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Stephen Chapman

, Grace Robinson

, John Stradling

, Sophie West

, and John Wrightson

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date: 29 June 2022

General points

Thoracentesis (‘pleural tap’ or pleural fluid aspiration) may be diagnostic or therapeutic. Site selection using US guidance (see Chapter 72) gives a higher success rate and a better adverse event profile and should be used routinely. Use a dedicated procedure room when possible. Avoid out-of-hours procedures unless an emergency.

Diagnostic thoracentesis


Undiagnosed pleural effusion.

There are no absolute contraindications to pleural aspiration, although, for non-urgent thoracentesis, anticoagulated patients should have their clotting corrected to INR <1.5.


  • Discuss procedure with patient, and obtain written consent.

  • Position patient sitting forward, leaning on a pillow over a table, with their arms folded in front of them

  • Double-check correct side from chest examination and CXR

  • Choose aspiration site using ultrasound, preferably in ‘safe triangle’ (see Thoracentesis p. [link]), unless loculated fluid makes this impossible. Avoid posterior approaches where possible (as the intercostal artery lies in the mid-intercostal space posteriorly)

  • Sterile skin preparation and aseptic technique

  • Infiltrate skin, intercostal muscle, and parietal pleura with 10mL of 1% lidocaine. Aim just above the upper border of the appropriate rib, avoiding the neurovascular bundle that runs below each rib. The parietal pleura is extremely sensitive; use the full 10mL of lidocaine

  • Aspirate pleural fluid with a green (21G) needle and 50mL syringe

  • Following diagnostic tap:

    • Record pleural fluid appearance

    • Send sample to biochemistry for measurement of glucose, protein, and LDH

    • Send a fresh 20mL sample in sterile pot to cytology for examination for malignant cells and differential cell count

    • Send samples in sterile pot and blood culture bottles to microbiology for Gram stain and microscopy, culture, and AFB stain and culture

    • Process non-purulent heparinized samples in ABG analyser for pH (consult biochemistry laboratory for local policy of pH analysis beforehand; never put purulent samples in the arterial blood analyser)

    • Consider measurement of cholesterol, triglycerides, chylomicrons, haematocrit, and amylase, depending on the clinical circumstances

  • There is no need for a routine CXR following aspiration, unless difficulties were encountered during the procedure

  • If unable to obtain fluid, re-ultrasound to confirm depth and conformation of fluid, and consider CT-guided aspiration.


of thoracentesis include pain, failure to obtain fluid, pneumothorax (2–4% with US), cough, bleeding, empyema, spleen or liver puncture, and malignant seeding down aspiration site.

Therapeutic thoracentesis


Symptomatic relief of breathlessness due to a pleural effusion, most commonly due to malignancy.


  • In most cases, can be performed as a day-case procedure. Commercial thoracentesis kits are available, but the following works just as well

  • The initial procedure of local anaesthetic infiltration is identical to that of diagnostic thoracentesis. It is important to verify that the insertion site is optimal using US; also always ensure that fluid is first obtained with a green (21G) needle

  • Carefully advance an IV cannula (with a syringe on the end) along the anaesthetized track

  • When fluid is aspirated, remove the inner needle while fully inserting the plastic cannula. Attach the cannula to a three-way tap

  • Aspirate fluid from the chest with a 50mL syringe via the three-way tap, and flush the fluid into a sterile jug through extension tubing (e.g. a blood giving set, cut using sterile scissors). Often, having ‘primed’ the tubing with pleural fluid, further syringe aspiration is not required, as the fluid siphons down out of the chest itself into the jug. Drain a maximum of 1.5L of fluid on one occasion (risk of re-expansion pulmonary oedema following sudden removal of large volumes). Stop the procedure if resistance is felt or the patient experiences discomfort or severe coughing

  • Apply dressing to aspiration site

  • CXR is not routinely required post-procedure, unless difficulties were encountered or air was aspirated. Post-procedural US is useful in assessing volume of remaining fluid.

Further information

Havelock T et al. Pleural procedures and thoracic ultrasound: British Thoracic Society pleural disease guideline 2010. Thorax 2010;65(suppl. 2):ii61–76.Find this resource: