Read the acidosis, choose the antidote — iron, salicylate and toxic alcohol poisoning

Station status

This is one MedVellum formative structured clinical encounter. The scoring, prompts and performance descriptions are educational feedback tools. They are not an official college station, timing, mark allocation, pass score or reproduced examination format. The encounter assesses first-impression recognition of a high-anion-gap metabolic acidosis, the reading of the poison-specific signature, the choice of decontamination and weight-based antidote, communication, reassessment, early escalation to dialysis and retrieval, and safeguarding in parallel. [1] [6] [9]

Candidate instructions

You are the paediatric registrar called to the acute assessment room. Assess the child from the doorway and say aloud what you see. Recognise the high-anion-gap metabolic acidosis as the shared lesion and identify the poison-specific signature for each agent. Choose the decontamination and the weight-based antidote for each poison. Avoid the three lethal traps. Reassess from A after every action. Call the poisons centre, senior, dialysis or retrieval support early. Run safeguarding alongside urgent care. Finish with a structured handover and disposition plan. Say what you would assess or do; do not perform painful or distressing manoeuvres on the actor. [1]

Room setup and observable starting state

The encounter. Maya is three years old and is supported on the assessment trolley by a parent. The parent says, "She got into my handbag." Maya is drowsy, opens her eyes briefly to voice, is tachypnoeic with deep sighing respirations, looks flushed and sweaty, and has vomited once with streaks of blood. An open bottle of adult ferrous sulphate 325 mg tablets and an open bottle of adult aspirin are on the trolley beside her; several tablets are missing from each. These are abnormalities in appearance, work of breathing and circulation. The candidate should describe these signs objectively, declare concern, call for help and the poisons centre, and begin the hands-on ABCDE primary survey and the calculation of the elemental-iron dose immediately. [1] [2]

Simulation safety. Maya remains on the trolley and is never forcibly positioned. Cards or the assessor supply the respiratory rate, breathing sounds, monitor readings and examination findings. The parent does not obstruct urgent care. [1]

Actor cues

Parent actor

• Begin with "She got into my handbag." If asked what has changed, answer: "She found my iron tablets and my aspirin. I think she ate some of each about two hours ago. She's been sick twice and there was blood in it."
• If asked about baseline, give the card: Maya is previously healthy, fully immunised, with no allergies and no regular medications of her own.
• If the candidate explains what is wrong and what they will do, stay beside Maya and ask one clear question about what to expect. If the candidate dismisses the concern, repeat once: "She's not herself."
• Do not add safeguarding history unless directly and appropriately asked. [1]

Child actor

• Respond briefly to voice early in the encounter; become drowsier and harder to rouse as the scenario progresses, following the assessor's cue card.
• Indicate deep sighing respirations with the cue card; do not act out breath-holding. [6]

Assessor cues and clinical data

Release findings as the candidate reaches each step. Reward reading-the-signature behaviour and penalise anchoring on a single poison. [1] [9]

A and B — Airway and breathing

Airway is patent but the voice is weak. Respiratory rate 38 with deep sighing respirations, good bilateral air entry, oxygen saturation 96 percent on air. Expected strong behaviour: give high-flow oxygen because the child is in metabolic failure; recognise that the deep sighing respirations are the compensatory hyperventilation of a metabolic acidosis and must NOT be blunted; judge effectiveness by air entry, colour and interaction, not the number alone; prepare for the possibility of intubation with maintained hypocapnia if breathing fails. [6]

C — Circulation

Heart rate 150, weak central pulses, capillary refill 3 seconds, blood pressure low-normal, warm flushed limbs, reduced urine output. Expected strong behaviour: diagnose the circulation state from the whole picture; gain IV or IO access; give isotonic crystalloid in aliquots with dextrose added for the salicylate, stating the expected response and reassessing after each; call for retrieval or critical care early because dialysis may be needed. [1] [6]

D — Disability

Responds to voice but cannot sustain interaction; pupils equal and reactive; no seizure. Expected strong behaviour: screen with AVPU and plan a formal age-adapted Glasgow Coma Scale; check bedside glucose now and give dextrose even if the plasma glucose is near-normal, because cerebral hypoglycaemia can coexist with a normal plasma glucose in salicylate toxicity. [6]

E — Exposure

No rash; the abdomen is mildly tender; the two open bottles are on the trolley. Expected strong behaviour: identify the agents, ask the parent how many tablets are missing and estimate the time since ingestion; begin safeguarding documentation in parallel; preserve the bottles. [1] [2]

The laboratory release

The venous gas shows pH 7.24 with a high anion gap and a low bicarbonate. The serum salicylate is 540 mg per L. The serum iron is pending. The capillary glucose is 3.1 mmol per L. The serum potassium is 3.2 mmol per L. Expected strong behaviour: recognise the mixed high-anion-gap acidosis; start urinary alkalinisation to urine pH 7.5 to 8.0 with potassium correction to over 4 mmol per L (the reason alkalinisation would fail otherwise); prepare intravenous desferrioxamine 15 mg per kg per hour for the iron once the level returns or for acidosis, shock or severe gastrointestinal symptoms; begin whole-bowel irrigation because charcoal is useless for iron; give activated charcoal 1 g per kg for the salicylate component. [1] [6] [7]

Escalation event — the rising salicylate and the latent-phase risk

The salicylate rises to 680 mg per L over the next two hours, and the child becomes more tachypnoeic. The team suggests intubation. Expected strong behaviour: recognise that intubation without maintaining hypocapnia is the deadliest pitfall; give a bicarbonate bolus and optimise pH, pre-oxygenase, use rapid sequence, and set the ventilator to maintain the pre-intubation hypocapnia; have haemodialysis ready; continue to treat the iron on its own trigger and do not be reassured if the child transiently looks better (the latent phase). [6] [7]

Weight and escalation

The candidate must obtain a working weight for drug and device sizing. Expected strong behaviour: use a measured weight if available immediately; otherwise document a working weight from a recent reliable value, a credible parent estimate, or the trained length-and-habitus tool; use the local paediatric cognitive aid and the poisons centre for each weight-based dose. Call retrieval early for a child who may need dialysis, ventilation or intensive care unavailable locally. [1] [7]

Marking domains

Debrief prompts

• What was the shared metabolic lesion, and how did you read each poison-specific signature out of it?
• Which antidote did you give for each poison, and on what trigger, and at what weight-based dose?
• How did you decide when to intubate and how to set the ventilator, and could you have avoided the trap?
• How did you run safeguarding in parallel without delaying resuscitation? [1] [6]