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Chapter 8
Approach to the Patient
Whenever a patient with an abnormal chest radiograph is evaluated, the possibility of a pleural effusion should be considered. Increased densities on the chest radiograph are frequently attributed to parenchymal infiltrates when they actually represent pleural fluid. Most patients with pleural effusions have blunting of the posterior costophrenic sulcus on thelateral chest radiograph. If this angle is blunted, the patient should be evaluated with ultrasound or bilateral decubitus chest radiographs to ascertain whether free pleural fluid is present (see Chapter 6). Alternatively, the possibility of fluid can be evaluated by chest computed tomography (CT) scan. This chapter provides a guide to the approach to a patient with an undiagnosed pleuraleffusion. The British Thoracic Society has recently published guidelines for the investigation of a unilateral pleural effusion in adults (1). The management of patients with pleural effusions due to specific diseases is discussed in the chapters dealing with those diseases.
Frequencies of Various Diagnoses
Pleural effusions can occur as complications of many different diseases (Table 8.1). The vigorwith which various diagnoses are pursued depends on the likelihood that the individual has that particular disease. Table 8.2 shows the approximate annual incidence for the most common causes of pleural effusions. An epidemiologic study from the Czech Republic found that the four leading causes of pleural effusions in order of incidence were congestive heart failure, malignancy, pneumonia, andpulmonary embolism (2). Congestive heart failure and cirrhosis cause almost all transudative pleural effusions, whereas malignant disease, pneumonia, and pulmonary embolization are the three main causes of exudative pleural effusions. Two other frequent causes of exudative pleural effusions are viral infections and the effusion that occurs after coronary artery bypass graft (CABG) surgery.
Separationof Exudates from Transudates
If free pleural fluid is demonstrated on the decubitus film, with ultrasound or with a CT scan, one should consider performing a diagnostic thoracentesis (Fig. 8.1). It has been my experience that diagnostic thoracentesis is difficult if the thickness of the fluid on the decubitus radiograph, ultrasound, or the CT scan is less than 10 mm. If the thickness of thefluid is greater than 10 mm, however, consideration should be given to performing a diagnostic thoracentesis (see Chapter 28). If the patient has obvious congestive heart failure, I perform a diagnostic thoracentesis if any of the following three conditions are met: (a) the effusions are not bilateral and comparably sized, (b) the patient has pleuritic chest pain, or (c) the patient is febrile.Otherwise, treatment of the congestive heart failure is initiated. If the pleural effusions do not rapidly disappear, I then perform a diagnostic thoracentesis several days later. It must be remembered, however, that the characteristics of the pleural fluid may change from those of a transudate to those of an exudate with diuresis. Romero et al. (3) performed a thoracentesis on 21 patients withcongestive heart failure before and every 48 hours after diuretic therapy was initiated. Before diuretics were administered, only one effusion was misclassified as an exudate by Light's criteria, but at the time of the third thoracentesis 10 effusions were misclassified as exudates. Between the first and the third thoracentesis, the mean protein level increased from 2.3 to 3.5 gm/dL and the mean lactatedehydrogenase (LDH) level increased from 176 to 262 IU/L (3).
One of the main purposes of the diagnostic thoracentesis is to determine whether the patient has a transudative or an exudative pleural effusion. This distinction is made by analysis of the levels of protein and LDH in the pleural fluid and in the serum (4).
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If none of the criteria in Fig. 8.1 is met, the patient has a...