GGC Medicines

Adult Therapeutics Handbook

Investigation of Unilateral Pleural Effusion

Investigation of Unilateral Pleural Effusion


Pleural effusions, the result of the accumulation of fluid in the pleural space, are a common medical problem. They can be caused by several mechanisms including increased permeability of the pleural membrane, increased pulmonary capillary pressure, decreased negative intrapleural pressure, decreased oncotic pressure, and obstructed lymphatic flow.

Pleural effusions are classified into transudates and exudates:

  • A transudative pleural effusion occurs when the balance of hydrostatic forces influencing the formation and absorption of pleural fluid is altered to favour pleural fluid accumulation. The permeability of the capillaries to proteins is normal. (Common causes - left ventricular failure (LVF), liver cirrhosis, hypoalbuminaemia and peritoneal dialysis).
  • In contrast, an exudative pleural effusion develops when the pleural surface and/or the local capillary permeability are altered. (Common causes - malignancy and parapneumonic effusions).

Assessment / monitoring

  • The differential diagnosis of an effusion is wide, and may include pulmonary, pleural or extrapulmonary disease. Please contact local Respiratory team early to guide 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 upper limit normal range in your hospital.
  • An accurate drug history should be taken during clinical assessment. Although uncommon, a number of medications have been reported to cause exudative pleural effusions. Discuss with a respiratory physician or your clinical pharmacist if necessary.
  • Aspiration should not be performed for bilateral effusions in a clinical setting strongly suggestive of a pleural transudate, unless there are atypical features or they fail to respond to therapy.

Safety and timing of pleural procedures

  • Current BTS guidance recommends the use of bedside pleural ultrasound at the time of procedure where available to guide the site of pleural aspiration and chest drain insertion for pleural effusion. The aim is to reduce complications from perforation of viscera.
  • Diagnostic / therapeutic aspiration should occur during normal working hours where possible, unless urgently indicated (e.g. large effusion causing significant breathlessness or hypoxia).
  • Avoid chest drain placement out of hours if possible unless empyema present on diagnostic tap. Removal of all fluid prior to definitive diagnosis may delay further investigations and definitive management, especially of possible malignant effusions.
  • Anticoagulation (raised prothrombin time, warfarin), low platelets (<50x109/L), low molecular weight heparin (enoxaparin, dalteparin) and clopidogrel are relative contraindications to pleural aspiration / drainage and the procedure should be delayed until these factors are corrected, unless required as an emergency. Aspirin alone is not a contraindication to pleural procedures.

General management

The aim of this guideline is to assist in the investigation of pleural effusion. Treatment is dependent on the cause e.g. if the cause is found to be pulmonary embolism then refer to Diagnosis and treatment of DVT / PTE

The flowchart above adapted by permission from BMJ Publishing Group Limited. Thorax, Hooper C, Lee YCG, Maskell N on behalf of BTS Pleural Guideline Group, 65 (Suppl 2), page ii4-ii17, 2010.

Management of unilateral pleural effusion by suspected cause

Suspected cause: Parapneumonic
  • Test results:
    • Straw coloured exudate
    • Normal pH / glucose
  • Management:
    • Treat as pneumonia
    • Therapeutic aspirate / drainage if large / symptomatic
Suspected cause: Complicated parapneumonic
  • Test results:
    • May look opaque / turbid
    • Acidic (pH <7.2)
    • Glucose <2.2mmol/L
  • Management:
    • Treat as pneumonia
    • Early drainage - risk of progression to empyema
Suspected cause: Empyema
  • Test results:
    • Frank pus / organisms on gram film
    • Positive culture)
  • Management:
    • Discuss antibiotics with microbiology
    • Urgent drainage (same day)
Suspected cause: Malignant (lung, mesothelioma, lymphoma, breast most common)
  • Test results:
    • Often bloodstained (if in doubt - haematocrit)
    • Normal pH.
    • High LDH
    • Send for cytology (as much as possible)
  • Management:
    • Do not drain until discussed with Respiratory.
    • Therapeutic aspirate if symptomatic
    • Further investigation and definitive management may be affected if drained
Suspected cause: Chylothorax (e.g. post thoracic surgery / injury, haem malignancy)
  • Test results:
    • Looks like milky tea
    • Test for cholesterol and TGs
    • Consider flow cytometry if available
  • Management:
    • Do not drain until discussed with Respiratory
    • Therapeutic aspirate if symptomatic
Suspected cause: Rheumatoid
  • Test results:
    • Turbid fluid
    • Very low pH / glucose
    • Very high LDH
  • Management:
    • Discuss with Respiratory and/or Rheumatology
    • May mimic empyema - if in doubt treat as this
Suspected cause: Tuberculous
  • Test results:
    • Normal pH / glucose
    • Ensure sample for AAFB sent
  • Management:
    • Do not drain until discussed with Respiratory.