Thoracentesis

Thoracentesis

Definition

Also known as pleural fluid analysis, thoracentesis is a procedure that removes fluid or air from the chest through a needle or tube.

Purpose

The lungs are lined on the outside with two thin layers of tissue called pleura. The space between these two layers is called the pleural space. Normally, there is only a small amount of lubricating fluid in this space. Liquid and/or air accumulates in this space between the lungs and the ribs from many conditions. The liquid is called a pleural effusion; the air is called a pneumothorax. Most pleural effusions are complications emanating from metastatic malignancy (movement of cancer cells from one part of the body to another). Most malignant pleural effusions are detected and controlled by thoracentesis. Thoracentesis is also performed as a diagnostic measure. In these cases, only small amounts of material need to be withdrawn.

Symptoms of a pleural effusion include breathing difficulty, chest pain, fever, weight loss, cough, and edema. Removal of air is often an emergency procedure to prevent suffocation from pressure on the lungs. Negative air pressure within the chest cavity allows normal respiration. The accumulation of air or fluid within the pleural space can eliminate these normal conditions and disrupt breathing and the movement of air within the chest cavity. Fluid removal is performed to reduce the pressure in the pleural space and to analyze the liquid. In addition, thoracentesis was traditionally used to remove blood from the chest cavity. This is rare now that the placement of a thoracostomy tube has proven to be a more effective and safer method.

Thoracentesis often provides immediate abatement of symptoms. However, fluid often begins to reaccumulate. A majority of patients will ultimately require additional therapy beyond a simple thoracentesis.

There are two types of liquid in the pleural space, one having more protein in it than the other. More watery liquids are called transudates; thicker fluids are called exudates. On the basis of this difference, the cause of the effusion can more easily be determined.

Transudates

Thin, watery fluid oozes into the chest either because back pressure from circulation squeezes it out or because the blood has lost some of its osmotic pressure.

Exudates

Thicker, more viscous fluid is usually due to greater damage to tissues, allowing blood proteins as well as water to seep out.

Blood

Blood in the chest (hemothorax) is infrequently seen outside of two conditions:

Chyle

Occasionally, the liquid that comes out of the chest is neither transparent nor bloody, but milky. This is due to a tear of the large lymphatic channel—the thoracic duct carrying lymph fluid from the intestines to the heart. It is milky because it is transporting fats absorbed in the process of digestion. The major causes of chylothorax are:

Air

Air in the pleural space is called pneumothorax. Air can enter the pleural space either directly through a hole between the ribs or from a hole in the lungs. Holes in the lungs are sometimes spontaneous, sometimes traumatic, and sometimes the result of disease opening a communication to the air in the lung.

Precautions

Care must be taken not to puncture the lung when inserting the needle. Thoracentesis should never be performed by inserting the needle through an area with an infection. An alternative site needs to be found in these cases. Patients who are on anticoagulant drugs should be carefully considered for the procedure.

Description

The usual place to tap the chest is below the armpit (axilla). Under sterile conditions and local anesthesia, a needle, a through-the-needle-catheter, or an over-the-needle catheter may be used to perform the procedure. Overall, the catheter techniques may be safer. Fluid or air is withdrawn. Fluid is sent to the laboratory for analysis. If the air or fluid continue to accumulate, a tube is left in place and attached to a one-way system so that it can drain without sucking air into the chest.

Preparation

The location of the fluid is pinpointed through x ray or ultrasound. Ultrasound is a more accurate method when the effusion is small. A sedative may be administered in some cases but is generally not recommended. Oxygen should be given to the patient.

Aftercare

As long as the tube is in the chest, the patient must lie still. After it is removed, x rays will determine if the effusion or air is reaccumulating%—though some researchers and clinicians believe chest x rays do not need to be performed after routine thoracentesis.

Risks

Reaccumulation of fluid or air is a possible complications, as are hypovolemic shock (shock caused by a lack of circulating blood) and infection. Patients are at increased risk for poor outcomes if they have a recent history of anticoagulant use, have very small effusions, have significant amounts of fluid, have poor health leading into this condition, have positive airway pressure, and have adhesions in the pleural space. A pneumothorax can sometimes be caused by the thoracentesis procedure. The use of ultrasound to guide the procedure can reduce the risk of pneumothorax.

Thoracentesis can also result in hemothorax, or bleeding within the thorax. In addition, such internal structures as the diaphragm, spleen, or liver, can be damaged by needle insertion. Repeat thoracenteses can increase the risk of developing hypoproteinemia (a decrease in the amount of protein in the blood).

Resources

Books

Abeloff, Martin D., et al., editors. Clinical Oncology. New York: Churchill Livingstone, 2000.

Celli, R. Bartolome. "Diseases of the Diaphragm, Chest Wall, Pleura and Mediastinum." In Cecil Textbook of Medicine, edited by J. Claude Bennett. Philadelphia: W. B. Saunders, 2000.

Periodicals

Colt, Henri G. "Factors Contributing to Pneumothorax After Thoracentesis." Chest 117 (February 2000).

Petersen, W.G. "Limited Utility of Chest Radiograph After Thoracentesis." Chest 117 (April 2000): 1038-1042.

Key terms

Axilla — Armpit.

Catheter — A tube that is moved through the body for removing or injecting fluids into body cavities.

Hypovolemic shock — Shock caused by a lack of circulating blood.

Osmotic pressure — The pressure in a liquid exerted by chemicals dissolved in it. It forces a balancing of water in proportion to the amount of dissolved chemicals in two compartments separated by a semi-permeable membrane.

Pleura — Two thin layers lining the lungs on the outside.

thoracentesis /tho·ra·cen·te·sis/ (-sen-te´sis) pleurocentesis; surgical puncture of the chest wall into the parietal cavity for aspiration of fluids.

Thoracentesis.

tho·ra·cen·te·sis (thôr

-s

n-t

Paracentesis of the pleural cavity. Also called pleurocentesis, thoracocentesis.

thoracentesis (thōˈ·r

·sen·tēˑ·sis),

n a surgical procedure involving the creation of an opening or hole through the wall of the chest and pleural space to aspirate fluid or air as a diagnostic tool or therapeutic approach; used as a therapy for pleural effusion, which is commonly seen in patients diagnosed with bronchogenic carcinoma. The samples of fluid can be analyzed to determine the concentration of amylase, protein, and glucose and the level of erythrocytes and leukocytes, and also cultured to study microbes. Also called
thoracocentesis.