When deciding to incorporate a new procedure into clinical practice, it is essential to carefully evaluate the reasons for doing so. The procedure should ideally add useful clinical information that will impact management, be easy to perform, have few risks to the patient, and not add significant costs to the care of the patient. The routine use of pleural manometry to thoracenteses satisfies all of these requirements and should be performed with every thoracentesis.
There are approximately 1.5 million patients diagnosed with pleural effusions each year in the United States, making thoracentesis one of the most commonly performed medical procedures.1 Although investigations of pleural pressures have been undertaken for > 120 years,2 the clinical use of pleural manometry has become more popular only over the last 3 decades. The measurement of pleural pressure during thoracentesis provides information regarding both the cause of the effusion and the ability of the lung to expand as fluid is withdrawn. Pleural fluid formation is dependent on the balance of hydrostatic and oncotic pressures between the pleural space and the visceral and parietal pleural capillaries. In the normal thorax, at functional residual capacity (FRC), pleural pressure is slightly subatmospheric, approximately −3 to −5 cm H2O. This results from the equilibrium achieved by the elastic recoil forces of the lung and the tendency of the chest wall to expand. As fluid accumulates in the pleural space, pleural pressure typically rises. This, however, is dependent on the cause of the effusion, as diseases that cause a drop in pleural pressure will clearly increase the hydrostatic gradient for pleural fluid formation. Likewise, as pleural fluid is removed, one would expect the lung to expand, the chest wall to contract, and pleural pressure to reach its steady state at FRC. The ability for the lung to expand, however, can greatly affect pleural pressure, especially toward the terminal portion of the thoracentesis. The measurement of pleural pressure is the only way to assess the underlying physiology of the lung and pleural space and provides clinically useful information regarding the cause of the effusion, minimizes pressure-related complications of thoracentesis, and can predict the success of pleurodesis in patients with malignant pleural effusions.