Definition and Overview

Thoracentesis is a procedure performed on patients with pleural effusion, which is the build-up of fluid in the pleural space. In a normal individual, there is a balance between continuous fluid production and absorption by the pleura, allowing pleural fluid to be maintained at 10 to 20 ml at any particular time. Any abnormality or disease that affects these processes can lead to the development of pleural effusion.

In thoracentesis, a large bore needle is used to obtain and drain fluid from the pleural space. The pleural fluid samples can then be sent to the laboratory for testing. Pleural fluid examinations allow the analysis of pleural fluid characteristics, identification of bacteria, and determination whether the fluid is a transudate or an exudate. All these tests are useful in determining the etiology of the pleural and in establishing a diagnosis.

Aside from being a diagnostic procedure, thoracentesis can also be therapeutic. The presence of pleural effusion, especially in large amounts, can lead to the compression of the adjacent lung, resulting in symptoms such as difficulty of breathing. Pleural fluid drainage via thoracentesis can lead to remarkable symptom relief in these patients. In some cases, thoracentesis may actually lead to complete resolution of the effusion, with no further intervention necessary.

Who Should Undergo the Procedure and Expected Results

Not all patients with pleural effusion need to undergo thoracentesis. Some patients, particularly those cases wherein the effusion is small, or when it can be attributed to congestive heart failure or uremia, may respond to diuresis or other treatment strategies.

The procedure is recommended:

  • In cases wherein the etiology of the pleural effusion is not known
  • For patients suffering from pleural effusion for the first time
  • For patients with large effusions
  • For patients with recurrent pleural effusions

The goal of therapeutic thoracentesis is to remove as much pleural fluid as possible in one sitting. This can produce profound relief in difficulty of breathing. Also, patients with empyema thoracis, or purulent fluid in the pleural space, can benefit from thoracentesis by the removal of the infected fluid.

Adequate drainage of infected effusions and source control are cornerstones in the management of empyema. Finally, drainage of pleural effusion allows a clearer radiographic evaluation of the lungs, which can aid in the proper management of the disease.

How Does the Procedure Work?

The procedure is performed with the patient typically in the sitting or upright position. In bedridden patients where sitting is not possible, putting them in the lateral decubitus position, where they lie down on the side with the effusion, is an alternative. Once properly positioned, the area for thoracentesis is determined. Percussion and auscultation of the chest, along with an imaging study, can help in selecting the best point of entry for the bore needle. The procedure can be performed blindly, with the needle inserted 2 to 3 cm below the most superior border of the effusion, usually along the patient’s back. Smaller or loculated effusions, however, are best drained with ultrasound guidance.

The area is then exposed and cleaned. The thoracentesis needle, usually gauge 18 or 20, is then inserted right above the superior aspect of the rib. This ensures that the intercostal bundle, containing the nerve and vessels, are avoided. The needle is inserted up to the parietal pleura, and pleural fluid is then aspirated. If, instead of fluid, air is aspirated, the thoracentesis site may be too high. Unsuccessful thoracentesis may be due to several reasons, such as the pleural effusion being too viscous or the chest wall being too thick. Using longer and larger bore needles may help, as well as performing the procedure under ultrasound guidance.

Depending on the kit used, the needle may be connected to a 3-way stopcock, which allows multiple aspirations using a syringe, without opening the pleural cavity to air. Some kits allow the insertion of a catheter over a wire that can be inserted through the needle to reach the pleura. Pleural fluid is then drained, and samples are placed in sterile containers for examination. Once the procedure has been completed, the needle or catheter is removed, and the site for thoracentesis is covered with a sterile dressing.

Possible Complications and Risks

Although thoracentesis is a simple procedure, it is not without complications. The most common complication encountered is pneumothorax, or air in the pleural space. Previous studies have reported the incidence of post-thoracentesis pneumothorax to be 11%. Of these, 2% of patients required further management with a tube thoracostomy. Most cases can be managed conservatively, with high oxygen support.

Bleeding is another possible risk of the procedure. When performed properly, bleeding is uncommon. However, this can occur in elderly patients who have tortuous intercostal vessels. It is also a risk in patients with coagulation abnormalities who develop pleural effusions. This risk can be minimized by using a smaller needle when performing the procedure.

A rare, but dreaded complication of thoracentesis is the re-expansion pulmonary edema. This condition is typically caused by the rapid expansion of a collapsed lung. Previously, it was believed that this is associated with the removal of large amounts of pleural fluid; although no consensus exists as to how much fluid can be safely removed, experts recommend a maximum of 1 Li of pleural fluid drainage at any one time. Recent studies, however, are implicating that more than the amount of effusion, it is the speed of drainage that induces the development of this condition.

Other uncommon complications include empyema caused by the introduction of bacteria into the pleural cavity, and tumor spread over the tract of the needle.


  • Broaddus C, Light RW. Pleural effusion. In: Mason RJ, Broaddus CV, Martin TR, et al, eds. Textbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Saunders Elsevier; 2010:chap 73.

  • Celli BR. Diseases of the diaphragm, chest wall, pleura, and mediastinum. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 99.

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