Paracetamol Toxicity — Written Clinical Reasoning

SAQ 1 — Late single acute paracetamol overdose with established hepatotoxicity (20 marks)

Prompt: Outline immediate assessment, the investigations you would order, your integrated management plan, and the shared decision-making framework. Justify each decision with evidence. [17]

Model Answer

Problem list (4 marks): [17][7]

1. Single acute paracetamol overdose with established hepatotoxicity — late presentation (beyond the eight-hour complete-protection window); transaminitis and coagulopathy already present.
2. Host with chronic alcohol use — comorbidity for withdrawal and nutrition; not a reason to apply a separate lower nomogram line (Rumack found no consistent chronic-alcohol difference; UK 2012 ceased risk assessment). [13][8]
3. Evolving acute liver injury — coagulopathy, hypoglycaemia, raised lactate, mild encephalopathy; transplant triage using O'Grady markers plus Bernal lactate. [3][5]
4. Acute kidney injury — tracked because creatinine greater than 300 micromol/L is an O'Grady poor-prognosis marker. [3]
5. Alcohol use disorder and deliberate self-harm — withdrawal prophylaxis and psychiatry once medically stable.

Step 1 — Immediate actions (5 marks): [1][11][4]

Start intravenous acetylcysteine immediately. He is late with established injury; Hodgman notes that standard courses may need to be extended when hepatic injury is present, and Keays continued the infusion until recovery from encephalopathy or death even after fulminant hepatic failure. For ANZ practice name the Chiew two-bag regimen (200 mg/kg over 4 hours, then 100 mg/kg over 16 hours); know the classic three-bag 150 mg/kg over 15 minutes or 1 hour, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours as the historical intravenous skeleton. [11][7][4]

Protect the airway if drowsy. Correct hypoglycaemia and hypovolaemia. Charcoal is not indicated at 14 hours — the position paper reserves consideration for a potentially toxic ingestion up to one hour previously, and not routinely. Notify the liver service early because lactate already exceeds Bernal's early 3.5 mmol/L threshold. [12][5]

Step 2 — Investigations (3 marks): [3][5][7]

Paracetamol concentration (to confirm and to decide whether the course must be extended), AST/ALT, prothrombin time, creatinine, arterial blood gas with lactate, glucose. Track O'Grady acetaminophen markers: arterial pH below 7.30, prothrombin time greater than 100 s, creatinine greater than 300 micromol/L. Bernal: lactate 3.5 mmol/L early (sensitivity 67%, specificity 95%) or 3.0 mmol/L after fluids (76%, 97%) identified non-survivors earlier than KCH criteria (4 versus 10 hours). [3][5]

Step 3 — NAC reactions (2 marks): [10]

Yarema: anaphylactoid reactions in 8.2% of 6,455 21-hour intravenous courses; 75.4% cutaneous; 95.4% in the first 5 hours; 92% of medicated reactions received an antihistamine. Stop, treat, restart more slowly. Do not quote an unsourced "20 per cent". [10]

Step 4 — Transplant decision (3 marks): [3][4][5]

Refer when O'Grady poor-prognosis markers are met, and discuss earlier when lactate is above Bernal thresholds. Continue acetylcysteine: Keays survival 48% versus 20%, with less cerebral oedema and less inotrope requirement. [4]

Step 5 — Alcohol and psychiatry (3 marks): [13][17]

Symptom-triggered benzodiazepines, thiamine, nutrition. Do not invent a 2–3 g therapeutic ceiling from memory. Psychiatric liaison once capacity allows. [17]