Provider Practice Essentials registered nurse continuing education

Carbon Monoxide – The Silent Killer

Lindee Abe, APRN

Every winter there is a potential for a silent, deadly killer in your home. We are all familiar with the diagnosis of carbon monoxide poisoning, but how often are we really considering it in our differential diagnoses? Do we know who is at risk for carbon monoxide poisoning? Or how to educate patients to prevent this from happening? What are the most common symptoms of carbon monoxide poisoning as the underlying cause? I want to review the answers to these questions and move this diagnosis up on the differential list as we head into the winter months. We most certainly need to be vigilant for patients that may present with carbon monoxide poisoning in order to prevent significant disabilities that can result from the exposure.

As a child growing up I remember being reminded that the greatest risk of poisoning occurred in the transition months (i.e. October, November). This was when we first started using the furnace. The Texas Poison Center says that the months with the highest rates of carbon monoxide poisoning are January and December. The highest number of deaths associated with carbon monoxide poisoning also occur in some of the coldest states in the U.S.: Alaska, Montana, North Dakota, Nebraska, and Wyoming. Colder months also lead to increased use of gas powered furnaces that can increase the risk of poisoning. The coldest states would likely have to highest use of gas powered and alternate heating sources.

Causes of Carbon Monoxide Poisoning

Carbon monoxide gas Is the result of incomplete combustion of fuels. These fuels include gasoline, oil, coal, and wood. Likewise, the sources for potential carbon monoxide exposure mirror conditions where fuels cannot burn completely. These are seen most commonly in poorly ventilated areas. Examples include a car idling in a closed garage, indoor barbeques, or a fire place or stove with a closed chimney. Incorrect installation and maintenance of heaters, broilers, and cookers are also common causes of exposure. Poorly maintained vehicles with blocked exhaust also cause accumulation of carbon monoxide. There is also a risk in a chemical found in paints and cleaners, dichloromethane, that is broken down by the body into carbon monoxide.

I attended a continuing education conference some years ago and remember there also being a discussion regarding summer time carbon monoxide poisoning. This is a potential concern with larger boats that sit idle in the water and people swimming off the back platform of the boat. Carbon monoxide can accumulate from the gas generator at the back of the boat. These patients have a history of going boating and then stopping for some time to swim or laying on the back portion of the boat while cruising or idling. Poisoning becomes difficult to diagnose because the symptoms of poisoning often mimic heat exhaustion, heat stroke, or dehydration. All of these diagnoses revolve around sun and heat. While heat exhaustion may be more likely, carbon monoxide poisoning may also make a contribution.


One of the main difficulties in the detection of carbon monoxide poisoning is that the symptoms associated with poisoning are vague. The most common symptom is a headache. There are other symptoms that can include everything from tiredness and confusion, to nausea and stomach pain, to shortness of breath. Higher levels of exposure can also cause chest pain, seizures, ataxia, loss of consciousness, respiratory failure, and death. In the winter months, these symptoms can often be disregarded In favor of viral gastroenteritis or influenza.

Another characteristic of carbon monoxide poisoning is seeing multiple patients with the same symptoms from the same house. Of course this could also be an illness spreading through household contacts, but in that scenario the symptoms typically have a different time of onset in every person. Gastrointestinal symptoms in multiple household members can also be attributed to food poisoning. Carbon Monoxide poisoning in patients from the same household will typically have the patients presenting with symptoms that all begin around the same time. Family pets may also be Ill.


There is one primary test for carbon monoxide poisoning, carboxyhemoglobin. This can be measured by a blood draw or using a pulse co-oximeter. A traditional pulse oximeter cannot differentiate between oxygen and carbon monoxide and the O2 sat will likely be normal. There have been several studies comparing the accuracy of the pulse co-oximeter testing versus laboratory tests with the most common conclusion being that the pulse co-oximeter is most useful as an initial diagnostic tool with confirmation by laboratory testing.

Another key factor with detecting carbon monoxide levels is the half-life of carbon monoxide being several hours on room air or less than an hour with 100% O2. This is when the accuracy of the co oximeter up to 50% carboxyhemoglobin levels is most useful, as it allows a more rapid result. Patients with a moderate exposure or cardiovascular symptoms should also have a cardiovascular workup that includes an EKG and cardiac enzyme levels. Cardiac ischemia is a known complication of carbon monoxide poisoning.

Carbon Monoxide Levels


  • Less than 3%


  • 3-11%
  • Could be due to other causes such as smoking
  • Does not require treatment if asymptomatic.


  • Above 12%
  • Immediate treatment required
Carbon Monoxide


The traditional treatment for carbon monoxide poisoning involves 100% O2 or hyperbaric oxygen chamber. Hyperbaric treatment results in the quickest resolution of symptoms and the half-life goes from about 1 hour with oxygen to only 22 minutes in a hyperbaric oxygen chamber. This is normally only used for patients with significant symptoms including neurovascular or cardiovascular complications, metabolic acidosis, and unconsciousness. These patients should have a level >25% or, if pregnant, >15%.

The lack of availability of a hyperbaric oxygen chamber in a short period of time is also a limiting factor when it comes to treatment. Also consider that even though a patient recovers from poisoning without any intervention does not mean that they don’t require any further testing or work up, especially if the exposure was over a prolonged period time. The provider should still be considering ordering additional testing based on complaints and ensure proper follow up for ongoing evaluation.


There are several key takeaways from the information discussed regarding carbon monoxide poisoning. The first is to make sure to consider the diagnosis in the list of differential diagnoses for patients that present as a household with influenza symptoms or influenza symptoms without a fever or exposure. A provider will miss 100% of the diagnoses they have not considered. The other big takeaway is the importance of rapid initiation of treatment in these patients, but not forgetting to complete a full work up for those that may have resolving levels of carboxyhemoglobin by the time they arrive in the ER or urgent care.


Center for Disease Control. (August 29, 2017). Prevent Carbon Monoxide Poisoning on your
Boat. Retrieved from

Masimo. (n.d.). Detecting Carbon Monoxide Poisoning in the Emergency Department.
Retrieved from Detecting Carbon Monoxide Poisoning in the Emergency Department.

National Health Institute. (April 10, 2019) Carbon Monoxide Poisoning. Retrieved from

Texas Poison Control Center. (n.d.). January is the Deadliest Month for Carbon Monoxide
Poisoning. Retrieved from

Check out the Provider Practice Essentials Emergency Medicine, Acute Care, and Hospitalist Medicine Board Review Series. These are available for Nurse Practitioners and Physician Assistants.

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