What is the treatment for carbon monoxide (CO) poisoning?

Treatment of Carbon Monoxide Poisoning

Immediately administer 100% normobaric oxygen to any patient with suspected carbon monoxide poisoning while awaiting diagnostic confirmation, and strongly consider hyperbaric oxygen therapy for patients with loss of consciousness, neurological deficits, cardiac ischemia, or pregnancy. 1

Immediate Management

All patients require high-flow 100% oxygen therapy as the cornerstone of treatment:

• Administer 100% normobaric oxygen via tight-fitting non-rebreather mask immediately upon suspicion of CO poisoning, before laboratory confirmation 1
• This reduces carboxyhemoglobin (COHb) elimination half-life from 320 minutes on room air to approximately 74 minutes 2
• Continue oxygen therapy until COHb normalizes (<3%) and presenting symptoms resolve, typically requiring about 6 hours 2
• Do not withhold oxygen while awaiting laboratory confirmation 1

Critical diagnostic steps:

• Confirm diagnosis with laboratory measurement of COHb levels, especially when considering hyperbaric oxygen therapy 1
• Assess for severe metabolic acidosis or elevated lactate in fire victims, as this indicates possible concomitant cyanide poisoning requiring hydroxocobalamin treatment 1
• Perform toxicology screening for intentional poisonings, as coingestions occur in up to 44% of cases 1
• Check blood alcohol levels if mental status changes seem disproportionate to CO exposure 1

Hyperbaric Oxygen Therapy (HBOT) Indications

HBOT should be strongly considered for the following patients, as it reduces cognitive sequelae and accelerates COHb elimination to approximately 20 minutes: 1

• Any loss of consciousness during or after exposure 1
• Neurological deficits of any kind 1
• Ischemic cardiac changes or cardiovascular instability 1, 3
• Significant metabolic acidosis 1
• COHb levels >25% 1
• All pregnant women with any symptoms of CO poisoning 1
• Persistent mental or neurologic deficits despite initial oxygen therapy 3

HBOT protocol:

• Treat at 3.0 atmospheres absolute (atm abs) for initial treatment 1
• Persistently symptomatic patients may benefit from up to three treatments within 24 hours 1
• The Weaver study (2002) demonstrated HBOT reduced cognitive sequelae from 46% to 25% at 6 weeks (NNT = 4.8), with benefits persisting to 12 months 2

Important caveat: While multiple studies comparing HBOT to normobaric oxygen show mixed results, the highest quality double-blind randomized trial by Weaver demonstrated significant reduction in long-term cognitive sequelae 2. Most other studies had significant methodological limitations including inadequate follow-up, clinically irrelevant outcomes, or poor study design 2.

Special Clinical Scenarios

Fire victims with suspected cyanide poisoning:

• Treat empirically for cyanide poisoning with hydroxocobalamin if severe metabolic acidosis is present 1
• This combination of CO and cyanide toxicity is common in structure fires 1

Burn patients:

• Evaluate HBOT case-by-case considering patient stability, burn severity, and availability of specialized equipment 1
• Do not automatically exclude these patients from HBOT 1

Intentional poisoning:

• Mandatory psychiatric follow-up due to high subsequent suicide risk 1
• Screen for coingestions and check blood alcohol levels 1

Critical Pitfalls to Avoid

Do not rely on COHb levels alone for clinical decision-making:

• COHb levels correlate poorly with symptoms, severity, or prognosis 1, 3, 4
• Levels may be normal or low if several hours elapsed since exposure 1
• Clinical presentation and history of loss of consciousness are more important than absolute COHb values 4

Do not withhold HBOT based solely on clinical appearance:

• Patients appearing clinically well may still develop delayed neurological sequelae 1
• The decision for HBOT should be based on established criteria, not subjective clinical impression 1

Do not use CO2-oxygen mixtures:

• Adding CO2 to oxygen for spontaneously breathing patients is unreliable and risky 2
• Individual ventilatory responses vary markedly, and CO2 may exacerbate acidosis in patients with ventilatory depression 2

Mandatory Follow-Up Care

All patients require structured follow-up regardless of initial treatment:

• Clinical follow-up at 1-2 months post-exposure to assess for delayed neurological sequelae 1
• Screen specifically for memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, and motor dysfunction 1
• Refer patients not recovered to baseline for formal neuropsychological evaluation 1
• Cardiology follow-up for patients with evidence of cardiac damage 1
• Ensure CO source is identified and eliminated before discharge to prevent re-exposure 1

Recognize long-term implications:

• Delayed neurological sequelae occur in 12-68% of poisoned patients, typically appearing 2-21 days post-exposure 2
• CO poisoning survivors have up to 3-fold increased long-term mortality compared to matched controls 2, 1
• Neurologic sequelae can persist for 3-12 months or result in lifelong disability 2, 1