The underlying mechanism for this can largely be split into two categories:
Increased fluid entering the pleural space:
- Increased capillary pressure: Forces fluid out of blood vessels into the pleural space e.g. congestive cardiac failure.
- Decreased oncotic pressure: Less ability to hold fluid in the blood vessels, leading to fluid leaking into the pleural space e.g. cirrhosis.
- Increased capillary permeability: Usually secondary to an inflammatory process which leads to leaking of fluid and protein from blood vessels into the pleural space e.g. pneumonia or malignancy.
- Reduced pressure in the pleural space: Atelectasis
Decreased fluid clearance: Obstruction of the lymphatics which drain pleural fluid e.g. malignancy.
Causes
There are two main ways of classifying a pleural effusion – either transudative or exudative.
Transudates
Transudative pleural effusions occur when there is an increased hydrostatic pressure or decreased oncotic pressure. They are usually bilateral. Common causes include:
- Cardiac failure
- Renal failure
- Cirrhosis
- Hypothyroidism
- Meigs’ syndrome: A triad of benign ovarian tumour, ascites and pleural effusion.
Exudates
Exudative pleural effusions occur as a result of inflammatory causes and are usually unilateral, with higher amounts of protein, and reduced amounts of glucose found in the fluid.
- Pneumonia
- Malignancy
- Tuberculosis
- Acute Pancreatitis
- Rheumatoid arthritis
Types
The name given to a pleural effusion stems from the type of fluid present in the pleural space. A pleural effusion typically refers to the presence of serous fluid, while other fluids are termed differently:
- Haemothorax (blood): Blunt trauma or iatrogenic complication of surgery
- Chylothorax (chyle): From a malignancy
- Empyema or pyothorax (pus): Occur secondary to a localised infection e.g. pneumonia
Clinical Features
- Pleuritic chest pain
- Dyspnoea
- Quiet or absent breath sounds
- Pleural rub on auscultation
- Dull percussion notes due to fluid
- Tracheal deviation if the pleural effusion is significantly large
Investigations
Bloods
- Full blood count and CRP: Check for underlying infection
- Serum protein
- Serum LDH
Imaging
- Chest X-ray:
- White opacity indicative of fluid accumulation
- Blunted costophrenic and cardiophrenic angles.
- A fluid level can be seen if the effusion is large. This is seen as a concave upper edge known as the meniscus sign.
- A sub pulmonary effusion can occur, whereby pleural fluid becomes trapped inferior to the lower lung lobes, subsequently elevating the hemidiaphragm.
James Heilman, MD, CC BY 3.0 , via Wikimedia Commons
Compared to the right hand side, you can see the blunted costophrenic angle on the left indicating a small pleural effusion.
- Ultrasound: Smaller pleural effusions can be detected through ultrasound.
- CT: Useful if malignancy is thought to be the underlying cause of the pleural effusion.
Special Tests
- Pleural aspiration: LDH, protein, glucose, pH, gram stain, culture, cytology.
- Pleural biopsy
Light’s Criteria
One or more of the following criteria suggest an exudative pleural effusion. LDH = Lactate Dehydrogenase
- Pleural effusion protein:Serum Protein Ratio > 0.5 (i.e. Effusion protein is at least double of serum protein levels)
- Pleural effusion LDH:Serum LDH Ratio > 0.6
- Pleural effusion LDH > 2/3 Upper limit of normal serum LDH
Management
The underlying cause should be treated e.g. if the patient has congestive cardiac failure, giving a diuretic, or effusions caused by tuberculosis treated with anti-tuberculosis antibiotics. If the patient is symptomatic, the effusion can be drained though this should be done slowly to avoid re-expansion pulmonary oedema – therefore, a maximum of 1.5L should be drained per 24 hours. Fast draining can also cause pain.
If patients are having recurrent symptomatic pleural effusions e.g. secondary to a malignancy, pleurodesiscan be performed. This involves draining the pleural space of fluid and then injecting a sclerosing agent such as talc. This stimulates the formation of adhesions within the pleural space, thus stopping the accumulation of pleural fluid in the space.
