Pleural Effusion: Causes, Clinical features, Investigations And Management

Pleural effusion is the accumulation of serous fluid in the pleural cavity.

Mechanism of Pleural Fluid Formation

Elevation of venous pressure (rare in pure Right Ventricular failure)
Decreased plasma oncotic pressure (except in congenital hypoalbuminuaemia)
Increased capillary permiability due to local inflammation, toxins or vasoactive substances as occurs in collagen-vascular diseases, pancreatitis, pulmonary emboli and pneumonitis
Increase in pleural space oncotic pressure as a result of : Protein leak through capillaries, Protein exudation due to local pleural inflammation, Defective lymphatic absorption.
Simple transfer of ascitic fluid across diaphragmatic defect and also through transdiaphragmatic lymphatics as occurs in cirrhosis and Meig's syndrome.
Increased negativity of pressure in the pleural also results in pleural effusion as occurs in atelectasis.
Obstruction of lymphatics.

Pleural fluid, on aspiration in normal person is 3-20 ml. Normal protein content is below 1.5 gm/ dl.

Congestive heart failure: Acute diuresis resulting in high PF/serum protein ratio.
Hepatic hydrothorax: Usually associated with ascites.
Nephrotic syndrome: Small, bilateral and subpulmonic.
Peritonial dialysis: Acute onset within 72 hours after dialysis-large right effusion.
Hypoalbuminaemia: Anasarca-serum albumin < 1.5 gm/dl.
Urinothorax: Associated with ipsilateral obstructive uropathy.
Atelectasis: Small effusion caused by increased intrapleural negative pressure.
Constructive pericarditis: Due to pulmonary and systemic venous hypertension-bilateral.
Trapped lung: As a result of remote inflammation
SVC obstruction: Due to venous hypertension or obstruction to thoracic lymph flow.
Subarachnoid pleural fistula: CSF leak into pleural space after disc surgery.
Myxoedema: Associated features of hypothyroidism.

Neoplasms: Metastatic disease, mesothelioma.
Infectious diseases: Bacterial, viral, fungal, parasitic, tuberculous.
Pulmonary embolism
Collagen vascular disease (rheumatoid arthritis, SLE, Wegener's granulomatosis).
Gastrointestinal disease: Oesophageal perforation, pancreatic disease, diaphragmatic hernia, intra-abdominal abscess, endoscopic sclerotherapy.
Uraemia.
Meig's syndrome: Ovarian fibroma, ascitis, right sided pleural effusion.
Drug-induced: Bromocriptine, amiodarone, nitrofuratoin, dantrolene.
Chylothorax, haemothorax.
Ovarian hyperstimulation syndrome.
Asbestose exposure.
Radiation therapy.
Intravascular insertion of central lines.
Transplant surgery.

Pleuritic chest pain.
Dyspnoea.
Tracheal and mediastinal shift to opposite side.
Diminished or absent breath sounds.
Stony dull percussion note.
Aegophony and bronchial breath sounds just above the level of effusin due to relaxed lung.

1. Chest X-ray

Minimal amount of fluid that can be detected in the PA view is 300 ml. Smaller quantities of fluid can be detected in lateral decubitus position (in this position, fluid layers along the dependent chest wall).
Tracheal and mediastinal shift to the opposite side (fluid > 1500 cc). When mediatinal shift does not occur, think of parenchymal collapse, previous mediastinal fixation or mesothelioma.
Obliteration of costophrenic and cardiophrenic angles.
There may be a collection in interlobular fissure which disappears on treatment with diuretics.
Subpulmonic effusion of about 1000 ml may appear only as an elevated diaphragm.

Obliteration of left costophrenic angle

2. Ultra Sound

More accurate than chest x-ray for determining the presence of fluid.
Clear hypoechoic space is consistent with a transudate and the presence of moving, floating densities suggest an exudate.
Presence of septation most likely indicates an evolving empyema or resolving haemothorax.

3. CT scan

4. Pleural aspiration and biopsy

Simple aspiration provides information on colour and texture of fluid and these alone may immediately suggest an empyema or chylothorax.
The presence of blood is consistent with pulmonary infarction or malignancy but may result from a traumatic tap.
Biochemical analysis allows classification into transudate and exudate.
Gram staining may suggest paraneumonic effusion.
Low pH suggests infection but may also seen in rheumatoid arthritis, oesophageal rupture or advanced malignancy.
Ultrasound or CT-guided pleural biopsy provide tissue for pathological and microbiological analysis.

Therapeutic aspiration may be required to palliate breathlessness but removing more than 1.5 L at a time is associated with small risk of re-expansion pulmonary oedema.
Effusion should never be drained to dryness before establishing a diagnose.
Treatment of underlying cause- e.g. heart failure, pneumonia, pulmonary embolism or subphrenic abscess.