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

Treatment of Carbon Monoxide Poisoning

Immediately administer 100% oxygen via non-rebreather mask or endotracheal tube to all patients with suspected CO poisoning, even before obtaining carboxyhemoglobin levels, as this is critical to prevent disability and mortality. 1

Immediate Oxygen Therapy

• Do not delay oxygen therapy while waiting for laboratory confirmation – start 100% normobaric oxygen immediately upon suspicion of CO exposure 1, 2
• Oxygen reduces the carboxyhemoglobin (COHb) elimination half-life from 320 minutes on room air to approximately 74 minutes, preventing progression to delayed neurological sequelae that occur in 12-68% of poisoned patients 3, 1
• Continue 100% oxygen until COHb normalizes AND the patient becomes asymptomatic, typically requiring approximately 6 hours of treatment 1
• If intubation is required, deliver 100% FiO2 for 6-12 hours 4

Diagnostic Confirmation

• Obtain COHb level via CO-oximetry on venous or arterial blood to confirm diagnosis 1
• Standard pulse oximetry is unreliable – it will show 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, 5
• Negative COHb levels should not rule out CO poisoning if the history and symptoms are consistent, especially if several hours have elapsed since exposure 2, 5

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 (persistent mental status changes, focal findings)
• Ischemic cardiac changes on ECG
• Significant metabolic acidosis
• COHb level >25%
• Pregnancy with any symptoms of CO poisoning 2

HBOT Protocol Details

• Treat at 2.5-3.0 atmospheres absolute pressure, which reduces COHb half-life to approximately 20 minutes 3, 1
• Initiate HBOT within 6 hours if indicated 5
• Persistently symptomatic patients may benefit from up to three treatments 2
• Do not withhold HBOT solely because a patient appears to be doing well clinically – delayed neurological sequelae can still develop 2

Cardiac Monitoring and Assessment

• 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
• Patients with evidence of cardiac damage require appropriate cardiology follow-up 2

Special Considerations for Fire Victims

Suspect concomitant cyanide poisoning if the CO source is a house fire 1, 2

• Consider empiric hydroxocobalamin treatment if arterial pH <7.20 or plasma lactate ≥8-10 mmol/L 1, 4
• Adult dosage: 5g hydroxocobalamin (10g for cardiac arrest) 4
• Pediatric dosage: 70 mg/kg (maximum 5g) 4
• Hydroxocobalamin is preferred over methemoglobin-forming agents because it does not impair oxygen delivery 4

Intentional Poisoning Considerations

• Perform toxicology screening to assess for coingestions, present in up to 44% of intentional CO poisoning cases 2
• Check blood alcohol levels if mental status changes are disproportionate to COHb level 2
• Mandatory psychiatric follow-up is required due to high risk of subsequent suicide 2

Follow-Up Care

• Schedule follow-up in 4-6 weeks (or 1-2 months) to screen for delayed neurological sequelae in all accidental poisoning cases 1, 2
• Screen specifically for: memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, and motor dysfunction 2, 4
• Refer for formal neuropsychological evaluation if patient has not returned to baseline functioning 2
• Long-term mortality is increased up to 3-fold compared to unexposed individuals at median follow-up of 7.6 years, suggesting possible residual brain injury even in "recovered" patients 3, 1

Critical Pitfalls to Avoid

• Never withhold oxygen while awaiting laboratory confirmation – clinical suspicion alone warrants immediate treatment 1, 2
• Do not rely on COHb levels alone to determine treatment duration – continue oxygen until patient is asymptomatic 1, 5
• Ensure the CO exposure source is identified and eliminated before discharge to prevent re-exposure 2
• Do not assume normal pulse oximetry rules out CO poisoning 1
• Reevaluate for other differential diagnoses if no improvement occurs despite treatment 5