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The goal of the initial evaluation is to establish whether an exudate is present or not and alleviate dyspnea if present. Because clinical judgment is inferior to biochemical parameters to classify effusions, 5 initial assessment should include a thoracentesis, which can also be therapeutic to alleviate dyspnea (suggested analyses in Table 1). Based on a small randomized controlled trial7 and a well-conducted 2010 systematic review and metaanalysis, 8 the British Thoracic Society guideline recommends performing thoracentesis with guidance by ultrasonography to reduce the rate of pneumothorax and dry aspiration. 1 In the systematic review, risk of pneumothorax was 9.3% without and 4% with ultrasonography guidance. 8 Minimal fluid depths of 10 mm9 to 15 mm10 have been recommended as safe thresholds for aspiration, but no comparative data exists. Ultrasonography cannot reliably distinguish exudates from transudates because their characteristics substantially overlap. For example, although an anechoic ultrasonography pattern is encountered in most transudates, one-third of exudates may also have an anechoic appearance based on small single-centre series. 11, 12 A detailed discussion of the periprocedural management of antiplatelet therapy, anticoagulation and abnormal coagulation parameters is beyond the scope of this review. However, in the presence of respiratory distress or a high suspicion of infection, a thoracentesis could be performed, if the expected benefits outweigh the potential risks.

In some situations, thoracentesis may be deferred. A mediastinal or tracheal shift toward the effusion on radiography (Figure 1B …