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Thoracentesis: Before Your Procedure

Lungs in chest showing fluid in right lung pleural space, and view of person's back showing site between two ribs for fluid removal.

What is thoracentesis?

Thoracentesis (say "thor-uh-sen-TEE-sis") is a procedure to remove fluid from the space between the lungs and the chest wall. This is called the pleural space. The procedure may also be called a "chest tap."

It is normal to have a small amount of fluid in the pleural space. Too much fluid can build up because of problems such as infection, heart failure, and lung cancer. The procedure may be done to help with shortness of breath and pain caused by the fluid buildup, or you may have it done so the doctor can test the fluid to find the cause of the buildup.

Your doctor will put a long, thin needle or a thin plastic tube, called a catheter, between two of your ribs. The doctor will use the needle or catheter to take fluid out.

You may get medicine before the procedure. This helps with pain and helps you relax. The procedure will take about 15 minutes. Most people go home shortly after. You can go back to work or your normal activities as soon as you feel up to it.

If the doctor sends the fluid to a lab for testing, it usually takes a few hours to get the results. Some of the test results may take a few days. The doctor or nurse will discuss the results with you.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse advice line (811 in most provinces and territories) if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

How do you prepare for the procedure?

Preparing for the procedure

  • Bring a list of questions to ask your doctors. It is important that you understand exactly what procedure is planned, the risks, benefits, and other options before your procedure.
  • Tell your doctors ALL the medicines and natural health products you take. Some of these can increase the risk of bleeding or interact with medicines. Your doctor will tell you which medicines to take or stop before your procedure.
  • If you take blood thinners, ask your doctor if you should stop taking them before your procedure. Make sure that you understand exactly what your doctor wants you to do.
  • You may need to stop taking certain medicines a week or more before your procedure, so talk to your doctor as soon as you can.
  • Be sure to have someone take you home. Anesthesia and pain medicine will make it unsafe for you to drive or get home on your own.

Taking care of yourself before the procedure

Build healthy habits into your life. Changes are best made several weeks before the procedure, since your body may react to sudden changes in your habits.

  • Stay as active as you can.
  • Eat a healthy diet.
  • Cut back or quit alcohol and tobacco.

If you have an advance care plan, let your doctor know. If you do not have one, you may want to prepare one so your doctor and loved ones know your health care wishes. Doctors recommend that everyone prepare these papers before a procedure, regardless of the type of procedure or condition.

Procedures can be stressful. This information will help you understand what you can expect and it will help you safely prepare for your procedure.

What happens on the day of the procedure?

  • Take off all jewelry and piercings.

At the hospital, surgery centre, or doctor's office

  • Bring a picture ID.
  • The doctor may take a chest X-ray or use ultrasound or CT scan pictures to help find the exact spot where fluid has built up.
  • The doctor will give you a shot of numbing medicine in the skin where the needle or catheter will go.
  • The procedure will take about 15 minutes.
  • The doctor may take a chest X-ray after the procedure.

When should you call your doctor?

  • You have questions or concerns.
  • You don't understand how to prepare for your procedure.
  • You become ill before the procedure (such as fever, flu, or a cold).
  • You need to reschedule or have changed your mind about having the procedure.

Where can you learn more?

Go to

Enter U836 in the search box to learn more about "Thoracentesis: Before Your Procedure".

Adapted with permission from copyrighted materials from Healthwise, Incorporated (Healthwise). This information does not replace the advice of a doctor. Healthwise disclaims any warranty and is not responsible or liable for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.