Pleural effusion is defined as an abnormal collection of fluid in the pleural
space. Normally each pleural space contain only about 15 to 20 ml of serous
fluid, which is intended to lubricate the movement between the parietal and
visceral pleura during respiratory movements. When it is more than 25 ml it is
termed pleural effusion.
Pleural effusion can be a transudate or exudate. A transudative effusion
is thin and clear fluid, where as a n exudative pleural effusion is thicker and
turbid in nature. Pleural effusion can be unilateral or bilateral. It is more likely to
be bilateral in case of a transudate. Transudative pleural effusion is also termed
as a hydrothorax.
A pleural effusion associated with pneumonia is called syn-pneumonic or
para-pneumonic effusion. A syn-pneumonic effusion can be simple or
complicated. A pleural effusion, which is loculated by adhesions, is called an
encysted effusion. When there is hemorrhage into a pleural effusion it is called a
hemorrhagic effusion. Presence of frank blood in the pleura is called a
hemothorax. An infected effusion is called a purulent effusion and when there is
frank pus it is termed as empyema or pyo-thorax. A collection of fluid in the
space between visceral and parietal pleural of the base of the lung is called a
The important cause of a bilateral transudative effusion is cardiac failure.
It can also be seen in hypoprotinemia, cirrhosis of the liver, chronic malnutrition,
acute nephritic syndrome, and nephrotic syndrome. Transudative can also occur
in myxedema, constrictive pericarditis, and superior venacaval obstruction and
after peritoneal dialysis.
The most common cause of exudative pleural effusion is in association
with bacterial pneumonia, the so-called syn-pneumonic effusion. Other causes of
exudative pleural effusions are tuberculosis, malignancy, connective tissue
disorders and sarcoidosis. Left sided pleural effusion in patients with ovarian
tumor is called Meig’s syndrome. In acute pancreatitis is also associated with left
sided pleural effusions.
Normally there is a very slow but constant movement of fluid from the
capillaries of the parietal pleura into the pleural space. This fluid is absorbed
back into the parietal pleura through the lymphatic channels. Since these two are
balanced there is no net accumulation of fluid in the pleural space
Five different pathophysiological mechanisms account for the
accumulation of pleural fluid. First of all there is increased formation of pleural
fluid due an increase in the pleural capillary hydrostatic pressure and a decrease
in the oncotic pressure, in the setting of normal capillaries. The second
mechanism is the increased production of fluid due to increased capillary
permeability resulting in the formation of an exudative effusion. Decreased
lymphatic clearance of fluid also contributes to the production of exudates.
Infection of the pleural space is another mechanism and bleeding occurring into
the pleural space is the fifth mechanism responsible.
Patients with small pleural effusions are likely to remain asymptomatic, so
also the patients with moderate effusion, which develop over a long period of
time. The patient may experience a pleuritic type of catching pain over the lateral
aspect of the chest during the early days. This is due to the rubbing against each
other of the visceral and parietal pleura. But when fluid starts accumulating the
pleural layers are separated and the pain usually disappears. Later the patient
may complain of a dull aching pain over the area of effusion.
Dyspnoea is the more classical symptom of pleural effusion. It is constant
and progressive over days or weeks, as the amount of fluid accumulating
increases. It is likely to be more when the patient tries to lie on the normal side,
since the fluid in the pleural cavity compresses the heart and opposite lung.
Patient may find free from dyspnoea while lying on the affected side. The size of
effusion and the rate of accumulation are important in the severity of dyspnoea.
Cough, if present is irritable, dry and sputum production is unlikely unless
there is associated lung parenchymal lesion also. Hemoptysis is also unusual.
The exception to this rule is when a broncho-pleural fistula develops, which
connects the pleural space with the bronchus; profuse purulent sputum may be
The patient is usually dyspnoeic at rest and sometimes orthopneic and
prefers to lie on the affected side. Respiratory rate is increased and the ali nasi
may be working prominently. The trachea and mediastinum are found deviated
to the opposite side and the trails sign may be positive. The chest movements
on the affected side are reduced markedly and differential expansion is
diminished. The percussion note is stony dull over the area of effusion with a
higher level in the axilla. This indicates a capillary suction of the fluid into the
axillary area where the two pleural layers are closely approximated.
