eMedicine Specialties > Emergency Medicine > Pulmonary
Pneumonia, Empyema and Abscess
Updated: Nov 7, 2007
Introduction
Background
A lung abscess is a subacute infection in which an area of necrosis forms in the lung parenchyma. It usually is in a dependent section of the lung, more often involves the right lung than the left, and is most commonly seen after aspiration of oropharyngeal secretions. Lung abscesses have a slow, insidious presentation and usually develop 1-2 weeks after the initial aspiration event.
Empyema is defined as pus in the pleural space. It typically is a complication of pneumonia. However, it can also arise from penetrating chest trauma, esophageal rupture, complication from lung surgery, or inoculation of the pleural cavity after thoracentesis or chest tube placement. An empyema can also occur from extension of a subdiaphragmatic or paravertebral abscess.
Pathophysiology
A lung abscess involves the lung parenchyma, while an empyema involves the pleural space. In many patients with pneumonia, a sterile simple parapneumonic effusion develops in the pleural space. If this pleural effusion becomes infected, it is labeled a complicated parapneumonic effusion, while the presence of frank pus in the pleural space defines an empyema. The development stages of an effusion can be divided into 3 phases: exudative, fibropurulent, and organizational. The initial effusion develops from increased pulmonary interstitial fluid along with progressive capillary vascular permeability. A simple effusion is frequently sterile and resolves with antibiotic treatment of the underlying pulmonary infection. In 5-10% of the patients with a pleural effusion, the effusion becomes infected and neutrophils buildup. This inflammatoryresponse also causes the production of chemokines, cytokines, oxidants, and protease mediators. This more complicated parapneumonic effusion needs both antibiotics and some form of surgical drainage or alternative treatment modality to remove the purulent effusion. In these more complicated effusions, fibrinolysis and activation of the coagulation cascade leads to the production of fibrin with subsequent adhesions and loculated fluid collections. This process ultimately can cause pleural fibrosis and impairment of lung expansion.
Frequency
United States
An estimated 60,000 pleural infections are diagnosed annually in the United States.
Mortality/Morbidity
The mortality rate for lung abscesses is approximately 4-7% but varies with the type of material aspirated. Aspiration of fluids with mixed gram-negative flora has a mortality rate approaching 20%, while aspiration of acidic materials has an even higher rate. The fatality rate for complicated parapneumonic effusions is estimated to be as high as 15%.
Age
Complicated effusions and empyema are more common in elderly persons and during childhood. An increase has occurred in the incidence of empyema in the pediatric population. Lung abscess is more common in elderly persons.
Clinical
History
The patient's history may reveal the following findings:
- Recent diagnosis and treatment of pneumonia
- Recent history of penetrating chest trauma (should raise clinical suspicion for empyema)
- Cough productive of bloody sputum that frequently has a fetid odor or offensive appearance
- Fever
- Shortness of breath
- Anorexia, weight loss
- Night sweats
- Pleuritic chest pain
Physical
The physical examination may reveal the following findings:
- Temperature frequently elevated but usually not greater than 102°F
- Tachypnea
- Rales
- Rhonchi
- Egophony
- Tubular breath sounds
- Decreased breath sounds
- Dullness to percussion
Causes
- The most common cause of lung abscess is aspiration. Patients at the highest risk are those who have the following:
- Poor dentition
- Seizure disorder
- Alcohol abuse
- Inability to protect their airway because of an absent gag reflex (eg, patients who are comatose, have a change in mentation, or who might be undergoing general anesthesia)
- Primary lung disorders, such as septic emboli, vasculitic disorders, cavitating lung malignancies, or pulmonary cystic disease
- Penetrating chest trauma
- The microbiologic organisms involved in lung abscesses typically are polymicrobial oral flora, including Bacteroides, Fusobacterium, and Peptostreptococcus species. Other organisms include Pseudomonas species, Klebsiella species, Staphylococcus aureus, Streptococcus pneumoniae, Nocardia species, and less commonly fungi.
- The most common cause of an empyema is from a parapneumonic effusion that becomes infected; these account for about half of all empyemas. Other causes of an empyema include the following:
- Penetrating chest trauma
- Contamination of a wound because of inadequate skin preparation during procedures such as needle decompression, chest tube placement, thoracentesis, or lung surgery
- Microbiologic organisms that cause an empyema include streptococcus species such as Streptococcus intermedius, Streptococcus constellatus, Streptococcus inonia, S pneumoniae, staphylococci, and a variety of gram-negative organisms and anaerobes. In the pediatric population, S aureus has become the predominant organism associated with empyemas because of the widespread use of the pneumococcal conjugate vaccine. One should always consider methicillin-resistant Staphylococcus aureus (MRSA), enterobacteria, enterococcus, and Mycobacterium tuberculosis as potential pathogens.
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Further Reading
Keywords
aspiration, lung abscess, pleural pus, penetrating chest trauma, esophageal rupture, inoculation of the pleural cavity, thoracentesis, chest tube placement, subdiaphragmatic abscess, paravertebral abscess, poor dentition, absent gag reflex, septic emboli, vasculitic disorders, cavitating lung malignancies, pulmonary cystic disease, needle compression, polymicrobial oral flora, Bacteroides species, Fusobacterium species, Peptostreptococcus species, Staphylococcus aureus, S aureus, MRSA, Mycobacterium tuberculosis, M tuberculosis, skin flora, Staphylococcus epidermis, S epidermis, pleural effusion
