Carbon Monoxide Poisoning

Whole household ill together, better away from home = CO until proven otherwise. SpO₂ and PaO₂ are both falsely normal — only co-oximetry (COHb) detects it. Treat with 15L via tight non-rebreather regardless of saturations. LOC, neuro signs, cardiac…

CO Poisoning Pathway (TOXBASE)

The pathway

1 · Suspect it

Multiple occupants/pets affected together
Better away from home, worse on return
Faulty boiler, blocked flue, indoor BBQ
'Cherry-red' skin is rare and unreliable

2 · Don't trust the sats

SpO₂ falsely normal — oximetry can't distinguish COHb
PaO₂ also normal
Send COHb on co-oximetry (venous adequate)

3 · Interpret COHb

Non-smokers <3%, smokers ≤10%
Falls quickly once away from source/on O₂
Correlates poorly with severity — treat the patient

4 · High-flow oxygen

15L tight-fitting non-rebreather regardless of SpO₂
Half-life: ~5h air → ~1h on 100% O₂ → ~20 min HBO
Continue until asymptomatic and COHb <3%

5 · Assess end-organs

ECG + troponin — myocardial ischaemia
Neurological examination
Pregnancy test — fetal Hb binds CO avidly, treat longer
Lactate (consider cyanide if fire)

6 · Hyperbaric discussion

LOC, neuro deficit, cardiac involvement, pregnancy, COHb >20–25%
NPIS / TOXBASE 0344 892 0111

7 · Safety & follow-up

Delayed neuropsychiatric sequelae 3–240 days — warn and follow up
Gas Safe engineer must clear the property
Notify environmental health; advise CO alarms; check neighbours

Drugs

Drug	Dose	Route	Notes
Oxygen	15L via tight non-rebreather	INH	The treatment — give regardless of SpO₂. Continue until asymptomatic + COHb <3%.
Hydroxocobalamin	5g	IV	If concurrent cyanide exposure suspected (fire, high lactate).

When to escalate

Loss of consciousness or neurological signs — HBO discussion with NPIS,Myocardial ischaemia or arrhythmia on ECG/troponin,Pregnancy — treat longer, involve obstetrics, low HBO threshold,COHb >20–25% or persistent symptoms despite oxygen

Reference: TOXBASE / NPIS (0344 892 0111) / UKHSA carbon monoxide guidance

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