ICU · Respiratory

Pleural effusion and empyema in the ICU

Also known as Pleural effusion · Parapneumonic effusion · Empyema · Light's criteria · Chest tube drainage · Intrapleural tPA/DNase · Hepatic hydrothorax · MIST2 trial

Pleural effusion is one of the commonest bedside findings in the ICU — present in over half of mechanically ventilated patients, and the cause is rarely the diagnosis on admission. The single most useful decision in pleural medicine is the transudate vs exudate split, made with Light's criteria (pleural/serum protein ratio >0.5, OR pleural/serum LDH ratio >0.6, OR pleural LDH >2/3 of the upper limit of normal — ANY ONE = exudate). Transudates are systemic (heart failure 1, hepatic hydrothorax, nephrotic, hypoalbuminaemia, atelectasis) — treat the cause, do not drain routinely. Exudates are local (parapneumonic 1, malignancy, pulmonary embolism, autoimmune, pancreatitis, TB, chylothorax) — sample and investigate. A parapneumonic effusion evolves through three stages: (1) simple/exudative — sterile free-flowing fluid, pH >7.2, antibiotics only; (2) complicated/fibrinopurulent — infected, loculated by fibrin septae, pH <7.2, LDH >1000, glucose <2.2 mmol/L, Gram stain/culture may be positive, requires chest tube drainage + antibiotics; (3) organised/empyema — frank pus and a thick fibrous peel entrapping the lung, pH <7.2, requires drainage ± intrapleural tPA/DNase (MIST2) ± VATS decortication. pH <7.2 is the single best pleural-fluid discriminator for drainage. Ultrasound guidance is mandatory before any pleural procedure. MIST2 showed the COMBINATION of intrapleural alteplase (tPA) 10 mg + DNase 5 mg daily x 3 improved drainage, reduced surgery, and shortened stay — but tPA alone or DNase alone is useless or harmful.