INTRODUCTION AND EPIDEMIOLOGY
Empyema is pus in the pleural space. A parapneumonic effusion is a pleural effusion associated with a lung infection, usually pneumonia but infrequently a lung abscess. Bacterial pneumonia with a parapneumonic effusion is the most common precursor, seen in about 60% of empyema patients.1 Other causes of empyema are complications of chest surgery (22%), trauma (4%), esophageal perforation (4%), complications of chest tube/thoracentesis (4%), an extension from a subdiaphragmatic infection (3%), and assorted triggers (7%), including a hemothorax, chylothorax, or hydrothorax that becomes infected due to a systemic infection with hematogenous spread such as septicemia.1,2
Of the approximately 1 million pneumonia patients hospitalized each year in the United States, 20% to 40% develop a parapneumonic effusion; 5% to 10% of patients with a parapneumonic effusion develop an empyema.3,4 Mortality in adults is about 20%.5 With the advent of antibiotics, the incidence of empyema decreased in the first half of the 20th century, but since the 1990s, the incidence of empyema has increased in the United States and worldwide.3,6
Predisposing factors for empyema include aspiration (and the conditions causing this event, notably altered swallowing), respiratory disease impairing ciliary function, immunocompromise, malignancy, IV drug abuse, alcoholism, diabetes, gastroesophageal reflux disease, and poor oral hygiene.1
Suspect empyema if symptoms of pneumonia (fever, cough, dyspnea, pleuritic chest pain, and malaise) do not resolve with therapy. The onset of empyema may be insidious, with patients appearing chronically ill with weight loss, anemia, and night sweats.3
Physical examination findings include decreased breath sounds, dullness to percussion, decreased tactile fremitus, and occasionally a friction rub.7 Pain from an underlying effusion or empyema may cause splinting with respiration. If there is an underlying pulmonary infection, rales or rhonchi may exist.
Diagnostic criteria for empyema are aspiration of grossly purulent material on thoracentesis and at least one of the following: thoracentesis fluid with a positive Gram stain or culture, pleural fluid glucose <40 milligrams/dL, pH <7.2, or lactate dehydrogenase >1000 IU/L. For empyema from tuberculosis, absolute lymphocyte count on pleural fluid is useful, although other markers such as interferon release assays or adenosine deaminase show promise.4 Pleural biopsy is diagnostic in 55% to 70% of patients, demonstrating a granuloma and/or being culture positive.4
A pleural-based opacity on a chest radiograph, including a lateral decubitus film, suggests a pleural effusion or empyema. POCUS accurately identifies pleural effusions and empyemas, differentiates a loculated effusion from a mass, and guides thoracentesis and chest tube placement. A chest CT scan with IV contrast can assess for a loculated effusion or empyema and identify any other abnormalities present.
The definitive treatment of an empyema is drainage ...