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

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. 1, 2

Immediate Oxygen Therapy

• Do not delay oxygen therapy while waiting for laboratory confirmation – this is the single most critical intervention to prevent disability and death 1, 2
• Continue 100% normobaric oxygen until COHb normalizes and the patient becomes asymptomatic, typically requiring approximately 6 hours of treatment 1, 3
• Oxygen reduces the COHb elimination half-life from 320 minutes on room air to approximately 74 minutes 1, 2
• In pregnant patients, extend oxygen therapy beyond 6 hours due to slower fetal CO elimination 3

Diagnostic Confirmation

• Obtain carboxyhemoglobin level via CO-oximetry on venous or arterial blood to confirm diagnosis 1, 2
• 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, 2
• COHb levels may be normal or low if several hours have elapsed since exposure 2

Hyperbaric Oxygen Therapy Indications

Consider HBO therapy for patients with ANY of the following high-risk features: 1, 2, 3

• Loss of consciousness (transient or ongoing)
• Altered mental status or neurological deficits
• Ischemic cardiac changes on ECG
• Significant metabolic acidosis
• COHb level >25%
• Pregnancy with ANY symptoms of CO poisoning (regardless of COHb level)

HBO Technical Details

• HBO at 2.5-3.0 atmospheres absolute pressure reduces COHb half-life to approximately 20 minutes 4, 1, 2
• The first HBOT session should be performed as soon as possible, ideally within 6 hours of exposure 3
• Persistently symptomatic patients may benefit from up to three treatments 2
• HBO complications are rare (0.10% major complications), with anxiety and middle ear barotrauma being most common (0-8% of cases) 4

Pregnancy-Specific Considerations

• HBO is always indicated in pregnant women with CO poisoning, regardless of COHb concentration or clinical presentation 3
• CO can cause fetal demise, limb and vertebral abnormalities, and brain injury even when the mother appears mildly affected 4
• The fetus may be more severely poisoned than the mother due to higher fetal hemoglobin affinity for CO 4

Cardiac and Metabolic 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
• Check for severe metabolic acidosis or elevated lactate (pH <7.20 or lactate >10 mmol/L) in patients exposed to CO from house fires 1, 2

Concomitant Cyanide Poisoning

• Suspect cyanide poisoning if the CO source is a house fire and severe metabolic acidosis is present 1, 2
• Consider empiric cyanide treatment with hydroxocobalamin if arterial pH <7.20 or plasma lactate >10 mmol/L 1, 2
• Perform toxicology screening in intentional CO poisoning cases, as coingestions occur in up to 44% of cases 2

Follow-Up Care

• Schedule follow-up in 4-6 weeks (1-2 months) to screen for delayed neurological sequelae in accidental poisoning cases 1, 2
• Delayed neurological sequelae occur in 12-68% of poisoned patients and may appear after a latent period of 2-21 days 4
• Symptoms include memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, motor dysfunction, and parkinsonism 4, 2
• Patients not recovered to baseline functioning should be referred for formal neuropsychological evaluation 2
• Patients with evidence of cardiac damage require cardiology follow-up 2
• Patients with intentional CO poisoning require mandatory psychiatric follow-up due to high risk of subsequent suicide 2

Critical Pitfalls to Avoid

• Never withhold oxygen therapy while awaiting laboratory confirmation 1, 2
• Never withhold HBO solely because a patient appears to be doing well clinically – delayed neurological sequelae can still develop 2
• Do not rely on COHb levels alone to determine treatment – clinical features are more important 1, 2
• Ensure the CO exposure source is identified and eliminated before discharge to prevent re-exposure 2
• Recognize that CO poisoning survivors have increased long-term mortality (up to 3-fold) compared to unexposed individuals, suggesting possible residual brain injury even in "recovered" patients 1, 2