Pleural effusion is not a distinct disease but it is an important and common presentation of various conditions. Most frequently it is due to cardiac failure, pneumonia, or malignancy. It occurs when there is an increase in the volume of fluid in the pleural space (the space between the visceral pleura and parietal pleura which line the lungs and pulmonary cavity respectively). The normal volume of fluid in this space is between 10-20ml.

This article will cover the clinical presentation and approach to a patient with pleural effusion, the causes of pleural effusion, and the principles of management.


Pleural anatomy

Clinical Presentation

Listed here are the main symptoms and signs that should raise your clinical suspicion of pleural effusion. This is not an exhaustive list and because pleural effusion is a presentation of underlying disease there may be additional elements of the history and examination to suggest the cause. 


  1. Could be asymptomatic unless the volume of fluid is >300ml
  2. Shortness of breath (may only be on exertion)
  3. Cough (typically dry)
  4. Pleuritic chest pain



    1. On observation the patient may have a raised respiratory rate and show signs of respiratory distress (e.g. use of accessory muscles, abdominal breathing, tracheal tug)
    2. On palpation there will be reduced chest expansion on the affected side. If the effusion is large there may be tracheal deviation away from the affected side
    3. On pecussion there will be stony dullness over the effusion
    4. On auscultation there will be absent or reduced breath sounds over the effusion with bronchial breathing directly above it.


    Further Assessment

    Following history and examination there are a number of investigations relevant to the patient with a pleural effusion.

    • The key investigation is a chest x-ray to confirm the clinical findings (see below). PA or AP chest x-ray will demonstrate an effusion >200ml in volume. However, a lateral chest x-ray is more sensitive, showing an effusion >50ml in volume. The usual appearance ranges from blunting of the costophrenic angle(s) to complete white-out of the hemithorax.


    • An ECG should be performed to help exclude significant cardiac pathology


    • Simple blood tests, such as FBC/LFT's/U&E's/cultures, are likely to help guide the differential diagnosis. Which ones are relevant will depend upon the clinical picture. Serum protein and LDH levels will be necessary for the application of Light's criteria.


    • If there is doubt as to the underlying diagnosis a pleural aspirate should be performed. The pleural fluid can be tested for protein and LDH to determine whether it is a transudate or an exudate.


    • Simple observation of the pleural fluid may suggest the diagnosis. Clear and straw coloured suggests transudate. Turbid and pus filled suggests infective exudate. Chylothorax fluid has a milky appearance and a bloody sample suggests haemothorax.


    • Aspirated pleural fluid can also be sent for MC&S, cytology, or other special tests.

    Radiographs of Pleural Effusion

    Small right sided pleural effusion Moderate right sided pleural effusion



    • Defined as a protein content <30g/L
    • Caused by an increased hydrostatic pressure or decreased osmotic pressure in the capillary circulation


    • Defined as a protein content >30g/L
    • Caused by increased capillary permeability and impaired pleural fluid resorption

    Light's Criteria

    If the pleural fluid protein level is 25-35g/L then Light's criteria should be applied to help differentiate between transudates and exudates.

    The effusion is considered an exudate if any of the following criteria are met:

    1. Pleural fluid protein/serum protein ratio >0.5
    2. Pleural fluid LDH/serum LDH ratio >0.6
    3. Pleural fluid LDH greater than two thirds of the normal upper limit of serum LDH



      1. Cardiac failure
      2. Hepatic failure with cirrhosis
      3. Pulmonary embolism (10-20% are transudates)




      • Above are the main causes. Less common causes include nephrotic syndrome, peritoneal dialysis, hypothyroidism, and Meig's syndrome


          1. Pneumonia (parapneumonic effusion or empyema)
          2. Malignancy (about 50% due to lung or breast)
          3. PE (80-90% are exudates)
          4. Rheumatoid arthritis



          • Above are the main causes. Less common causes include post myocardial infarction, asbestos exposure, TB, pancreatitis, and iatrogenic (e.g. radiotherapy, amiodarone, methotrexate, phenytoin)


              Differential Diagnosis

              The differential diagnosis for pleural effusion includes other pleural diseases.

              1. Pleural thickening
              2. Haemothorax
              3. Chylothorax/Pseudochylothorax
              4. Mesothelioma


                Once a pleural effusion has been diagnosed the differential diagnosis is between the conditions listed in the previous section.

                • For transudates think of organ failures and PE
                • For exudates think of infection, malignancy, PE, and inflammation

                Principles of Management

                Diagnostic algorithm for unilateral pleural effusion

                The patient with a pleural effusion does not necessarily need treatment for the effusion itself. For example, small asymptomatic effusions can be managed with observation while the underlying condition resolves. Also, you should avoid aspirating transudates. However, effusions may need to be treated if the patient is strongly symptomatic, if it is a complicated parapneumonic effusion or an empyema. In these cases consider:

                • Therapeutic aspiration (n.b. no more than 1-1.5L should be drained at a time due to the risk of pulmonary oedema)
                • Indwelling chest drain
                • Non-draining infective effusions may require surgical decortication


                  Where the effusion is recurrent (e.g. a malignant effusion) management may be more aggressive. In these cases consider:

                  • Indwelling tunneled chest catheter (e.g. PleurX)
                  • Pleurodesis (using talc, bleomycin, or doxycycline)
                  • Pleurectomy (rarely performed)


                      The most important treatment to resolve a pleural effusion will be treatment aimed at the underlying cause.


                      References and Further Reading

                      1. Moore KL, Dalley AF (eds.), Clinically Oriented Anatomy 5th ed. Philadelphia: Lippincott, Williams & Wilkins, 2006: 112-134
                      2. Kumar V, Abbas AK, Fausto N (eds.), Robbins & Cotran Pathologic Basis of Disease 2nd ed. Philadelphia: Elsevier Saunders, 2005: 766-767
                      3. Chapman S, Robinson G, Stradling J, West S, Oxford Handbook of Respiratory Medicine 2nd ed. Oxford: Oxford University Press, 2009: 45-55 and 345-361
                      4. Patient UK. Pleural Effusion. (accessed 11th March 2011)
                      5. Emedicine. Pleural Effusion. (accessed 11th March 2011)
                      6. Emedicine. Pleural Effusion Imaging. (accessed 11th March 2011)
                      7. British Thoracic Society. BTS Pleural Disease Guideline 2010. (accessed 11th March 2011)

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