50% has been reported. In patients who are older and debilitated, mortality is high.
Clinical
History
Clinical manifestations of parapneumonic effusion and empyema largely depend on whether the patient has an aerobic or anaerobic infection. If fever persists for more than 48 hours after initiation of antibiotic treatment, a complicating parapneumonic effusion or empyema likely exists.
- Aerobic bacterial pneumonia
- Clinical presentation in patients with aerobic bacterial pneumonia is similar to that of bacterial pneumonia.
- Patients present with an acute febrile illness with chest pain, sputum production, and leukocytosis.
- A complicated parapneumonic effusion is suggested by the presence of a fever lasting more than 48 hours after initiation of antibiotic therapy.
- Anaerobic bacterial infection
- Patients with anaerobic bacterial infections involving the pleural space usually present with a subacute illness.
- Most of these patients have symptoms persisting for more than 7 days.
- Approximately 60% of patients have weight loss.
- Most of these patients have poor oral hygiene, many suffer from alcoholism, and others have factors that predispose them to recurrent aspiration.
Physical
- Patients may have a fever and appear toxic.
- The signs of pleural effusion, including dullness on percussion and absence of breath sounds, are evident.
Causes
In the preantibiotic era, as many as 11% of incidents of pneumococcal pneumonia were associated with empyema, and 64% of empyemas were caused by S pneumoniae. Beta-hemolytic streptococci caused 15% of empyemas, and staphylococci caused 8% of empyemas.
- Anaerobic infections currently comprise as many as 40% of empyemas.
- Empyema is most often associated with pneumonia, particularly aspirational events with anaerobic microbiology.
- Increasingly, empyema is a complication of previous surgery, which accounts for 30% of cases. The usual organisms are Staphylococcus species and gram-negative bacteria.
- Trauma may also be associated with superinfection of pleural space.
- In the absence of trauma or surgery, the infecting organism may spread from blood or other organs into the pleural space. These are subdiaphragmatic abscesses (eg, ruptured esophagus, mediastinitis, osteomyelitis, pericarditis, cholangitis, diverticulitis, pericarditis).
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References
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Further Reading
Keywords
pleuropulmonary empyema, complicated parapneumonic pleural effusion, Staphylococcus aureus, S aureus, Streptococcus pneumoniae, S pneumoniae, Klebsiella, Pseudomonas, Haemophilus, Bacteroides, Peptostreptococcus, uncomplicated parapneumonic effusion, thoracic empyema, thoracoplasty, decortication, pneumonia, parapneumonic effusion, esophageal perforation, trauma, surgical procedure on pleural space, septicemia
