[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Clinical skills](https://durgical.com/en/clinical-skills/) › [Procedures](https://durgical.com/en/clinical-skills/areas/procedures/) › Diagnostic and therapeutic pleural aspiration

# Diagnostic and therapeutic pleural aspiration

- Procedure

A needle or thin tube is placed between the ribs to take fluid from around the lung, to test it or to ease breathing.

Updated Nov 13, 2026

## Key points

- Use ultrasound to choose and mark the site: it lowers the risk of pneumothorax and organ injury.
- Go over the upper border of the lower rib: the neurovascular bundle runs under each rib.
- Send protein and LDH with paired serum values so Light's criteria can be applied.
- Measure pleural pH in a blood gas syringe, kept airtight and analysed promptly, when infection is possible.
- Stop a therapeutic tap at the protocol limit or at chest tightness or cough: re-expansion pulmonary oedema.

On this page

- The basics Key points
- What it is
- Indications
- Equipment
- Step by step (and why)
- Next step
- Elsewhere in DurgiPedia

- Clinical Complications

- Safety Contraindications and precautions

- Study Test yourself

- Connections Connections

## What it is

Thoracentesis (pleural aspiration) removes fluid from the pleural space. A diagnostic tap takes a small sample to find the cause of a new effusion; a therapeutic tap drains more fluid to relieve breathlessness. Bedside ultrasound is now standard: it confirms the fluid, measures its depth, shows the diaphragm, liver or spleen and septations, and lowers the risk of pneumothorax and organ puncture. The patient usually sits upright, leaning forward over a table with the arms folded. The usual site is in the posterior axillary or mid-scapular line, one or two intercostal spaces below the top of the effusion and not too low, so the needle stays above the diaphragm. Every intercostal space carries a vein, artery and nerve along the lower edge of the rib above, so the needle always goes just over the upper border of the rib below. Fluid is removed slowly, and a therapeutic tap stops at a limited volume set by local protocol, or earlier if the patient develops chest tightness, cough or breathlessness, which warn of re-expansion pulmonary oedema. Typical bilateral effusions in known heart failure are usually treated first rather than tapped.

## Indications

- New pleural effusion of unknown cause: diagnostic aspiration.
- Suspected parapneumonic effusion or empyema, to decide whether a chest drain is needed.
- Suspected malignant or tuberculous effusion, with cytology and tests for tuberculosis.
- Breathlessness from a large effusion: therapeutic aspiration for relief.
- Atypical effusion in heart failure: unilateral, with fever or chest pain, or not settling with treatment.

## Contraindications and precautions

- Very small or loculated effusion that cannot be safely reached: ultrasound decides.
- Coagulopathy, low platelets or anticoagulants: relative; weigh the urgency and follow local guidance.
- Skin infection or burn over the site: choose another site.
- Mechanical ventilation raises the risk of tension pneumothorax; only experienced operators, with ultrasound.
- Uncooperative patient who cannot sit still, or unstable patient who cannot be positioned.

## Equipment

- Ultrasound machine with a sterile probe cover or a marked site.
- Sterile gloves, drape, antiseptic, gauze and dressing.
- Local anaesthetic with needles and syringes for skin and pleura.
- Aspiration needle or catheter-over-needle with a three-way tap, syringes and a drainage bag or bottle for therapeutic taps.
- Sterile tubes, blood culture bottles, a blood gas syringe for pH and labels with request forms.

## Step by step (and why)

- Check imaging, clotting and drugs; explain and consent — risks include pneumothorax and bleeding.
- Sit the patient up, leaning forward on a table with arms folded — this opens the spaces and lets fluid lie low behind.
- Scan and mark the site over the deepest fluid, above the diaphragm, in the posterior axillary or mid-scapular line.
- Clean widely and drape with sterile technique — an infected pleural space (empyema) is a serious complication.
- Infiltrate local anaesthetic down to the pleura over the upper border of the lower rib — the parietal pleura is very sensitive.
- Advance the needle over the rib, aspirating, until fluid comes back — this confirms the pleural space at a known depth.
- Fill the sample syringes, then the blood gas syringe for pH — air and delay distort the pH.
- For a therapeutic tap, drain slowly through the tap, stopping at the protocol limit or if symptoms appear.
- Withdraw during expiration, cover the site and recheck the patient — air may enter if the patient inhales deeply.

