	Headline
Etiology	Transudative or exudative (see below), local or systemic effect. About 20ml fluid is physiologic. Drug-induced: amiodarone, nitrofurantoin, phenytoin, methotrexate, pergolide
Epidemiology
Clinical presentation	SOB, hypoxia...
Pathogenesis
Diagnostic investigations	CXR - NB - pleural effusion without a meniscus may indicate concurrent pneumothorax diagnostic aspiration suspected malignant effusion - send 25-50ml fluid for cytology
Management	Therapeutic thoracocentesis Chest drain (<1.5L in 1st h then clamp) Recurrent: pleurodesis, direct vision etc.
Complications	Re-expansion pulmonary oedema

Light's criteria

	Transudate	Exudate
Possible underlying diagnoses	nephrotic syndrome, portal hypertension (= hepatic hydrothorax), congestive heart failure, OHSS	cancer, trauma, PE, infection
How formed?	caused by altered hydrostatic pressure, pleural permeability, and oncotic pressure	changes to formation and absorption of pleural fluid
Threshold (Light’s)	Protein <30g/dL	Protein >30g/dL (or pleural:serum protein >0.5, pleural:serum LDH > 0.6)

pH (?)
fluid LDH and protein → to match with serum LDH and protein
glucose
cell count

Culture might not yield much:

fluid might be sterile after abx
aerobic organisms have died in the swampy depths of the effusion
anaerobic organisms have died in the oxygen rich sample bottle
organisms were killed by the neutrophils
possibly what you end up growing is the plucky survivor and not what's the majority of the bugs

sources/links

https://derangedphysiology.com/main/required-reading/respiratory-intensive-care/Chapter-10/pleural-effusion
things to keep you up at night: https://litfl.com/broken-hearted-chest-drain/
https://litfl.com/pulmonary-re-expansion/
https://litfl.com/own-the-chest-tube/
https://www.rcemlearning.co.uk/reference/pleural-effusion/#1571046545819-65806fc0-b2d9
https://www.brit-thoracic.org.uk/quality-improvement/guidelines/pleural-disease/ → https://thorax.bmj.com/content/78/Suppl_3/s1