What are the indications for thoracentesis (removal of fluid from the pleural space)?

Indications for Thoracentesis

Thoracentesis is primarily indicated for relief of dyspnea in patients with pleural effusions, as well as for diagnostic purposes when the etiology of the effusion is unknown. 1

Diagnostic Indications

• Undiagnosed unilateral pleural effusion or bilateral effusion with normal heart size on chest radiograph to determine the etiology 1
• Suspected malignancy requiring cytological examination of pleural fluid 1
• Suspected pleural infection requiring microbiological analysis 2
• Evaluation of pleural fluid characteristics to differentiate between exudative and transudative effusions using Light's criteria 3

Therapeutic Indications

• Relief of dyspnea in patients with symptomatic pleural effusions 1
• Management of malignant pleural effusions, especially when recurrent and causing respiratory compromise 1
• Drainage of parapneumonic effusions, particularly when complicated (pH < 7.2) 2
• Palliative therapy in patients with far advanced disease and poor performance status who may benefit from periodic outpatient thoracentesis 1

Pre-Procedure Assessment

• Imaging evaluation is essential before thoracentesis:

  • Chest radiography to determine size, laterality, and presence of mediastinal shift 1
  • Ultrasound to accurately locate fluid and identify potential complications such as loculations or septations 1

• Assessment of pleural fluid pressure during thoracentesis can help determine:

  • Presence of trapped lung (initial pleural fluid pressure < 10 cm H₂O) 1
  • Safe volume of fluid removal (monitoring to prevent pressure below -20 cm H₂O) 1

Technical Considerations

• Image-guided thoracentesis should always be used to reduce the risk of complications 1

• Benefits of ultrasound guidance include:

  • Reduced risk of pneumothorax (38/1000 vs 50/1000 with non-guided technique) 1
  • Improved success rate of obtaining fluid samples (1000/1000 vs 782/1000) 1
  • Ability to detect small effusions and features suggesting complicated effusion or malignancy 3

• Volume considerations:

  • For diagnostic purposes, at least 25 mL (ideally 50 mL) should be obtained for cytological examination 1
  • For therapeutic purposes, generally limit to 1-1.5 L at one sitting unless pleural pressure is monitored 1
  • Larger volumes may be safely removed in patients with contralateral mediastinal shift who tolerate the procedure without symptoms 1

Special Considerations

• Patients with ipsilateral mediastinal shift may have trapped lung or endobronchial obstruction, limiting the benefit of thoracentesis 1
• Repeated thoracenteses in transudative effusions may induce inflammatory changes that alter fluid characteristics and potentially impair resolution 4
• Minimal pleural effusions that are difficult to access may require specialized techniques such as EUS-guided transesophageal thoracentesis 5

Contraindications

• Relative contraindications include:
  • Minimal effusion (< 1 cm in thickness on lateral decubitus view) 1
  • Bleeding diathesis or anticoagulation (though mild to moderate coagulopathy with INR/PTT up to twice normal and platelets > 50,000/ml is generally acceptable) 1
  • Mechanical ventilation 1
  • Severe renal failure (serum creatinine > 6.0 mg/dL) 1

Complications to Monitor

• Pneumothorax (reduced risk with ultrasound guidance) 1
• Re-expansion pulmonary edema (related to rapid fluid removal) 1
• Bleeding (rare with both guided and non-guided techniques, approximately 3/1000) 1
• Infection 1
• Hemothorax 6
• Organ laceration (spleen or liver) 1

Follow-up Considerations

• If dyspnea is not relieved after thoracentesis, investigate other causes such as:

  • Lymphangitic carcinomatosis 1
  • Atelectasis 1
  • Thromboembolism 1
  • Tumor embolism 1
  • Endobronchial obstruction 1

• For recurrent malignant effusions, consider more definitive interventions such as:

  • Chemical pleurodesis 1
  • Thoracoscopy with talc poudrage 6
  • Indwelling pleural catheter placement 3