Pleural effusion
Pathophysiology
Pleural effusion refers to any fluid accumulation in the pleural space. Fluid types can include purulent exudate (pyothorax), blood (haemothorax), chyle (chylothorax), neoplastic effusions or pure/modified transudates. Any fluid recovered from the chest should be classified as one of the following:
1. Pure transudate
These fluids are typically clear, with low protein and cell counts. They develop secondary to low oncotic pressure (e.g. hypoalbuminaemia) or high hydrostatic pressure or vascular permeability (e.g. congestive heart failure)
Total protein: <2.5 g/dl
Total nucleated cell count: <1500/ul
2. Modified transudate
These fluids are moderately cellular and usually result from either increased vascular permeability or increased hydrostatic pressure (e.g. neoplastic effusions, congestive heart failure, lung lobe torsion, etc)
Total protein: 2.5-7.5 g/dl
Total nucleated cell count: 1000-7000/ul
3. Exudate
These fluids are highly cellular and can be septic (pyothorax) or aseptic (neoplastic). They develop as a result in increased vascular permeability.
Total protein: >3.0 g/dl
Total nucleated cell count: >7000/ul
Management
The treatment of pleural effusion depends on the type of effusion present. A diagnostic thoracentesis should be performed on any patient presenting with a pleural effusion. Inhouse analysis of the fluid should include cytology, glucose/lactate concentration (compare these to peripheral glucose taken at the same time). The goal here is to quantify the fluid as neoplastic, infectious or inflammatory. Any fluid that is suspicious for a neoplastic or infectious process should be sent for culture and cytology. Always repeat imaging following drainage to confirm that sufficient fluid has been drained (especially if draining therapeutically) and to assess pulmonary pathology.