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

Treatment of Carbon Monoxide Exposure

Immediately administer 100% normobaric oxygen via tight-fitting non-rebreather mask to all patients with suspected CO poisoning while awaiting diagnostic confirmation, as this is the cornerstone of treatment and reduces carboxyhemoglobin half-life from 320 minutes to approximately 74 minutes. 1

Immediate Initial Management

• Remove the patient from the CO source and begin 100% oxygen immediately using a tight-fitting mask, continuing for at least 6 hours, without waiting for laboratory confirmation 1, 2
• Obtain arterial blood gas and carboxyhemoglobin (COHb) levels for diagnostic confirmation, but do not delay oxygen therapy while awaiting results 1
• Recognize that COHb levels may be normal or low if several hours have elapsed since exposure, and negative levels should not rule out CO poisoning if history and symptoms are consistent 1, 3
• COHb levels correlate poorly with symptoms or prognosis and should not guide treatment decisions 1, 4

Assessment for Severe Complications

Metabolic Acidosis and Cyanide Poisoning

• Check arterial blood gas for severe metabolic acidosis (pH <7.20) or plasma lactate ≥10 mmol/L in patients exposed to CO from house fires 5, 1
• If severe metabolic acidosis is present with pH <7.20 or lactate ≥10 mmol/L in house fire victims, administer empiric hydroxocobalamin for presumed concomitant cyanide poisoning, as mortality reaches 30-50% in this scenario 5, 1

Intentional Poisoning

• Perform toxicology screening in all cases of suspected intentional CO poisoning, as 44% have coingestions (66% of which involve ethanol) 5, 1
• Check blood alcohol level at minimum if mental status changes seem disproportionate to reported CO exposure 5, 1

Hyperbaric Oxygen Therapy (HBOT) Decision-Making

HBOT is a therapeutic option but cannot be mandated, as evidence remains conflicting with two Class II studies showing opposite results. 5

Indications to Consider HBOT (if available within 6 hours):

• Loss of consciousness during or after exposure 1, 3
• Neurological deficits (memory disturbance, confusion, focal findings) 1
• Ischemic cardiac changes or cardiovascular instability 1, 4
• Significant metabolic acidosis 1
• COHb levels >25% 1
• Any pregnant woman with symptoms of CO poisoning 1
• Persistent symptoms despite normobaric oxygen therapy 1

HBOT Protocol:

• Treat at 3.0 atmospheres absolute (atm abs) for the first treatment 1
• Persistently symptomatic patients may benefit from up to three treatments 1
• HBOT reduces COHb half-life to approximately 20 minutes 1
• Initiate HBOT within 6 hours if indicated 3

Evidence Limitations:

• The American College of Emergency Physicians provides only Level C recommendations, noting that no clinical variables, including COHb levels, reliably identify which patients will benefit most from HBOT 5
• Studies show conflicting results, with one Class II study supporting HBOT and another Class II study showing no benefit 5

Special Patient Populations

Pregnant Patients:

• HBOT is recommended for any pregnant woman with symptoms of CO poisoning, regardless of COHb level 1

Patients with Burns:

• Evaluate HBOT case-by-case considering patient stability, burn severity, and availability of specialized equipment 1

Cardiac Involvement:

• Patients with ischemic heart disease may experience chest pain and decreased exercise tolerance at COHb levels as low as 1-9% 2
• Refer all patients with evidence of cardiac damage for cardiology follow-up 5, 1

Mandatory Follow-Up Care

All Accidental CO Poisoning Patients:

• Schedule clinical follow-up at 1-2 months post-exposure to assess for delayed neurological sequelae (DNS), which can develop 2-40 days after apparent recovery 5, 1, 2
• Have a family member accompany the patient to provide observations 5, 1
• Screen for memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, and motor dysfunction 5, 1
• Refer for formal neuropsychological evaluation if not recovered to baseline functioning 5, 1
• Recognize that 75% of patients with DNS recover within 1 year 2

Intentional CO Poisoning Patients:

• Mandatory psychiatric follow-up is required due to extremely high risk of subsequent suicide completion 5, 1
• Recruit family members to ensure compliance with psychiatric care 5

Critical Pitfalls to Avoid

• Never withhold oxygen therapy while awaiting laboratory confirmation of CO poisoning 1
• Do not rely on COHb levels to determine severity or guide treatment, as they correlate poorly with outcomes 1, 4
• Do not assume a patient is safe for discharge based on clinical improvement alone, as delayed neurological sequelae can occur after apparent recovery 5, 1
• Do not withhold HBOT solely because a patient appears clinically well 1
• Ensure the CO source is identified and eliminated before discharge to prevent re-exposure 1
• Remember that pulse oximetry will be normal in CO poisoning despite tissue hypoxia 2
• Recognize that survivors have increased long-term mortality compared to the general population, suggesting residual brain injury 5, 1