Paeds SAQs · acute-care-resuscitation-and-toxicology
Paracetamol poisoning — formative SAQs
Two MedVellum formative short-answer questions on paediatric paracetamol poisoning: using the Rumack-Matthew nomogram for a single acute ingestion with a known time, giving activated charcoal early, starting intravenous N-acetylcysteine on or above the 150 mg per litre treatment line, recognising the staggered and unknown-time rules, managing an anaphylactoid reaction to NAC, and escalating when King's College criteria are met. The marks and timing support transparent self-assessment. They are not an official board format or pass standard.
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Target exams
SAQ 1 — A single acute ingestion with a known time
Question 1 — 10 formative marks; suggested time 15 minutes [1]
A six-year-old, twenty-kilogram child is brought in fifty minutes after swallowing approximately twelve 500-milligram paracetamol tablets (300 milligrams per kilogram) as a single ingestion at a known time. The child is alert and vomiting. The four-hour paracetamol level is 180 milligrams per litre, and the ALT and INR are normal. [1] [11]
- Explain the nomogram decision in this child and state whether activated charcoal is indicated, with the dose and window. (2 marks)
- State the standard intravenous N-acetylcysteine regimen in full. (3 marks)
- During the loading dose the child develops flushing, an itchy rash and mild wheeze. Interpret this and describe the immediate management. (3 marks)
- State the endpoints that would let you stop the standard course, and what you would do if the ALT and INR are rising at twenty-one hours. (2 marks) [1]
Full-credit answer — SAQ 1
Reveal full-credit answer for SAQ 1
1. Nomogram decision and activated charcoal
This is a single acute ingestion with a known time, so the four-hour level can be plotted on the Rumack-Matthew nomogram. A level of 180 milligrams per litre at four hours is above the 150 milligrams per litre treatment line, so intravenous N-acetylcysteine is indicated. Because the child presents within one hour of ingestion and has taken a significant dose, activated charcoal is indicated: 1 gram per kilogram by mouth, that is 20 grams (maximum 50 grams), given now before absorption completes, weighing the benefit against the ongoing vomiting and airway risk. [1]
2. The intravenous N-acetylcysteine regimen
The standard intravenous regimen is 150 milligrams per kilogram over one hour, then 50 milligrams per kilogram over four hours, then 100 milligrams per kilogram over sixteen hours, a total of 300 milligrams per kilogram over twenty-one hours. For this twenty-kilogram child that is a 3-gram loading dose, then 1 gram, then 2 grams, given in glucose-containing fluid per the local protocol. I confirm the exact regimen with the poisons information centre because it is region-specific. [1] [9]
3. An anaphylactoid reaction to NAC
This is an anaphylactoid (non-IgE) reaction to the loading dose of N-acetylcysteine, driven by the high peak concentration: flushing, rash, itch and mild bronchospasm are typical. I slow or briefly pause the infusion and give an antihistamine, then resume the regimen once the reaction settles. It is not a reason to abandon the antidote. If bronchospasm or hypotension is severe I treat along the standard anaphylaxis pathway, but most reactions are rate-related and settle with slowing. [9]
4. Stopping and extending the course
I stop the standard course if the ALT and INR are normal or falling, the paracetamol level is negligible, the child is clinically well, and there is no co-ingestant or safeguarding concern. If the ALT and INR are rising at twenty-one hours, the child has ongoing hepatotoxicity, so I extend the N-acetylcysteine (commonly continuing the third-bag rate) until the liver is recovering, monitor the prothrombin time trend closely, and escalate to the liver transplant centre if King's College criteria appear. [1] [10]
SAQ 2 — A staggered ingestion in an adolescent
Question 2 — 10 formative marks; suggested time 15 minutes [1]
A fifteen-year-old presents after taking paracetamol in several doses over six hours for distress, the total and the last time uncertain. The ALT is 450 units per litre and the INR is 1.8. The paracetamol level is 90 milligrams per litre but the time of the last dose is not reliable. [1] [11]
- Explain why the nomogram must not be used here, and state the immediate decision. (2 marks)
- Outline the initial medical management and monitoring plan. (3 marks)
- State the King's College criteria for paracetamol-induced acute liver failure and the action if they are met. (3 marks)
- Describe the safeguarding and mental health response that must run in parallel. (2 marks) [1]
Full-credit answer — SAQ 2
Reveal full-credit answer for SAQ 2
1. Why the nomogram is invalid and the immediate decision
This is a staggered ingestion with an uncertain time of the last dose, so the Rumack-Matthew nomogram is invalid and must not be plotted against an assumed time. The raised ALT and INR already show hepatotoxicity, so I start intravenous N-acetylcysteine empirically on the standard regimen regardless of the level. I take the history privately and sensitively, including the likely total, the formulations, co-ingestants and intent. [1] [11]
2. Initial medical management and monitoring
I secure the airway, breathing and circulation, check bedside glucose and correct a dangerous low, and take bloods including ALT, INR, renal function, venous blood gas, lipase and a drug screen with salicylate and ethanol levels if co-ingestion is suspected. I start intravenous N-acetylcysteine at 150 milligrams per kilogram over one hour, then 50 over four hours, then 100 over sixteen hours. I monitor ALT and INR serially (the prothrombin time trend is the key prognostic marker), the acid-base balance, renal function and conscious level, and I manage any anaphylactoid reaction by slowing the infusion and giving an antihistamine. I call the poisons information centre and the toxicology service early. [1] [10]
3. King's College criteria and the action
For paracetamol-induced acute liver failure the King's College criteria are an arterial pH below 7.3 after adequate fluid resuscitation, regardless of the grade of encephalopathy, or the combination of all three of an INR above 6.5 (prothrombin time above 100 seconds), a creatinine above 300 micromoles per litre, and grade three to four encephalopathy. Meeting the criteria predicts a poor outcome without transplant and is the trigger to contact the regional liver transplant centre immediately, before the NAC course finishes, and to arrange transfer. [10]
4. Safeguarding and mental health response
Paracetamol poisoning in an adolescent is a deliberate self-harm presentation until shown otherwise, so I begin a mental health and psychosocial assessment in parallel with medical care, after medical stabilisation. I take a private, sensitive history of intent, precipitants, prior attempts and protective factors, and I involve the mental health team and the appropriate senior clinician. I follow the local safeguarding pathway, document objective findings, and apply the local consent and mandatory-reporting rules. I do not discharge until both the medical and the mental health risk are addressed and a safe plan is in place. [11]
References
- [1]Rumack, Barry H Acetaminophen hepatotoxicity: the first 35 years Journal of toxicology. Clinical toxicology, 2002.PMID 11990202
- [4]Sivilotti, Marshall L A Treating acetaminophen overdose CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne, 2022.PMID 35440504
- [9]Daoud, Ahmed Two-bag intravenous N-acetylcysteine, antihistamine pretreatment and high plasma paracetamol levels are associated with a lower incidence of anaphylactoid reactions to N-acetylcysteine Clinical toxicology (Philadelphia, Pa.), 2020.PMID 31601129
- [10]Harrison, Philip M Serial prothrombin time as prognostic indicator in paracetamol induced fulminant hepatic failure BMJ (Clinical research ed.), 1990.PMID 2249026
- [11]Karabacak, Busra Clinical characteristics and outcomes of pediatric paracetamol poisoning presenting to the emergency department BMC pediatrics, 2026.PMID 41998668