On January 22, 2025, the ACEP Board of Directors approved a clinical policy developed by the ACEP Clinical Policies Committee on the management of adult patients presenting to the emergency department with acute carbon monoxide poisoning. This clinical policy was published in the April 2025 issue of the Annals of Emergency Medicine, can be found on ACEP’s website, and also will be included in the ECRI Guidelines Trust upon its acceptance.

Carbon monoxide (CO) is one of the leading causes of poisoning with over a million cases of CO poisoning reported worldwide each year. In the United States, CO poisoning is a leading cause of non-suicidal poisoning deaths, with nearly 50,000 emergency department (ED) visits annually.

Acute CO toxicity can cause a wide range of clinical effects, from mild headache or flu-like symptoms to chest pain, shortness of breath, myocardial infarction, dysrhythmia, confusion, altered mental status, and coma. Flu-like symptoms in occult cases of CO poisoning, especially during colder weather, further confound diagnosis.

After the initial CO exposure, patients can develop new neurologic findings 2 to 40 days later. These central nervous system abnormalities can range from problems in concentration and memory to seizures and Parkinson’s-like syndrome. Virtually any neuropsychologic abnormality can be seen, including psychiatric ones like depression and psychosis. These late onset findings are called delayed neurologic sequelae (DNS). Risk factors for DNS include older age (≥36 years), higher CO level (≥25%), longer CO exposure interval (≥24 hours), loss of consciousness due to CO poisoning, low Glasgow Coma Score, low Mini-Mental Status Examination score, and positive findings on brain computed tomography scans (general swelling, white matter and/or globus pallidus abnormalities).

Given the continued controversy for the use of HBO2 to treat CO poisoning, this 2025 clinical policy revisited question 2 from the 2017 clinical policy. A writing committee reviewed the eligible literature published since the 2017 clinical policy recommendation, a systematic review of the evidence was conducted, and the committee made recommendations (Level A, B, or C) based on the strength of evidence available. This clinical policy underwent internal and external review expert review and was available for review by ACEP membership during an open comment period. Responses received were used to refine and enhance the final policy.

CRITICAL QUESTION

In ED patients diagnosed with acute CO poisoning, does HBO2 therapy, compared with normobaric oxygen therapy, improve long-term neurocognitive outcomes?

• Patient Management Recommendations
  • Level A recommendations. None specified.
  • Level B recommendations. None specified.
  • Level C recommendations. In symptomatic CO poisoning, selected patients may benefit from HBO2 treatment based on severity of symptoms and availability (distance and time).

More on ACEP’s Class of Evidence framework and Recommendation Levels can be found here.

Dr. Shih is currently a professor at the Schmidt College of Medicine at Florida Atlantic University in Boca Raton, Florida. In his spare time he likes to play guitar and pickleball.