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Carbon Monoxide Poisoning: A Cautionary Tale


A man in his mid-40s presents to the emergency department (ED) at 4 am complaining of intermittent nighttime headaches of 2 weeks’ duration; the pain often wakens him at about 3 am. He had been to the ED 2 weeks earlier with similar symptoms concerned that he had the avian flu because one of his pet canaries had died. Results of evaluation at that time, including routine blood work, a CT of the head and a lumbar puncture, were all unremarkable, so he had been discharged home with a recommendation to see his PCP.

He returns to the ED today claiming that his left arm has been numb for 45 minutes. He denies weakness or chest pain but says the headache has been ongoing and that he had 2 episodes of vomiting earlier that evening. His vital signs and physical examination are all entirely normal.

He mentions that he saw a chiropractor just after New Year’ Day (about 2 weeks ago) and had neck manipulation so a CT angiogram of the neck was performed and was negative for vascular dissection. His CBC is remarkable for a hemoglobin of 20 g/dL, but the WBC and platelet counts are both normal (making polycythemia vera unlikely). Blood chemistries also are normal. He does not appear clinically dehydrated so hemoconcentration is not likely to be the cause of the elevated hemoglobin.

During observations you notice that his pulse oximetry is normal while he is awake, but drops to the low 90s when the patient falls asleep. Suspecting chronic hypoxia and/or sleep apnea as a cause of his high hemoglobin you consider ordering an arterial blood gas (ABG).

-- Would the results likely be helpful? 

-- What finding might explain night-time headaches and possible polycythemia as well?

-- What's your diagnosis?

Answer: Carbon monoxide poisoning

Findings of co-oximetry combined with ABG values would provide valuable results. Co-oximetry measures various types of hemoglobin (eg, carboxy-hemoglobin and met-hemoglobin) and in the case of CO poisoning will report carboxy-hemoglobin as elevated and oxy-hemoglobin as reduced.


While chronic hypoxia can cause an elevated hemoglobin it is not likely to be the cause for the night time headaches that this patient has had for 2 weeks. Chronic or intermittent carbon monoxide poisoning, however, explains all of the clinical aspects of this case:

-- The dead canary
-- The headaches that were occurring nightly (You learn that the patient was using the fireplace to heat the house in mid-winter. The likely scenario is that the fire began to smolder and smoke by about 1:00 or 2:00 am causing him to awaken within an hour with a headache 
-- The hemoglobin elevation-a result of approximately 2 weeks of persistent exposure  

Carbon monoxide poisoning is one of the most common causes of accidental poisoning death in the United States, responsible for more than 500 deaths annually. Symptoms can often be nonspecific and mimic a viral syndrome. Headache, malaise, and nausea or vomiting are common but during the winter months such a triad rarely leads to testing for carbon monoxide unless there are other clues such as a reported exposure (see list of sources in chart below).  Ataxia, confusion and ischemic chest pain may occur in more severe cases and are less likely to be missed.

When the history includes multiple household members who report symptoms simultaneously (rather than serially) or pets that have become ill or incapacitated, the clinician should have carbon monoxide toxicity high on the differential diagnosis.


The mainstay of treatment for carbon monoxide poisoning is high flow oxygen by non-rebreather mask initially, followed by transfer to a hyperbaric facility in more serious cases (see list of indications in chart below). It is also critical to notify the local fire department to make sure there are not and will not be other victims from the same source concurrently or in the future. Symptom-specific treatment includes advanced life support for comatose patients, antiemetics for vomiting, sodium bicarbonate for severe acidosis, and nitroglycerine for chest pain. Female patients with positive pregnancy tests will require more aggressive and prolonged oxygen therapy.

This gentleman’s carbon monoxide level came back elevated at 28%. A hyperbaric specialist was consulted and recommended hyperbaric oxygen (HBO), but the patient refused. He did agree to stay in the ED for 4 hours of high flow mask oxygen via non-rebreather mask even though he felt much better after only 2 hours. He was told to air out his house when he got home, to have the fire department come out to check carbon monoxide levels, and to use an alternate source of heating.



>500 deaths/yr in US. Family members ill, pets vomiting ill or dead. O2 sat usually normal

HA (pulsatile), malaise/N/V >weak,
Furnace, water heater, gas oven, fireplace, exhaust, barbeque/hibachi, methylene chloride







Admit if symptoms after 4h O2, acidosis (give bicarb if pH <7.1), rhabdomyolysis, seizure, Chest pain (give nitro, O2), pregnant (give at least 24h O2), LOC



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