What is the treatment for suspected carbon monoxide poisoning?

Treatment of Suspected Carbon Monoxide Poisoning

Immediately administer 100% high-flow oxygen via non-rebreather mask (10-15 L/min) to any patient with suspected carbon monoxide poisoning while awaiting diagnostic confirmation. 1

Immediate Oxygen Therapy

• Do not delay oxygen administration while waiting for carboxyhemoglobin (COHb) measurement – early treatment prevents disability and mortality 1
• Oxygen accelerates CO elimination, reducing the half-life from approximately 320 minutes on room air to about 74 minutes on 100% normobaric oxygen 1
• Continue 100% oxygen until COHb normalizes (<3% in nonsmokers, <10% in smokers) and symptoms resolve, typically requiring approximately 6 hours of treatment 1

Diagnostic Confirmation

• Obtain COHb level immediately via co-oximetry on venous or arterial blood 1
• Standard pulse oximetry cannot differentiate between oxyhemoglobin and carboxyhemoglobin – patients can show SpO2 readings >90% even with COHb levels as high as 25% 2, 1
• Fingertip pulse CO-oximetry can be used for initial screening but requires laboratory confirmation before making treatment decisions about hyperbaric oxygen 1
• COHb levels correlate poorly with symptoms or prognosis and may be normal or low if several hours have elapsed since exposure 1

Hyperbaric Oxygen Therapy (HBOT) Indications

Consider HBOT for patients meeting any of the following criteria: 1

• Loss of consciousness during or after exposure
• Neurological deficits (persistent or new-onset)
• Ischemic cardiac changes on ECG
• Significant metabolic acidosis
• COHb levels >25%
• Pregnancy with any symptoms of CO poisoning (fetal hemoglobin has higher affinity for CO than maternal hemoglobin) 1

HBOT Protocol

• Treatment at 3.0 atmospheres absolute (atm abs) is common practice 1
• HBOT reduces COHb elimination half-life to approximately 20 minutes 2, 1
• Persistently symptomatic patients may benefit from up to three treatments 1
• The role of HBOT remains controversial despite extensive literature attention – the American College of Emergency Physicians acknowledges ongoing debate about its superiority over normobaric oxygen for preventing long-term neurocognitive outcomes 2

Critical Assessments and Coingestions

• Assess for severe metabolic acidosis or elevated lactate in patients exposed to CO from house fires, as this may indicate concomitant cyanide poisoning requiring specific treatment with hydroxocobalamin 1
• For intentional CO poisoning, perform toxicology screening to assess for coingestions (present in up to 44% of cases) 1
• Check blood alcohol levels in intentional poisoning cases with disproportionate mental status changes 1
• Obtain 12-lead ECG and monitor for cardiac ischemia, as CO has direct toxic effects on myocardium 1

Source Elimination and Disposition

• Ensure the CO exposure source is identified and eliminated before discharging the patient to prevent re-exposure 1
• Obtain information about ambient CO levels from emergency personnel if available 1

Follow-up Care Requirements

• All patients with accidental CO poisoning require clinical follow-up 1-2 months after exposure to assess for delayed neurological sequelae (DNS), which can occur 2-21 days after exposure in 12-68% of poisoned patients 2, 1
• DNS manifestations include memory loss, impaired concentration or language, depression, anxiety, parkinsonism, vestibular problems, and motor dysfunction 2, 1
• Patients not recovered to baseline functioning should be referred for formal neuropsychological evaluation 1
• Patients with evidence of cardiac damage require appropriate cardiology follow-up 1
• Patients with intentional CO poisoning require mandatory psychiatric follow-up due to high risk of subsequent suicide 1

Common Pitfalls to Avoid

• Do not withhold HBOT solely because a patient appears to be doing well clinically – clinical severity does not correlate with COHb levels 1
• Do not rely on calculated oxygen saturation from older blood gas analyzers without CO-oximetry capabilities, as they may report falsely normal values despite high COHb levels 1
• Recognize that CO poisoning survivors have increased long-term mortality (up to 3-fold) compared to the general population at median follow-up of 7.6 years, suggesting possible residual brain injury 2, 1