Etiology
- Increased influx from pleural vessels and decreased efflux via lymphatic system of pleural fluid
Differential Diagnosis
Clinical Manifestations
- History of CHF, cirrhosis, CKD, TB, malignancy
- Decreased lung sounds with dullness on percussion
Investigations
- Labs: pleural fluid and serum protein and LDH
- Imaging
- CXR is first-line imaging
- Blunting suggests at least 200mL of effusion
- Lateral more sensitive (50mL)
- Lateral decubitus is also helpful to rule out loculations
- Bedside ultrasound is best for internal medicine
- More sensitive than CXR (3-5mL)
- Better than CT for assessing the pleura
- Diagnostic thoracentesis
- Risks
- Pneumothorax <5%
- Hemothorax 1%
- Avoid if INR >3 or platelets <25
- Re expansion pulmonary edema <1%
- Avoid taking more than 1-2L
- Diagnostic requires 50mL (5-10 for microbiology, 2-5 for biochemistry, 20-40 for cytology)
Fluid Analysis
- Light's Criteria
- Exudate is exudative if at least one of:
- Pleural fluid to serum protein ratio > 0.5
- Pleural fluid to serum lactate dehydrogenase (LD) ratio > 0.6
- Pleural fluid LD level > 2/3 of upper limit of normal
- ULN usually ~220, so LD > 148
- Modified Light's Criteria
- Protein >29
- LDH >0.45 times serum LDH
- Pleural cholesterol >1.165 mmol/L
- Also albumin gradient and BNP can help differentiate
- pH
- Normal: 7.60-7.64
- Exudate: 7.30-7.45
- Transudate: 7.40-7.55
- <7.2
- Malignancy
- Empyema (low glucose)
- TB
- Rheumatoid arthritis (especially if really low glucose)
- Glucose <3.3
- Malignancy
- Empyema
- TB
- Rheumatoid arthritis (especially when <1.6)
