History Taking · Intermediate · Neurology

Headache, Dizziness and Nausea with Faulty Heating

Practise this PLAB 2 history taking station on Carbon Monoxide Poisoning. 8-minute voice AI simulation with feedback on all 3 marking domains.

Clinical scenario

You are an FY2 doctor in the Emergency Department. Mr Robert Walsh, a 46-year-old man, presents with a 36-hour history of headache, dizziness, and nausea. He mentions their gas boiler has not been serviced and has been making a strange noise. He mentions they live in a poorly ventilated flat. Please take a focused history to assess for carbon monoxide poisoning.

Background notes: PMH: Hypertension

What this station tests

  • Connecting environmental clues to non-specific symptoms: faulty boiler, poor ventilation, and multiple household members simultaneously unwell
  • Asking about symptom improvement away from the source: improvement with open windows or when outside is a key diagnostic clue
  • Identifying that multiple household members with the same symptoms at the same time is not coincidence: this is the hallmark of environmental poisoning
  • Understanding that pulse oximetry is unreliable in CO poisoning: COHb is read as oxyhaemoglobin, giving falsely normal SpO2
  • Taking immediate safety actions: family must not return to the flat, children must not go home, gas emergency line contacted

How to use your 8 minutes

  • 0-1 min — Introduction: Introduce yourself, confirm identity, open question. 'What's brought you in today?'
  • 1-4 min — Systematic History: Presenting complaint detail (SOCRATES for pain, timeline, severity). Systems review. PMH, medications, allergies.
  • 4-6 min — Context and ICE: Social history (smoking, alcohol, occupation, living situation). Family history. Ideas, Concerns, Expectations.
  • 6-7 min — Summary and Plan: Summarise findings back to patient. Share differential/working diagnosis. Outline investigation and management plan.
  • 7-8 min — Closing: Safety netting with specific red flags. Arrange follow-up. Check for questions.

Consultation approach

The opening

Carbon monoxide poisoning is one of the most commonly missed diagnoses because its symptoms mimic flu, migraine, and depression. The candidate must connect environmental clues (faulty appliance, poor ventilation, multiple household members affected) with non-specific symptoms. Mr Walsh is 46, presenting with 36 hours of headache, dizziness, and nausea. He mentions a faulty gas boiler and a poorly ventilated flat. Open with: 'Tell me about these symptoms and when they started.' But listen for the environmental clues: the boiler, the ventilation, and crucially, whether anyone else in the household is unwell.

Core approach

The symptoms are non-specific: global throbbing headache (not unilateral like migraine), dizziness, nausea, vomiting 3 to 4 times, poor concentration, and fatigue. Paracetamol has not helped. These could be flu, migraine, or a viral illness. The diagnostic clue is the environmental context.

Ask the critical questions. Is anyone else unwell? His wife Catherine has the same symptoms. Multiple household members with simultaneous onset of headache and nausea is the hallmark of CO poisoning. Do symptoms improve when they leave the house? Yes: both feel better with windows open and when outside. This is the second major clue. When did the boiler start making noise? Two days ago, coinciding with symptom onset.

Ask about the children (ages 15 and 12). They are currently at school. Have they been symptomatic? Children and elderly are more vulnerable to CO toxicity. The children's safety is an immediate concern.

Assess severity. Ask about confusion (his concentration has been poor, wife helped with work), chest pain (none), syncope (none), and neurological symptoms (none). These would indicate severe poisoning. His symptoms suggest moderate exposure. Ask about the flat's ventilation, boiler location, and when it was last serviced (3 years ago).

Do not get drawn into alternative diagnoses until you have excluded CO. The combination of non-specific neurological symptoms, multiple household members affected, improvement away from the source, and a faulty gas appliance is CO poisoning until proven otherwise.

Closing and safety netting

Communicate urgency clearly. 'Mr Walsh, based on your symptoms, your wife's symptoms, the timing with the boiler problem, and the fact that you both feel better outside, I am very concerned about carbon monoxide poisoning. We need to check your blood levels now.'

Immediate management: check carboxyhaemoglobin (COHb) level via venous or arterial blood gas (pulse oximetry is unreliable as it cannot distinguish COHb from oxyhaemoglobin). High-flow oxygen via non-rebreather mask at 15L/min (half-life of COHb reduces from 4 to 5 hours on room air to 60 to 90 minutes on high-flow O2). ECG (CO can cause cardiac ischaemia). Bloods including troponin.

Critical safety actions: the family must not return to the flat until the boiler has been inspected and certified safe by a Gas Safe registered engineer. The children must not go home after school. Contact the gas emergency line (0800 111 999). Notify environmental health if landlord is uncooperative. His wife needs assessment too. Safety net: if symptoms worsen (confusion, chest pain, collapse), this may need hyperbaric oxygen therapy.

