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Patient education: Thoracentesis (Beyond the Basics)

John E Heffner, MD
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, called the pleural space. This fluid is called pleural fluid and normally exists only as a thin layer in the area between the lungs and chest wall. However, some conditions can cause an increased amount of pleural fluid to collect, called a pleural effusion.

During a thoracentesis, your doctor will put a needle between your ribs into the pleural space to collect a sample of the pleural fluid, which can help determine why the fluid developed and what, if anything, should be done to treat it.

Pleural effusions can be caused by many different conditions, including pneumonia, heart failure, cancer, or tuberculosis. In some cases, blood or other fluid may leak into the pleural space from another part of the body, causing the effusion.

A pleural effusion may be detected during a physical examination or by a chest X-ray or chest CT scan.


The main reasons to perform a thoracentesis are to determine the cause of the pleural fluid and to relieve shortness of breath caused by the fluid.

A diagnostic thoracentesis is performed by removing a small sample of pleural fluid (about 2 ounces [60 mL]) to determine the cause of a pleural effusion and to help doctors select the best treatment.

A therapeutic thoracentesis is used to remove a larger volume of pleural fluid (about 20 ounces [600 mL] to 40 ounces [1200 mL]) to relieve symptoms, such as shortness of breath.

By doing laboratory tests on the pleural fluid, the cause of the pleural effusion can usually be determined. Depending on the cause, different treatments may be indicated. For instance, if the pleural fluid is infected, a patient may require insertion of a catheter into the pleural space to ensure complete drainage of all infected pleural fluid.


Before a thoracentesis, a chest X-ray or ultrasound will be done to identify the exact location of the pleural effusion. For most patients, an ultrasound is preferred because it is more accurate than a chest X-ray or physical examination. The doctor will explain the procedure, describe potential complications, and discuss why thoracentesis is necessary. If ultrasound is not available, he or she will examine the chest closely by listening to the lungs with a stethoscope and tapping on the chest to determine the best area to perform the thoracentesis.

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 before the procedure to exclude any blood clotting abnormalities caused by disease or medications. Thoracentesis, however, is considered safe for most patients with blood clotting disorders.

Ultrasound machines are used routinely in most institutions to improve the safety of the procedure. Ultrasound guidance is strongly recommended when the fluid is trapped in small pockets around the lung, as small pockets of fluid can be difficult to locate by tapping on the chest.

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. You should expect the doctor to confirm with you and the staff that the procedure is being performed on the correct side of your chest.

After the needle insertion site is cleaned with an antiseptic solution, a small amount of numbing medicine (a local anesthetic, similar to novocaine) is injected with a small needle through the skin and into the deeper tissues between two ribs. This medicine helps minimize discomfort during the procedure.

A slightly larger needle attached to a syringe is then inserted where the anesthetic was injected. The needle passes between ribs into the pleural space, and then a thin plastic tube (called a catheter) is exchanged for the needle. Once the catheter is in place, the needle is removed, and fluid is withdrawn through the catheter into the syringe. If you have been experiencing symptoms from the effusion (eg, shortness of breath), a large amount of fluid may be drained, which allows the lung to more fully expand.


In most cases, a thoracentesis is performed without complications. When complications do occur, they are usually 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.

Feeling faint – Some people may feel faint or dizzy during or after the procedure. This feeling generally resolves after lying down for a few minutes.

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 of blood collected in the chest by insertion of a catheter 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 making infection a very rare complication.

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 from the pleural space and allow the lung to re-expand. A pneumothorax happens in approximately 6 percent of thoracentesis procedures, but in less than 3 percent of procedures when the thoracentesis is performed with the assistance of ultrasound imaging.

Pneumothoraces that do occur are usually small and resolve on their own. About a third of pneumothoraces become large, continue to expand, or cause shortness of breath. In these patients a catheter or chest tube is placed through the skin into the pleural space to withdraw the air.

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. Ultrasound imaging to guide placement of the thoracentesis needle also decreases the risk of these complications.

Pulmonary edema – Rarely after thoracentesis, a person can experience pulmonary edema, which is the sudden collection of fluid within the lung on the side of the chest where the thoracentesis was performed. Some people may experience shortness of breath or cough, but usually recover quickly. Pulmonary edema tends to occur when a large volume of pleural fluid is removed during a therapeutic thoracentesis.


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, you will need to be observed in the office for a few hours after the procedure, and you will need assistance getting home. Patients should discuss these issues with their physician before 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 education: Pleuritic chest pain (The Basics)
Patient education: 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.

Medical thoracoscopy (pleuroscopy): Equipment, procedure, and complications
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


British Thoracic Society




The editorial staff at UpToDate would like to acknowledge Peter Doelken, MD, FCCP, who contributed to an earlier version of this topic review.

Literature review current through: Nov 2017. | This topic last updated: Thu Sep 14 00:00:00 GMT 2017.
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