How should carbon monoxide poisoning be managed?

Treatment for Carbon Monoxide Poisoning

Immediately administer 100% oxygen via non-rebreather mask or endotracheal tube to all patients with suspected CO poisoning, even before obtaining laboratory confirmation, and continue until the patient is asymptomatic and carboxyhemoglobin normalizes. 1, 2

Immediate Oxygen Therapy

• Start 100% normobaric oxygen immediately upon suspicion—do not delay for laboratory confirmation, as this intervention is critical to prevent disability and death 1, 2
• Oxygen reduces the carboxyhemoglobin (COHb) elimination half-life from 320 minutes on room air to approximately 74 minutes 1, 2
• Continue oxygen therapy for approximately 6 hours minimum, or until COHb normalizes and symptoms resolve 1, 3
• Use a tight-fitting non-rebreather mask or endotracheal tube if the patient requires intubation 1

Diagnostic Confirmation

• Obtain COHb level via CO-oximetry on venous or arterial blood to confirm diagnosis 1
• Critical pitfall: Standard pulse oximetry is unreliable and shows falsely normal SpO2 readings even with COHb levels as high as 25% 1
• COHb levels correlate poorly with symptoms or prognosis and serve primarily to confirm exposure, not to guide treatment intensity 1, 2
• Negative COHb levels should not rule out CO poisoning if history and symptoms are consistent, especially if several hours have elapsed since exposure 2, 4

Hyperbaric Oxygen Therapy (HBOT) Indications

Consider HBOT for patients with any of the following high-risk features: 1, 2

• Loss of consciousness during or after exposure
• Neurological deficits
• Ischemic cardiac changes on ECG
• Significant metabolic acidosis
• COHb level >25%
• Pregnancy with any symptoms of CO poisoning
• Persistently symptomatic despite normobaric oxygen

HBOT protocol: 1, 2

• Administer at 2.5-3.0 atmospheres absolute pressure
• Reduces COHb half-life to approximately 20 minutes
• Persistently symptomatic patients may benefit from up to three treatments
• Initiate within 6 hours of exposure when possible 4, 5

Cardiac Monitoring

• Obtain 12-lead ECG and continuous cardiac monitoring for all patients with moderate to severe poisoning 1
• CO causes direct myocardial injury through tissue hypoxia and cellular damage, with cardiac complications possible even at relatively low COHb levels 1
• Measure cardiac biomarkers in patients with severe poisoning 5

Special Considerations

Cyanide co-poisoning: 1, 2

• Suspect concomitant cyanide poisoning if the CO source is a house fire
• Consider empiric cyanide treatment with hydroxocobalamin if arterial pH <7.20 or plasma lactate >10 mmol/L

Intentional poisoning: 2

• Perform toxicology screening to assess for coingestions (present in up to 44% of cases)
• Check blood alcohol levels if mental status changes are disproportionate
• Mandatory psychiatric follow-up due to high suicide risk

Pregnancy: 2

• HBOT is recommended for pregnant women with any symptoms of CO poisoning, regardless of COHb level

Source Elimination

• Ensure the CO exposure source is identified and eliminated before discharge to prevent re-exposure 2, 3

Follow-Up Care

• Schedule clinical follow-up in 1-2 months (4-6 weeks) after exposure to screen for delayed neurological sequelae (DNS) 1, 2, 3
• DNS occurs in 12-68% of poisoned patients and includes memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, motor dysfunction, and sleep disturbances 1, 2, 3
• Patients not recovered to baseline functioning require formal neuropsychological evaluation 2, 3
• Patients with evidence of cardiac damage require cardiology follow-up 2
• Long-term mortality is increased up to 3-fold compared to unexposed individuals, suggesting possible residual brain injury even in "recovered" patients 1

Common Pitfalls to Avoid

• Never withhold oxygen therapy while awaiting laboratory confirmation 1, 2, 3
• Never withhold HBOT solely because a patient appears clinically well 2
• Never rely on COHb levels alone to determine severity or need for HBOT 3, 4
• Never assume a normal neurological exam at discharge means no long-term sequelae 3
• Never skip the 1-2 month follow-up appointment, as this is when DNS becomes apparent 2, 3