ESSENTIALS OF DIAGNOSIS
May be asymptomatic; chest pain frequently seen in the setting of pleuritis, trauma, or infection; dyspnea is common with large effusions.
Dullness to percussion and decreased breath sounds over the effusion.
Radiographic evidence of pleural effusion.
Diagnostic findings on thoracentesis.
There is constant movement of fluid from parietal pleural capillaries into the pleural space at a rate of 0.01 mL/kg body weight/h. Absorption of pleural fluid occurs through parietal pleural lymphatics. The resultant homeostasis leaves 5–15 mL of fluid in the normal pleural space. A pleural effusion is an abnormal accumulation of fluid in the pleural space. Pleural effusions may be classified by differential diagnosis (Table 9–25) or by underlying pathophysiology. Five pathophysiologic processes account for most pleural effusions: increased production of fluid in the setting of normal capillaries due to increased hydrostatic or decreased oncotic pressures (transudates); increased production of fluid due to abnormal capillary permeability (exudates); decreased lymphatic clearance of fluid from the pleural space (exudates); infection in the pleural space (empyema); and bleeding into the pleural space (hemothorax). Parapneumonic pleural effusions are exudates that accompany bacterial pneumonias.
Table 9–25.Causes of pleural fluid transudates and exudates. |Favorite Table|Download (.pdf) Table 9–25. Causes of pleural fluid transudates and exudates.
|Transudates ||Exudates |
Heart failure (> 90% of cases)
Cirrhosis with ascites
Superior vena cava obstruction
Pneumonia (parapneumonic effusion, including empyema)
Bacterial infection (including empyema)
Connective tissue disease
Post–myocardial injury syndrome
Diagnostic thoracentesis should be performed whenever there is a new pleural effusion and no clinically apparent cause. Observation is appropriate in some situations (eg, symmetric bilateral pleural effusions in the setting of heart failure), but an atypical presentation or failure of an effusion to resolve as expected warrants thoracentesis. Sampling allows visualization of the fluid in addition to chemical and microbiologic analyses to identify the underlying pathophysiologic process.
Patients with pleural effusions most often report dyspnea, cough, or respirophasic chest pain. Symptoms are more common in patients with existing cardiopulmonary disease. Small pleural effusions are less likely to be symptomatic than larger effusions. Physical findings are usually absent in small effusions. Larger effusions may present with dullness to percussion and diminished or absent breath sounds over the effusion. Compressive atelectasis may cause bronchial breath sounds and egophony just above the effusion. A massive effusion with increased intrapleural pressure may cause contralateral shift of the trachea and bulging of the intercostal spaces. A pleural friction rub indicates pulmonary infarction or pleuritis (AUDIO 9–13).