What are the steps of pleural tapping (thoracentesis)?

Steps of Pleural Tapping (Thoracentesis)

Thoracentesis should be performed under ultrasound guidance to improve success rates and reduce complications such as pneumothorax, with initial drainage limited to 1-1.5 liters to prevent re-expansion pulmonary edema. 1

Pre-Procedure Preparation

1. Patient Positioning

   • Position patient sitting upright with arms elevated and supported on a table, if possible
   • For patients who cannot sit, use supine position with access to the posterolateral approach, which provides greater depth of pleural effusion than the lateral approach 2

2. Equipment Preparation

   • Sterile field setup with:
     • Antiseptic solution (chlorhexidine preferred)
     • Sterile drapes and gloves
     • Local anesthetic (1-2% lidocaine)
     • Needles (25G for skin, 22G for deeper infiltration)
     • Syringes (5-10mL)
     • Thoracentesis kit with catheter
     • Collection system
     • Ultrasound machine with sterile probe cover

3. Ultrasound Assessment

   • Identify optimal entry site with maximum fluid depth (>1cm)
   • Mark the site (typically posterolateral chest wall at mid-axillary or posterior axillary line)
   • Measure depth from skin to pleura
   • Identify surrounding structures to avoid (diaphragm, lung, heart)

Procedure Steps

1. Site Preparation

   • Clean area with antiseptic solution in circular motion from center outward
   • Apply sterile drapes to create sterile field
   • Prepare ultrasound probe with sterile cover

2. Local Anesthesia

   • Infiltrate skin with 25G needle using 1-2% lidocaine
   • Advance 22G needle while infiltrating deeper tissues
   • Continue until pleura is reached (indicated by patient cough)
   • Anesthetize periosteum of rib and pleura

3. Needle Insertion

   • Insert thoracentesis needle with attached syringe just above the superior border of the rib (to avoid neurovascular bundle)
   • Advance slowly under ultrasound guidance until pleural space is entered (indicated by fluid aspiration)
   • For diagnostic tap: collect 50-60mL of fluid
   • For therapeutic tap: connect to drainage system

4. Fluid Drainage

   • Limit initial drainage to 1-1.5 liters to prevent re-expansion pulmonary edema 1
   • In children, clamp after removing 10mL/kg body weight for 1 hour 1
   • Monitor patient for chest discomfort, persistent cough, dyspnea, or vasovagal symptoms
   • Stop immediately if these symptoms develop

5. Catheter Removal

   • For diagnostic tap: remove needle after obtaining sample
   • For therapeutic tap: remove catheter after adequate drainage
   • Apply pressure to site for 1-2 minutes
   • Apply occlusive dressing

6. Post-Procedure

   • Obtain post-procedure chest imaging to assess lung re-expansion and rule out pneumothorax
   • Monitor vital signs for 30-60 minutes

Laboratory Analysis

For diagnostic thoracentesis, the following tests should be ordered 1:

• Nucleated cell count and differential
• Total protein
• Lactate dehydrogenase (LDH)
• Glucose
• pH (using blood gas analyzer with heparinized sample)
• Amylase
• Cytology (essential for diagnosing malignancy)

Complications and Prevention

1. Pneumothorax

   • Most common complication (rate reduced from up to 39% to 1-8.9% with ultrasound guidance) 3
   • Prevention: Use ultrasound guidance, avoid advancing needle during patient inspiration

2. Re-expansion Pulmonary Edema

   • Rare (0.5-2.2%) but serious complication 1
   • Risk factors: Poor performance status, removal of ≥1.5L fluid, initial pleural pressure <10 cm H₂O, long-standing collapsed lung 1
   • Prevention: Limit initial drainage to 1-1.5 liters

3. Bleeding

   • Prevention: Avoid intercostal vessels by inserting above the rib
   • Use ultrasound to identify and avoid vascular structures

4. Infection

   • Prevention: Maintain strict aseptic technique

5. Organ Puncture

   • Prevention: Use ultrasound guidance to identify surrounding structures
   • Posterolateral approach in supine position is safer than lateral approach 2

Special Considerations

• For malignant effusions, consider definitive management options after diagnostic thoracentesis 1
• If pleural fluid cytology is negative but malignancy is suspected, proceed with pleural biopsy 3
• For recurrent symptomatic effusions with confirmed lung expansion, consider chemical pleurodesis or permanent pleural catheter placement 1
• Ultrasound-guided thoracentesis catheter drainage is more efficient and safer than standard pleural puncture 4

By following these steps systematically and using ultrasound guidance, thoracentesis can be performed safely with minimal complications while providing valuable diagnostic information and therapeutic relief.