A pleural effusion is an abnormal buildup of fluid in the intrapleural space, which is lined by a thin membrane called the pleura.
Each pleura is a continuous sheet of serous tissue, which folds back upon itself, creating a double-layered structure that encloses each lung. The inner layer (visceral pleura) covers the lung’s outer surface. The outer layer, (parietal pleura), lines the inside of the chest wall and covers the superior surface of the diaphragm.
A space known as the pleural cavity, 10 to 20 µm wide, is created between the layers of the pleura. Each cavity normally contains a small amount of pleural fluid (approximately 20 milliliters), which is a clear, straw-colored fluid similar in composition and viscosity to plasma.
Pleural fluid functions to:
- Reduce friction between the lung and chest wall, as they expand and contract during respiration;
- Provide surface tension preventing the separation of the pleural membranes. This maintains the lungs close to the chest wall and creates negative pressure inside the chest cavity when the chest wall lifts up and out during inhalation, causing the lungs to inflate with air.
In a healthy person, pleural fluid is continually formed. To maintain the proximity of the lungs and chest wall, the volume of pleural fluid is kept to a minimum by the lymphatic system.
Any of the following will result in increased pleural fluid formation or decreased absorption of pleural fluid:
- an obstruction in the flow of either the blood vessels or lymphatic system;
- a change in the permeability of pleural membranes;
- a change in either the oncotic or hydrostatic pressure in the pulmonary capillaries;
- vascular inflammation.
Any imbalance in the normal rate of pleural fluid production or absorption, or both, will cause fluid to accumulate in the pleural space. This accumulation is known as pleural effusion, which is always indicative of an underlying medical condition.
Pleural effusions can occur in a variety of diseases or as a complication of therapeutic procedures. The causes are numerous, here are just a few:
- malignant neoplasms especially breast, and lung cancers;
- lung conditions or diseases: asbestosis, mesothelioma, and pulmonary edema;
- Congestive Heart Failure;
- Autoimmune disorders: Lupus, or SLE, and rheumatoid arthritis;
- renal failure or nephrotic syndrome;
- hypoproteinemia and severe hypoalbuminemia;
- complications from cardiac surgery, or peritoneal dialysis;
- accidental fluid overload.
Depending on the amount of fluid accumulated in the pleural space, an effusion can negatively affect the functioning of the respiratory system, producing symptoms that can include:
- chest pain or tightness;
- labored breathing;
- and nonproductive cough.
The discovery of an effusion is often an incidental finding during a physical examination or chest X-rays.
Pleural fluid becomes visible on the upright lateral film with as little as 50 milliliters of fluid. Clinical findings on physical examination may include:
- decreased or absent breath sounds;
- dullness to percussion in the area over the effusion;
- pleural friction rub;
- egophony, which is ncreased resonance of voice sounds heard during auscultation);
- decreased tactile fremitus;
- and asymmetrical chest expansion.
The history and physical examination are critical in guiding the evaluation of pleural effusion and providing clues to etiology. Treatment is based on the underlying cause and whether the effusion is causing severe respiratory symptoms.
An analysis of the fluid is typically carried out using Light’s criteria to distinguish exudative effusions from transudative effusions. According to Light’s criteria, a pleural effusion is exudative if one of the following is present:
- The ratio of pleural fluid protein to serum protein is greater than 0.5
- The ratio of pleural fluid LDH and serum LDH is greater than 0.6
- Pleural fluid LDH is greater than 0.6 or two-thirds times the normal upper limit for serum
This analysis also aids in the determination of underlying cause and the course of treatment. Despite extensive diagnostic workup, the etiology remains unknown 15% of the time.
In effusions classified as transudative, movement of fluid into the pleural cavity results from a change in either the oncotic pressure or hydrostatic pressure of the pulmonary capillaries and generally reflect a systemic process (for example, heart failure or cirrhosis.)
In effusions classified as exudative, fluid leaks into the pleural cavity due to either inflammation or blockage of blood or lymph vessels; and commonly signifies an underlying disorder (e.g., lung cancer, or pulmonary embolism.)
Asymptomatic transudative effusions generally do not require treatment and most resolve spontaneously when the underlying disorder is treated.
Medications may be used alone or in conjunction with other treatment modalities. Types of medications may include:
- or chemotherapeutic agents.
Treatment goals for symptomatic transudates and exudative effusions are:
- relieve symptoms by removing the extra fluid from the pleural space
- and prevent reoccurrence.
Removal of the pleural fluid can be accomplished through two options:
First: thoracentesis, which is the insertion of a cannula into the pleural space to remove excess fluid. Normally 1500 mL of fluid is removed during the procedure. This is an arbitrary amount with no evidence to suggest removing a greater amount of fluid would be contraindicated.
The second option is a tube thoracostomy. This is the insertion of a chest tube into the pleural cavity. The tube is connected to a chest drainage and will remain in place to drain the fluid.
A procedure called Pleurodesis, involves instilling a sclerosing agent to obliterate the pleura cavity; preventing further accumulation of fluid.
In effusions that cannot be managed through drainage or pleural sclerosis, one of the following surgical procedures may be indicated:
- Placement of a Pleuroperitoneal shunt;
- Pleurectomy to remove part of the pleura to prevent continued fluid buildup;
- Thoracoscopy or Video-assisted Thoracoscopic Surgery (VATS) to lyse or remove adhesions or fibrous tissue;
- thoracotomy to remove either scar tissue or fibrous membrane surrounding the lung.
Ok, let’s review by going over a few questions:
The pleura consists of two layers, the ________.
- mediastinum and parietal pleura
- visceral and parietal pleura
- visceral and mediastinum pleura.
- none of the above
If you chose b, you’re correct.
Which statement about pleural fluid is false:
- pleural fluid acts as a lubricant to reduce friction between the lungs and the chest walls during respiration.
- the volume of pleural fluid is controlled by the lymphatic system.
- instilling a sclerosing agent into the pleural space decreases the production of pleural fluid.
- pleural fluid is continually formed and removed.
If you chose c, you are correct. A sclerosing agent induces an inflammatory response, obliterating the pleural space.
All of the following are goals of treating an exudative treatment except:
- relief of any respiratory symptoms
- removal of the accumulated fluid
- preventing recurrence
- diagnosing the underlying cause
If you chose d, you’re correct. The underlying cause of the pleural effusion determines the treatment.
Thanks for watching, and happy studying.