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



Thoracentesis can be performed as a diagnostic or treatment procedure. For diagnosis, only a small amount of fluid is removed for analysis. For treatment, larger amounts of air or fluid are removed to relieve symptoms.

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, or the movement of cancer cells from one part of the body to another; these are known as malignant pleural effusions. Other causes include trauma,infection, congestive heart failure, liver disease, and renal disease. Most malignant pleural effusions are detected and controlled by thoracentesis.

Symptoms of a pleural effusion include shortness of breath, 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.

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


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. Before undergoing this procedure, a patient must make their doctor aware of any allergies, bleeding problems or use of anticoagulants, pregnancy, or possibility of pregnancy.


Prior to thoracentesis, the location of the fluid is pinpointed through x ray, computed tomography (CT) scan, or ultrasound. Ultrasound and CT are more accurate methods when the effusion is small or walled off in a pocket (loculated). A sedative may be administered in some cases but is generally not recommended. Oxygen may be given to the patient.

The usual place to tap the chest is below the armpit (axilla) or in the back. 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. Once fluid is withdrawn, it 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.


Patients should check with their doctor about continuing or discontinuing the use of any medications (including over-the-counter drugs and herbal remedies). Unless otherwise instructed, patients should not eat or drink milk or alcohol for at least four hours before the procedure, but may drink clear fluids like water, pulp-free fruit juice, or tea until one hour before. Patients should not smoke for at least 24 hours prior to thoracentesis. To avoid injury to the lung, patients should not cough, breathe deeply, or move during this procedure.


After the tube 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.


Reaccumulation of fluid or air are 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, or 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

What the risks are
  • Bleeding
  • Fluid build-up
  • Infection
  • Pneumothorax
  • Pulmonary edema
  • Respiratory distress

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