Transudative pleural effusions.

A transudative pleural effusion develops when the systemic factors influencing the formation or absorption of the pleural fluid are altered. The pleural surfaces are not involved by the primary pathologic process. The diagnosis of transudative effusion is simple to establish by examining the characteristics of the pleural fluid. Transudates have all of the following three characteristics: The ratio of the pleural fluid to the serum protein is less than 0.5. The ratio of the pleural fluid to the serum LDH is less than 0.6. The pleural fluid LDH is less than two thirds the upper limit of normal for the serum LDH. Among the conditions that produce transudative pleural effusion, congestive heart failure is by far the most common. Pulmonary embolism, cirrhosis of the liver with ascites, and the nephrotic syndrome are the other common causes. Management of transudative pleural effusions involves managing the primary disease. Refractory, massive effusions can be controlled by tetracycline pleurodesis.