(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, pus (from infection), serum, or lymph. Alternately, the pleural fluid may be prevented from being reabsorbed, causing an accumulation of fluid in the pleural space. 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,  indicates an 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). 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 due to the pressure caused by fluid accumulation.

Other related procedures that may be used to diagnose problems with the lungs and respiratory tract include bronchoscopy, computed tomography (CT scan) of the chest, chest fluoroscopy, chest x-ray, chest ultrasound, lung biopsy, lung scan, mediastinoscopy, oximetry, peak flow measurement, positron emission tomography (PET) scan, pleural biopsy, pulmonary angiography, and pulmonary function tests. Please see these procedures for additional information.

Anatomy of the respiratory system:

The respiratory system is made up of the organs involved in the interchanges of gases, and consists of the:

  • nose

  • pharynx

  • larynx

  • trachea

  • bronchi

  • lungs

The upper respiratory tract includes the:

  • nose

  • nasal cavity

  • ethmoidal air cells

  • frontal sinuses

  • maxillary sinus

  • larynx

  • trachea

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).

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