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Pleural Effusion and Empyema

Normally, the pleural space contains a small amount of extracellular fluid that lubricates the pleural surfaces, but if fluid builds up from either increased production or inadequate removal, pleural effusion results. An accumulation of pus and necrotic tissue in the pleural space results in empyema, a type of pleural effusion. Blood (hemothorax) and chyle (chylothorax) may also collect in this space.

The incidence of pleural effusion increases with heart failure (the most common cause), parapneumonia, cancer, and pulmonary embolism.

Causes

A transudative pleural effusion - an ultrafiltrate of plasma containing a low concentration of protein ­may result from heart failure, hepatic disease with ascites, peritoneal dialysis, hypoalbuminemia, and disorders that increase intravascular volume.

The effusion stems from an imbalance of osmotic and hydrostatic pressures. Normally, the balance of these pressures in parietal pleural capillaries causes fluid to move into the pleural space; balanced pressure in visceral pleural capillaries promotes reabsorption of this fluid. But when excessive hydrostatic pressure or decreased osmotic pressure causes excessive fluid to pass across intact capillaries, a transudative pleural effusion results.

Exudative pleural effusions can result from tuberculosis, subphrenic abscess, pancreatitis, bacterial or fungal pneumonitis or empyema, cancer, parapneumonia, pulmonary embolism (with or without infarction), collagen disease (lupus erythematosus and rheumatoid arthritis), myxedema, intra-abdominal abscess, esophageal perforation, and chest trauma.

Such an effusion occurs when capillary permeability increases, with or without changes in hydrostatic and colloid osmotic pressures, allowing protein-rich fluid to leak into the pleural space.

Empyema usually stems from an infection in the pleural space. The infection may be idiopathic or may be related to pneumonitis, carcinoma, perforation, penetrating chest trauma, or esophageal rupture.

Signs and Symptoms

The most common symptoms of pleural effusion are shortness of breath and chest pain caused by compression of the lungs. Cough also can occur and there may be fever with empyema.

Diagnostic tests

Chest X-rays show radiopaque fluid independent regions (usually with fluid accumulation of more than 250 ml).

Thoracentesis allows analysis of aspirated fluid and may show the following:

  • Transudative effusion usually has a specific gravity less than 1.015 and contains less than 3 g/dl of protein.
  • Exudative effusion has a ratio of protein in the fluid to serum of greater than or equal to 0.5, pleural fluid lactate dehydrogenase (LD) of greater than or equal to 200 IU, and a ratio of LD in pleural fluid to LD in serum of greater than or equal to 0.6.
  • Aspirated fluid in empyema contains acute inflammatory white blood cells and microorganisms and shows leukocytosis.
  • Fluid in empyema and rheumatoid arthritis, which can be the cause of an exudative pleural effusion,shows an extremely decreased pleural fluid glucose level.
  • Pleural effusion that results from esophageal rupture or pancreatitis usually has fluid amylase levels higher than serum levels.

Aspirated fluid may also be tested for lupus erythematosus cells, antinuclear antibodies, and neoplastic cells. It may also be analyzed for color and consistency: acid-fast bacillus, fungal, and bacterial cultures: and triglycerides (in chylothorax).

Other diagnostic tests may also be ordered. A negative tuberculin skin test helps to rule out tuberculosis as a cause. If thoracentesis doesn't provide a definitive diagnosis in exudative pleural effusion, a pleural biopsy can help confirm tuberculosis or cancer.

Treatment

Depending on the amount of fluid present, symptomatic effusion may require thoracentesis to remove fluid or careful monitoring of the patient's own reabsorption of the fluid. Chemical pleurodesis - the instillation of a sclerosing agent, such as tetracycline, bleomycin, or nitrogen mustard through the chest tube to create adhesions between the two pleurae - may prevent recurrent effusions.

The patient with empyema needs one or more chest tubes inserted after thoracentesis. These tubes allow purulent material to drain. The patient may also need decortication (surgical removal of the thick coating over the lung) or rib resection to allow open drainage and lung expansion. He also requires parenteral antibiotics and, if he has hypoxia, oxygen administration.

Hemothorax requires drainage to prevent fibrothorax formation.



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