PLEURAL EFFUSIONS



Causes of pleural effusions are best considered in terms of the underlying pathophysiology: tran­sudates due to abnormalities of hydrostatic or os­motic pressures, and exudates resulting from in­creased permeability or trauma.

Patients present with dyspnea, nonspecific dis­comfort, or pleuritic chest paina sharp, stabbing pain exacerbated by coughing or breathing. Such pain must be carefully differentiated from peri­cardial or musculoskeletal pain. Rarely, the ef­fusion will be asymptomatic and discovered only on chest x-ray.

Physical examination reveals decreased vocal fremitus, dullness on percussion, and decreased breath sounds over the effusion, with bronchial breathing and egophony at its upper limit. Greater than 250 ml of fluid can be seen on the upright chest x-ray as blunting of the costophrenic angle. Increasing amounts cause dense opacification of the lung fields with a concave meniscus. In cer­tain situations the initial x-ray is misleading and further studies are required: [1] a subpulmonic ef­fusion presenting as an elevated hemidiaphragm can be confirmed on lateral decubitus x-ray; (2) a hazy diffuse density on the supine film in a se­riously ill patient will disappear on an upright x-ray; and (3} a loculated effusion, especially with coexisting parenchymal disease, may require ul­trasound or CT scan for diagnosis.

Thoracentesis is essential in the differential di­agnosis. The gross appearance of the fluid is rarely helpful except when frank blood or the milky fluid of a chylous effusion is encountered. Criteria for the separation of the fluid into transudate and exudate (Table 26-2) are not infallible, and an ef­fusion due to congestive heart failure may occa­sionally be exudative, while a transudate may occur with malignancy. Pleural fluid glucose con­centrations less than 10 to 20 mg/dl are usually diagnostic of rheumatoid arthritis but may be seen in cancer and infection. Pleural fluid amylase is about twice normal in effusions due to pancrea­titis and esophageal perforation, while smaller el­evations may be seen with malignancy. The pres­ence of a high rheumatoid factor or LE cells in the fluid is strong evidence that the effusion is due to rheumatoid arthritis and systemic lupus erythe­matosus, respectively. Measurement of pleural fluid pH is usually of little value in the diagnosis and management of empyema.

Surprisingly few red blood cells are required to impart a red color to the fluid, and a hemothorax should be diagnosed only when the pleural fluid hematocrit is greater than 20 per cent. Bloody fluid should arouse suspicion of malignancy, trauma, or pulmonary embolus but may also occur with other disease entities. The number of poly­morphonuclear neutrophils is of little or no spe­cific diagnostic value. A high eosinophil count is usually due to air or blood in the pleural space. There is a high probability that an exudate is due to tuberculosis or malignancy if small lympho­cytes constitute more than 50 per cent of the white cells. Cytological examinations for malignant cells is positive in about 60 per cent of patients on first thoracentesis, rising to about 80 per cent if three separate samples are obtained. Gram’s stain and routine culture should always be done and special stains and cultures added when tu­berculosis or fungal disease is suspected.

Transcutaneous needle biopsy at the bedside with subsequent histology and culture is positive in over 90 per cent of tuberculous effusions, whereas fluid culture is positive in only 25 per cent. Although less frequently positive than cytological examination, biopsy occa­sionally makes a diagnosis of malignant effusion when cytology is negative.

Treatment depends on the underlying etiology and the degree of physiological impairment. Spe­cific therapy to control the underlying etiology is the only successful approach. Although removal of fluid results in symptomatic improvement, lung volumes and gas exchange improve very lit­tle. Parapneumonic effusions resolve with anti­biotic therapy , but empyemas, i.e., fluid with positive smear or culture, should be drained by repeated aspirations or tube thoracos­tomy; otherwise the fluid may spontaneously drain through the chest wall (empyema necessi­tous) or lead to subpleural lung necrosis with re­sultant bronchopleural fistula and endobronchial spread of infection. Palliative therapy should be considered for a malignant effusion only if the pa­tient is symptomatic and displays benefit from thoracentesis. Repeated thoracentesis should be avoided, as significant protein loss results and the fluid reaccumulates within one to three days. Chemical pleurodesis using intrapleural tetracy­cline obliterates the pleural space and is helpful in about 80 per cent of malignant effusions.





PLEURAL EFFUSIONS