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What is Thoracentesis?

Inside the ribcage, there is a thin space separating the lungs from the ribs, called the pleural space. Usually, this space contains only a very small amount of fluid so the lungs slide easily against the ribs during breathing.

Various diseases can cause larger amounts of fluid to gather in the pleural space, with the result that there is less room for the lungs to breathe. In some cases the fluid may be inflammatory or infected, or bloody. A pleural tap or thoracentesis is a procedure to remove fluid from the pleural space, whether it is done to identify the disease causing the problem, or simply to make room for flung to expand in order to make breathing easier.

How should I prepare?

Very little preparation is needed. Blood tests are usually done to check your blood clotting. You will be asked to remove your shirt and wear a gown.  

How is the procedure performed?

The patient is usual sitting upright, with elbows resting on a table. An ultrasound is done to locate the fluid, and a safe path between the ribs in back is found. Local anesthetic is placed along the intended needle path and a needle with a plastic sheath is advanced into the fluid.  The needle is removed, and the fluid is aspirated through the sheath. After the desired amount of fluid has been removed, the plastic sheath will be removed and a dressing applied. No stitches are necessary. A chest X-ray will be done immediately after the procedure.

What will I experience during and after the procedure and how will I get my results?

The local anesthetic is likely to sting briefly, but otherwise the procedure should be painless.

The interventional radiologist will inform you whether the procedure has been technically successful, and will review the results of the chest X-ray before you leave. The results of lab tests on the fluid will take a day or two, and will be available to your ordering physician.


What are the benefits and risks?

Thoracentesis is a safe and effective technique for removing fluid from the pleural space, whether for diagnosis or making breathing easier. There is a very small risk of serious bleeding requiring another procedure or surgery.

There is a small risk of the needle puncturing the lung and allowing air to escape from the lung into the pleural space. When ultrasound is used for guidance, this risk is very uncommon. If a small amount of air leaks, it will be seen on the chest X-ray and require a hours of observation to determine if the leak has closed. If a large amount of air escapes, the lung may collapse and require the immediate placement of a thin plastic tube between the ribs to remove the air and allow the lung to re-expand. This would require an overnight stay in the hospital.

Radiologyinfo.org for Patients

The radiology information resource for patients. RadiologyInfo.org tells you how various X-ray, CT, MRI, ultrasound, radiation therapy and other procedures are performed. It also addresses what you may experience and how to prepare for the exams. The website contains over 200 procedure, exam and disease descriptions covering diagnostic and interventional radiology, nuclear medicine, radiation therapy and radiation safety and is updated frequently with new information. All material on the RadiologyInfo.org website is reviewed and approved by experts in the field of radiology from the ACR and RSNA, as well as other professional radiology organizations.

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