What is the treatment for a patient with elevated carbon monoxide (CO) levels?

Treatment of Elevated Carbon Monoxide Levels

Immediately administer 100% oxygen via non-rebreather mask or endotracheal tube to any patient with suspected or confirmed CO poisoning, without waiting for laboratory confirmation. 1

Immediate Oxygen Therapy

• Start 100% normobaric oxygen immediately upon suspicion of CO poisoning, even before obtaining carboxyhemoglobin (COHb) levels, as this is the front-line treatment that prevents disability and mortality 1, 2
• Use high-flow oxygen delivery via tight-fitting non-rebreather mask or endotracheal tube if the patient requires intubation 1, 2
• Continue oxygen therapy until COHb normalizes to <3% AND the patient's symptoms resolve, typically requiring approximately 6 hours of treatment 1, 2
• Oxygen reduces COHb elimination half-life from 320 minutes on room air to approximately 74 minutes on 100% oxygen 1, 2, 3

Important caveat: No clinical trials have actually demonstrated superior efficacy of 100% normobaric oxygen over room air, but it remains standard of care based on physiologic rationale 1

Diagnostic Confirmation

• Obtain COHb level via CO-oximetry on venous or arterial blood using laboratory spectrophotometry to confirm diagnosis 1, 2
• Do not rely on standard pulse oximetry, as it will show falsely normal SpO2 readings (>90%) even with COHb levels as high as 25-50% 1, 2
• Recognize that COHb levels may be low or normal if several hours have elapsed since exposure or if the patient received oxygen before measurement 1, 3
• COHb levels do not predict symptoms or outcomes and serve only to confirm exposure, not to guide treatment intensity 1, 2

Hyperbaric Oxygen Therapy (HBOT) Indications

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

• Loss of consciousness during or after exposure
• Neurological deficits on examination
• Ischemic cardiac changes on ECG
• Significant metabolic acidosis
• COHb level >25%
• Pregnancy with any symptoms of CO poisoning
• Persistent symptoms despite normobaric oxygen therapy

HBOT Protocol

• Treat at 2.5-3.0 atmospheres absolute pressure, which reduces COHb half-life to approximately 20 minutes 2, 3
• Persistently symptomatic patients may benefit from up to three HBOT treatments 3
• The evidence for HBOT preventing delayed neurological sequelae remains controversial, with multiple studies showing methodological limitations including inadequate randomization, impractical normobaric oxygen durations, and poor follow-up rates 1

Critical Supportive Measures

• Obtain 12-lead ECG and initiate continuous cardiac monitoring for all patients with moderate to severe poisoning, as CO causes direct myocardial injury even at relatively low COHb levels 2
• Suspect concomitant cyanide poisoning if the CO source is a house fire, particularly if arterial pH <7.20 or plasma lactate >10 mmol/L, and consider empiric hydroxocobalamin treatment 2, 3
• For intentional CO poisoning, perform toxicology screening as coingestions occur in up to 44% of cases 3
• Check blood alcohol levels in intentional poisoning with disproportionate mental status changes 3

Source Identification and Prevention

• Identify and eliminate the CO exposure source before discharge to prevent re-exposure 1, 3
• Emergency personnel should measure ambient CO levels when possible, though these may be lower than actual exposure levels due to ventilation 1

Follow-Up Care

• Schedule clinical follow-up at 1-2 months (4-6 weeks) after exposure to screen for delayed neurological sequelae, which occur in 12-68% of poisoned patients 2, 3
• Assess for memory disturbance, depression, anxiety, calculation difficulties, vestibular problems, motor dysfunction, and sleep disturbances 3
• Refer patients not recovered to baseline for formal neuropsychological evaluation 3
• Provide cardiology follow-up for patients with evidence of cardiac damage 3
• Mandatory psychiatric follow-up for intentional CO poisoning due to high subsequent suicide risk 3
• Recognize that long-term mortality is increased up to 3-fold compared to unexposed individuals, suggesting possible residual brain injury even in "recovered" patients 2

Common Pitfalls to Avoid

• Do not delay oxygen therapy while awaiting laboratory confirmation 2, 3
• Do not withhold HBOT solely because a patient appears clinically well 3
• Do not use CO2-O2 mixtures to hasten COHb removal, as individual ventilatory responses vary markedly and may exacerbate acidosis in patients with ventilatory depression 1
• Do not repeat COHb levels if the patient has been compliant with high-flow oxygen for approximately 6 hours and feels well 1