When should a pleural effusion be drained?

When to Drain a Pleural Effusion

Drain symptomatic pleural effusions, but avoid draining asymptomatic effusions unless diagnostic sampling is needed, as drainage without symptoms subjects patients to procedural risks without clinical benefit.

Primary Indications for Drainage

Symptomatic Effusions

• Drain all symptomatic pleural effusions to provide relief from dyspnea, cough, or pleuritic chest pain 1
• For malignant pleural effusions (MPE), perform large-volume thoracentesis when it is uncertain whether symptoms are related to the effusion and/or to assess lung expandability if pleurodesis is contemplated 1
• The potential benefits of identifying nonexpandable lung and confirming symptomatic improvement outweigh procedural harms 1

Asymptomatic Effusions

• Do not perform therapeutic drainage on asymptomatic effusions, as this exposes patients to procedural risks without providing clinical benefit 1
• The only exception is when pleural fluid is required for diagnostic purposes (e.g., to define clinical stage, obtain molecular markers, or establish etiology) 1
• This recommendation applies specifically to malignant effusions but can be extrapolated to other etiologies 1

Drainage Volume Limitations

Initial Drainage

• Limit initial drainage to 1-1.5 liters at a single session to prevent re-expansion pulmonary edema (RPO) 2
• Stop aspiration immediately if the patient develops chest discomfort, persistent cough, or vasovagal symptoms 2
• In pediatric patients, clamp the drain for 1 hour once 10 ml/kg is initially removed 1

Continued Drainage

• If continued drainage is needed after initial evacuation, slow the rate to approximately 500 ml/hour 2
• The primary goal is radiographic confirmation of fluid evacuation and lung re-expansion rather than targeting a specific daily drainage volume 2

Special Clinical Scenarios

Heart Failure-Related Effusions

• Only drain heart failure effusions that are refractory to maximal tolerated medical therapy (including diuretics and novel agents like SGLT2 inhibitors) 1
• Perform repeat pleural aspiration for recurrent symptomatic cardiac effusions, with consideration of indwelling pleural catheters (IPCs) only if frequent re-intervention is required 1
• IPCs were comparable to talc poudrage for palliation with fewer adverse events in heart failure patients 1

Post-Surgical Effusions

• Cardiac surgery: Most postoperative effusions resolve spontaneously; drain only if symptomatic 1
• Thoracic surgery: Higher drainage thresholds up to 450 ml/day for chest tube removal are safe, with low re-intervention rates (2.8%) and improved patient experience 1
• Post-pericardiotomy syndrome may benefit from anti-inflammatory therapy rather than drainage 1

Infected Effusions (Empyema/Parapneumonic)

• Always drain infected pleural effusions with tube thoracostomy or surgical intervention, combined with 2-6 weeks of antibiotic therapy 3
• Intrapleural enzymatic therapy significantly decreases treatment failure rates and length of hospital stay but carries risk of pleural hemorrhage 3

Technical Considerations

Ultrasound Guidance

• Always use ultrasound guidance for thoracentesis, as it reduces pneumothorax risk by 19% (odds ratio 0.81) 1
• Ultrasound can identify intercostal vessels to decrease hemorrhagic complications and evaluate for nonexpandable lung before drainage 1

Drainage System

• Connect all chest tubes to a unidirectional water seal drainage system kept below the patient's chest level at all times 4
• If suction is used, apply low pressure (5-10 cm H₂O) via the underwater seal to prevent tube blockage 1, 4
• Never clamp a bubbling chest drain due to tension pneumothorax risk 1, 4

Catheter Size

• Small bore tubes (10-14F) should be considered initially for malignant effusions due to reduced patient discomfort and comparable success rates 2

Critical Pitfalls to Avoid

Re-expansion Pulmonary Edema

• RPO is rare but potentially life-threatening, occurring most commonly in young adults with lung collapse for ≥7 days 1
• Pathophysiology involves reperfusion injury, increased capillary permeability, and neutrophil chemotactic factors 2
• Strict adherence to volume limitations (1-1.5 L initial drainage) minimizes this risk 2

Nonexpandable Lung

• Occurs in at least 30% of patients with MPE and is associated with significantly worse survival (7.5 vs 12.7 months median survival) 1
• Absence of lung expansion after fluid evacuation should steer clinicians away from futile pleurodesis attempts toward IPC placement 1
• Large-volume thoracentesis helps identify this condition before definitive intervention 1

Pneumothorax After Drainage

• Pneumothorax occurs in 31% of cases after small-bore catheter placement for malignant effusions, likely related to rapid fluid removal from noncompliant lung 5
• Most resolve spontaneously (79% within average 3.5 days) without requiring intervention 5
• Patients whose lungs do not fully re-expand in several days will probably not benefit from sclerotherapy 5