MBBS OSCE · Emergency & Toxicology
OSCE — Lithium Toxicity
Eight-minute OSCE station on Lithium Toxicity: focused history, examination priorities, investigations, emergency and definitive management.
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Brief (to candidate)
You will assess a patient with a presentation consistent with Lithium Toxicity.
You have 8 minutes to take a focused history, outline examination, investigations, and management including red flags.
Clinical context
Lithium toxicity results from excess of lithium carbonate (the mood-stabiliser used for bipolar affective disorder prophylaxis), a drug with a narrow therapeutic index (therapeutic 0.6-1.2 mmol/L). Lithium is a small monovalent cation handled by the kidney like sodium — freely filtered, reabsorbed proximally, almost entirely renally excreted — so reduced GFR or sodium/water loss (dehydration, vomiting, diarrhoea, fever, low-salt diet) and interacting drugs (thiazides, NSAIDs, ACE-inhibitors/ARBs) are the classic precipitants of accumulation. Three patterns exist: acute overdose, acute-on-chronic, and chronic accumulation (the commonest and most dangerous). Toxicity is predominantly NEUROLOGI
Candidate tasks
- Clarify onset, severity, associated features, and red-flag symptoms.
- State focused examination priorities.
- List first-line investigations and any named score/criteria.
- Give immediate resuscitation steps.
- Outline definitive management with doses/routes where standard.
- Name complications and disposition (ward / HDU / theatre / discharge safety-net).
- Mention one special-population modifier (pregnancy, child, elderly, CKD).
Examiner checklist
| Domain | Pass behaviours |
|---|---|
| Definition | Correct working diagnosis language |
| Assessment | Focused, prioritised, red flags sought |
| Investigations | Appropriate first-line + interpretation |
| Emergency care | ABC / time-critical actions first |
| Definitive care | Specific drugs/procedures, not generic phrases |
| Safety | Patient on lithium with new coarse tremor, ataxia, fasciculations, dysarthria, c |
| Safety | Lithium level over 2.5 mmol/L with symptoms, or over 4.0 mmol/L — severe; arrang |
| Safety | Dehydration, vomiting/diarrhoea, NSAID, ACE-inhibitor or thiazide in a lithium p |
| Communication | Clear plan and safety-netting |
Model outline
Lead with the working diagnosis and life threats. Resuscitate before definitive tests when unstable. Use guideline-standard therapy with named agents and doses. Document escalation criteria and follow-up. A safe candidate is specific, structured, and never delays critical care for non-urgent imaging.