What are the indications, contraindications, and step‑by‑step technique for performing thoracentesis?

Thoracentesis: Indications, Contraindications, and Technique

Indications

Diagnostic Indications

Perform thoracentesis for any new, undiagnosed unilateral pleural effusion or bilateral effusion with normal heart size to determine etiology. 1

• Suspected malignancy requiring cytological examination of pleural fluid 1
• Obtain at least 25 mL (ideally 50 mL) of pleural fluid for initial cytological examination 1
• Thoracentesis has higher diagnostic yield than closed needle biopsy, leaving less than 10% of effusions undiagnosed 2

Therapeutic Indications

Therapeutic thoracentesis is indicated for relief of dyspnea in symptomatic pleural effusions. 1

• Large-volume thoracentesis should be performed when uncertain whether symptoms relate to the effusion or to assess lung expandability before considering pleurodesis 2
• Recurrent malignant pleural effusions causing respiratory compromise 1
• Palliative therapy for patients with advanced disease and poor performance status who may benefit from periodic outpatient thoracentesis 1

When NOT to Perform Thoracentesis

Do not perform therapeutic pleural interventions in asymptomatic patients with malignant pleural effusion. 2

• Asymptomatic patients rarely require intervention during follow-up based on observational data 1
• Drainage of asymptomatic effusions subjects patients to procedural risks without clinical benefit 1

Contraindications

Relative Contraindications

The following are relative contraindications that require risk-benefit assessment 1:

• Minimal effusion (insufficient fluid for safe access) 1
• Bleeding diathesis or anticoagulation 1
• Mechanical ventilation (though studies show no greater morbidity than non-ventilated patients) 3
• Severe renal failure 1

Absolute Contraindications

• Patient cannot tolerate single-lung ventilation for VATS procedures 2
• Pleural space contains extensive adhesions preventing safe insertion 2

Pre-Procedure Preparation

Imaging and Site Selection

Always use ultrasound guidance for thoracentesis—this reduces pneumothorax risk from 8.9% to 1.0% (90% reduction). 1

• Perform ultrasound examination immediately before the procedure to accurately locate fluid, identify loculations or septations, and mark the optimal insertion site 1
• Ultrasound increases successful fluid sampling from 78% to 100% of attempts 1
• Ultrasound can identify intercostal vessels to decrease hemorrhagic complications 1
• Typical insertion site is mid-scapular or posterior axillary line, one to two intercostal spaces below the upper border of the effusion 1

Patient Preparation

NPO is not required for standard thoracentesis without sedation. 1

• If procedural sedation is used, follow standard sedation fasting guidelines: NPO for solid foods for 4 hours, clear fluids permitted up to 2 hours before procedure 1
• Establish IV access before the procedure as a general safety precaution 1

Step-by-Step Technique

1. Patient Positioning

• Position patient sitting upright, leaning forward over bedside table with arms supported 3
• Alternative: lateral decubitus position with affected side down for patients unable to sit 3

2. Site Identification and Marking

• Use ultrasound in real-time to identify optimal insertion site 1
• Mark site in mid-scapular or posterior axillary line, one to two intercostal spaces below upper border of effusion 1
• Identify intercostal vessels with ultrasound to avoid vascular injury 1

3. Sterile Preparation

• Apply sterile technique with full barrier precautions 3
• Prepare and drape the insertion site 3

4. Local Anesthesia

• Infiltrate skin, subcutaneous tissue, and pleura with local anesthetic 3
• Insert needle just above the superior border of the rib to avoid neurovascular bundle 3

5. Needle Insertion

• Use small-gauge needles (21 or 22 gauge) for diagnostic thoracentesis removing 35-50 mL to minimize pneumothorax risk 3
• Insert needle perpendicular to chest wall, advancing slowly while aspirating 3
• Stop advancing when pleural fluid is obtained 3

6. Fluid Removal and Monitoring

Limit fluid removal to 1-1.5 L per session unless pleural pressure monitoring is available. 1, 4

• Stop the procedure immediately if patient develops cough during thoracentesis—this signals excessive negative pleural pressure 4
• Monitor for symptoms of re-expansion pulmonary edema: chest discomfort, persistent cough, or dyspnea 1, 4

7. Pleural Pressure Monitoring (When Available)

Pressure >19 cm H₂O with removal of 500 mL or >20 cm H₂O with removal of 1 L predicts trapped lung. 1

• Pleural manometry can distinguish lung entrapment from trapped lung 5
• Manometry may minimize risk of re-expansion pulmonary edema when large volumes are removed 5
• Initial pleural pressure <-10 cm H₂O suggests trapped lung 6

8. Post-Procedure Assessment

• Obtain chest radiograph to assess for pneumothorax, lung expansion, and residual fluid 1, 4
• Evaluate symptom response—if dyspnea not relieved, investigate alternative causes: lymphangitic carcinomatosis, atelectasis, thromboembolism, tumor embolism, or endobronchial obstruction 2, 1

Complications and Their Prevention

Pneumothorax

Ultrasound guidance reduces pneumothorax risk by 90% (from 8.9% to 1.0% in malignant effusions). 1

• Meta-analysis of 6,605 thoracenteses showed ultrasound reduces overall pneumothorax risk by 19% 1
• Use small-gauge needles (21-22 gauge) for diagnostic procedures 3

Hemorrhage

• Ultrasound identification of intercostal vessels decreases hemorrhagic complications 1
• Chest tube placement required in 2.2% of non-ultrasound-guided procedures versus 0% with ultrasound 1

Re-expansion Pulmonary Edema

• Related to rapid removal of large fluid volumes 1
• Limit removal to 1-1.5 L unless monitoring pleural pressure 1, 4
• Stop immediately if patient develops persistent cough 4

Other Complications

• Solid organ puncture (liver, spleen) reduced with ultrasound guidance 1
• Infection 1
• Hemothorax 1

Critical Pitfalls to Avoid

Never perform blind thoracentesis without ultrasound guidance—this increases pneumothorax risk nearly 9-fold. 1

• Do not drain asymptomatic effusions routinely unless fluid needed for diagnostic purposes 1
• Do not remove chest tubes prematurely if trapped lung is suspected (lack of mediastinal shift with large effusion, failure of complete lung expansion) 4, 6
• Do not assume inadequate drainage if dyspnea persists—investigate alternative causes of respiratory compromise 4
• Do not continue fluid removal if patient develops cough during procedure 4

Special Considerations

Trapped Lung

Nonexpandable lung occurs in at least 30% of patients with malignant pleural effusions and contraindicates pleurodesis. 1

• Identify through lack of mediastinal shift on initial chest radiograph with large effusion 4, 6
• Failure of complete lung expansion after adequate drainage 4, 6
• Elevated pleural pressure during drainage 1
• Patients with trapped lung have significantly shorter median survival (7.5 vs. 12.7 months) 1

Malignant Pleural Effusions

• Use ultrasound guidance for all pleural interventions 2
• Perform large-volume thoracentesis to assess symptomatic response and lung expansion before definitive therapy 2
• Consider indwelling pleural catheter or chemical pleurodesis for symptomatic patients with expandable lung 2
• Use indwelling pleural catheter instead of pleurodesis for nonexpandable lung or failed pleurodesis 2