What is the treatment for carbon monoxide poisoning?

Treatment of Carbon Monoxide Poisoning

Immediate Oxygen Therapy

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

• Start oxygen therapy before obtaining carboxyhemoglobin (COHb) levels, as delay increases risk of disability and mortality 1
• Continue 100% normobaric oxygen until COHb normalizes to <3% AND the patient becomes asymptomatic, typically requiring approximately 6 hours 3, 1, 4
• Oxygen reduces COHb elimination half-life from 320 minutes (room air) to approximately 74 minutes 3, 1
• Do not rely on pulse oximetry—it shows falsely normal SpO2 readings even with COHb levels as high as 25% 1

Diagnostic Confirmation

• Obtain COHb level via CO-oximetry on venous or arterial blood to confirm diagnosis 1, 2
• Recognize that COHb levels correlate poorly with symptoms or prognosis and serve primarily to confirm exposure, not guide treatment intensity 1
• COHb may be normal or low if several hours have elapsed since exposure 2
• Obtain 12-lead ECG and continuous cardiac monitoring for all patients with moderate to severe poisoning 1

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

HBOT Protocol

• Treat at 2.5-3.0 atmospheres absolute pressure, which reduces COHb half-life to approximately 20 minutes 1, 2
• Administer up to three HBOT sessions within 24 hours for persistently symptomatic patients 3, 2
• The highest quality evidence (Weaver 2002 double-blind RCT) demonstrated that three HBOT sessions at 3.0 ATA reduced cognitive sequelae from 46% to 25% at 6 weeks, with benefits persisting to 12 months (NNT = 4.8) 3
• Initiate first HBOT session as soon as possible, ideally within 6 hours of exposure 4

Special Clinical Scenarios

Pregnancy

• HBOT is indicated for ALL pregnant women with any symptoms of CO poisoning, regardless of COHb level 2, 4
• Fetal CO elimination is slower than maternal, and fetal hemoglobin has higher CO affinity 3
• Extend normobaric oxygen therapy duration in pregnant patients due to slower fetal CO elimination 4

House Fire Exposure

• Suspect concomitant cyanide poisoning if 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
• Assess for severe metabolic acidosis or elevated lactate as indicators of cyanide toxicity 2

Intentional Poisoning

• Perform toxicology screening—coingestions occur 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 required due to high subsequent suicide risk 2

Common Pitfalls to Avoid

• Do not withhold oxygen therapy while awaiting laboratory confirmation 2
• Do not withhold HBOT solely because a patient appears clinically well—delayed neurological sequelae occur in 12-68% of poisoned patients 1
• Do not use standard pulse oximetry to assess oxygenation—it cannot distinguish oxyhemoglobin from carboxyhemoglobin 1
• Do not discharge patients without identifying and eliminating the CO source to prevent re-exposure 2
• Do not use fixed CO2-O2 mixtures to increase ventilation—this may exacerbate acidosis in patients with ventilatory depression 3

Follow-Up Care

• Schedule clinical follow-up at 4-6 weeks (1-2 months) after exposure to screen for delayed neurological sequelae 1, 2
• Delayed sequelae include memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, and motor dysfunction 2
• Refer patients not recovered to baseline functioning for formal neuropsychological evaluation 2
• Provide appropriate cardiology follow-up for patients with evidence of cardiac damage 2
• Long-term cognitive improvement can continue for 3-12 months post-poisoning, even in patients with structural brain injury 3
• Long-term mortality is increased up to 3-fold compared to unexposed individuals, suggesting possible residual brain injury even in "recovered" patients 1

Genetic Considerations

• Patients with apolipoprotein E (APOE) ε4 allele (present in 14-25% of population) may not derive the same benefit from HBOT as those without this allele 3, 2
• However, because most individuals do not carry the ε4 allele, HBOT should still be offered to all patients meeting clinical criteria 3