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

Treatment of Carbon Monoxide Poisoning

Administer 100% normobaric oxygen immediately to any person suspected of carbon monoxide poisoning, and strongly consider hyperbaric oxygen therapy for patients with loss of consciousness, neurological deficits, cardiac ischemia, pregnancy, or severe metabolic acidosis. 1

Immediate Initial Management

All patients with suspected CO poisoning require 100% oxygen therapy without delay while awaiting diagnostic confirmation. 2, 1 This is the single most critical intervention, as oxygen accelerates carboxyhemoglobin (COHb) elimination from approximately 320 minutes on room air to 74 minutes on 100% normobaric oxygen. 2

• Administer high-flow 100% oxygen via non-rebreather mask or endotracheal tube if intubated 1
• Do not withhold oxygen while awaiting laboratory COHb levels 1
• Continue oxygen until COHb normalizes (<3%) AND symptoms resolve, typically requiring approximately 6 hours 2

Diagnostic Confirmation

• Measure COHb levels to confirm diagnosis, especially when considering hyperbaric oxygen therapy 1
• Obtain ECG and cardiac biomarkers in patients with severe poisoning to assess for myocardial ischemia 3
• Check for severe metabolic acidosis or elevated lactate in house fire victims, as this may indicate concomitant cyanide poisoning requiring hydroxocobalamin treatment 1
• Perform toxicology screening in intentional CO poisoning cases, as coingestions occur in up to 44% of cases 1

Important caveat: COHb levels correlate poorly with symptoms or prognosis and may be falsely low if several hours have elapsed since exposure. 1 Never use COHb levels alone to determine treatment decisions.

Hyperbaric Oxygen Therapy (HBOT) Indications

HBOT should be strongly considered for the following patients: 2, 1

• Loss of consciousness during or after exposure
• Any neurological deficits (altered mental status, focal findings, seizures)
• Cardiac ischemia or ECG changes
• Pregnancy with ANY symptoms of CO poisoning 1
• COHb levels >25% 2
• Severe metabolic acidosis 1

HBOT Protocol

• Treat at 3.0 atmospheres absolute (ATA) for the initial session 1
• HBOT reduces COHb half-life to approximately 20 minutes 1
• Persistently symptomatic patients may benefit from up to three treatments within 24 hours 1

Evidence for HBOT

The evidence for HBOT remains controversial despite multiple trials. 2 The highest quality double-blind randomized trial (Weaver 2002, n=152) demonstrated that three HBOT sessions at 3 ATA reduced cognitive sequelae at 6 weeks (25% vs 46%, NNT=4.8) with benefits persisting to 12 months. 2 However, other trials showed conflicting results, with the 2011 Annane study (n=385) showing no benefit for single HBOT session and paradoxically worse outcomes with two sessions versus one. 2

Despite methodological limitations in the literature, the potential for preventing devastating neurological sequelae justifies HBOT use in severe cases. 1

Special Populations and Considerations

Pregnant Patients

• All pregnant women with ANY symptoms of CO poisoning should receive HBOT 1
• Fetal hemoglobin has higher CO affinity and slower elimination than maternal hemoglobin

Cyanide Co-Poisoning

• Suspect in house fire victims with severe metabolic acidosis 1
• Treat empirically with hydroxocobalamin and 100% oxygen, with or without sodium thiosulfate 2

Intentional Poisoning

• Check blood alcohol levels if mental status changes are disproportionate 1
• Mandatory psychiatric follow-up required due to high subsequent suicide risk 1

What NOT to Do

• Do not add CO₂ to oxygen for spontaneously breathing patients, as individual ventilatory responses are unpredictable and may exacerbate acidosis in patients with ventilatory depression 2
• Do not withhold HBOT solely because a patient appears clinically stable 1
• Do not discharge patients without ensuring the CO source is identified and eliminated to prevent re-exposure 1

Follow-Up Care

All patients require clinical follow-up at 1-2 months post-exposure to assess for delayed neurological sequelae (DNS). 1 DNS occurs in approximately 10% of patients and may manifest 2-40 days after exposure. 4

• Screen for memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, and motor dysfunction 1
• Refer patients not recovered to baseline for formal neuropsychological evaluation 1
• Provide cardiology follow-up for patients with evidence of cardiac damage 1
• Recognize that CO poisoning survivors have increased long-term mortality compared to the general population 1