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Make the Diagnosis: Thoracentesis

Why Do a Thoracentesis?

Once a pleural effusion is identified, thoracentesis yields a sample of fluid that can be analyzed to assess the likelihood of a transudative vs an exudative effusion. Transudative effusions are caused by differences in hydrostatic or oncotic pressure between the intravascular and pleural space, whereas exudative effusions are caused by infection, inflammation, or malignancy within the pleural space.

Adverse Events

  1. Pneumothorax is the most important complication from thoracentesis and occurs in about 6% of patients, though only about 2% of patients with a pneumothorax from a thoracentesis will require a chest tube.

  2. The bleeding risk complication rate is low (about 1%).

  3. Procedural hypoxemia (incidence, 0%-16%) can be caused by either rapid removal of the effusion from applying a large negative pressure when withdrawing fluid, or by removing a large volume (>1 L).

  4. A dry tap, where no fluid is obtained, occurs in about 7.4% of procedures.


The contraindications are severe hemodynamic instability or respiratory compromise not relative to the effusion itself. Patients with a coagulopathy generally have the procedure performed by a radiologist using imaging guidance, with need for reversal of the coagulopathy based on clinical judgment rather than absolute thresholds from markers of coagulopathy.

Performing the Procedure

  1. Review the rationale and adverse events with the patient so that informed consent is obtained.1

  2. Have the patient sit on the edge of the bed, leaning forward, with arms resting on a bedside table. If the patient is unable to sit upright, the lateral recumbent or supine position is acceptable.

  3. The operator should mark the site, prepare the skin with antiseptic solution (0.05% chlorhexidine or 10% povidine iodine solution), and apply a sterile drape.

  4. The overlying epidermis of the superior edge of the rib that lies below the selected intercostal space should be anesthetized using a small (25-gauge) needle.

  5. A larger (20-gauge) needle should then be inserted 1 or 2 intercostal spaces below the level of the effusion, 5 to 10 cm lateral to the spine. To avoid intra-abdominal injury, the needle should not be inserted below the ninth rib. It should be "walked" along the superior edge of the rib, alternately injecting anesthetic (1% or 2% lidocaine) and pulling back on the plunger every few millimeters to rule out intravascular placement and to check for proper intrapleural placement.

  6. The needle should not touch the inferior surface of the rib so as to avoid injury to the intercostal nerves and vessels. Once pleural fluid is aspirated, additional lidocaine should be injected to anesthetize the highly sensitive parietal pleura.

  7. When pleural fluid is obtained, the needle should no longer be advanced, to avoid puncture of the lung. Additional lidocaine should be injected to anesthetize the highly sensitive parietal pleura. After removal of the needle, the open ...

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