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Pleural Tap (Thoracentesis)

Pleural tap (thoracentesis) — drainage and analysis of fluid from around the lung using a needle.

A diagnostic and therapeutic procedure in which fluid that has collected between the membranes of the lung is removed with a thin needle. It both relieves shortness of breath and helps investigate the underlying cause.

Indication

  • Diagnosis of unexplained pleural effusion (fluid around the lung)
  • Marked shortness of breath and chest pain due to fluid accumulation
  • Evaluation of fluid associated with pneumonia, heart failure, or kidney and liver disease
  • Suspected tuberculous pleurisy and microbiological investigation
  • Cellular analysis of fluid related to malignancy (cancer)
  • Drainage of empyema (infected fluid collection)

Preparation

  • Blood tests (especially coagulation studies) and lung imaging (X-ray or ultrasound) are obtained
  • Blood thinners may be temporarily stopped with physician approval
  • Adequate hydration and loose-fitting clothing are recommended before the procedure
  • The patient is positioned sitting upright or leaning slightly forward
  • The consent form is reviewed and signed

How it's performed

  1. The safest entry point for the fluid is identified using ultrasound guidance
  2. The skin is cleaned with antiseptic and local anesthesia is administered
  3. A thin needle is advanced between the ribs into the pleural space
  4. Fluid is aspirated in a controlled manner; about 30-60 mL is withdrawn for diagnostic sampling, and up to 1-1.5 L may be removed for therapeutic purposes
  5. The fluid is sent to the laboratory; transudate-versus-exudate distinction is made using Light's criteria, and biochemistry, microbiology, and cytology studies are performed
  6. After the needle is removed, a pressure dressing is applied at the entry site

Post-procedure

  • A follow-up chest X-ray after the procedure is used to assess for pneumothorax (collapsed lung)
  • Any worsening shortness of breath, chest pain, or cough should be reported immediately
  • The entry site should be kept dry for 24-48 hours
  • Treatment for the underlying disease is planned based on the test results

Risks

  • Pneumothorax (collapsed lung) — about 5%, lower with ultrasound guidance
  • Bleeding or hematoma at the entry site
  • Vagal reaction (low blood pressure, fainting)
  • Re-expansion pulmonary edema (when a large volume of fluid is drained)
  • Infection (rare)

FAQ

Is the procedure painful?

Because it is performed with local anesthesia, no significant pain is felt; you may notice a brief pressure sensation when the needle is inserted.

Can I go home the same day?

If there are no complications, same-day discharge after a follow-up chest X-ray is usually possible.

Could I need more than one procedure?

If the fluid recurs or the response to treatment is insufficient, additional interventions such as pleurodesis or catheter placement may be considered.

What are Light's criteria?

These are diagnostic criteria that use protein and LDH values to distinguish whether the fluid is related to inflammation (exudate) or to a pressure imbalance (transudate).