What is the treatment for carbon monoxide poisoning?

Treatment of Carbon Monoxide Poisoning

Immediately administer 100% oxygen via non-rebreather mask or endotracheal tube to all patients with suspected carbon monoxide poisoning, even before obtaining laboratory confirmation. 1, 2

Immediate Management

• Start 100% normobaric oxygen immediately upon suspicion of CO poisoning—do not delay for laboratory confirmation, as this is critical to prevent disability and mortality 1, 2
• Oxygen reduces carboxyhemoglobin (COHb) elimination half-life from approximately 320 minutes on room air to about 74 minutes 1, 2
• Continue oxygen therapy until COHb normalizes and the patient becomes asymptomatic, typically requiring approximately 6 hours of treatment 2
• Standard pulse oximetry is unreliable and will show falsely normal SpO2 readings even with COHb levels as high as 25%—do not rely on it 2

Diagnostic Confirmation

• Obtain COHb level via CO-oximetry on venous or arterial blood to confirm exposure 2
• Important caveat: COHb levels correlate poorly with symptoms or prognosis and may be normal or low if several hours have elapsed since exposure 1, 2
• COHb levels serve primarily to confirm exposure, not to guide treatment intensity or predict outcomes 2, 3
• Obtain 12-lead ECG and continuous cardiac monitoring for all patients with moderate to severe poisoning 2

Hyperbaric Oxygen Therapy (HBOT) Indications

Consider HBOT for patients with any of the following high-risk features: 4, 1, 2

• Loss of consciousness during or after exposure
• Neurological deficits (persistent confusion, memory problems, focal findings)
• Ischemic cardiac changes on ECG or cardiovascular instability
• Significant metabolic acidosis
• COHb level >25%
• Pregnancy with any symptoms of CO poisoning (special consideration per ACOG) 1

HBOT Protocol

• Treatment at 2.5-3.0 atmospheres absolute (atm abs) is standard practice 1, 2
• HBOT reduces COHb elimination half-life to approximately 20 minutes 1, 2
• Persistently symptomatic patients may benefit from up to three treatments 1
• Timing is critical: If HBOT is indicated, initiate within 6 hours of exposure 3

Evidence Considerations for HBOT

The evidence for HBOT remains mixed but favors its use in severe cases. The American Heart Association notes that some studies suggest improved neurological outcomes in patients with severe toxicity, while other studies found no difference 4. A systematic review concluded that improvement in neurologically intact survival is "possible but unproven" 4. However, because HBOT has a low incidence of severe side effects and may prevent delayed neurological sequelae (which occur in 12-68% of poisoned patients), it should be offered to patients meeting high-risk criteria 4, 1, 2.

The decision to transfer patients to a hyperbaric facility following resuscitation should weigh the risk of transport against possible improvement in outcomes 4.

Special Considerations

Cyanide Co-Poisoning

• Suspect concomitant cyanide poisoning if the CO source is a house fire 1, 2
• Check for severe metabolic acidosis (arterial pH <7.20) or elevated lactate (>10 mmol/L) 1, 2
• Consider empiric cyanide treatment with hydroxocobalamin if these criteria are met 1, 2

Intentional Poisoning

• Perform toxicology screening to assess for coingestions, present in up to 44% of intentional CO poisoning cases 1
• Check blood alcohol levels if mental status changes are disproportionate to COHb level 1
• Mandatory psychiatric follow-up is required due to high risk of subsequent suicide 1

Cardiac Arrest

• Follow standard BLS and ACLS protocols for patients in cardiac arrest from CO poisoning 4
• Prognosis is poor: Very few patients who develop cardiac arrest from CO poisoning survive to hospital discharge, regardless of treatment administered 4

Follow-Up Care

All patients with accidental CO poisoning require clinical follow-up 1-2 months after exposure to assess for delayed neurological sequelae (DNS), which can develop after a lucid interval of 2-40 days 1, 5

Screen for DNS symptoms:

• Memory disturbance and calculation difficulties
• Depression and anxiety
• Vestibular problems
• Motor dysfunction (including parkinsonian features) 1, 5

Additional follow-up:

• Refer patients not recovered to baseline for formal neuropsychological evaluation 1
• Arrange cardiology follow-up for patients with evidence of cardiac damage 1
• Inform all patients about the risk of DNS, as 75% of patients with DNS recover within 1 year 5

Critical Pitfalls to Avoid

• Do not withhold oxygen therapy while awaiting laboratory confirmation 1, 2
• Do not withhold HBOT solely because a patient appears to be doing well clinically—symptoms do not correlate with COHb elimination, and DNS can develop after apparent recovery 1, 3
• Do not rely on COHb levels alone for treatment management—they do not predict severity or guide therapy intensity 2, 3
• Ensure the CO exposure source is identified and eliminated before discharge to prevent re-exposure 1
• Recognize that CO poisoning survivors have increased long-term mortality (up to 3-fold) compared to the general population, suggesting possible residual brain injury even in "recovered" patients 2