From the Guidelines
Carbon monoxide (CO) poisoning is confirmed by elevated carboxyhemoglobin (COHb) levels, with a level above 3% in non-smokers or above 10% in smokers being indicative of CO exposure, as stated in the practice recommendations for the diagnosis, management, and prevention of carbon monoxide poisoning 1. The diagnosis of CO poisoning involves a combination of clinical symptoms and laboratory findings. Key symptoms include headache, dizziness, nausea, confusion, and in severe cases, loss of consciousness, as outlined in the key messages on carbon monoxide poisoning 1.
- The primary diagnostic marker is elevated COHb levels in the blood, which can be measured through arterial or venous blood gas analysis using co-oximetry 1.
- Standard pulse oximetry is inadequate for diagnosing CO poisoning as it cannot distinguish between oxyhemoglobin and carboxyhemoglobin.
- Additional laboratory findings may include:
- Metabolic acidosis
- Elevated lactate levels
- Abnormal cardiac enzymes in severe cases
- Complete blood count
- Basic metabolic panel
- Cardiac biomarkers to assess for end-organ damage The severity of CO poisoning does not always correlate perfectly with COHb levels, as symptoms depend on exposure duration, individual susceptibility, and the time elapsed between exposure and testing 1.
- COHb has a half-life of 4-6 hours in room air, so levels may be falsely low if testing is delayed.
- Therefore, diagnosis should incorporate both laboratory values and clinical presentation. Administering 100% oxygen while waiting for COHb level results is crucial, as it helps to reduce the half-life of COHb and alleviate symptoms 1.
From the Research
CO Poisoning Diagnosis and Treatment
- CO poisoning is diagnosed through carboxyhemoglobin (COHb) levels, with severe cases often presenting with coma, hemodynamic instability, and high COHb levels 2, 3
- Initial symptoms of CO exposure include headache, dizziness, nausea, fatigue, and impaired manual dexterity, with more severe cases leading to loss of consciousness and death 3
- COHb levels between 30% and 70% can lead to loss of consciousness and death, while levels between 15-30% may cause nonspecific symptoms 3
Laboratory Findings
- COHb levels are used to diagnose and monitor CO poisoning, with a short half-life requiring prompt measurement 3, 4
- Arterial blood gas analysis may show hypoxia and decreased oxygen-carrying capacity 2
- Other biomarkers of CO neurotoxicity, such as inflammation or neuronal damage, have not demonstrated consistent results 3
Treatment Options
- Normobaric oxygen therapy using a tight-fitting mask is the cornerstone of treatment for CO poisoning, with administration of 100% oxygen for greater than 6 hours 3, 4
- Hyperbaric oxygen therapy (HBOT) is recommended for severe cases, particularly those with coma, hemodynamic instability, or high COHb levels, to prevent permanent neurological deficits 2, 5
- High-flow nasal cannula (HFNC) is a potential alternative to non-rebreather masks for treating CO poisoning, with theoretical advantages and successful case reports 4