Pharmacology, Toxicology and Addiction MedicineTier 2Approach to a presentation

Poisonings - carbon monoxide

Red flags

Reduced consciousness, chest pain (myocardial ischaemia from tissue hypoxia), and significant carboxyhaemoglobin elevation (>25%, or lower with cardiac/neurological symptoms) warrant urgent, aggressive treatment
Multiple simultaneous casualties from the same environment (house fire, faulty heating, enclosed space) strongly supports the diagnosis and should prompt evacuation and assessment of all exposed individuals, not just the most symptomatic

Differential by mechanism

Carbon monoxide poisoning (headache, nausea, confusion, classically with a source - faulty heater, house fire, enclosed space generator use)

Other causes of headache/confusion with environmental exposure (other toxic gas exposure, heat-related illness)

Primary cardiac or neurological event (mimicking CO poisoning's chest pain/confusion presentation, particularly if the environmental exposure history is unclear)

Focused history

Exposure source and setting (heating appliance, generator use, fire, enclosed/poorly ventilated space, vehicle exhaust), duration of exposure, symptoms in other people in the same environment (a strong diagnostic clue), symptom pattern (headache, nausea, confusion, chest pain)
Pre-existing cardiac or respiratory disease increases vulnerability to CO's tissue hypoxia effects at a given exposure level

Focused examination

Neurological status (confusion, reduced consciousness), cardiovascular assessment (chest pain, arrhythmia), and standard pulse oximetry is unreliable and can be falsely normal, since it cannot distinguish carboxyhaemoglobin from oxyhaemoglobin

Investigation strategy

Carboxyhaemoglobin level via co-oximetry (not standard pulse oximetry) confirms diagnosis and quantifies severity
ECG and troponin if cardiac symptoms/significant exposure, given CO-induced myocardial ischaemia risk
Consider cyanide co-exposure in house fire victims specifically, given combustion of synthetic materials can produce both toxins simultaneously

Management

High-flow 100% oxygen immediately, which substantially accelerates carboxyhaemoglobin dissociation compared with room air
Hyperbaric oxygen therapy considered for severe poisoning (significant neurological symptoms, loss of consciousness, pregnancy with significant exposure, very high carboxyhaemoglobin levels) given faster CO clearance and evidence for reduced delayed neurological sequelae in selected patients
Remove from the source and ensure the environment is assessed/ventilated to prevent further exposure to the patient or responders

Traps

Relying on pulse oximetry to exclude significant hypoxia - it does not detect carboxyhaemoglobin and will read falsely normal

Missing multiple-casualty clustering as a diagnostic clue, particularly in less classic presentations (headache/nausea misattributed to viral illness)

Discharging without addressing the exposure source - the patient will be re-exposed if the faulty appliance/ventilation issue isn't identified and fixed before return home

Talk track

"Carbon monoxide is an invisible, odourless gas that can build up from faulty heaters or fires, and it stops your blood carrying oxygen properly - that's why you're feeling confused and unwell. We're going to give you high-flow oxygen to help clear it from your system, and it's important we make sure wherever you were exposed is checked and made safe before you go back."

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