is ''excess'' fluid that accumulates in the
Pleural Cavity , the fluid-filled space that surrounds the
Lung s.
Four types of fluids can accumulate in the pleural space:
Healthy individuals have less than 10 ml of fluid in each pleural space. Normally, fluid enters the pleural space from the
Capillaries in the
Parietal Pleura , from interstitial spaces of the lung via the
Visceral Pleura , or from the
Peritoneal Cavity through small holes in the
Diaphragm . This fluid is normally removed by
Lymphatics in the parietal pleura, which have the capacity to absorb 20 times more fluid than is normally formed. When this capacity is overwhelmed, either through excess formation or decreased lymphatic absorption, a pleural effusion develops.
Pleural effusion is diagnosed by chest
X-ray . Chest films acquired in the
Lateral Decubitus position (with the patient lying on her side) are more sensitive, and can pick up as little as 50 ml of fluid. At least 300 ml of fluid must be present before upright chest films can pick up signs of pleural effusion (e.g., blunted
Costophrenic Angle s). Once accumulated fluid is more than 500 ml, there are usually detectable clinical signs in the patient, such as decreased movement of the chest on the affected side, dullness to percussion over the fluid, diminished breath sounds on the affected side, decreased vocal
Fremitus and resonance, pleural friction rub, and
Egophony .
Once a pleural effusion is diagnosed, the cause must be determined. Pleural fluid is drawn out of the pleural space in a process called
Thoracentesis . A needle is inserted through the back of the chest wall into the pleural space. The fluid may then be evaluated for the following:
# Chemical composition including
Protein ,
Lactate Dehydrogenase (LDH),
Albumin ,
Amylase ,
PH and
Glucose
#
Gram Stain and culture to identifies bacterial infections
#
Cell count and differential
#
Cytology to identify cancer cells, but may also identify some infective organisms
# Other tests as suggested by the clinical situation -
Lipid s,
Fungal Culture ,
Viral Culture , specific
Immunoglobulin s
The first step in the evaluation of pleural fluid is to determine whether the effusion is a transudate or an exudate. Transudative pleural effusions are caused by ''systemic'' factors that alter the balance of the formation and absorption of pleural fluid (e.g.,
Left Ventricular Failure ,
Pulmonary Embolism , and
Cirrhosis ), while exudative pleural effusions are caused by alterations in ''local'' factors that influence the formation and absorption of pleural fluid (e.g.,
Bacterial Pneumonia , cancer, viral infection, and pulmonary embolism).
Transudative and exudative pleural effusions are differentiated by comparing protein and lactate dehydrogenase levels in the pleural fluid to those in the blood. Exudative pleural effusions meet at least one of the following criteria (Light's criteria), whereas transudative pleural effusions meet none:
# 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 more than two-thirds normal upper limit for serum
Twenty-five percent of patients with transudative pleural effusions are mistakenly identified as having exudative pleural effusions by Light's criteria. Therefore, additional testing is needed if a patient identified as having an exudative pleural effusion appears clinically to have a condition that produces a transudative effusion. In such cases
Albumin levels in blood and pleural fluid are measured. If the difference between the albumin levels in the blood and the pleural fluid is greater than 1.2 g/dL (12 g/L), it can be assumed that the patient has a transudative pleural effusion.
If the fluid is definitively identified as exudative, additional testing is necessary to determine the local factors causing the exudate.
Once identified as exudative, additional evaluation is needed to determine the cause of the excess fluid, and pleural fluid amylase, glucose, and cell counts are obtained. The fluid is also sent for Gram staining and culture, and, if suspicious for tuberculosis, examination for TB markers (
Adenosine Deaminase > 45 IU/L,
Interferon Gamma > 140 pg/mL, or positive
Polymerase Chain Reaction (PCR) for tuberculous DNA).
Pleural fluid amylase is elevated in cases of esophageal rupture,
Pancreatic Pleural Effusion , or cancer. Glucose is decreased with cancer, bacterial infections, or
Rheumatoid Pleuritis . If cancer is suspected, the pleural fluid is sent for cytology. If cytology is negative, and cancer is still suspected, either a
Thoracoscopy , or needle biopsy of the pleura may be performed.
In the United States, the most common causes of transudative pleural effusions in the United States are
Left Ventricular Failure , pulmonary embolism, and cirrhosis (causing
Hepatic Hydrothorax ), while the most common causes of exudative pleural effusions are bacterial pneumonia, cancer (with
Lung Cancer ,
Breast Cancer , and
Lymphoma causing approximately 75% of all malignant pleural effusions), viral infection, and pulmonary embolism. Although pulmonary embolism can produce either transudative or exudative pleural effusions, the latter is more common.
Other causes of pleural effusion include,
Tuberculosis (the most common cause of pleural effusion in some developing countries), autoimmune disease such as
Systemic Lupus Erythematosus , bleeding (often due to chest trauma), chylothorax (most commonly caused by trauma), and accidental infusion of fluids. Less common causes include, esophageal rupture or pancreatic disease, intraabdominal abscess, asbestos pleural effusion,
Meigs Syndrome (ascites and pleural effusion due to a benign ovarian tumor), and
Ovarian Hyperstimulation Syndrome .
Pleural effusions may also occur through medical interventions, including the use of medications (pleural fluid is usually
Eosinophilic ),
Coronary Artery Bypass Surgery , abdominal surgery,
Endoscopic Variceal Sclerotherapy ,
Radiation Therapy , liver or lung transplantation, and intravascular insertion of central lines.
Treatment depends on the underlying cause of the pleural effusion. Therapeutic aspiration may be sufficient; larger effusions may require insertion of an
Intercostal Drain (either pigtail or surgical). Repeated effusions may require chemical (talc, bleomycin, tetracycline) or surgical
Pleurodesis , in which the two pleural surfaces are attached to each other and no fluid can accumulate between them.
