Therapeutic thoracentesis, or drainage of a pleural effusion, is a simple procedure done to relieve the symptoms of the effusion. Thoracentesis may also be used as a diagnostic test to look for causes of a pleural effusion.   

Why is Thoracentesis done?

Therapeutic thoracentesis, or drainage of pleural effusions, is done to relieve the symptoms of pleural effusion. These commonly include shortness of breath, chest pain, or dry cough. Thoracentesis may also help stop the cycle of inflammation that may occur with a pneumonia-associated (parapneumonic) effusion. This may help the effusion resolve faster. The fluid drained from the effusion can be sent off for analysis, and may provide clues as to the cause of the effusion.

How does Thoracentesis work?

Drainage of a pleural effusion (thoracentesis) involves insertion of a needle into the pleural space so that the fluid can be aspirated (suctioned) out. This relieves the pressure on the lungs and makes breathing easier. Thoracentesis is most appropriate for free-flowing pleural fluid accumulations. Thicker pleural effusions, such as those associated with some pneumonias, may not drain easily through the thoracentesis needle. In these cases, a tube thoracostomy may be needed.

What should I expect during the procedure?

Drainage of a pleural effusion is a simple procedure which can be done at a patient’s bedside. It does not require a general anaesthetic. Before drainage is performed, a chest x-ray will usually be ordered to confirm the presence of a pleural effusion and to establish the precise location. Ultrasound may also be used during the procedure to guide needle insertion.

  1. Patients are usually asked to sit upright during the procedure. It is important to remain still so that the needle is inserted into the correct place.
  2. Antibacterial solution will be used to clean the skin around the needle insertion site. This is usually between the ribs at the back of the chest.
  3. Local anaesthetic is injected into the back to help reduce discomfort.
  4. A larger needle or catheter is then inserted in the same spot, passing deeper into the chest wall and into the pleural space. This needle may be attached to flexible plastic tubing and vacuum bottles, which collect the fluid as it drains out of the pleural space.
  5. The needle or catheter will be removed, and a sterile dressing applied over the insertion site to help prevent infection. If the patient develops a cough or chest pain at any time during the procedure, it should be stopped immediately. After the procedure, another chest x-ray may be ordered to check for the presence of a pneumothorax (see ‘complications’ below), or to determine whether the fluid was successfully drained.

What are the risks?

Risks of thoracentesis include:

  • Pneumothorax: this complication occurs in approximately one in ten cases. Many are very mild and require no treatment; some may require placement of a tube thoracostomy to drain the air.
  • Pain at the puncture site
  • Bleeding
  • Infection of the chest wall or pleural space (empyema)
  • Puncture of the spleen or liver
  • Tumour seeding along the needle tract
  • Re-expansion pulmonary oedema: with drainage of very large volumes of fluid, there is a small chance that the lungs might react badly to the rapid re-expansion, and the air spaces may fill with fluid. This is a very rare complication, but may be fatal. Patients who have a bleeding disorder, or who are taking anticoagulant medications such as warfarin, may be at increased risk of bleeding during the procedure. Always tell your health provider if this applies to you. There is also a risk that the thoracentesis will be unsuccessful, or that the drained fluid may reaccumulate. This is particularly common in pleural effusions associated with malignancy.


  1. Hanley ME, Welsh CH. Current Diagnosis & Treatment in Pulmonary Medicine. McGraw-Hill, 2006.
  2. Rubins, J. ‘Pleural Effusion’ [online], 2005. Available at URL: (last accessed 6/9/06)
  3. Sahn, SA. ‘Diagnostic thoracentesis’ [online], UpToDate, 2005. Available at URL:
  4. Stone CK, Humphries RL. Current Emergency Diagnosis and Treatment. McGraw-Hill, 2006.

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