Investigation of Unilateral Pleural Effusion

This is a brief guideline on unilateral pleural effusion, with further details available on the NHSGGC Clinical Guidelines Platform:


  • The differential diagnosis of an effusion is wide, and may include pulmonary, pleural or extrapulmonary disease. Please contact local Respiratory Team early to consider ultrasound guided aspiration and further systematic investigation and management (see flow diagram below).
  • According to Light's criteria an effusion is an exudate if any one of the following is true of pleural fluid aspirate:
    • Pleural total protein: serum total protein >0.5
    • Pleural LDH: serum LDH >0.6
    • Pleural LDH >0.66 times upper limit normal range in your hospital.
  • Aspiration should not be performed for bilateral effusions in a clinical setting strongly suggestive of a pleural transudate (cardiac, renal or liver failure) unless there are atypical features or the patient fails to respond to therapy.

Safety and timing of pleural procedures

  • Standard operating procedures for diagnostic / therapeutic pleural aspiration and intercostal chest drain insertion can be found. See the 'Chest drain' guideline on NHSGGC Clinical Guidelines Platform.
  • Pleural procedures should occur during normal working hours, unless urgently indicated (e.g. large effusion causing significant breathlessness or hypoxia, empyema). This should always be discussed with senior clinicians before being undertaken. 
  • Bedside pleural ultrasound should always be used to guide the site of pleural aspiration and chest drain insertion for pleural effusion. 
  • A 6F Rocket aspiration catheter can be used to safely perform a large volume pleural aspiration, avoiding unnecessary insertion of intercostal chest drains; removal of all fluid prior to definitive diagnosis may delay further investigations and definitive management. Do not drain any more than 1 litre of pleural fluid in one sitting as this is associated with risk of re-expansion pulmonary oedema and some patients may experience pain or coughing. The catheter can be left in for up to 24 hours if needed - discuss with senior clinician if felt indicated. 


See 'Anticoagulation and Antiplatelet Management, Pleural Disease Investigation and Treatment' guideline on NHSGGC Clinical Guidelines Platform for details on management of patients on oral anticoagulants or antiplatelets undergoing elective procedures. Consult with senior if pleural procedure is deemed to be an emergency.


Talc pleurodesis is performed with the aim of preventing recurrence of malignant pleural effusion. The decision to undertake pleurodesis should always be discussed with a senior respiratory physicianSee the 'Chest drain' guideline on NHSGGC Clinical Guidelines Platform for the standard operating procedure.

Pleural infection

  • Refer to respiratory team if suspected pleural infection. Antibiotic choice should be guided by the respiratory team or microbiology. Most pleural infection will require drainage. 
  • If chest drain inserted it should be flushed four times a day with 20ml sterile sodium chloride 0.9% and left on free drainage afterwards. Further details can be found in the 'Chest drain' guideline on NHSGGC Clinical Guidelines Platform.
  • Fibrinolytic therapy is used to improve drainage and outcomes in empyema. Alteplase (t-PA) and dornase alpha (DNase, Pulmozyme®) are used and are unlicensed for this indication. The decision to administer fibrinolytic therapy (and the dose of t-PA used) in pleural infection should always be discussed with a senior respiratory physician. See guidance in the  'Chest drain' guideline on NHSGGC Clinical Guidelines Platform.  


Guideline reviewed: August 2021

Page updated: March 2022