Robert Wood Johnson University Hospital



(Pleural Tap, Pleural Fluid Analysis)

Procedure overview

What is thoracentesis and pleural fluid analysis?

Thoracentesis is a procedure in which a needle is inserted through the back of the chest wall into the pleural space (a space that exists between the two lungs and the interior chest wall) to remove fluid or air. Pleural fluid analysis is the microscopic and chemical lab analysis of the fluid obtained during thoracentesis.

The normal function of the lungs is to expand with each breath taken in (like a balloon), fitting closely to the rib cage. With each expansion of the lungs, there is a corresponding expansion of the chest. There is only a little space (the pleural space) between the lungs and the interior wall of the chest. The pleural space is lubricated by fluid that is secreted and reabsorbed at relatively constant rates by the pleura (tissue that encases the lungs). Because of the constant rate of secretion and reabsorption, there is generally only a small amount of fluid in the area at any time. The pleural fluid functions to prevent friction against the chest wall as the lungs inflate and deflate with breathing.

In a disease process, the pleural space may fill with fluid, such as blood or pus (from infection). Alternately, the normal fluid in the pleural space may simply accumulate because of abnormal reabsorption. When such an accumulation occurs, it becomes difficult for the lungs to fully inflate because of the fluid pressing on the lungs. Pleural fluid accumulation can cause shortness of breath, which may become more pronounced with increased activities. It may become necessary to perform a thoracentesis to remove the fluid.

The accumulation of fluid in the pleural space, referred to as a pleural effusion, usually indicates an underlying abnormality. A thoracentesis may be performed to identify the reason (diagnostic) and/or to relieve the discomfort and symptoms (therapeutic) of excessive fluid in the pleural space.

A diagnostic thoracentesis involves the removal of fluid for analysis (pleural fluid analysis). In general, pleural fluid is classified as exudate (seen in inflammatory, cancerous, or infectious conditions) or transudate (fluid that has leaked from blood or lymph vessels for various reasons, such as congestive heart failure). Pleural fluid analysis may help to confirm or rule out infections or diseases such as cancer, congestive heart failure, liver failure, or pulmonary hypertension (high pressure in the lungs’ blood vessels). Therapeutic thoracentesis may help to relieve discomfort from shortness of breath because of a pleural effusion.

Other related procedures that may be used to diagnose problems with the lungs and respiratory tract include bronchoscopy, computed tomography (CT scan) or magnetic resonance imaging (MRI) of the chest, chest X-ray, chest ultrasound, and oximetry. Please see these procedures for additional information.

Anatomy of the respiratory system

Illustration of the anatomy of the respiratory system, adult
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The respiratory system is made up of the organs involved in the exchange of gases--primarily oxygen and carbon dioxide--and consists of the:

The upper respiratory tract includes the:

The lower respiratory tract includes the lungs, bronchi, and alveoli.

What are the functions of the lungs?

The lungs take in oxygen, which cells need to live and carry out their normal functions. The lungs also get rid of carbon dioxide, a waste product of the body's cells.

The lungs are a pair of cone-shaped organs made up of spongy, pinkish-gray tissue. They take up most of the space in the chest, or the thorax (the part of the body between the base of the neck and diaphragm).

The lungs are enveloped in a membrane called the pleura.

The lungs are separated from each other by the mediastinum, an area that contains the following:

The right lung has three sections called lobes. The left lung has two lobes. When you breathe, the air enters the body through the nose or the mouth. It then travels down the throat through the larynx (voice box) and trachea (windpipe) and goes into the lungs through tubes called mainstem bronchi.

One mainstem bronchus leads to the right lung and one to the left lung. In the lungs, the mainstem bronchi divide into smaller bronchi and then into even smaller tubes called bronchioles. Bronchioles end in tiny air sacs called alveoli.

Reasons for the procedure

Thoracentesis may be performed for diagnostic and/or therapeutic reasons. The diagnostic use of a thoracentesis involves pleural fluid analysis to distinguish between exudate, which may result from inflammatory or malignant conditions, and transudate, which may result from failure of organ systems that affect fluid balance in the body. This analysis aids in determining the cause of the abnormality.

The diagnostic findings are classified into two categories, exudate and transudate, and include, but are not limited to, the following:

The therapeutic use of thoracentesis may be helpful in relieving symptoms such as shortness of breath and pain.

There may be other reasons for your doctor to recommend a thoracentesis and a pleural fluid analysis.

Risks of the procedure

As with any surgical procedure, complications can occur. Some possible complications may include, but are not limited to, the following:

Thoracentesis is contraindicated in certain bleeding conditions.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Before the procedure

During the procedure

Illustration of a thoracentesis procedure
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A thoracentesis may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor’s practices.

Generally, a thoracentesis follows this process:

  1. You will be asked to remove any clothing, jewelry, or other objects that may interfere with the procedure.
  2. If you are asked to remove clothing, you will be given a gown to wear.
  3. Your vital signs (heart rate, blood pressure, breathing rate, and oxygen level) may be monitored before and during the procedure.
  4. You may receive supplemental oxygen as needed, through a face mask or nasal cannula (tube).
  5. You will be placed in a sitting position with your arms raised and resting on an overbed table. This position aids in spreading out the spaces between the ribs for needle insertion. If you are unable to sit, you may be placed in a side-lying position on the edge of the bed on your unaffected side.
  6. You may be asked not to cough, breathe in deeply, or move during the procedure.
  7. The skin at the puncture site will be cleansed with an antiseptic solution.
  8. You will receive a local anesthetic at the site where the thoracentesis is to be performed. You may experience a brief stinging sensation at the site of the anesthetic injection.
  9. When the area is numb, the doctor will insert a needle between the ribs in your back. You may experience some pressure at the site where the needle is inserted.
  10. Once the doctor has entered the pleural space with the needle, fluid will slowly be withdrawn.
  11. If a pleural fluid analysis is to be done, several lab tubes will be filled with fluid and sent to the lab.
  12. If there is a large amount of pleural fluid, the physician may attach tubing to the needle to allow the fluid to drain into a bottle or other type of drainage system. In some cases, the doctor may choose to leave the tubing attached for a longer period of time, such as a day or two. In this case, you will be admitted to the hospital until the tubing is removed.
  13. When the fluid has been removed, the needle will be removed.
  14. A sterile bandage or dressing will be applied.

After the procedure

After the procedure, you will be monitored until your blood pressure, pulse, and breathing are stable. If the procedure was done at the bedside, you will remain in your hospital room. If the procedure was performed on an outpatient basis, you will be discharged to your home, unless your doctor decides otherwise. If the procedure was performed on an outpatient basis, you should plan to have another person drive you home.

The dressing over the puncture site will be monitored for bleeding or other drainage.

You may have a chest X-ray performed after the procedure.

When the recovery period is over, you may resume your usual diet and activities unless your doctor advises you differently.

Notify your doctor to report any of the following:

Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

Online resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Cancer Society

National Cancer Institute (NCI)

National Heart, Lung, and Blood Institute (NHLBI)

National Institutes of Health (NIH)

National Library of Medicine


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