How examiners mark this station

Examiners will focus on the thoroughness and structure of your history taking for carbon monoxide poisoning. Domain 1 (Data Gathering) carries the most weight: expect marks for systematic coverage of presenting complaint, red flags, PMH, medications, social and family history. Domain 2 (Clinical Management) requires a clear differential, appropriate investigations, and a safe management plan with safety netting. Domain 3 (Interpersonal Skills) is assessed throughout: genuine exploration of ICE, active listening, empathic responses, and clear communication without jargon.

Domain 1: Data Gathering, Technical and Assessment Skills (Primary focus)

Scores well: Asking about other household members (wife symptomatic). Asking about symptom variation with location (better outside). Connecting boiler timing with symptom onset. Asking about children's safety. Assessing severity indicators (confusion, chest pain, syncope). Asking about ventilation and boiler servicing history.

Costs marks: Not asking about wife's symptoms. Not asking about improvement away from home. Not asking about children. Accepting flu diagnosis without environmental assessment.

Domain 2: Clinical Management Skills (Primary focus)

Scores well: Requesting COHb on blood gas (not relying on SpO2). High-flow oxygen via non-rebreather mask. ECG and troponin. Correct safety actions: do not return to flat, contact gas emergency line, arrange children's safety. Knowledge of COHb half-life and oxygen therapy. Environmental health notification.

Costs marks: Relying on pulse oximetry. Not providing oxygen. Not addressing household safety. Not mentioning the children. Not arranging boiler inspection.

Domain 3: Interpersonal Skills (Throughout)

Scores well: Clear explanation of CO poisoning in lay terms. Addressing his anger at the landlord constructively. Practical advice about children's safety without causing panic. Reassurance about prognosis (most patients recover fully with treatment).

Costs marks: Causing unnecessary panic. Not explaining why the family cannot go home. Dismissing his concern about the landlord. Not addressing the children.

Common examiner feedback (and how to fix it)

Did not gather sufficient information to make an adequate assessment of the patient's condition

Fix: Use a consistent framework for every history. After covering the presenting complaint, systematically move through PMH, drug history, social history, family history, and ICE. Keep a mental checklist.

Did not identify the patient's problems and/or did not develop a management plan adequately

Fix: Reserve the final 2 minutes to summarise your findings, share your working diagnosis with the patient, and outline your investigation and management plan including safety netting.

Common mistakes in this station

  1. Diagnosing flu or viral illness without asking about household contacts. Two people in the same household developing the same symptoms at the same time, with improvement when leaving the house, is not viral illness. Candidates who accept the flu diagnosis without asking about Catherine's symptoms miss the environmental cause.
  2. Not asking about the children. Mr Walsh has two children (15 and 12) who are at school. They will go home after school to a flat with a CO leak if nobody intervenes. This is a safeguarding and safety issue that must be addressed immediately.
  3. Relying on pulse oximetry. In CO poisoning, SpO2 reads normally because the pulse oximeter cannot distinguish carboxyhaemoglobin from oxyhaemoglobin. Candidates who check SpO2 and are reassured by a normal reading demonstrate a dangerous knowledge gap. COHb must be measured directly on blood gas.

Resitting PLAB 2?

If you have previously struggled with history taking stations, focus on building a consistent systematic framework that you apply to every case. Practise structuring your history into clear phases (presenting complaint, systems review, PMH, social, ICE) so that even under pressure, you cover all domains. Many resitters lose marks not on knowledge but on organisation and time management.

Example opening

Good morning/afternoon, my name is Dr [Name], I'm one of the doctors here today. Could I confirm your name and date of birth please? Thank you. So, what's brought you in to see me today?

Frequently asked questions

How do I approach the consultation in this carbon monoxide poisoning station?

Carbon monoxide poisoning is one of the most commonly missed diagnoses because its symptoms mimic flu, migraine, and depression. The candidate must connect environmental clues (faulty appliance, poor ventilation, multiple household members affected) with non-specific symptoms. Mr Walsh is 46, presenting with 36 hours of headache, dizziness, and nausea.

What does a strong performance look like to the examiner in this station?

Strong performances show: Asking about other household members (wife symptomatic). Asking about symptom variation with location (better outside). Connecting boiler timing with symptom onset. Weak performances: Not asking about wife's symptoms. Not asking about improvement away from home. Not asking about children. Accepting flu diagnosis without environmental assessment.

What is the biggest pitfall in this carbon monoxide poisoning station?

Diagnosing flu or viral illness without asking about household contacts. Two people in the same household developing the same symptoms at the same time, with improvement when leaving the house, is not viral illness.

How should I prepare for carbon monoxide poisoning if I have never seen it in practice?

This station rewards process over personal experience. The skill being assessed: Asking about symptom improvement away from the source: improvement with open windows or when outside is a key diagnostic clue. Use the domain breakdown on this page to target your preparation, then practise the station aloud so your structure survives exam pressure.

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