What is the recommended procedure for performing thoracentesis (thoracentesis) on a patient with a significant pleural effusion?

Recommended Procedure for Thoracentesis

Image-guided thoracentesis should always be used to reduce the risk of complications when performing thoracentesis on a patient with a significant pleural effusion. 1

Pre-procedure Assessment

• Confirm the presence and location of pleural fluid using ultrasound
• Ultrasound guidance is essential as it:
  • Improves success rate (97% for loculated effusions) 2
  • Decreases pneumothorax risk 1, 2
  • Differentiates between pleural fluid and pleural thickening 2
  • Identifies septations with higher sensitivity than CT (81-88% vs 71%) 2

Procedure Technique

Equipment and Setup

• Sterile field with appropriate draping
• Ultrasound machine with appropriate probe
• Local anesthetic (typically lidocaine)
• Thoracentesis kit with appropriate needles and collection system

Step-by-Step Procedure

1. Patient positioning: Seated position with arms supported on a table, or lateral decubitus position with affected side up if patient cannot sit
2. Site selection: Use ultrasound to identify optimal entry site, avoiding areas near vital structures
3. Skin preparation: Clean with antiseptic solution and drape
4. Local anesthesia: Infiltrate skin, subcutaneous tissue, intercostal muscles, and parietal pleura
5. Needle insertion: Under real-time ultrasound guidance, insert needle just above the superior border of the rib to avoid neurovascular bundle
6. Fluid collection:
   • For diagnostic purposes: Collect 25-50 mL of fluid 1
   • For therapeutic purposes: Remove fluid gradually while monitoring patient symptoms
   • Limit initial drainage to 1-1.5 liters per session to prevent re-expansion pulmonary edema 2
7. Specimen handling:
   • For cytology: Submit at least 25 mL, preferably 50 mL 1
   • For microbiology: Send samples in both plain containers and blood culture bottles 1

Diagnostic Testing of Pleural Fluid

For Suspected Malignancy

• Cytological analysis (25-50 mL of fluid) 1, 2
• Process samples by direct smear and cell block preparation 1
• Consider a second thoracentesis if first cytology is negative but suspicion remains high 2

For Suspected Infection

• Send fluid in both plain containers and blood culture bottles 1
• If volume is limited (2-5 mL), prioritize blood culture bottles over plain containers 1

For Undetermined Etiology

• Order: nucleated cell count, differential, total protein, LDH, glucose, pH, amylase, and cytology 2
• Consider ADA and/or IFN-gamma tests in populations with high TB prevalence 1

Monitoring During Procedure

• Monitor for chest discomfort, which may indicate excessive negative pleural pressure
• Consider pleural manometry to:
  • Distinguish lung entrapment from trapped lung 3
  • Predict ability to perform pleurodesis 3
  • Monitor for excessive negative pleural pressure

Volume Considerations

• Traditional teaching has limited drainage to 1-1.5 liters to prevent re-expansion pulmonary edema
• However, recent evidence suggests clinical and radiographic re-expansion pulmonary edema is rare (0.5% and 2.2% respectively) even with large-volume thoracentesis 4
• Complete drainage can be considered as long as the patient doesn't develop chest discomfort 4

Post-procedure Care

• Obtain post-procedure chest imaging to rule out pneumothorax if clinically indicated
• Monitor for complications including:
  • Pneumothorax (3-15% incidence) 2
  • Re-expansion pulmonary edema
  • Pain at insertion site
  • Hemothorax

Special Considerations

Risk Factors for Complications

• Poor performance status (ECOG ≥3)
• Removal of ≥1.5L of fluid
• Initial pleural pressure <10 cm H₂O
• Long-standing collapsed lung 2

Follow-up

• If pleural fluid cytology is negative but malignancy is still suspected, pleural biopsy should be considered 1
• CT follow-up should be considered for patients with pleural infection to exclude occult malignancy if symptoms persist 1

Pitfalls to Avoid

• Performing thoracentesis without ultrasound guidance
• Inserting needle too close to the lower border of the rib (risk of neurovascular injury)
• Removing fluid too rapidly, which may cause re-expansion pulmonary edema
• Relying solely on radiographic lung re-expansion as a surrogate for normal pleural elastance 5
• Performing therapeutic thoracentesis in asymptomatic patients with malignant pleural effusions 2