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Physicians or other clinicians perform an estimated 173,000 thoracenteses in the United States every year. The strict indications for thoracentesis are the presence of pleural fluid of unknown etiology where the physician cannot initiate care prior to diagnosis and severe dyspnea (Table 124-1).

Pleural effusions develop secondarily to systemic changes (transudates) or to local causes (exudates). Systemic causes that lead to the formation and absorption of pleural fluid most commonly include left ventricular heart failure, pulmonary embolism, cirrhosis, and renal disease. Acute pancreatitis may cause a left-sided pleural effusion. Pleural effusions commonly occur after abdominal surgery due to the porous diaphragm and are usually benign. Renal diseases that can cause pleural effusion include the nephrotic syndrome and urinothorax from hydronephrosis. Myxedema and cerebrospinal fluid leak to the pleura are other causes of transudates.

Local causes (exudates) are most commonly bacterial pneumonia, viral infection, malignancy, and pulmonary embolism. Parapneumonic effusions start out as sterile, reactive effusions and can rapidly progress to loculated empyema in immunocompromised patients or when there is a delay in administration of appropriate antibiotics. Failure to identify those patients with empyema or significant inflammation necessitating pleural drainage can result in trapped lung. Other infectious causes include tuberculosis, fungal infection and intra-abdominal abscess. Pancreatic pseudocyst, postcoronary artery bypass grafting or cardiac contusion, pericardial disease, drug-induced pleuritis, rheumatologic disease, uremia, and gynecologic disorders may also cause exudates. The most common causes of malignant pleural effusions in descending order of frequency are lung cancer, breast cancer, and lymphoma. In a patient with a prior history of asbestos exposure, mesothelioma should be suspected, especially if the pleural effusion is grossly hemorrhagic. (See Chapter 236 [Pleural Diseases].)

While dullness to percussion and reduced tactile fremitus are valuable findings to help identify a pleural effusion (positive likelihood ratio [LR+], 8.7 and 5.7, respectively), the physical examination is usually not helpful in diagnosing the cause of the pleural effusion or in ascertaining the best location to perform the thoracentesis.

The first step is to determine whether there is fluid by radiographic imaging. On chest x-ray (CXR), a pleural effusion will characteristically push the heart to the opposite side. If, however, the opacified space does not shift the heart, it is possible that the patient has significant atelectasis as the cause. A lateral decubitus film should reveal whether there is free-flowing fluid, and should be ordered to document free flow in most patients prior to thoracentesis. If there is doubt, ultrasonography can identify solid from liquid pleural effusions with 98% accuracy when combined with CXR. Computed tomography (CT) imaging may be indicated prior to definitive drainage in some instances, and CT-PE protocol imaging should be performed if pulmonary embolism is suspected. (See Chapter 114 [Basic Chest Radiography] and Chapter 115 [Advanced Cardiothoracic Imaging].)

In general, the procedure is usually safe and well tolerated (Table 124-2). However, when iatrogenic ...

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