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Patient information: Thoracentesis (Beyond the Basics)

Peter Doelken, MD, FCCP
Section Editor
V Courtney Broaddus, MD
Deputy Editor
Helen Hollingsworth, MD
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Thoracentesis is a procedure used to obtain a sample of fluid from the space around the lungs. Normally, only a thin layer of fluid is present in the area between the lungs and chest wall. However, some conditions can cause a large amount of fluid to accumulate. This collection of fluid is called a pleural effusion. Thoracentesis is done to collect a sample of the fluid, which can help determine why the pleural effusion developed.


A thoracentesis is performed to determine the cause of a pleural effusion. In some cases, a physician may perform thoracentesis to relieve symptoms caused by the pleural effusion, including shortness of breath and low blood oxygen levels. A pleural effusion may be detected during a physical examination or on a chest x-ray.

Pleural effusions can be caused by many different conditions, including infections, heart failure, cancer, or tuberculosis. In some cases, blood or other fluid may be leaking into the pleural space from another part of the body, causing the effusion. By examining the fluid and the types of cells it contains, the cause of the effusion can usually be determined.


Before a thoracentesis, a chest x-ray will be taken to identify the location of the pleural effusion. The doctor will explain the procedure and discuss why it is necessary. He or she will examine the chest closely; the edge of the effusion can often be identified by listening to the lungs and tapping on the chest wall.

If you have a bleeding disorder or are on medications that affect blood clotting, you may need extra care to minimize the risk of bleeding. Tell your healthcare provider if you have a history of bleeding problems or if you are taking a medicine that decreases blood clotting. In some cases, a blood test will be taken prior to the procedure to exclude any blood clotting abnormalities caused by disease or medications.

Ultrasound machines are used routinely in many institutions to increase the safety of the procedure. Ultrasound guidance is recommended when the fluid is trapped in small pockets around the lung.

The procedure takes a short time and can be performed at a patient's bedside or in a physician's office.


A thoracentesis involves the following steps:

You will be placed in a position that allows the doctor to access the effusion. Usually, you are asked to sit upright during the procedure. It is important to remain still during the procedure so that the fluid does not shift.

A small amount of numbing medicine (a local anesthetic, similar to novocaine) is injected into the skin and deeper tissues with a small needle. This medicine helps minimize discomfort during the procedure.

A slightly larger needle is then inserted in the same location. A syringe is attached to this needle and is used to withdraw fluid from around the lung. If you have been experiencing symptoms from the effusion (eg, shortness of breath), a large amount of fluid may be removed, which allows the lung to re-expand.


In most cases, a thoracentesis is performed without complications. Most complications are minor and resolve on their own or are easily treated. Potential complications include the following:

Pain – There may be some discomfort when the needle is inserted. Using a local anesthetic helps to reduce the pain. Pain generally resolves once the needle is removed.

Bleeding – A blood vessel may be nicked as the needle is inserted through the skin and chest wall, causing bleeding. The bleeding is usually minor and stops on its own, although it may cause bruising around the puncture site. In rare cases, there may be bleeding into or around the lung, requiring drainage or surgery.

Infection – Infection can develop if bacteria are introduced by the needle puncture. Using disinfectant solution to clean the area and using sterile technique during the procedure minimize this risk.

Pneumothorax or collapsed lung – Occasionally, the needle used to obtain a fluid sample can puncture the lung. The hole created by the puncture usually seals quickly on its own. If it does not, air can build up around the lung, causing the lung to collapse. This is called a pneumothorax. When a pneumothorax occurs, a chest tube may be used to drain the air and allow the lung to re-expand. A pneumothorax happens in less than 12 percent of thoracentesis procedures. Those that do occur are usually small and resolve on their own. A chest tube to help re-expand the lung is necessary only if the pneumothorax is large, continues to expand, or causes symptoms.

Pneumothorax due to a non-expanding lung – Air may enter the pleural space if the lung fails to expand when fluid is withdrawn. This is considered to be a drainage-related pneumothorax and is most commonly caused by disorders of the surface lining of the lung and not by the puncture needle. Treatment is rarely needed.

Liver or spleen puncture – In very rare cases, the liver or spleen may be punctured during thoracentesis. Sitting upright and remaining still during the procedure helps to keep the liver and spleen away from the insertion area and minimizes the risk of this complication.


After the procedure, the doctor will observe the insertion site for signs of bleeding and assess your breathing for signs of lung collapse (pneumothorax). If a pneumothorax is suspected, a chest x-ray will be obtained. The doctor will examine the fluid, particularly its color and consistency, and will also send the fluid for laboratory tests.

In general, sedating medicines are not used during thoracentesis. If sedating medicines are used, the patient will need assistance getting home. Patients should discuss these issues with their physician prior to the procedure.


Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information — UpToDate offers two types of patient education materials.

The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.

Patient information: Pleuritic chest pain (The Basics)
Patient information: Pleural effusion (The Basics)

Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.

This topic currently has no corresponding Beyond the Basics content.

Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.

An overview of medical thoracoscopy
Diagnostic evaluation of a pleural effusion in adults: Initial testing
Diagnostic thoracentesis
Imaging of pleural effusions in adults
Management of malignant pleural effusions

The following organizations also provide reliable health information.

American Thoracic Society


American Lung Association


National Heart Lung & Blood Institute


National Library of Medicine



Literature review current through: Jan 2016. | This topic last updated: Mar 24, 2015.
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