What Is Carbon Monoxide Poisoning?

Carbon monoxide poisoning occurs when you breathe in too much carbon monoxide (CO), a colorless, odorless gas produced by the combustion of fuel.

Carbon monoxide poisoning symptoms include headaches, dizziness, weakness, vomiting, chest pain, and confusion. Excessive exposure to CO can lead to severe heartbeat irregularities, seizures, unconsciousness, and even death.

Carbon monoxide poisoning can be diagnosed with a CO-oximeter, a non-invasive device that measures CO compounds in the blood. Treatment typically involves pressurized oxygen delivered through a non-circulating mask. Severe cases may require treatment in a hyperbaric oxygen chamber.

Carbon Monoxide Poisoning Symptoms

Carbon monoxide poisoning will manifest with symptoms stemming from parts of the body that require oxygen most, namely the heart and the central nervous system (CNS). Initial carbon monoxide poisoning symptoms typically include nausea, malaise, fatigue, and a dull but persistent headache.

As the CO continues to build up in the bloodstream, the depletion of oxygen in tissues will trigger an ever-worsening cascade of symptoms, including:

• Dizziness
• Shortness of breath (dyspnea)
• Chest pain
• Vomiting
• Irregular heart rate (arrhythmia) or rapid heart rate (tachycardia)
• An unsteady gait
• Confusion
• Decreased rate of breathing
• Decrease heart rate
• Delirium
• Seizures
• Unconsciousness

Death most often occurs as a result of respiratory arrest.

Even after a person has been treated for CO poisoning, there is a risk of long-term and even permanent neurological complications, including memory problems, irritability, depression, speech disturbances, partial vision loss, dementia, and Parkinson's disease-like symptoms.

Causes

Carbon monoxide easily enters the body through the lungs. As CO is transferred into the bloodstream, it will preferentially bind to hemoglobin, the protein in red blood cells responsible for transporting oxygen throughout the body. By doing so, CO prevents oxygen from getting to the tissues and cells that need it to survive.

Carbon monoxide is a natural byproduct of combustion. Most cases of poisoning result from the inhalation of the gas as it quickly accumulates in an enclosed space (usually due to faulty ventilation).

Riding in the back of a pickup truck is a common cause of carbon monoxide poisoning in children. Similar, idling your car in winter can poison passengers if the exhaust pipe is blocked with snow. In fact, any perforation in the exhaust manifold of a car or boat can allow CO to flood the interior.

Carbon monoxide poisoning may also occur intentionally. According to research published in the Annals of the American Thoracic Society, 831 suicides in 2014 were a result of carbon monoxide poisoning, either from a vehicle's exhaust fumes or a combustible fuel source in the house.

With that being said, suicide by this method has been on the decline since 1975 when federal law dictated the installation of catalytic converters in all motor vehicles.

Diagnosis

Unless carbon monoxide is recognized as the cause of your symptoms, it may be misdiagnosed when you first arrive at the emergency room. It is important, therefore, to advise the ER doctor of your suspicions if you believe CO is involved. 

The diagnosis is relatively straightforward. It involves a non-invasive probe, called a CO-oximeter, which can be placed on your finger, toe, or other parts of the body. The oximeter contains two diodes that emit light beams of different wavelengths. The amount of light absorbed by tissue can tell doctors how much carboxyhemoglobin (the compound created by the binding CO and hemoglobin) is in the blood.

Under normal circumstances, you would have less than 5% carboxyhemoglobin compared to free hemoglobin. Generally, poisoning occurs if the level is above 10%. Death can occur at levels over 25%.

Regular pulse oximeters are not useful as they are not able to distinguish between carboxyhemoglobin and oxyhemoglobin (the compound created by the binding of oxygen and hemoglobin).

Treatment

If carbon monoxide poisoning is suspected, the first course of action is to remove yourself and others from the source of the CO. Even if symptoms are mild, emergency medical treatment should be sought.

Treatment may involve the administration of pressurized oxygen through a non-circulating mask. By increasing oxygen levels in the blood, CO can be cleared from the body four times faster than on its own. The oxygenation can actually break up carboxyhemoglobin and release hemoglobin back into the bloodstream.

In severe cases, a hyperbaric chamber may be used, which can deliver 100% oxygen in a high-pressure environment. Hyperbaric oxygen clears CO from the blood nearly four times faster than oxygen delivered at normal atmospheric pressure. It also allows oxygen to partially bypass hemoglobin and be delivered directly to tissue.

In addition to oxygen, other treatments may be required, including:

• Cardiac life support to treat dangerous arrhythmias
• Intravenous fluids to treat hypotension
• Intravenous sodium bicarbonate to treat metabolic acidosis (the build-up of acids in the blood due to suppressed kidney function) 
• Valium (diazepam) or Dantrium (dantrolene) to treat seizures
• Vasopressor medications to constrict blood vessels and stabilize depressed heart activity

Prevention

The most effective means of prevention in the home is a carbon monoxide alarm. They are readily available online and in most hardware stores, ranging in price from $20 for a plug-in monitor to $80 for a combination CO/smoke alarm.

Among the other recommended safety tips:

• Make sure your gas appliances are properly vented.
• Have your heating system, water heater, and any gas- or coal-burning appliance serviced by a technician every year.
• Never use an electrical generator inside the home, garage, or less than 20 feet from any window, door, or vent.
• Have your chimney checked and cleaned annually.
• Open the fireplace damper before lighting a fire and well after it has been extinguished.
• Never use a gas oven to heat your home.
• Never let a car idle in the garage.
• Know the symptoms of carbon monoxide poisoning.

A Word From Verywell 

If your carbon monoxide alarm goes off, never assume that it's a false alarm even if you have no symptoms. Because CO is tasteless and odorless, you need to assume that the risk is real and to take the appropriate action.

First and foremost, do not look for the source of gas. The CPSC instead recommends that you:

• Immediately move outside into the fresh air.
• Call the fire department, emergency services, or 911.
• Do a head count to check to ensure everyone is accounted for.
• Do not re-enter the building until the emergency responders give you permission to do so.