Causes of Thoracentesis
Thoracentesis is performed for two primary reasons: diagnostic evaluation of undiagnosed pleural effusions and therapeutic relief of dyspnea from symptomatic effusions. 1
Diagnostic Indications
Thoracentesis should be performed for any unilateral pleural effusion or bilateral effusion with normal heart size on chest radiograph to determine the underlying cause. 2, 1 This recommendation is particularly important because malignancy must be excluded in these presentations, as malignant pleural effusion accounts for 42-77% of exudative effusions. 2
Specific Diagnostic Scenarios
Suspected malignancy requiring cytological examination of pleural fluid is a key indication, as lung carcinoma accounts for approximately one-third of all malignant effusions, followed by breast carcinoma. 2, 1
Exudative effusions of unknown etiology warrant thoracentesis, with at least 25-50 mL of fluid needed for comprehensive analysis including cell count, protein, LDH, glucose, pH, and cytology. 1
Parapneumonic effusions require diagnostic thoracentesis to differentiate simple from complicated effusions, as pH <7.2 indicates complicated parapneumonic effusion requiring drainage. 3
Important Diagnostic Pitfall
Even transudative effusions may require cytologic examination in the appropriate clinical setting when malignancy is suspected and congestive heart failure is absent, as some malignant effusions (particularly paramalignant effusions from mediastinal node involvement) can present as transudates. 2 Small bilateral effusions in patients with decompensated heart failure, cirrhosis, or kidney failure are likely transudative and do not require diagnostic thoracentesis. 3
Therapeutic Indications
Thoracentesis provides relief of dyspnea in patients with symptomatic pleural effusions and should be performed when respiratory compromise is present. 2, 1
Specific Therapeutic Scenarios
Malignant pleural effusions causing dyspnea require therapeutic thoracentesis, as dyspnea occurs in more than half of cases and is the primary symptom requiring palliation. 2, 1
Recurrent malignant effusions with respiratory compromise benefit from thoracentesis, though more definitive interventions like pleurodesis should be considered for recurrent cases. 1
Palliative care in patients with far advanced disease and poor performance status who may benefit from periodic outpatient thoracentesis rather than more invasive procedures. 1
Therapeutic Considerations
The average survival with malignant pleural effusion is 4-7 months, so treatment should aim to relieve dyspnea in a minimally invasive manner while minimizing repeated procedures. 2 Hepatic hydrothorax from cirrhosis has particularly poor prognosis with 74% mortality at 90 days despite mean MELD of only 14, making thoracentesis an important palliative intervention. 2
Common Underlying Causes Requiring Thoracentesis
Malignant Causes
- Lung carcinoma (most common, ~33% of malignant effusions) 2
- Breast carcinoma (second most common) 2
- Lymphomas (Hodgkin's and non-Hodgkin's, accounting for ~10% of malignant effusions) 2
- Ovarian and gastrointestinal carcinomas 2
Non-Malignant Causes
- Heart failure (leading cause overall in adults) 3
- Parapneumonic effusions/infection (most common cause of exudates) 3
- Pulmonary embolism 3
- Hepatic hydrothorax (4-12% prevalence in cirrhosis) 2
- Chronic kidney disease (can cause exudative effusions, often uremic pleuritis) 4
Critical Pre-Procedure Requirements
Ultrasound guidance should be used for all thoracentesis procedures to reduce pneumothorax risk and improve success rates. 1, 5 Image-guided thoracentesis reduces pneumothorax rates, "dry taps," and solid organ puncture compared to blind procedures. 2, 1
Relative contraindications include minimal effusion (<1 cm thickness on lateral decubitus view), bleeding diathesis, anticoagulation, mechanical ventilation, and serum creatinine >6.0 mg/dL. 2 However, recent evidence suggests patients with mild to moderate coagulopathy (PT/PTT up to twice normal, platelets >50,000/mL) can safely undergo thoracentesis without correction. 2, 5