Pleural effusions can occur as the consequence of a localized disease (exudative), or they can be a manifestation of systemic disease (transudative). They are fairly common, and chest physicians are often asked to diagnose and manage them. This chapter reviews the criteria for exudative and transudative pleural effusions, as well as the diagnostic techniques and medical management of several types of nonmalignant pleural effusions, including parapneumonic, connective tissue disease-related effusions, hepatic hydrothorax, and chylothorax. Therapeutic methods, including ultrasound-guided thoracentesis and the indications for chest tube drainage and pleuroscopy are discussed, as well as the use of thrombolytic therapy.

Four types of fluid can occupy the pleural space: serous fluid (hydrothorax), blood (hemothorax), lipid (chylothorax), and pus (empyema). Once the presence of a pleural effusion is established, it is important to determine whether it is a transudate or an exudate. A transudative pleural effusion indicates the presence of a systemic process, implicating organ systems other than the lung. This transudative pleural effusion is caused by medical conditions that lead to volume overload, such as renal failure, heart failure, and hypoalbuminemia (Table 127-1). In contrast, exudative pleural effusions indicate a local pleural process and necessitate a different treatment approach (Table 127-2). In 1972, Light defined the classic criteria for distinguishing between exudative and transudative pleural effusions.¹ To qualify as an exudate, the pleural effusion must meet one of the following criteria: pleural fluid lactate dehydrogenase (LDH) greater than 200 IU/L, ratio of pleural fluid LDH to serum LDH greater then 0.6, or a ratio of pleural fluid protein to serum protein greater than 0.5 (Table 127-3). These criteria have a high sensitivity and low specificity.

Chest Radiography

The chest radiograph is usually the first diagnostic tool used for assessing a pleural effusion. An effusion that causes blunting of the costophrenic angle in the posteroanterior view usually has a fluid volume of approximately 300 mL. In many cases, decubitus films are also obtained to assess whether the effusion is free flowing or is loculated. It is equally important to look for signs of mediastinal shift. An effusion usually shifts the mediastinum to the contralateral side. When the mediastinum is shifted to the ipsilateral side, other causes are implicated, including atelectasis of the underlying lung secondary to an endobronchial lesion, fixation of the mediastinum by fibrosis, or encasement of the lung by a peel.²

Other Imaging Modalities

CT scanning further enhances the abnormalities imaged by chest radiography. Most important, CT scanning differentiates between pulmonary parenchymal and pleural abnormalities. The importance and role of MRI in evaluating pleural effusions are yet to be elucidated.

Ultrasound

Ultrasound has a variety of therapeutic and diagnostic uses, including the ability to image the pleural space at the bedside. It is helpful for determining the presence, size, extent, and location of the pleural effusion. It also can suggest the presence of a complicated and loculated effusion. In complicated effusions, thin echogenic bands appear in the fluid. Ultrasound also can reveal pleural-based masses, which suggest a malignant cause. Therapeutically, ultrasound is used to direct pleural fluid aspiration under visual guidance. Ultrasound guidance decreases the incidence of pneumothorax in nonventilated and ventilated patients.

Thoracentesis

Diagnostic pleural aspiration is essential to the workup. Pleural effusions in patients with congestive heart failure are not usually aspirated; however, the presence of fever or an elevated white blood cell count justifies pleural fluid sampling by means of thoracentesis. The appearance of the thoracentesis sample suggests the etiology of the effusion. The sample is often bloody in patients with trauma, cancer, pulmonary embolism, or tuberculosis. It is milky white in patients with chylothorax and empyema. A yellow-green color suggests rheumatoid pleurisy, and food particles in the pleural fluid suggest esophageal rupture. Once obtained, the pleural fluid is sent for Gram stain and culture. In addition, cell count with differential, amylase, glucose, protein, LDH, pH, and albumin determinations should to be obtained. Despite all these tests, cultures of infected pleural fluid are still negative in 40% of cases. The presence of pus, organisms, or both on pleural fluid Gram stain indicates empyema and requires drainage of the pleural space. Pleural fluid pH less than 7.2 in the setting of infection also suggests a complicated effusion that should be drained.³ Reduced glucose (<35 mg/dL) and elevated LDH (>1000 IU/L) levels similarly support the diagnosis of a complicated effusion.

Before being considered for an elective thoracentesis, the patient must have an international normalization ratio of less than or equal to 1.5 and a platelet count of greater than or equal to 50,000 per microliter. The volume of fluid that can be aspirated safely at thoracentesis is still unknown. It is important to monitor pleural pressures as the fluid is being withdrawn and to stop drainage when the pleural pressure reaches –25 cm H₂O or if the patient complains of chest pain and discomfort because both are signs of lung entrapment. Whenever a thoracentesis is performed, however, it is important to withdraw as much fluid volume as is safely possible to avoid the necessity of a repeat procedure.