What is Thoracentesis?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 22 August 2019
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Lungs have a special double tissue lining on the outside called pleura, and sometimes fluid or air can get sandwiched in between these two layers of tissue. These conditions are known as a pleural effusion or pneumothorax, respectively, and they may occur under many different circumstances, creating pressure on the lungs. When they occur, doctors may do a procedure called thoracentesis, where they remove some of the fluid or let air come out, by inserting a needle in between the pleural layers. Fluids may be removed to produce greater comfort, but they can also be taken as samples to determine what is causing fluid buildup.

As anyone could guess, placing a needle into the lung’s exterior is a dramatic business, and it’s often depicted in medical television shows as simply jamming a needle into the chest. This is not how thoracentesis is usually performed. It’s often a slow and nuanced procedure that may take some scanning first to determine exactly where the needle should be inserted. Things like x-ray or ultrasound could determine this so that the needle actually reaches an area of fluid or pocket of air. It’s not a procedure doctors want to repeat on the same patient unless absolutely necessary because it creates risk for infection, additional air getting into the lungs, a decrease in amount of proteins in the blood, or bleeding into the chest.


The area in which the needle may be inserted depends on area of pleural effusions or pneumothorax. Usually the procedure takes place below the armpits, instead of on the upper chest, and the needle is inserted in between two of the ribs. Patients may or may not be conscious.

In emergency settings, people usually are conscious, but conscious sedation might be used for a planned thoracentesis, since the procedure works best if people do not move and do not panic. However, sometimes only a local anesthetic is used. The procedure usually isn’t performed if there is active skin infection because there is too significant a risk of transferring this infection to the lungs.

When doctors use thoracentesis to analyze fluid, they tend to look at the fluid’s appearance and then may send it to a lab for analysis. They can be looking for presence of infectious agents, cancer, or other illnesses. Fluid appearance may give some indication as to the cause of pleural effusions. Watery liquids are called transudates and could be the result of blood clot, heart failure or kidney problems, and thick liquids (exudates) may indicate pneumonia, swelling around the heart, some forms of cancer, and other conditions. Sometimes the liquid sampled is blood, which may suggest chest trauma or certain cancers.

Occasionally, the primary purpose of thoracentesis is not to test or examine the fluid but to remove enough of it so that pressure on the lungs is reduced. This may or may not be a long-term solution to the problem. If the underlying condition causing fluid to accumulate in the pleural space is not addressed, it’s likely fluid will build up again.



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