What is thoracentesis? This is a medical procedure used to remove fluid that has collected in the space between the outsides of the lungs (visceral pleura) and the insides of the chest wall (parietal pleura). Normally, there is a tiny amount of fluid in this space, but certain conditions or diseases can cause an abnormal accumulation (pleural effusion). General physicians may be qualified to perform this procedure, but often this is done by a lung specialist (pulmonologist), radiologist, or surgeon.

Indications for thoracentesis:

  1. Test the fluid to determine the cause (“diagnostic”)
  2. Relieve symptoms caused by the fluid (“therapeutic”)

About 90% of the time, testing and analyzing the fluid can help your doctor determine the cause. Sometimes, a repeat thoracentesis is helpful. If the fluid volume is large (sometimes 1-2 liters or more), you can have relief of symptoms by removing all or most of the fluid.

How is the procedure done?

  1. Before undergoing thoracentesis, your doctor will usually obtain x-rays to confirm the presence of fluid in the chest. This may be done by regular chest x-ray, CT scan, or special chest x-rays done on your side (decubitus x-rays). Alternatively, an ultrasound can help determine the presence of fluid. The fluid can also be detected by your doctor on physical examination.
  2. After obtaining consent to perform the procedure, your doctor will usually place you in a sitting position, with your arms resting on a table in front of you.
  3. He/she will then cleanse your upper back (usually with Betadine) over the side with the fluid.
  4. Next, your doctor will inject a local anesthetic to numb the area. This may cause a slight burning or stinging sensation at first.
  5. Once the site is sufficiently numbed, he/she will insert a small bore catheter or needle into the fluid cavity and begin removing the fluid. As the fluid is removed, you may feel a pressure sensation or urge to cough.
  6. At the end of the procedure, the catheter or needle is usually removed and a band-aid is placed over the small insertion site.
  7. Usually, you will have an x-ray taken after the procedure.


Are there any contraindications to thoracentesis? Yes. The main contraindications are an uncooperative patient or a patient with an uncorrectable coagulation disorder. Relative contraindications include patients with bullous emphysema, patients on mechanical ventilators, hemodynamically unstable patients, patients with skin infection or Herpes Zoster at the needle site, and patients with only one functioning lung.

What are the risks of thoracentesis? The main risks are bleeding, infection, and collapse of the lung (pneumothorax). If too much fluid is removed all at once (usually > 2 liters), you can develop pulmonary edema (water/fluid inside the lung itself). Other complications include pain and respiratory distress or breathing difficulty.

After the procedure, you should call your doctor if you develop:

  1. Bleeding from the needle site
  2. Pain when taking a deep breath
  3. A cough that produces blood or frothy sputum
  4. New and sudden breathing difficulty
  5. New onset fever

How do I prepare? No special preparation is necessary. Eating or drinking beforehand will not interfere with the procedure, although you will need to be able to sit still for 15-30 minutes. Your doctor will ask you to not move during the procedure and try to avoid coughing or taking a sudden deep breath. You should inform your doctor if you have allergies to iodine (used in the cleanser) or lidocaine (the anesthetic).

Where can I find more information?

New England Journal of Medicine video
National Institutes of Health