What is the initial evaluation and treatment approach for a patient presenting with pleural effusion?

Initial Evaluation and Treatment of Pleural Effusion

Begin with chest radiography or CT chest with IV contrast as the initial imaging study, followed by ultrasound-guided diagnostic thoracentesis using a 21-gauge needle to obtain pleural fluid for comprehensive analysis including protein, LDH, pH, cytology, Gram stain, AAFB stain, and microbiological culture in both sterile vials and blood culture bottles. 1, 2

Initial Clinical Assessment

Skip thoracentesis only if bilateral effusions occur in the clear clinical context of heart failure, cirrhosis, or nephrotic syndrome with typical features—otherwise proceed to sampling. 1, 3

Look specifically for:

• Dyspnea out of proportion to effusion size (suggests pulmonary embolism) 1
• Pleuritic chest pain (75% of PE-related effusions) 1
• Recent pneumonia with fever (parapneumonic effusion/empyema) 1
• Constitutional symptoms (weight loss, malaise suggest malignancy) 1
• Drug history (numerous medications cause exudative effusions) 1

Imaging Algorithm

First-Line Imaging

• Chest radiography OR CT chest with IV contrast are equivalent initial options 1
• If CT is performed, acquire images 60 seconds post-contrast to optimize pleural visualization 1

Mandatory Pre-Procedure Ultrasound

• Perform thoracic ultrasound on every patient before any pleural procedure 2, 4
• Ultrasound guidance reduces pneumothorax risk from 8.9% to 1.0% 2, 4
• Ultrasound identifies effusion size, character, pleural nodularity (malignancy), and loculations 2

Diagnostic Thoracentesis Technique

Procedure Specifics

• Use 21-gauge fine-bore needle with 50 ml syringe 1, 2
• Limit fluid removal to maximum 1.5 liters to prevent re-expansion pulmonary edema 1, 2, 4
• Always use ultrasound guidance 2, 4

Mandatory Pleural Fluid Tests

Send fluid for ALL of the following 1, 2:

• Protein and LDH (to apply Light's criteria if protein 25-35 g/L)
• pH measurement (critical for parapneumonic effusions)
• Cytology (60% sensitivity for malignancy)
• Gram stain and culture
• AAFB stain and TB culture
• Blood culture bottles (increases microbiological yield)

Interpreting Results

Apply Light's criteria to differentiate exudate from transudate when pleural fluid protein is 25-35 g/L: 1

• Pleural/serum protein ratio >0.5, OR
• Pleural/serum LDH ratio >0.6, OR
• Pleural LDH >2/3 upper limit of normal serum LDH

Key diagnostic thresholds for exudates: 5, 3

• LDH >1000 IU/L: empyema, parapneumonic effusion, or rheumatoid pleuritis
• Lymphocytes ≥80%: tuberculosis or malignancy
• pH <7.2: complicated parapneumonic effusion requiring drainage
• Eosinophils >10%: air or blood in pleural space, drug reaction, or parasitic infection

Treatment Based on Effusion Type

Transudative Effusions

• Treat the underlying condition (heart failure, cirrhosis, nephrotic syndrome) 1, 4
• Therapeutic thoracentesis only if symptomatic while treating underlying cause 4

Exudative Effusions

Parapneumonic Effusion/Empyema

• If pH <7.2, glucose low, or purulent appearance: immediate chest tube drainage required 4, 3
• Use small-bore chest tube (14F or smaller) 4
• Hospitalize all patients for IV antibiotics covering respiratory pathogens 4
• Consider tissue plasminogen activator/DNase therapy if loculated 3

Malignant Pleural Effusion

For symptomatic patients: 2, 4

1. Perform large-volume thoracentesis first (up to 1.5L) to assess symptom relief and lung expandability
2. If lung expands completely: offer either indwelling pleural catheter OR chemical pleurodesis (talc 4-5g)
3. If non-expandable lung or failed pleurodesis: use indwelling pleural catheter only

For asymptomatic malignant effusions: observation only—do not perform therapeutic interventions 4

Chemotherapy-responsive tumors (small-cell lung cancer, breast cancer, lymphoma): 4

• Prioritize systemic chemotherapy over local pleural interventions
• Consider pleurodesis only if chemotherapy fails or is contraindicated

Tuberculosis

• If lymphocyte-predominant effusion (≥80%) with positive AAFB or TB culture: initiate anti-TB therapy 5
• Consider pleural biopsy if TB suspected but fluid analysis negative 1, 6

Critical Pitfalls to Avoid

• Never remove >1.5L in single thoracentesis (re-expansion pulmonary edema risk) 1, 2, 4
• Never attempt pleurodesis without confirming lung expandability on post-thoracentesis chest X-ray 4
• Never perform intercostal tube drainage without pleurodesis (100% recurrence rate at 1 month) 1, 4
• Never delay systemic therapy in chemotherapy-responsive tumors for local pleural treatment 4
• Do not routinely perform bronchoscopy unless hemoptysis, atelectasis, or suspected endobronchial obstruction present 1

When to Obtain Pleural Tissue

Refer to pulmonology for pleural biopsy (ultrasound/CT-guided, closed needle biopsy, or thoracoscopy) if: 1

• Cytology negative but malignancy suspected
• Exudative effusion remains undiagnosed after initial fluid analysis
• TB suspected but fluid studies negative
• Contrast-enhanced CT thorax should be performed with fluid present to visualize pleura and guide biopsy site 1