Diagnostic and therapeutic pleural aspiration

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)

1. Check imaging, clotting and drugs; explain and consent — risks include pneumothorax and bleeding.
2. Sit the patient up, leaning forward on a table with arms folded — this opens the spaces and lets fluid lie low behind.
3. Scan and mark the site over the deepest fluid, above the diaphragm, in the posterior axillary or mid-scapular line.
4. Clean widely and drape with sterile technique — an infected pleural space (empyema) is a serious complication.
5. Infiltrate local anaesthetic down to the pleura over the upper border of the lower rib — the parietal pleura is very sensitive.
6. Advance the needle over the rib, aspirating, until fluid comes back — this confirms the pleural space at a known depth.
7. Fill the sample syringes, then the blood gas syringe for pH — air and delay distort the pH.
8. For a therapeutic tap, drain slowly through the tap, stopping at the protocol limit or if symptoms appear.
9. 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).

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Elsewhere in DurgiPedia

• Pleural effusion on the chest X-ray
• Pleural effusion syndrome
• Chest percussion: resonance, dullness and hyperresonance
• Pleural fluid: formation and drainage

Connections

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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 (StatPearls (NCBI Bookshelf), 2024); Pleural Effusion (StatPearls (NCBI Bookshelf), 2024).

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