Question 12

College answer

Not available.

Discussion

The original college nomogram is not available, so this one is entirely the invention of the author. 

Anyway: this is a relatively large overdose, 33.25g. Assuming this lady weighs 70kg, that would be 475mg/kg, an overdose which would be described as "massive" by local definitions. 

a) Initial specific investigations and management:

• Investigations:
  • EUC/CMP, looking for renal failure
  • LFTs, looking for hepatic enzyme elevation
  • Coags, looking for coagulopathy
  • ABG, looking for acidosis
  • BSL, looking for hypoglycaemia
• Management:
  • Usually, one would say that this would be too late for activated charcoal (as it is only useful within 4 hours of ingestion), but considering the overdose was large and the patient appears to be cooperative, 50g of activated charcoal should be administered
  • N-acetylcysteine infusion should start (high dose, 200mg/kg over first 4 hours, followed by 200mg/kg over 16 hours).

Role and rationale of N-acetylcysteine (NAC) (based on nomogram) in this patient

• The nomogram cannot be used to guide therapy in this patient, as she has overdosed on a sustained-release formulation.
• NAC infusion will continue for the full 20 hours, minimum - irrespective of the initial level
• Paracetamol levels are still useful to guide further NAC dosing (beyond the initial 24 hrs) and the need for more charcoal decontamination
• If the levels continue to rise in the first 24 hrs, or remain over 100mg/L, the dose of NAC may need to increase.
  Which brings us to:

The criteria for cessation in patients who require NAC beyond 20 hours:

• Continue NAC if:
  • Paracetamol concentration remains more than 10 mg/L (66 µmol/L) 
  • ALT is > 50 U/L and increasing
  • INR is more than 2.0
  • Patient is clinically unwell

Criteria for referral to a liver transplant unit:

• INR more than 3.0 at 48 hours or greater than 4.5 at any time;
• Oliguria or creatinine greater than 200 μmol/L
• Persistent acidosis (pH <  7.3) or arterial lactate greater than 3 mmol/L
• Hypotension with blood pressure below 80  mmHg
• Hypoglycaemia, severe thrombocytopenia, or encephalopathy of any degree
• Any unexplained alteration of consciousness (Glasgow Coma Score <  15)