What is the treatment for carbon monoxide poisoning?

Treatment of Carbon Monoxide Poisoning

Immediate Oxygen Therapy

Administer 100% normobaric oxygen immediately via non-rebreather mask or endotracheal tube to all patients with suspected CO poisoning, without waiting for laboratory confirmation. 1, 2

• Begin oxygen therapy at the highest possible flow rate using a tight-fitting non-rebreather mask to achieve maximum oxygen delivery 3, 4
• Continue 100% oxygen until carboxyhemoglobin (COHb) normalizes to <3% AND the patient becomes completely asymptomatic, typically requiring approximately 6 hours 5, 1, 3
• Oxygen reduces the COHb elimination half-life from 320 minutes on room air to approximately 74 minutes on 100% normobaric oxygen 5, 1, 2
• Do not delay oxygen therapy while awaiting COHb levels, as immediate treatment is critical to prevent disability and mortality 1, 2

Diagnostic Confirmation

• Obtain COHb level via CO-oximetry on venous or arterial blood to confirm diagnosis 1, 2
• Standard pulse oximetry is unreliable and will show falsely normal SpO2 readings even with COHb levels as high as 25% 1
• Recognize that COHb levels correlate poorly with symptoms, severity, or prognosis and serve primarily to confirm exposure rather than guide treatment intensity 1, 6, 4
• COHb may be normal or low if several hours have elapsed since exposure, so do not exclude the diagnosis based on low levels alone 2

Hyperbaric Oxygen Therapy Indications

Consider hyperbaric oxygen therapy (HBOT) at 2.5-3.0 atmospheres absolute for patients with ANY of the following high-risk features: 5, 1, 2, 3

• Loss of consciousness at any time during or after exposure
• Persistent neurological deficits (confusion, memory impairment, focal findings)
• Ischemic cardiac changes on ECG or evidence of myocardial injury
• Significant metabolic acidosis
• COHb level >25%
• Pregnancy with any symptoms of CO poisoning (HBOT is indicated regardless of COHb level or symptom severity) 2, 3

The highest quality evidence supporting HBOT comes from the 2002 Weaver study, which demonstrated that three HBOT sessions at 3.0 atmospheres within 24 hours reduced cognitive sequelae from 46% to 25% at 6 weeks, with benefits persisting to 12 months (NNT = 4.8). 5

• HBOT reduces COHb elimination half-life to approximately 20 minutes 5, 1, 2
• Perform the first HBOT session as soon as possible, ideally within 6 hours of exposure 3
• Up to three HBOT treatments may be administered for persistently symptomatic patients 2
• Do not withhold HBOT solely because a patient appears clinically stable, as delayed neurological sequelae can still develop 2

HBOT Controversy and Clinical Decision-Making

While multiple studies have compared HBOT to normobaric oxygen with mixed results, the 2012 American Thoracic Society guidelines identify the Weaver 2002 study as the best-designed trial that most closely addresses practical patient management 5. The 2011 Annane study showed conflicting results, with one trial showing no benefit and another showing worse outcomes with two HBOT sessions versus one 5. Given this evidence, prioritize HBOT for patients with the high-risk features listed above, recognizing that the benefit is most clearly established for preventing long-term cognitive sequelae rather than immediate symptom resolution. 5

Cardiac Monitoring and Assessment

• Obtain 12-lead ECG and initiate 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 ischemic heart disease may experience chest pain and decreased exercise tolerance at COHb levels as low as 1-9% 4

Special Populations and Considerations

Pregnant Patients

• Administer HBOT to all pregnant women with any symptoms of CO poisoning, regardless of COHb level or maternal symptom severity 2, 3
• Extend normobaric oxygen therapy duration in pregnant patients due to slower fetal CO elimination 3
• CO can cause fetal demise, limb and vertebral abnormalities, and brain injury even when the mother appears mildly affected 5

Fire Victims

• Suspect concomitant cyanide poisoning if the CO source is a house fire 1, 2
• Consider empiric cyanide treatment with hydroxocobalamin if arterial pH <7.20 or plasma lactate >10 mmol/L 1, 2

Intentional Poisoning

• 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 clinical follow-up at 4-6 weeks (1-2 months) after exposure to screen for delayed neurological sequelae (DNS) 1, 2
• DNS occurs in 12-68% of poisoned patients and may develop after a lucid interval of 2-40 days 5, 4
• Screen for memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, motor dysfunction, and parkinsonism 2, 4
• Refer patients not recovered to baseline functioning for formal neuropsychological evaluation 2
• Patients with cardiac damage require cardiology follow-up 2
• Recognize that long-term mortality is increased up to 3-fold compared to unexposed individuals, suggesting possible residual brain injury even in "recovered" patients 1

Critical Pitfalls to Avoid

• Never withhold oxygen therapy while awaiting laboratory confirmation 1, 2
• Do not rely on pulse oximetry, which will be falsely reassuring 1
• Do not use COHb levels alone to determine treatment intensity or predict outcomes 1, 6
• Ensure the CO exposure source is identified and eliminated before discharge to prevent re-exposure 2
• Do not assume patients are "fine" based on initial clinical appearance, as DNS can develop weeks later 2, 4

Genetic Considerations

• Patients with apolipoprotein E (APOE) ε4 allele (present in 14-25% of the population) may not derive the same benefit from HBOT for preventing cognitive sequelae 5, 2
• However, because most individuals do not carry the ε4 allele and genotyping is not immediately available, HBOT should still be offered to all patients meeting clinical criteria 5