## Complications

- Pneumothorax, from the needle touching the lung or from air entering through the system.
- Re-expansion pulmonary oedema after large or rapid drainage: cough, chest tightness, hypoxaemia.
- Bleeding: chest wall haematoma or haemothorax from an intercostal vessel.
- Infection of the pleural space or of the puncture site.
- Vasovagal reaction, pain, and rarely puncture of the liver or spleen when the needle is too low.

## Next step

- Send protein, LDH (with serum), pH, glucose, cell count with differential, Gram stain, culture and cytology; then apply Light's criteria.
- Add tests by suspicion: adenosine deaminase for tuberculosis, triglycerides for chylothorax, amylase for pancreatitis.
- Get a chest X-ray or repeat ultrasound if there is new pain, breathlessness, air on aspiration or several passes.
- Frank pus, low pH or organisms on Gram stain point to a chest drain: discuss with a senior the same day.
- Reaccumulating effusion: plan with the team (repeat drainage, pleurodesis or an indwelling catheter).

## Test yourself

Think of the answer, then tap the question to see it.

## Why is the needle passed over the upper border of the rib during thoracentesis?

The intercostal vein, artery and nerve run along the lower edge of each rib, so keeping to the upper border of the rib below avoids them.

## What does ultrasound add to pleural aspiration?

It confirms and measures the fluid, shows septations and the diaphragm, liver or spleen, and lowers the risk of pneumothorax and organ puncture.

## Which tests are sent so that Light's criteria can be applied?

Pleural fluid protein and LDH, with serum protein and LDH taken at about the same time.

## Which symptoms during a therapeutic tap mean drainage should stop?

Chest tightness, persistent cough, increasing breathlessness or chest pain, which may signal re-expansion pulmonary oedema or pneumothorax.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/clinical-skills/diagnostic-and-therapeutic-pleural-aspiration/)

## Elsewhere in DurgiPedia

- [Pleural effusion on the chest X-ray](https://durgical.com/en/radiology/pleural-effusion-on-the-chest-x-ray/)
- [Pleural effusion syndrome](https://durgical.com/en/clinical-exam/pleural-effusion-syndrome/)
- [Chest percussion: resonance, dullness and hyperresonance](https://durgical.com/en/clinical-exam/chest-percussion-resonance-dullness-and-hyperresonance/)
- [Pleural fluid: formation and drainage](https://durgical.com/en/physiology/pleural-fluid-formation-and-drainage/)

## Connections

## Related 4

- [Pleural fluid: exudate or transudate (Light's criteria)](https://durgical.com/en/clinical-skills/pleural-fluid-exudate-or-transudate/)
- [Chest drain insertion and care](https://durgical.com/en/clinical-skills/chest-drain-insertion-and-care/)
- [Needle aspiration and decompression of a pneumothorax](https://durgical.com/en/clinical-skills/needle-aspiration-and-decompression-of-a-pneumothorax/)
- [Infiltrating local anaesthetic and digital blocks](https://durgical.com/en/clinical-skills/infiltrating-local-anaesthetic-and-digital-blocks/)

## Related conditions 5

- [Pleural effusion](https://durgical.com/en/conditions/pleural-effusion/)
- [Parapneumonic effusion and empyema](https://durgical.com/en/conditions/parapneumonic-effusion-and-empyema/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Tuberculosis](https://durgical.com/en/conditions/tuberculosis/)
- [Pneumothorax](https://durgical.com/en/conditions/pneumothorax/)

## In Pharmacology 2

- [Local anesthetics](https://durgical.com/en/pharmacology/classes/local-anesthetics/)
- [Lidocaine](https://durgical.com/en/pharmacology/lidocaine/)

[← All clinical skills](https://durgical.com/en/clinical-skills/)

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: [Thoracentesis](https://www.ncbi.nlm.nih.gov/books/NBK441866/) (StatPearls (NCBI Bookshelf), 2024); [Pleural Effusion](https://www.ncbi.nlm.nih.gov/books/NBK448189/) (StatPearls (NCBI Bookshelf), 2024).

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