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Pleural effusion is defined as an excess accumulation of fluid in the pleural cavity which can sometimes restrict lung expansion.
The pleura are thin films of connective tissue, which line both the outer surface of the lungs and the inside of the chest cavity. The visceral pleura on the inside at the parietal pleura on the outside.
The pleural space is a potential cavity that usually contains a negligible amount of fluid. This balance is maintained by the fact that production and absorption are at equilibrium.
The accumulation of excess fluid in the pleural cavity can be an indicator of a local systemic illness.
The pleural fluid is similar to interstitial fluid and its made slippery by some proteins such as albumin.
Pleural effusion can be classified into two types;
Transudative pleural effusion or Exudative pleural effusion.
A transudate (specific gravity of less than 1.016 and a protein of less than 3g/dL) results from altered production or absorption of pleural fluid. As a consequence of this imbalance, there is an elevated systemic or pulmonary capillary pressures, lowered plasma oncotic pressure or lowered intrapleural pressure. There is no disorder of the pleural surfaces.
On the other hand, an exudate (specific gravity of more than .016 and protein content of more than 3 g/dL) is found in presence of a disease of the pleural surfaces or lymphatics where there is increased capillary permeability or lymphatic obstruction.
Transudative effusions are caused by some combination of increased hydrostatic pressure and decreased plasma oncotic pressure.
These are usually ultrafiltrates of plasma squeezed out of the pleura as a result of an imbalance in hydrostatic and oncotic forces in the chest.
Conditions associated with increased hydrostatic pressure include; heart failure and liver cirrhosis with ascites.(low proteins) The ones associated with hypoalbuminemia are usually nephrotic syndrome (protein loss). Because these diseases are systemic, they usually cause bilateral and equal effusion.
They are caused by local processes leading to increased capillary permeability due to inflammation.
This results in an exudation of fluid, protein, cells, and other serum constituents. An exudative effusion will cause unilateral effusions.
Causes of exudative pleural effusion are;
Pneumonia of any case may be complicated by the formation of pleural effusion. When pus is formed within the pleural cavity the condition is known as empyema thoracis.
Malignant pleural effusion develops as a result of secondary pleural deposits, an extension of primary lung or breast cancers or sometimes a lymphatic flow obstruction. Breast cancer is the most common causative of malignant pleural effusion.
In some cases when there is an intrathoracic metastatic lesion, the pleural effusion will be bloodstained or serosanguineous with positive cytology and positive pleural biopsy.
Accumulation of chyle in the pleural cavity due to disruption of the thoracic duct is referred to as chylothorax. It mostly results as a consequence of surgical trauma to the duct.
The clinical manifestations of pleural effusion are variable and often are related to the underlying disease process.
The most commonly associated symptoms are
~Difficulty in breathing,
~Pleuritic chest pain which is worse when the patient is lying flat.
~Hemoptysis can be present when there is malignant effusion.
The differentials that you should probably think of are;
Physical examination reveals
The pleural fluid analysis will reveal the type of effusion based on the appearance, biochemical and microscopic features.
A chest x-ray will indicate a tracheal deviation. It will also be helpful in finding the underlying cause.
An erect chest x-ray shows fluid accumulation at the costophrenic angle. X-ray taken when a patient is supine indicates the layering effect.
Helical chest CT Scan will reveal significant intrathoracic disease.
Pleural biopsy can also be done id pleural aspiration was undiagnostic.
Bronchoscopy can also be done.
Thoracentesis is done to relieve the symptoms and also help in diagnosis.
The physical appearance of pleural fluid with respect to the corresponding type of pleural effusion can be summarized as;
To differentiate them you use the Light's criteria
The fluid is considered an exudate when:
~The ratio of pleural fluid to serum protein is greater than 0.5.
~Ratio of pleural fluid to serum LDH is greater than 0.6.
~Pleural fluid LDL or cholesterol is greater than 2/3 of the upper limits of normal serum value.
If all these are absent the fluid is a transudate.
Treatment involves removal of the fluid and treatment of the underlying cause.
If the causative disease was pneumonia then antibiotics are useful.
If it resulted from heart failure it is treated with diuretics and sodium restriction diet.
Malignancy is treated with chemotherapy and radiotherapy
Thoracentesis can also be performed for large effusion
Surgery is indicated for large loculated effusion such as in bacterial pneumonia and tuberculosis.
Chylothorax usually responds to non-operative therapy; that is, chest tube drainage and no fat diet.
Empyema is managed with dependent chest tube drainage. The pleural space may be irrigated with an antiseptic solution.