• Diagnostic: determination of pleural effusion etiology (e.g. transudative versus exudative) usually requires the removal of 50 to 100mL of pleural fluid for laboratory studies. Most new effusions require diagnostic thoracentesis, an exception being a new effusion with a clear clinical diagnosis (e.g. CHF) with no evidence for superimposed pleural space infection

  • Therapeutic: reduce dyspnea and respiratory compromise in patients with large pleural effusions. This is typically achieved by removing a much larger volume of fluid compared to the diagnostic thoracentesis