OSCE — assessment of a unilateral pleural effusion and the drainage decision · MBBS OSCE

Brief (to candidate)

A 60-year-old man presents with a week of fever, pleuritic right-sided chest pain and progressive breathlessness. Examination shows reduced right chest expansion, stony-dull percussion, reduced breath sounds and reduced vocal resonance at the right base. He is tachypnoeic (RR 26) with SpO2 92% on air. A chest X-ray confirms a moderate right pleural effusion. You have 8 minutes to assess him, justify the diagnostic tap and its fluid panel, apply Light's criteria, and outline management including the drainage decision.

Candidate instructions

Take a focused history and examine, using an ABCDE approach, and confirm the effusion at the bedside.
Justify the diagnostic thoracentesis and list the pleural-fluid panel (with a simultaneous serum sample).
Apply Light's criteria and state the drainage thresholds (pH, glucose, LDH, pus, culture).
Outline the immediate and definitive management, including antibiotics, chest-drain insertion and intrapleural therapy, with doses, site and safety steps.

Examiner checklist (mark each domain / 10)

Domain	Key actions expected
ABCDE / resuscitation	Airway; oxygen to target SpO2 94–98%; IV access; sepsis assessment (cultures, lactate)
Bedside diagnosis	States the effusion tetrad (reduced expansion, stony-dullness, reduced breath sounds, reduced vocal resonance); distinguishes from consolidation and pneumothorax; notes trachea pushed away^[3]
Investigations	Ultrasound-guided thoracentesis; sends protein, LDH, glucose, pH, cell count, Gram stain/culture, cytology + serum protein/LDH; selected: amylase, triglyceride, ADA
Light's criteria	Reproduces all three (protein ratio over 0.5, LDH ratio over 0.6, fluid LDH over two-thirds serum ULN); any one → exudate^[4]
Drainage decision	States pH under 7.2 / glucose under 3.3 mmol/L / LDH over 1000 / pus / positive culture → chest drain^[1]
Empirical antibiotics	Amoxicillin-clavulanate (or ceftriaxone) plus metronidazole; add antipseudomonal if hospital-acquired; prolonged course
Intrapleural therapy	tPA 10 mg + DNase 5 mg twice daily for loculated infection (MIST2); neither agent alone works^[5]
Procedure & safety	Triangle of safety; needle above the lower rib; correct INR/coagulopathy; drain in stages (~1.5 L) to avoid re-expansion oedema; underwater seal

Model key actions

Oxygen target and rationale; recognise and treat sepsis.
Confirm the effusion and distinguish it from consolidation (bronchial breath sounds + increased vocal resonance = consolidation; the reverse = effusion).
Apply Light's criteria to classify, then apply the pH-under-7.2 drainage rule to decide on a chest tube.^[4]
Ultrasound-guided chest drain (small-bore 8–14 Fr preferred) + empirical antibiotics + intrapleural tPA + DNase if loculated.^[1]^[5]
State the VATS escalation pathway if drainage fails, and safety steps (re-expansion oedema, coagulopathy).

Common errors

Not applying Light's criteria (or omitting the serum sample for ratios).
Missing the pH-under-7.2 drainage trigger and treating a complicated effusion with antibiotics alone.
Using streptokinase alone — MIST1 showed it is ineffective; the active regimen is tPA + DNase (MIST2).
Over-draining (re-expansion oedema) or tapping an uncorrected coagulopathic patient.
Failing to consider TB (ADA) or malignancy (cytology/biopsy) in a lymphocytic exudate, or PE in a bloody effusion.

References4Show

[1]Roberts ME, et al. British Thoracic Society Guideline for pleural disease. Thorax, 2023.PMID 37433578
[3]Hooper C, Lee YCG, Maskell N. Investigation of a unilateral pleural effusion in adults: BTS 2010. Thorax, 2010.PMID 20696692
[4]Light RW, et al. Pleural effusions: the diagnostic separation of transudates and exudates. Annals of Internal Medicine, 1972.PMID 4642731
[5]Rahman NM, et al. Intrapleural use of tissue plasminogen activator and DNase in pleural infection (MIST2). New England Journal of Medicine, 2011.PMID 21830966