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By Noah Lechtzin, MD, MHS

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Patient Education

Thoracentesis is puncture through the chest wall for the purpose of aspirating pleural fluid. It is used to determine the etiology of a pleural effusion (diagnostic thoracentesis), to relieve dyspnea caused by pleural fluid (therapeutic thoracentesis), and, occasionally, to carry out pleurodesis.


There are no absolute contraindications to thoracentesis.

Relative contraindications include

  • Uncertain fluid location by examination

  • Minimal fluid volume

  • Altered chest wall anatomy

  • Pulmonary disease severe enough to make complications life threatening

  • Bleeding diatheses or coagulopathy

  • Uncontrolled coughing


Thoracentesis can be safely done at the patient’s bedside or in an outpatient setting. Presence and location of pleural fluid are verified by physical examination (chest percussion) and usually by imaging techniques. Ultrasonography, CT, or both may be useful if chest x-rays are equivocal, if prior thoracentesis attempts were unsuccessful, or if the fluid is loculated. The clinician doing the procedure usually uses bedside ultrasonography to localize the effusion and confirm that it is free flowing. Use of ultrasonography increases success rates and decreases complications.

Thoracentesis is best done with the patient sitting upright and leaning slightly forward with arms supported. Recumbent or supine thoracentesis (eg, in a ventilated patient) is possible but best done with ultrasound or CT guidance. Only unstable patients and patients at high risk of decompensation due to complications require monitoring (eg, pulse oximetry, ECG).

Under sterile conditions, 1 to 2% lidocaine is injected with a 25-gauge needle to anesthetize the skin. A larger (20- or 22-gauge) needle with anesthetic is then inserted at the upper border of the rib one intercostal space below the fluid level in the midscapular line. The needle is advanced with periodic aspiration (to avoid inadvertent insertion into a blood vessel and intravascular injection), and anesthetic is injected at progressively deeper levels. The most painful level after the skin is the parietal pleura, which should be infiltrated the most. The needle is then advanced beyond the parietal pleura until pleural fluid is aspirated, at which point the depth of the needle should be noted. A large-bore (16- to 19-gauge) thoracentesis needle-catheter device is then attached to a 3-way stopcock, which is connected to a 30- to 50-mL syringe and tubing that drains into a container. The thoracentesis needle is passed through the skin and subcutaneous tissue along the upper border of the rib into the effusion at about the same depth noted during anesthesia. The catheter is inserted through the needle, and the needle is withdrawn to decrease the risk of pneumothorax.

Pleural fluid can then be aspirated and, with a turn of the stopcock, collected in tubes or bags for further evaluation. Traditional guidelines have stated that fluid should be removed in stages not to exceed 1.5 L/day because hypotension and pulmonary edema may occur with removal of > 1.5 L of fluid at one time or with rapid evacuation of the pleural space using a vacuum or suction bottle. However, there is little evidence that re-expansion pulmonary edema is related to volume of pleural fluid removal, and therefore it may be reasonable for very experienced operators to completely drain effusions in one procedure. When large volumes of fluid must be removed, blood pressure should be monitored continuously and thoracentesis should be stopped if the patient develops chest pain, or if pleural manometry is being used, if the pleural pressure falls below negative 20 cm H2O.

It has been standard practice to obtain a chest x-ray after thoracentesis to rule out pneumothorax, document the extent of fluid removal, and view lung fields previously obscured by fluid, but evidence suggests that routine chest x-ray is not necessary in asymptomatic patients.

Coughing is common as the lung re-expands; it does not signify pneumothorax. If the pleural process is inflammatory, pleuritic pain, an audible pleural rub, or both may develop as fluid is removed because of approximation of inflamed visceral and parietal pleura. When substantial volumes of fluid are removed from the pleural space, the plunger on the syringe should be released periodically during aspiration. If the fluid in the syringe is drawn back into the pleural space when negative pressure on the syringe is decreased, pleural pressure may be too negative, and the lung may be restricted from re-expanding because of enveloping adhesions or tumor.


Complications include

  • Pneumothorax

  • Hemoptysis due to lung puncture

  • Re-expansion pulmonary edema or hypotension (uncommon, and probably not related to the volume of fluid removed)

  • Hemothorax due to damage to intercostal vessels

  • Puncture of the spleen or liver

  • Vasovagal syncope

Bloody fluid that does not clot in a collecting tube indicates that blood in the pleural space was not iatrogenic, because free blood in the pleural space rapidly defibrinates.

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* This is the Professional Version. *