According to the Centers for Disease Control and Prevention, carbon monoxide is the leading cause of unintentional poisoning deaths in people in the United States—and, of course, animals are in danger as well.
It is estimated that unintentional, non-fire-related carbon monoxide poisoning causes 15,000 emergency department visits and nearly 500 deaths every year in this country. While similar statistics for animals aren’t available, we do know that more than a third of the country’s households have either a dog or cat.
CO binds to hemoglobin and creates carboxyhemoglobin, which impairs the oxygen-carrying capacity of hemoglobin. CO doesn’t just bind to hemoglobin, it binds 250 times greater than oxygen, leading to cellular hypoxemia and ischemia.
Organs such as the heart and brain are most affected since they utilize the most oxygen.
Common sources of carbon monoxide include vehicle exhaust, household fires, home furnaces, stoves and water heaters.
Symptoms of poisoning may range from mild or moderate (depression, vomiting, weakness) to severe (coma, seizures, dyspnea, arrhythmias, acute lung injury, ARDS and death).
Permanent deafness and blindness are possible with exposures. For animals who recover from carbon monoxide poisoning, monitoring should continue for at least another 3-6 days (or longer) to watch for sudden worsening or return of neurological signs.
Delayed neurologic effects have been reported in animals and may result in a poor prognosis.
Oxygen is not only antidotal for carbon monoxide poisoning but will also help enhance elimination and should be continued until signs resolve or carboxyhemoglobin levels are less than 4%.
For humans the half-life of carbon monoxide in ambient air is 4-6 hours but is down to 60-75 minutes at 100% oxygen and 20 minutes in a hyperbaric oxygen chamber. Intubation and mechanical ventilation may be needed in more severe cases.
Addressing other clinical signs such as seizures with diazepam or similar benzodiazepine should be done as needed. Monitoring heart rate and rhythm, electrolytes, lactate and acid base are advised for more severe cases.
If coma or persistent neurological signs are seen a CT scan may help look for signs of cerebral edema. Remember that a pulse oximeter (which reads oxygen saturation) is not reliable when dealing with CO poisoning, however a CO-oximeter (which reads the oxygen carrying capacity of hemoglobin) is. Carboxyhemoglobin levels may also be determined.
Animals who remain asymptomatic (assuming the home has been evaluated by a utility company or fire department and determined safe to return to) may be monitored at home.
Carbon monoxide is roughly the same density as room air, so animals close to the ground are at no more risk that taller animals.
However birds, due to their unique respiratory system, are at higher risk for poisoning and will show evidence of symptoms at 900 ppm carbon monoxide.
In comparison, mice won’t show clinical signs until almost double that amount of carbon monoxide.