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

Management of Carbon Monoxide Poisoning

Immediate Treatment

Administer 100% oxygen immediately via non-rebreather mask or endotracheal tube to all patients with suspected CO poisoning, even before obtaining carboxyhemoglobin levels. 1, 2

• Do not delay oxygen therapy while waiting for laboratory confirmation—this is critical to prevent disability and mortality 1, 2
• Continue 100% normobaric oxygen until COHb normalizes (<3%) and the patient becomes asymptomatic, typically requiring approximately 6 hours of treatment 1
• Oxygen reduces the COHb elimination half-life from 320 minutes on room air to approximately 74 minutes 1, 2

Diagnostic Confirmation

• Obtain carboxyhemoglobin level via CO-oximetry on venous or arterial blood to confirm the diagnosis 2, 3
• Standard pulse oximetry is unreliable and will show falsely normal SpO2 readings (>90%) even with COHb levels as high as 25% 2, 3
• Recognize that COHb levels correlate poorly with symptoms or prognosis and serve primarily to confirm exposure, not to guide treatment intensity 1, 3
• PaO2 typically remains normal because CO poisoning causes "anaemic hypoxia" where oxygen content is reduced despite normal dissolved oxygen in plasma 2

Hyperbaric Oxygen Therapy Indications

Consider HBO therapy for patients with any of the following high-risk features: 1

• Loss of consciousness at any point 1
• Ischemic cardiac changes on ECG 1
• Neurological deficits on examination 1
• Significant metabolic acidosis 1
• COHb level >25% 1
• Pregnancy with significant CO exposure 3

HBO Protocol

• The optimal HBO protocol remains uncertain, but retreatment of persistently symptomatic patients up to a maximum of 3 treatments is recommended 1
• HBO at 2.5-3.0 atmospheres absolute pressure reduces COHb half-life to approximately 20 minutes 1, 3
• More mildly poisoned patients may be treated with normobaric oxygen at the managing physician's discretion 1

Special Considerations

Cardiac Monitoring

• Obtain 12-lead ECG and continuous cardiac monitoring for all patients with moderate to severe poisoning 2
• CO causes direct myocardial injury through tissue hypoxia and cellular damage, with cardiac complications possible even at relatively low COHb levels 2

Cyanide Co-Poisoning

• Suspect concomitant cyanide poisoning if the CO source is a house fire 1
• Consider empiric cyanide treatment if arterial pH <7.20 or plasma lactate >10 mmol/L 1

Intentional Poisoning

• Screen for co-ingestion of other toxins with toxicological testing 1
• Arrange mandatory psychiatric follow-up due to high rates of subsequent completed suicide 1

Pregnant Patients

• Provide special attention as fetal hemoglobin has higher affinity for CO than maternal hemoglobin, placing the fetus at greater risk 2
• Consider HBO therapy more liberally in pregnant patients 3

Alternative Oxygen Delivery

• Non-invasive CPAP ventilation with 100% FiO2 may accelerate CO elimination compared to reservoir face mask, though this requires further validation 4
• Consider CPAP for patients with pulmonary edema from CO-induced cardiac dysfunction 2

Source Identification and Prevention

• Do not discharge the patient without identifying and eliminating the CO source to prevent re-exposure 2, 3
• Obtain information about ambient CO levels from emergency personnel if available 2

Follow-Up Care

• Schedule follow-up in 4-6 weeks to screen for delayed cognitive sequelae in accidental poisoning cases 1, 3
• Delayed neurologic sequelae can occur 2-40 days after exposure with diffuse demyelination, memory loss, behavioral changes, and parkinsonian features 5
• Approximately 75% of patients with delayed neurologic sequelae recover within 1 year 5

Common Pitfalls to Avoid

• Never rely on pulse oximetry alone—it cannot differentiate carboxyhemoglobin from oxyhemoglobin 2, 3
• Do not use COHb levels to determine treatment duration or predict outcomes—clinical assessment is paramount 1, 3
• Do not overlook cardiac complications, which can occur even with relatively low COHb levels 2
• Do not misdiagnose as viral illness—CO poisoning presents with nonspecific symptoms (headache, dizziness, nausea, confusion, fatigue) that mimic flu 1, 6