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Pleural Effusion

See BTS Guidelines published in Thorax 2010;65 suppl II https://www.brit-thoracic.org.uk/guidelines-and-quality-standards/pleural-disease-guideline/.

Classification of Pleural Effusion

The differentiation between exudates and transudates is the essential first step in the diagnostic evaluation. See Exudate/Transudate.

Diagnostic pleurocentesis 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. At Christchurch Hospital it is suggested to refer patients with large unilateral effusions or with loculated effusions to the Respiratory Service early, before attempting therapeutic pleurocentesis. If you are uncertain whether to carry out a chest aspiration, contact the Respiratory Team on call.

Investigations for Pleural Effusion

• Diagnostic pleurocentesis. May be undertaken by medical staff with appropriate experience. Ultrasound guided aspiration should be performed, in particular if the effusion is small or loculated. Use a 20 mL syringe with a 22G needle under sterile conditions. See Clinical Procedures. Ultrasound should be performed at the bedside, rather than as an "x marks the spot" in the Radiology Department.
• Measure plasma total protein, glucose and LDH levels for comparison with pleural fluid.

Contraindications for pleural aspiration

• Unwilling or uncooperative patient.
• Abnormal bleeding tendency. Check history, medications, e.g., anticoagulants, examination, INR, APTT, fibrinogen and platelets. If in doubt, discuss with Consultant before proceeding.
• Insufficient pleural fluid.
• Chest pyoderma or herpes zoster.

Tests that should routinely be performed on pleural fluid

• Note and document the appearance and any odour of the fluid.
• pH. Accurate pH measurement requires about 2 mL of fresh sample in a capped ABG syringe.
• Glucose.
• LDH.
• Total protein.
• Total and differential WBC.
• Gram stain and culture.
• Cytology (if malignancy is a possibility).
• Consider additional tests as below depending on clinical context.

Exudate/Transudate

• 99% of exudates meet one or more of the following criteria (Light's criteria):
  • Pleural fluid total protein >30 g/L.
  • Pleural fluid total protein/serum total protein ratio >0.5.
  • Pleural fluid LDH/serum LDH >0.6.
  • Pleural fluid LDH > two-thirds of upper limit of normal serum LDH.
• If transudate, seek cause, e.g., heart failure, cirrhosis, nephrotic syndrome, acute glomerulonephritis, peritoneal dialysis, myxoedema

  Note: 5% of malignant effusions are transudates.

• If exudate - assess the differential white cell count; the total WBC is of limited diagnostic value.
  • If lymphocytes predominate consider malignancy, tuberculosis, connective tissue disease.
  • If neutrophils predominate consider parapneumonic effusion, empyema, pulmonary embolus, pancreatitis, subphrenic abscess, early tuberculosis.
  • If a tuberculous aetiology is suspected, consider a closed pleural biopsy before drainage of the fluid (refer Respiratory Services). Otherwise consider a CT thorax first and if there is focal nodularity/mass lesions, consider either an image-guided biopsy or a thoracoscopy (refer Respiratory Services). See Tuberculosis.
• Tests which may help elucidate the cause of an exudate:
  • Cytology - carcinoma, lymphoma. Repeat specimen if the initial aspirate is negative but malignancy is still suspected. Immuno-cytochemistry is important to differentiate between metastatic carcinoma or pleural malignant mesothelioma.
  • Cell surface markers - to distinguish between reactive and malignant lymphoid proliferation.
  • ZN stain and TB culture if tuberculosis is suspected. Consider pleural biopsy and PCR testing. Pleural adenosine deaminase activity (ADA) has shown some promise for the diagnosis of TB.
  • Haematocrit if heavily blood-stained effusion (use EDTA tube). If >50% of peripheral blood haematocrit = haemothorax.
  • Rheumatoid factor - rheumatoid effusion.
  • Triglyceride - if "milky" appearance - chylothorax.
  • Amylase - pancreatitis, ruptured oesophagus, malignancy.
• Other investigations and treatment options include:
  • CT scan. This should be contrast enhanced.
  • Closed or image guided pleural biopsy.
  • Intercostal drain.
  • Thoracoscopy. Options of local anaesthetic thoracoscopy or surgical thoracoscopy are available at Christchurch Hospital.

    Note: Malignant mesothelioma can be very difficult to diagnose using cytology alone and a thoracoscopy should be considered for those cases.

Notes:

• Do not drain the pleural fluid until the diagnosis is established, unless the patient is very dyspnoeic. The presence of some pleural fluid is necessary to perform a thoracoscopy.
• If a complicated parapneumonic effusion or empyema is suspected, do not delay Respiratory Specialist input.

Criteria for parapneumonic effusion and empyema

• Simple parapneumonic effusion.
  • pH ≥7.3, glucose >2.5, LDH <1000.
• Complicated parapneumonic effusion.
  • pH ≤7.2 glucose <2.5, LDH >1000.

    Note: pH 7.2-7.3 - observe closely. Repeat CXR and repeat pleural tap if not clinically improving.

• Empyema.
  • Organisms seen on Gram stain or frank pus.
  • The management of anything but a simple parapneumonic effusion should lead to referral to the Respiratory Services. If a complicated parapneumonic effusion or empyema is suspected, do not delay Specialist input. Early treatment with drainage is indicated.

Topic Code: 1672