Diagnosis of Pleural Effusions

Chest X-ray

Chest x-ray is a simple test to diagnose pleural effusion ( see figures 1,4,5 and 6). For pleural effusion of less than 50 ml the x-ray has to be taken in the lying position with the patient turned towards the side of effusion. This position is called lateral decubitus position. To get positive findings in the erect position there should be at least 300 ml of fluid in the pleural cavity.

Pleural fluid analysis

The pleural fluid is aspirated for diagnosis. This is called diagnostic thorococentesis.The fluid thus aspirated is used for biochemical, microscopic and microbiological investigations. These include

The investigations with pleural fluid are

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 - lipids, fungal culture, viral culture, specific immunoglobulins.

For treatment purpose the pleural effusion should diagnosed whether transudative or exudative. Richard Light’s criteria help in determining whether it is a transudative effusion or exudative effusion. Exudative pleural effusions meet at least one of the following 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
The other investigations which help in diagnosis of pleural effusion are
Ultrasonography
Chest CT scan
MRI scanning
Ventilation perfusion scanning

Some of the characteristic features of the pleural fluid may help in identifying the cause. The examples include:

Bloody – malignancy, pancreatitis, pulmonary embolism, tuberculosis
Amber colored – Tuberculosis
Brown as anchovy sauce- amebic liver abscess
Yellowish or whitish- chyle , pus
Black – Aspergillus
Highly viscous – mesothelioma
Foul smelling and purulent - pus

Treatment

Treatment depends on the underlying causes of pleural effusion. The fluid collected in the pleural cavity is aspirated by a procedure called thoracocentesis. If the effusion is a recurrent process then the pleural cavity is obliterated using certain chemicals so that fluid can get collected there.

Thoracocentesis

Thoracocentesis is a procedure by which the pleural fluid is aspirated. It is a very simple and safe procedure.

It can be either

Diagnostic when a minimal amount is aspirated for diagnosis
Therapeutic when a larger quantity is aspirated to relieve the symptoms

When the amount of fluid collected is very little there is no need to aspirate. Aspiration is also not indicated if the effusion is due to viral diseases, the patient has systemic diseases like cardiac failure and renal disease. In these cases treatment of the underlying cause will relieve the symptoms. But when the quantity is more it has to be aspirated to relieve symptoms. A 20 gauge needle is used to aspirate the fluid. The needle is inserted well below the armpit at the area of maximum dullness.

Normally about 1000 ml is aspirated in one sitting. If more than 1000 ml is aspirated it can precipitate pulmonary edema. If more than 1000 ml has to be aspirated then the pleural pressure has to be monitored. Some times aspiration may be difficult and it results in a dry tap especially if the effusion is a loculated one. In these cases aspiration is done under ultrasonographic guidance.

After thoracocentesis is done a chest x-ray is taken. This is done for two purposes.

To check the effectiveness of the thoracocentesis by seeing how much fluid is decreased in the pleural cavity
To look for the complication. Normally a little amount of air enters the pleural cavity during the procedure. It is called pneumothorax. If the amount of air entered is more it can worsen the symptoms. Its incidence is 3-20% with unguided thoracentesis and 2-7% with ultrasonographic guidance

Other complications of the procedure include

Subcutaneous hematoma
Infection of the pleural cavity
Cough
Chest pain
Hypoxemia
Laceration of spleen and liver
Pulmonary edema
Adverse reactions to the local anesthetic used

Tube Thoracostomy

If the fluid in the pleural cavity is thick as in empyema where pus is collected, it will be difficult to aspirate with a needle. In these cases tube thoracostomy is done. This procedure is also done in cases of hemothorax and large pneumothorax. In this procedure a large intercostals drain is inserted. The drainage tube could be either a pigtail tube or a surgical tube.

Pleurodesis

Pleurodesis is a procedure in which the potential space between the two layers of the pleural cavity is obliterated. As the cavity gets obliterated, the fluid can never get accumulated there gain. This procedure is done in patients with recurrent pleural effusions. Pleurodesis is of two types: surgical and chemical pleurodesis. The chemicals used are talc, bleomycin and tetracycline.

Monitoring of the pleural drainage is done by

Recording the amount and quality of fluid drained
Taking chest x-rays to look for complications
After discharge the patient has to be reviewed again for assessing his convalescence.
The outcome of the disease depends on the underlying cause. The outcome is usually grave if the effusion is due to malignancy.

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