Pleura

SECTION N

DISORDERS OF THE PLEURA CHAPTER 73

PLEURAL EFFUSION
V. Courtney Broaddus, MD • Richard W. Light, MD

INTRODUCTION THE PLEURA: FORM AND FUNCTION EMBRYOLOGY AND ANATOMY Blood Supply Lymphatics Nerve Supply PHYSIOLOGY OF THE PLEURAL SPACE Normal Pleural Liquid and Protein Turnover Pleural Pressure PATHOPHYSIOLOGY OF THE PLEURAL SPACE Pleural Effusions Effects of Pleural Effusionson Lung and Cardiac Function APPROACH TO PATIENTS WITH PLEURAL EFFUSION Differential Diagnosis of Pleural Effusion Separation of Exudates from Transudates Differentiating Exudative Pleural Effusions Other Diagnostic Tests for Pleural Fluid Useful Radiographic Tests in Patients with Suspected Pleural Disease Invasive Tests in Patients with Undiagnosed Exudative Pleural Effusions

TRANSUDATIVEPLEURAL EFFUSIONS Congestive Heart Failure Pericardial Disease Hepatic Hydrothorax Nephrotic Syndrome Peritoneal Dialysis Urinothorax Myxedema Fontan Procedure Other Causes of Transudative Pleural Effusions EXUDATIVE PLEURAL EFFUSIONS Parapneumonic Effusions and Empyema Tuberculous Pleuritis Actinomycosis Nocardiosis Fungal Infections Viral Infections Parasitic Diseases Pulmonary Embolism AbdominalDiseases Miscellaneous Diseases

INTRODUCTION
The pleural space is bounded by two membranes, the visceral pleura covering the lung and the parietal pleura covering the chest wall and diaphragm. Into this space, normal liquid and protein enter from the systemic circulation and are removed by the parietal pleural lymphatics. Pleural pressure is subatmospheric and ensures inflation of the lung.Because the mesothelial boundaries are leaky, excess liquid can move across into this lowerpressure, high-capacitance space and collect as a pleural effusion. Thus, pleural effusions are common and of highly diverse etiologies. These effusions can form based

on disease of the pleural membranes themselves or of thoracic or abdominal organs. Depending on the protein and lactate dehydrogenase (LDH)concentrations of the liquid and on the cellular composition, these effusions can be categorized initially as exudates or transudates. Exudative pleural effusions meet at least one of the following criteria, whereas transudative effusions meet none (Light’s criteria): pleural fluid protein–to–serum protein ratio of more than 0.5, pleural fluid LDH–to– serum LDH ratio of more than 0.6, and pleural fluidLDH more than two thirds of the upper normal limit for serum. In this chapter, we discuss both the physiology and the pathophysiology of liquid movement in the pleural space. 1719

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DISORDERS OF THE PLEURA distribute the forces produced by negative inflation pressures evenly over the lung. In this way, overdistention of alveoli at the pleural surface may be avoided, lessening the chanceof rupture and pneumothorax. One more recently recognized function of the pleural space is to provide a route by which edema can escape the lung.5 As has been shown in several experimental studies of either hydrostatic or increased permeability lung edema,6,7 the pleural space can function as an additional safety factor protecting against the development of alveolar edema. The formation oftransudative effusions in patients with congestive heart failure (CHF) apparently reflects the movement of edema from the lung to a space where its effects on lung function are relatively small.

THE PLEURA: FORM AND FUNCTION
These two pleural membranes meet at the hilar root of the lung. In the sheep, an animal with a pleural anatomy similar to that of humans, the surface area of the visceral pleuraof one lung, including that invaginating into the lung fissures, is similar to that of the parietal pleura of one hemithorax, approximately 1000 cm2.1 The normal pleural space is approximately 18 to 20 µm in width, although it widens at its most dependent areas.1 It has been shown that the pleural membranes do not touch each other and that the pleural space is a real, not a potential, space1 (Fig....