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For further information, see CMDT Part 9–36: Pleural Effusion

Key Features

Essentials of Diagnosis

  • May be asymptomatic

  • Chest pain occurs 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

General Considerations

  • Pleural fluid is produced at 0.01 mL/kg body weight/hour; a normal volume in the pleural space is 5–15 mL

  • Transudative effusions (see Laboratory Tests) occur in the absence of pleural disease; heart failure accounts for the majority of cases

  • Exudative effusions are most commonly due to pneumonia (parapneumonic effusions) and malignancy (malignant effusions)

  • Analysis of pleural fluid allows for identification of five pathophysiologic processes leading to accumulation of pleural fluid

    • Increased production due to increased hydrostatic or decreased oncotic pressures (transudates)

    • Increased production due to abnormal capillary permeability (exudates)

    • Decreased lymphatic clearance of fluid (exudates)

    • Infection in the pleural space (empyema)

    • Bleeding into the pleural space (hemothorax)

  • A definitive diagnosis is made through cytology or identification of causative organism in 25% of cases

  • In 50–60% of cases, classification of the effusion leads to a presumptive diagnosis

  • Diagnostic thoracentesis should be performed whenever there is a new pleural effusion and no clinically apparent cause

Clinical Findings

Symptoms and Signs

  • Dyspnea, cough, or chest pain with respirations

  • Symptoms are more common in patients with underlying cardiopulmonary disease

  • Large effusions are more likely to be symptomatic

  • Bronchial breath sounds and egophony above the effusion are caused by compressive atelectasis

  • Massive effusions may cause contralateral shift of the trachea and bulging of intercostal spaces

  • A pleural friction rub indicates infarction or pleuritis

Differential Diagnosis

  • Atelectasis

  • Chronic pleural thickening

  • Lobar consolidation

  • Subdiaphragmatic process

  • Table 9–23

Table 9–23.Causes of pleural fluid transudates and exudates.


Laboratory Tests

  • Pleural fluid should be sent for

    • Protein

    • Glucose

    • Lactate dehydrogenase (LD)

    • Cell count

    • Gram stain

    • Culture

  • Exudates have one or more of the following

    • Pleural fluid protein/serum protein > 0.5

    • Pleural fluid LD/serum LD > 0.6

    • Pleural fluid LD more than two-thirds of the upper limit of normal serum LD

  • Bacterial pneumonia, cancer, and tuberculosis (in endemic regions) are the most common causes of ...

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