Carboxyhemoglobin

Background

• Hemoglobin bound to carbon monoxide (CO); measured on co-oximetry (ABG)
• Pulse oximetry cannot distinguish COHb from oxyhemoglobin and may read falsely normal

Normal Values

• Non-smoker: <3%
• Smoker: <10%

Interpretation

• Symptoms correlate poorly with levels but generally: headache >10%, confusion >20%, seizures/coma >40%, death >60%
• Check in all patients with headache, AMS, or syncope in the setting of possible CO exposure (house fires, heaters, enclosed space)
• Co-oximetry on ABG is the only reliable measurement; standard pulse oximetry is unreliable
• Treat with 100% FiO2 via NRB; consider hyperbaric oxygen for levels >25%, loss of consciousness, cardiac ischemia, or pregnancy
• Half-life of COHb: ~5 hours on room air, ~90 min on 100% O2, ~30 min with hyperbaric O2

See Also

• Carbon monoxide poisoning
• Smoke inhalation