The breath sounds are markedly reduced in the affected side and there
may be a bronchial breath sound heard just above the level of effusion. This is
due to a compressive atelectasis of the lung parenchyma adjacent to it or the
presence of underlying consolidation of the lung. A pleural rub is likely only
during the initial days or if there is pulmonary infarction. There may be evidence
of chest wall edema and tenderness in the presence of empyema or pyo-thorax.
The routine blood examination is important in making a diagnosis of
diabetes mellitus or renal disease like nephrotic syndrome. Blood routine
examination is helpful in the presence of neutrophil-leucocytosis, which will
indicate the presence of infection. Lymphocytic predominance on the other hand
may be indicative of tuberculosis or viral etiology.
The X-Ray of the chest is diagnostic of pleural effusion in most of the
cases. It can pick up effusions as small as 50 ml by recognizing the obliteration
of the costo-phrenic angles. Moderate effusions also obliterate the cardio-phrenic
angles and have a dense homogenous opacity with out air bronchograms. These
are markings due to the patent bronchi seen in consolidation but not in effusion.
There is usually a higher level of the opacity in the axilla and a curved medial
In moderate and massive effusion there is significant shift of the trachea
and the apex of the heart to the opposite side. In the case of encysted effusions
the inner margins may be more convex and the mediastinal shift minimal. If the
encystment occurs in the inter lobar regions there may be formation of rounded
or ovel opacities which may resemble a tumor. This may disappear with
treatment and hence these are termed pseudo-tumors or phantom tumors.
Sub pulmonic effusions are more difficult to diagnose, unless there is a
high index of suspicion. On the right side they may resemble elevation of the
diaphragm. A lateral decubitus picture may be helpful in this situation,
demonstrating the tracking of the fluid to the sides. On the left side the presence
of a homogenous opacity more than 2 cm in thickness separating the air shadow
in the gastric fundus from the diaphragm is indicative of a sub-pulmonic effusion
Examination of the pleural fluid by pleural aspiration or thoracentesis is
indicated in all cases of new effusions and those without clinically apparent
cause. Patient may be observed closely in cases of symmetric bilateral pleural
effusions ass in cases of cardiac cfailure. But if the presentation is atypical or
the effusion fails to resolve with treatment pleural aspiration is warranted.
Pleural aspiration is done using a long needle specially designed for the
purpose and a three way-tapping device. This allows only the fluid to be drained
and the atmospheric air is not allowed to enter into the pleural cavity, if so
transforming it into a hydro-pneumo-thorax. The three-way device can also be
connected to a tubing allowing drainage of larger quantities of fluid. If only a
diagnostic sample is needed a syringe and needle combination can be used,
provided precaution is taken to avoid lung puncture and introduction of air into
the pleural cavity.
The pleural fluid is first examined grossly. If the fluid is frankly purulent, it
is an empyema. A straw colored fluid is characteristic of tuberculous pleural
effusion, where as a hemorrhagic effusion is either of tuberculous etiology or
malignant in nature. A milky white effusion is either inflammatory in nature or due
to a chylo-thorax, usually resulting from a rupture of the thoracic duct. Hemo-
thorax is the presence of gross blood in the pleural cavity and usually as a result
of trauma to the chest.
The pleural fluid is then sent for estimation of glucose, protein and LDH
estimation. This is in addition to total and differential WBC count. The
classification of the fluid in to transudate and exudate is based on these results.
A pleural exudate has one or more of the following laboratory features. The ratio
of pleural fluid protein to serum proteins is >0.5. The ratio of pleural fluid LDH to
serum LDH is >0.6 and pleural fluid LDH is greater than two-thirds the upper limit
of normal serum LDH.
Transudates have none of the above fatures. In addition the glucose level
corresponds to the blood glucose levels, The pH of the fluid is between 7.4 and
7.5. The total WBC count is less than 100/cmm and mono-nuclear cells
A markedly reduced level of pleural fluid glucose is characteristic of
connective tissue diseases like rheumatoid arthritis causing pleural effusion.
An elevated pleural fluid amylase level is seen in acute pancreatitis and
pseudocyst of pancreas as well as adenocardinoma of the pancreas and lung. It
is also seen in cases of rupture of the esophagus, but in this situation the source
of the amylase is saliva and not the serum.