From the Guidelines
Carboxyhemoglobin (COHb) levels above 25% are concerning for carbon monoxide poisoning, as they warrant hyperbaric oxygen (HBO) therapy, especially in patients with loss of consciousness, ischemic cardiac changes, neurological deficits, or significant metabolic acidosis. According to the practice recommendations in the diagnosis, management, and prevention of carbon monoxide poisoning 1, the role of carboxyhemoglobin level is to confirm the clinical diagnosis, although it correlates poorly with symptoms or prognosis.
Key Points to Consider
- COHb levels do not always correlate perfectly with clinical symptoms, as factors like exposure duration, individual susceptibility, and pre-existing conditions can influence how a person responds to carbon monoxide exposure.
- Symptoms of carbon monoxide poisoning can be nonspecific, including headache, dizziness, nausea/vomiting, confusion, fatigue, chest pain, shortness of breath, and loss of consciousness 1.
- Treatment should be initiated based on both clinical presentation and measured COHb levels, with 100% oxygen by nonrebreather facemask or endotracheal tube being the primary intervention to accelerate the elimination of carbon monoxide from the bloodstream 1.
- Hyperbaric oxygen therapy may be considered for patients with severe poisoning or those who do not respond to normobaric oxygen therapy, with the goal of preventing neurocognitive sequelae 1.
From the Research
Carboxyhemoglobin Levels in Carbon Monoxide Poisoning
- Carboxyhemoglobin (COHb) levels are used to diagnose carbon monoxide poisoning, but the levels do not correlate well with the clinical severity of the poisoning 2, 3.
- There is no specific COHb level that is considered concerning for carbon monoxide poisoning, as treatment plans based on COHb levels are not well founded 2.
- However, a study found that the mean baseline COHb level of patients with acute carbon monoxide poisoning was 22.5% (SD 8%) 4.
- Another study reported a case of a patient with an initial COHb level of 2.5% who still had significant neurological damage related to CO exposure 5.
Treatment and Management
- Treatment for carbon monoxide poisoning typically consists of removal from the source of exposure and administration of 100% supplemental oxygen 6.
- Hyperbaric oxygen therapy may be considered for patients with severe intoxication or those who have suffered an interval of unconsciousness 2.
- High flow nasal cannula oxygen therapy has been shown to be an effective method for reducing COHb levels, with a mean half-life of 36.8 minutes (SD 9.26 min) 4.