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Pleural effusion

Pleural effusion is excess fluid that accumulates in the pleural cavity, the fluid-filled space that surrounds the lungs. Excessive amounts of such fluid can impair breathing by limiting the expansion of the lungs during inhalation.

Types of fluids
Diagnosis

Transudate vs. exudate

Causes

Transudative
Exudative
Other/ungrouped

Treatment
See also
External links
References

Types of fluids

Four types of fluids can accumulate in the pleural space:

Diagnosis

CT scan of chest showing left sided pleural effusion. Effusion fluid often settles at the lowest space due to gravity; here at the back as the patient is lying under scanner.

Pleural effusion is usually diagnosed on the basis of medical history and physical exam, and confirmed by chest x-ray. Chest films acquired in the lateral decubitus position (with the patient lying on his 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 angles). 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 resonance and fremitus (though this is an inconsistent and unreliable sign), pleural friction rub. Above the effusion, where the lung is compressed, there may be bronchial breathing and egophony. In large effusion there may be tracheal deviation away from the effusion.

Micrograph of a pleural fluid cytopathology specimen showing malignant mesothelioma, one cause of a pleural effusion.

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 in the sixth, seventh or eighth intercostal space on the midaxillary line, 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 identify possible bacterial infections
Cell count and differential
Cytopathology to identify cancer cells, but may also identify some infective organisms
Other tests as suggested by the clinical situation - lipids, fungal culture, viral culture, specific immunoglobulins

Transudate vs. exudate

Needle biopsy of the pleura The third 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, renal failure, hepatic failure, 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, pulmonary embolism, and viral infection).^[1]

Transudative and exudative pleural effusions are differentiated by comparing chemistries in the pleural fluid to those in the blood. According to a meta-analysis, exudative pleural effusions meet at least one of the following criteria:^[2]

Pleural fluid protein >2.9 g/dL (29 g/L)
Pleural fluid cholesterol >45 mg/dL (1.16 mmol/L)
Pleural fluid LDH >60 percent of upper limit for serum

Previously criteria proposed by Light for an exudative effusion are met if at least one of the following exists (Light's criteria):^[3]

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^[4].

Causes

Transudative

The most common causes of transudative pleural effusions in the United States are left ventricular failure, and cirrhosis (causing hepatic hydrothorax). Pulmonary embolisms were once thought to be transudative but have been recently shown to be exudative^[5]

Exudative

Pleural effusion Chest x-ray of a pleural effusion. The arrow A shows fluid layering in the right pleural cavity. The B arrow shows the normal width of the lung in the cavity

Once identified as exudative, additional evaluation is needed to determine the cause of the excess fluid, and pleural fluid amylase, glucose, pH and cell counts are obtained.

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.
Pleural fluid pH is low in empyema (<7.2) and may be low in cancer.
- 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^[6] of the pleura may be performed.
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).

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.

Other/ungrouped

Other causes of pleural effusion include tuberculosis (though pleural fluid smears are rarely positive for AFB, this is 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, rheumatoid arthritis, 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/surgical 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 intra- or extravascular insertion of central lines.

Treatment

The free end of the Chest Drainage Device is usually attached to an underwater seal, below the level of the chest. This allows the air or fluid to escape from the pleural space, and prevents anything returning to the chest.

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). When managing these chest tubes it is important to make sure the chest tubes do not become occluded or clogged. A clogged chest tube in the setting of continued production of fluid will result in residual fluid left behind when the chest tube is removed. This fluid can lead to complications such as hypoxia due to lung collapse from the fluid, or fibrothorax, late, when the space scars down. Repeated effusions may require chemical (talc, bleomycin, tetracycline/doxycycline) or surgical pleurodesis, in which the two pleural surfaces are scarred to each other so that no fluid can accumulate between them. This is a surgical procedure that involves inserting a chest tube, then either mechanically abrading the pleura, or inserting the chemicals to induce a scar. This require the chest tube to stay in until the fluid drainage stops. This can be days to weeks and can require prolonged hospitilizations. If the chest tube becomes clogged fluid will be left behind and the pleurodesis will fail.

Pleurodesis fails in as many as 30% of cases. An alternative is to place a Pleurex or Aspira Drainage Catheter. This is a 15Fr chest tube with a one way valve. Each day the patient or care givers connect it to a simple vacuum tube and remove from 600 cc to 1000 cc. This can be repeated daily. When not in use, the tube is capped. This allows patients to be outside the hospital. For patients with malignant pleural effusions, it allows them to continue chemotherapy, if indicated. Generally the tube is in about 30 days and then it is removed when the space undergoes a spontaneous pleurodesis.