Atlas of pathophysiology, 2 Edition

Part II - Disorders

Respiratory Disorders

Pleural Effusion

Pleural effusion is an excess of fluid in the pleural space. Normally, this space contains a small amount of extracellular fluid that lubricates the pleural surfaces. Increased production or inadequate removal of this fluid results in transudative or exudative pleural effusion. Empyema is the accumulation of pus and necrotic tissue in the pleural space.

Causes

Transudative pleural effusion

·   Heart failure

·   Hepatic disease with ascites

·   Peritoneal dialysis

·   Hypoalbuminemia

·   Disorders causing expanded intravascular volume

Exudative pleural effusion

·   Tuberculosis

·   Subphrenic abscess

·   Pancreatitis

·   Bacterial or fungal pneumonitis or empyema

·   Malignancy

·   Pulmonary embolism with or without infarction

·   Collagen disease such as systemic lupus erythematosus

·   Myxedema

·   Chest trauma

Empyema

·   Idiopathic infection

·   Pneumonitis

·   Carcinoma

·   Perforation

·   Esophageal rupture

Pathophysiology

The balance of osmotic and hydrostatic pressures in parietal pleural capillaries normally results in fluid movement into the pleural space. Balanced pressures in visceral pleural capillaries promote reabsorption of this fluid. Excessive hydrostatic pressure or decreased osmotic pressure can cause excessive amounts of fluid to pass across intact capillaries. The result is a transudative pleural effusion, an ultrafiltrate of plasma containing low concentrations of protein.

Exudative pleural effusion results 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 is usually associated with infection in the pleural space.

Signs and symptoms

·   Characteristically related to underlying pathologic condition

·   Dyspnea

·   Pleuritic chest pain

·   Fever

·   Malaise

·   Displaced point of maximum impulse, based on size of effusion

·   Decreased breath sounds

·   Dullness over the effused areas (doesn't change with breathing)

Diagnostic test results

·   Chest X-ray shows radiopaque fluid in dependent regions.

·   Computed tomography scan will show the location of the pleural effusions.

Diagnosis also requires other tests to distinguish transudative from exudative effusions and to help pinpoint the underlying disorder. The most useful test is thoracentesis, in which analysis of aspirated pleural fluid shows:

·   transudative effusions—lactate dehydrogenase (LD) levels less than 200 IU and protein levels less than 3 g/dl

·   exudative effusions—ratio of protein in pleural fluid to serum of 0.5 or more, LD in pleural fluid of 200 IU or more, and ratio of LD in pleural fluid to LD in serum of 0.6 or more

·   empyema—acute inflammatory white blood cells and microorganisms

·   empyema or rheumatoid arthritis—extremely decreased pleural fluid glucose levels.

In addition, if a pleural effusion results from esophageal rupture or pancreatitis, fluid amylase levels are usually higher than serum levels. Aspirated fluid may 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). Cell analysis shows leukocytosis in empyema. A negative tuberculin skin test strongly rules against tuberculosis (TB) as the cause. In exudative pleural effusions in which thoracentesis isn't definitive, pleural biopsy may be done. It's particularly useful for confirming TB or malignancy.

Treatment

·   Thoracentesis

·   Chest tube insertion

·   Pleurodesis (injection of a sclerosing agent such as talc)

·   Decortication

·   Rib resection

·   Parenteral antibiotics

·   Oxygen therapy

·   Pleuroperitoneal shunt

·   Pleurex catheter

P.99

LUNG COMPRESSION IN PLEURAL EFFUSION

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