General Considerations

Indications:

• Diagnostic: to determine the cause of a pleural effusion.
• Therapeutic: to relieve symptoms of dyspnea and/or pain.

Contraindications:

• Absolute (pick another site):
  • Cellulitis or herpes zoster over entry site.
• Relative (weigh risks and benefits in each patient):
  • Consider reversing coagulopathy if INR >2 and/or platelets <50K for a standard thoracentesis; no cutoffs for a modified thoracentesis (using a smaller angiocatheter without scalpel incision).
  • Be cautious in patients on mechanical ventilation as positive-pressure may increase the risk of tension pneumothorax and/or bronchopleural fistula.
  • Defer in patients unable to tolerate requisite positioning or with severe hemodynamic/respiratory instability.
  • Be cautious in patients with non-functioning hemithorax due to anatomical or pathological complications. Complications of thoracentesis on functional side has greater risk of hemodynamic instability.

Technique

Preparation:

• Obtain informed consent.
• Review procedure with your supervisor and watch the NEJM “Thoracentesis” video.
• Gather supplies:
  • Marking pen or temperature probe cover, thoracentesis kit, chlorhexidine, angiocatheter, 10mL 1% lidocaine, Tegaderm, sterile gauze, 1-2 vacutainer bottles (if therapeutic), lavender, gold and black top specimen tubes, blood culture bottles, blood transfer device, 2 sets of sterile gloves, 2 face masks with shield, chuck, ultrasound with abdominal probe, skin marking pen, two bedside table trays, and a chair.
• Hold therapeutic enoxaparin for 12 hours and heparin gtt for at least 1 hour prior.
• If the effusion is small (<1cm on lateral decubitus film) or not free flowing, it is less likely that a bedside ultrasound-guided thoracentesis will be safe and successful. Reconsider risks and benefits of procedure before proceeding. 
• Have the patient sit with legs hanging over side of the bed, resting arms on a tray table and with feet on a chair.

Site selection:

• Perform an ultrasound using abdominal probe to select your entry site. The usual site is the posterolateral back (6-8cm lateral to spine), 1-2 interspaces below the fluid level but above the diaphragm.
• Ensure that: 1) the procedural site is above the diaphragm; 2) there is an adequate pocket (>2 cm) for a safe bedside attempt. If unable to identify a safe pocket, consider IR.
• Aim to go just above the rib to avoid hitting any neurovascular structures (neurovascular bundles run on the inferior aspect of the rib).
• Mark needle entry site with marking pen or temp probe cover.

From emdocs.net - ultrasound image of pleural effusion, with structures labeled

Procedural steps:

• Perform Time-Out. Ensure you have identified the correct patient, procedure, and site, reviewed relevant labs and medications, and confirmed allergies.
• Sterilize and drape the skin.
• Use a 25g or smaller needle for your initial wheal and subcutaneous anesthesia. Change to a 22g needle and while holding the needle perpendicular to the patient, infuse lidocaine on the rib, marching up until you are just above it and into the pleural space. When you obtain fluid, note the needle depth. Do not advance the needle further. Back needle up 1-2 mm and infuse lidocaine to thoroughly numb up the parietal lung pleura. While withdrawing the needle, further lidocaine may also be infused.
• Remember to use the same technique of marching up the rib when using your larger aspiration needle. For a diagnostic tap, use an 18-20g angiocath needle attached to a 30mL syringe and aspirate fluid as needed.
• If performing a therapeutic tap, use the catheter supplied in your kit. Create a small horizontal incision with the blade at the site of entrance. Slowly advance the needle while aspirating and continue to march up the rib until you hit fluid. Once you have aspirated fluid, advance the catheter and needle another 0.5 cm before then keeping the needle still and advancing the plastic catheter over the needle until hubbed. Remove the needle/syringe. Attach the non-collapsible tubing to the stopcock and then drain fluid in a vacutainer.
• Generally limit amount of fluid drained up to 1.5L, although some patients will tolerate more. Re-expansion pulmonary edema (RPE) is rare and may not necessarily be related to the amount of fluid drained or negative pleural pressure. Symptoms that may suggest RPE are persistent coughing (occasional cough within expectations), new dyspnea, and/or new pain/pressure in the back or chest. Decrease the flow rate into the vacutainer, to reduce negative pressure and RPE risk, by clamping the tubing.
• If some fluid comes out and then stops, check your catheter, tubing, etc. Having the patient Valsalva can increase intrathoracic pressure and help the fluid flow. As the fluid pocket decreases, inevitably the catheter will touch up again the lung, so systematically withdrawing the catheter in 0.5-1cm increments, until it is out of the fluid cavity, can maximize fluid drainage.
• If you aspirate air (see air bubbles in your syringe) or the patient develops hypotension, desaturation, or respiratory distress, stop immediately, obtain a portable CXR, and/or perform immediate needle decompression for tension PTX. Consult thoracic surgery.
• When removing the catheter, have the patient continuously hum or Valsalva and bandage the site. If intubated and on a mechanical ventilator, remove the catheter during expiratory phase.
• Obtain a post-procedure CXR only when concerned for complications such as aspirated air, chest pain, dyspnea, hypoxemia, multiple needle passes, or mechanical ventilation.
  • Note: if the patient has recently undergone thoracentesis, air bubbles may not indicate a PTX.

Complications

Pneumothorax (real-time ultrasound use reduces the risk), hemothorax, infection, hypotension, RPE, hepatic or splenic puncture, vasovagal, coughing (stop procedure if excessive).

Diagnostic Studies

• Always send fluid for cell count/differential (lavender top), LDH and total protein (gold top), gram stain (black top), and bacterial culture (inoculate blood culture bottles at the bedside).
  • Other studies (cytology, pH, glucose, AFB, etc.) only if clinically indicated.
  • If the fluid is bloody, send a hematocrit.
  • To calculate Light’s criteria, send simultaneous serum total protein and LDH.
  • pH must be sent quickly, on ice, and run in a blood gas analyzer or results can be falsely elevated. Discuss with your lab if this is possible before sending.
• Refer to Pulmonary: Pleural Effusions section for additional information.

Feller-Kopman, D. Ultrasound-guided thoracentesis. Chest 2006;129(6):1709-14.

Thomsen, TW, DeLaPena J, Setnik GS. Videos in clinical medicine: Thoracentesis. N Eng J Med 2006;355(15):e16.

Wilcox M, Chong CY, Stanbrook MB, Tricco AC, Wong C, Straus SE. Does this patient gave an exudative pleural effusion?: The Rational Clinical Examination systematic review. JAMA 2014;311(23):2422-31.