Thoracentesis (pleural aspiration): draining fluid from around the lung

The lungs are surrounded by a thin lining, and between the lung and the inside of the chest wall there is a space called the pleural space. Cambridge University Hospitals explains that this space normally contains a small amount of fluid, about four teaspoons, but some conditions can cause more to build up. When that happens it is called a pleural effusion.

Cambridge lists heart failure, lung infections and tumours as examples of conditions that can cause extra fluid, and says that a lot of extra fluid can press on the lungs and make breathing difficult. Thoracentesis is a procedure to remove some of that fluid, using a needle or thin tube.

It is a short, bedside or clinic procedure and is distinct from a chest drain, which is a tube left in place for longer. Where a more lasting drain is needed, the team will explain the next steps.

There are two main reasons, and they often overlap. Cambridge says thoracocentesis is done to try to find the cause of a pleural effusion and may also be done to help you breathe more easily. Gloucestershire says a pleural aspiration can be performed to relieve breathlessness, and is also used to obtain samples of fluid, which can be tested to try to find out what caused the problem.

Cambridge says the fluid removed is sent to the laboratory to try to establish the cause, so that appropriate treatment can then be discussed. In other words, the procedure is often a stage in an investigation, and the result may lead to further tests or a treatment plan from a respiratory or other specialist team.

Cambridge says no special preparations are needed before the test. It does ask you to tell the doctor or pleural nurse specialist about any previous bleeding problems or allergies to medicines or latex, and these are worth mentioning to whoever is looking after you.

Bring a list of your medicines and say if you take blood thinners, since the team may want to know. Your appointment letter will tell you if there is any specific instruction for your hospital, because practice varies.

You are usually positioned sitting comfortably and leaning forward, resting your arms on a table, according to Cambridge, or sitting on the edge of a bed or chair leaning forward slightly, in Gloucestershire. To reduce the chance of lung injury, Cambridge advises avoiding coughing, breathing deeply or moving during the procedure.

An ultrasound scan of the chest is used first to identify the best site. Both leaflets describe cleaning the skin and numbing it with local anaesthetic, and then inserting a thin needle or plastic tube into the pleural space between the ribs. Fluid is withdrawn with a syringe. Gloucestershire describes brief discomfort that is usually minor and similar to having blood taken.

Once enough fluid has been removed, the needle or tube is withdrawn and a small dressing is placed over the site. Cambridge says the whole procedure takes around 10 to 15 minutes. Gloucestershire says the dressing can be removed after 24 hours.

Cambridge says you will need a chest X-ray after the test to check for any lung problems, and your blood pressure, breathing and oxygen levels will be checked for up to a couple of hours before you can go home. Gloucestershire says you will be observed for up to an hour and may be sent for a chest X-ray.

Cambridge advises calling your own doctor or GP immediately if you have any breathing problems once at home. The fluid sample goes to the laboratory and the result is discussed with you by the team who arranged the procedure, so ask how and when you will be told.

If breathlessness returns or the fluid builds up again, tell the team that arranged the procedure so that they can decide what to do next.

Cambridge says the risks are usually minor and easily treated. The main one is pneumothorax, where air collects in the pleural space, either because air enters through the needle or because the needle makes a hole in the lung. It will usually self heal, but a large amount of air may cause the lung to collapse and necessitate insertion of a chest drain.

Pain, bleeding, bruising or infection where the needle was inserted occurs in less than 5% of cases, according to Cambridge. In rare cases bleeding may occur in or around the lungs, and a chest drain or even surgery may be required. Gloucestershire similarly describes the risk of serious complications as very low, with a small risk of infection or bleeding and, occasionally, air entering the chest.

After going home, new or worsening breathlessness, chest pain, a high temperature, or bleeding or swelling at the needle site should be taken seriously. The Cambridge leaflet advises calling your GP immediately for breathing problems, and the Gloucestershire leaflet advises contacting the respiratory ward or your clinician if you become unwell afterwards.

If you are severely short of breath, struggling to speak, or have severe chest pain, call 999 rather than waiting to speak to a clinic. If the breathing difficulty is less severe but worrying, use NHS 111 or your hospital's out-of-hours number.

On the NHS, a pleural aspiration is usually arranged through a respiratory or acute medical team, often with a pleural nurse specialist or an ultrasound-trained doctor, and is carried out in a clinic or on a ward. Results are discussed in a follow-up appointment or through the doctor who referred you.

Private respiratory services can offer the same procedure. In either setting, it is worth asking what tests the fluid will be sent for, who will explain the results and what the plan is if the fluid returns.