It won’t be too long before we enter carbon monoxide (CO) season.  CO as we know is a colorless, odorless gas that prevents oxygen (O2) from binding to our hemoglobin.  In the United States somewhere between 170 and 400 people die every year of CO poisoning from nonautomotive sources.  These sources can be house fires, fireplaces, stoves, water heaters, and a faulty furnace.

CO has an affinity for hemoglobin 250 times greater than O2.  This then prevents the O2 from being delivered to the tissues of our body resulting a build-up of carbon dioxide (CO2) in the body.  The body responds by increasing respirations and our heart rate because of the increased myocardial oxygen demand and the lack of perfusion in the brain.  Eventually, the patient presents with an altered mental status (AMS) and the vital signs begin to slow leading to a failure of our critical body systems.

And of course, the pulse oximetry (SpO2) is inaccurate.  But in the absence of gas monitoring equipment SpO2 can be a clue to the patient’s medical problem.  We know that the SpO2 measures the amount of bound hemoglobin using an infrared light to calculate the time it takes for the light signal to travel through the patient’s finger. And since the CO attaches to the hemoglobin the patient’s SpO2 will read normal to high, but the patient has complaints associated this the CO poisoning.

The patient will initially present with nonspecific complaints like nausea, vomiting weakness, and chest pain.  Depending on the age, we would initially be worried that the patient is experiencing Acute Coronary Syndrome (ACS), which commonly presents with a normal SpO2.  As the patient remains in the environment, the symptoms will progress to complaints of a headache and shortness of breath and the patient will present with irritability, syncope, ataxia, AMS, coma, and death.  The patient can also hypotension, cardiac arrhythmias, myocardial ischemia, myocardial infarction, and noncardiogenic pulmonary edema.

The treatment of course starts with removing the patient from the environment and decontamination.  The patient needs immediate oxygen therapy.  The half-life of CO is between 5 and 9 hours on room air but drops to 60 to 90 minutes on 100% O2.  We also need to treat any underlying conditions, i.e., hypotension, arrythmias, or a cardiac event.  At the hospital blood gases will be obtained to confirm the elevated carboxyhemoglobin levels and if the levels are high enough the patient will be treated with hyperbaric oxygen.  The hyperbaric oxygen will reduce the half-life of CO to 20 minutes.  If your patient is pregnant or has comorbidities like cardiac or respiratory disease the patient will be treated with hyperbaric oxygen regardless of carboxyhemoglobin levels.

Richard Main

Richard is an EMS instructor who has worked in EMS since 1993 after obtaining his EMT from Johnson County Community College. He has lived in Kansas, Arizona and Nevada. While in Arizona, Main worked for Avra Valley Fire District in for 10 years and in private EMS in Southern Nevada.




Gerard, D.R. (2022, July 24). Carbon Monoxide Poisoning. EMS World.