Carbon Monoxide Poisoning

What to do right now

1. Get everyone outside into fresh air immediately, including pets. Do not stop to open windows or search for the source.
2. Call 911 or your local emergency number from outside. You can also call Poison Control at 1-800-222-1222 in the US for advice.
3. If someone has collapsed, do not enter a space with a high CO level unless it is safe. Firefighters have breathing equipment.
4. Start CPR if the person is not breathing normally and you are in fresh air.
5. Do not go back inside until emergency services or a qualified technician say it is safe.

How carbon monoxide harms the body

Carbon monoxide binds to hemoglobin, the oxygen-carrying protein in red blood cells, about 200 to 250 times more strongly than oxygen. This forms carboxyhemoglobin, which cannot carry oxygen. CO also interferes with oxygen release to tissues and damages cells directly. The brain and heart, which need the most oxygen, are hit hardest.

Because CO has no color, smell or taste, people often do not realize they are being poisoned, especially while asleep.

Common sources

• gas, oil or wood furnaces, boilers and water heaters that are faulty or poorly vented
• gas stoves and ovens used for heating
• portable generators, grills, camp stoves and charcoal used indoors, in garages or near windows
• car engines running in garages, even with the door open
• blocked chimneys and flues
• house fires
• boats, especially near exhaust outlets
• spray paint strippers containing methylene chloride, which the body converts to CO

CO poisoning rises in winter and after storms and power outages, when people use generators and alternative heating.

Symptoms

Clues that point to CO rather than a virus:

• several people or pets in the same home are ill at the same time
• symptoms improve when away from the home, car or workplace
• symptoms start when a heater, furnace or generator is in use
• no fever

The textbook "cherry-red" skin is rare and is usually seen only after death.

Who is most at risk

Unborn babies, infants, older adults, and people with heart disease, lung disease or anemia are at highest risk. Fetal hemoglobin binds CO even more tightly, so a pregnant woman with mild symptoms can have a severely affected baby.

Diagnosis

• Blood test for carboxyhemoglobin (COHb) from a vein or artery. Levels above about 3 percent in non-smokers or 10 percent in smokers indicate exposure, but levels fall once you breathe fresh air or oxygen, so a "normal" result after treatment does not rule out poisoning.
• CO-oximetry with a special finger probe in some EDs. Standard pulse oximeters can show falsely normal oxygen levels.
• ECG and troponin to check for heart damage.
• Neurological examination and sometimes brain imaging.
• Pregnancy test in women of childbearing age.

Treatment

• 100 percent oxygen through a tight-fitting mask speeds CO removal from the blood. Breathing room air takes about 4 to 5 hours to halve the CO level; high-flow oxygen shortens this to around 1 to 1.5 hours.
• Hyperbaric oxygen therapy (HBOT): breathing pure oxygen in a pressurized chamber clears CO faster and may reduce long-term brain effects. It is considered for loss of consciousness, neurological symptoms, heart damage, very high COHb levels, or pregnancy.
• Supportive care for breathing, heart rhythm and blood pressure.
• Check for other poisons such as cyanide in house fire victims. See smoke inhalation.

Complications

• Delayed neurological sequelae: memory loss, personality change, depression, movement disorders and concentration problems that can appear days to weeks after apparent recovery, in a significant minority of people with serious poisoning.
• Heart damage, including heart attacks and rhythm problems.
• Pregnancy loss or harm to the baby.
• Hypoxic brain injury after severe exposure.

Follow-up appointments check memory and thinking.

Prevention

• Install CO alarms on every level of your home and outside sleeping areas. Test them monthly and replace batteries as directed; replace alarms every 5 to 10 years.
• Have furnaces, water heaters, boilers and other fuel-burning appliances serviced yearly by a qualified technician.
• Never use a generator, grill, camp stove or charcoal indoors, in a garage, or within 20 feet (6 m) of windows, doors or vents.
• Never run a car or engine in a garage, even with the door open.
• Never use a gas stove or oven to heat your home.
• Have chimneys and flues checked and cleaned yearly.
• Clear snow from vehicle exhaust pipes and home vents.

Frequently asked questions

What are the first signs of carbon monoxide poisoning?

The first signs are usually headache, dizziness, nausea and tiredness, similar to flu but without fever. If several people in the home feel the same way, or symptoms ease when you go outside, suspect carbon monoxide and get into fresh air immediately.

How long does it take for carbon monoxide to make you sick?

It depends on the concentration. Very high levels can cause collapse within minutes. Lower levels over hours cause headaches and nausea. Chronic low-level exposure over days or weeks can cause recurring flu-like symptoms, fatigue and memory problems.

Can you recover from carbon monoxide poisoning?

Most people with mild poisoning recover fully once removed from the source and given oxygen. After severe poisoning, some people have lasting problems with memory, concentration or mood, which can appear weeks later. Hyperbaric oxygen may reduce this risk.

Can you smell carbon monoxide?

No. Carbon monoxide has no smell, color or taste. A smell of gas comes from an additive in natural gas, not from carbon monoxide. That is why CO alarms are essential in every home with fuel-burning appliances or an attached garage.

Where should carbon monoxide detectors be placed?

Place at least one CO alarm on every level of your home, including the basement, and one outside each sleeping area. Follow the manufacturer's instructions for height and keep alarms away from direct contact with appliances and vents.