Essentials of Diagnosis
• May be asymptomatic; chest pain
frequently seen in the setting of pleuritis,
trauma, or infection; dyspnea is common
with large effusions.
• Dullness to percussion and decreased breath
sounds over the effusion.
• Radiographic evidence of pleural effusion.
• Diagnostic findings on thoracentesis.
Light's criteria for distinguishing
pleural transudate from exudate
Pleural fluid is an exudate if one or more of
the following criteria are met:
• Pleural fluid protein:serum protein ratio > 0.5
• Pleural fluid LDH:serum LDH ratio > 0.6
• Pleural fluid LDH > two-thirds of the upper
limit of normal serum LDH
• Therapeutic aspiration may be required to palliate
breathlessness, but removing more than 1.5 L in one
episode is inadvisable as there is a small risk of re-
expansion pulmonary oedema.
• An effusion should never be drained to dryness before
establishing a diagnosis, as further biopsy may be
precluded until further fluid accumulates.
• Treatment of the underlying cause-for example, heart
failure, pneumonia, pulmonary embolism or subphrenic
abscess-will often be followed by resolution of the
• The management of pleural effusion in association with
pneumonia, tuberculosis and malignancy is discussed in
the relevant sections.
Position of patient and operator for the posterior
approach to thoracentesis
Technique of thoracentesis using a regular steel needle. A. Successful tap,
with fluid obtained. B. Air is obtained if the position of the needle is too
high. C. A bloody tap may result if the position of the needle is too low.
Catheter, three-way stopcock, syringe, and collection
bag ready for evacuation of pleural fluid.
Characteristics of important exudative pleural effusions.
Pleural effusion. The elevation of the left hemidiaphragm may be caused by a pleural effusion
at the left base. The appropriate way to determine the nature of this abnormality is to obtain a
left lateral decubitus film. Lateral decubitus film shows that a small effusion was also present
on the right side.
MECHANISMS THAT LEAD TO ACCUMULATION OF
• Increased hydrostatic pressure in the microvascular
circulation (heart failure)
Decreased oncotic pressure in the microvascular circulation
Decreased pressure in the pleural space (lung collapse)
Increased permeability of the microvascular circulation
Impaired lymphatic drainage from the pleural space
Movement of fluid from the peritoneal space (ascites)
Pleural effusion. A, Blood-stained pleural aspirate. This patient had pleural metastases from
carcinoma of the breast. B, Chylous pleural effusion. This patient had bronchial carcinoma that
had invaded and obstructed the thoracic duct. C, Pleural transudate. This pale effusion is
typically found in patients with heart failure or other causes of generalized edema.