Is Carbon Dioxide Poisonous?

Carbon dioxide is poisonous at high concentrations, but low concentrations within the body are essential for life.
Carbon dioxide is poisonous at high concentrations, but low concentrations within the body are essential for life.

Carbon dioxide (CO2) is a gas in air and produced by cells in the body from respiration. Plants need it for photosynthesis, to produce food (glucose) and oxygen. It’s added to soda and occurs in naturally carbonated beverages. So, carbon dioxide is everywhere, but is it poisonous? Here’s a look at carbon dioxide toxicity and the symptoms of carbon dioxide poisoning.

Your Body Needs Carbon Dioxide

Normally, carbon dioxide is not poisonous. It’s always present in the human body, where it performs critical physiological functions. As carbon dioxide levels rise in blood, it stimulates the impulse to breathe. Breathing rate increases when it isn’t sufficient to sustain the level of CO2. So, while you might think low levels of oxygen trigger breathing, it’s actually carbon dioxide concentration that determines breathing rate and depth.

You might wonder why the body needs carbon dioxide. It’s essential for the function of hemoglobin in red blood cells. Both oxygen and carbon dioxide bind to the hemoglobin molecule. When carbon dioxide binds hemoglobin, it changes the molecule’s conformation. The conformation change results in two effects that control the amount of oxygen stored by red blood cells and delivered to body tissues. The The Haldane Effect occurs when binding of carbon dioxide decreases the amount of oxygen bound for a particular partial pressure of the gas. The Bohr Effect occurs when rising CO2 partial pressure or decreased pH causes hemoglobin to offload oxygen to tissues.

Only 5% to 10% of carbon dioxide in blood gets bound to hemoglobin as carbamino compounds. Between 70% to 80% of carbon dioxide in blood is converted into bicarbonate ions by the enzyme carbonic anhydrase. Between 5% and 10% of carbon dioxide is a dissolved gas in blood plasma. Excess carbon dioxide goes to the lungs, where it is exhaled as a gas. The average adult exhales about 1 kg (2.3 lbs) of carbon dioxide each day (which is about 290 g or 0.63 lbs of carbon)!

Too Much Carbon Dioxide Is Toxic

While you need carbon dioxide too live, if the blood concentration rises too high, you can suffer carbon dioxide intoxication or carbon dioxide poisoning. Certain medical conditions can disturb the concentration of carbon dioxide in blood, but the most common reason for carbon dioxide poisoning is inhaling air that contains too much of the gas.

Causes of Carbon Dioxide Toxicity

There are several ways you can get exposed to too much carbon dioxide:

  • Hypoventilation: Hypoventilation is the opposite of hyperventilation. Basically, carbon dioxide accumulates to toxic levels if you don’t breathe often enough or deeply enough. Causes include sleep apnea, lung disease, or diminished consciousness.
  • Working with dry ice: Dry ice is solid carbon dioxide. When it changes into carbon dioxide gas, the concentration of CO2 in air increases. Carbon dioxide is heavier than air, so the risk of carbon dioxide intoxication or poisoning increases the closer you are to the floor. So, the risk is highest to children and pets.
  • Spending time in enclosed spaces: People, pets, and combustion all release carbon dioxide into the air. Carbon dioxide levels rise in closed rooms, tents, mines, or even under blankets, because gas exchange is reduced.
  • Rebreathing air: When you rebreathe air, you extract leftover oxygen, but add more carbon dioxide each time you exhale. Carbon dioxide levels may rise rapidly.
  • Environmental exposure: The air around volcanoes or geothermal vents tends to have increased levels of carbon dioxide.

Symptoms of Carbon Dioxide Intoxication and Poisoning

When carbon dioxide levels in the blood rise too high, the result is carbon dioxide poisoning. The medical term is hypercapnia or hypercarbia. The early stages of hypercapnia are commonly called carbon dioxide intoxication because the symptoms are similar to intoxication from alcohol consumption. Symptoms of carbon dioxide intoxication include difficulty concentrating, slower reaction time, headache, high blood pressure, dizziness, impaired vision and hearing, flushed skin, and muscle twitch.

After continued exposure or at higher concentrations, carbon dioxide poisoning occurs. This is a life-threatening condition, with symptoms including panic, irregular heartbeat, vomiting, and hallucinations. It can lead to unconsciousness and death. Keep in mind, carbon dioxide toxicity can progress rapidly! Also, note carbon dioxide toxicity occurs even when there is sufficient oxygen.

CO2 ConcentrationHealth Effects
<1000 ppmNo health effects
1000-2500 ppm“Stale air” sensation, fatigue, reduced concentration
2500-5000 ppmDrowsiness, headache
5000-40000 ppmIntoxication, severe headache. This level exceeds OSHA guidelines.
40000-100000 ppmImmediately dangerous to life. Difficulty breathing, increased heart rate, dizziness, sweating. Seizures and loss of consciousness with prolonged exposure.
>100000 ppmLoss of consciousness within minutes, ultimately leading to coma or death if not immediately corrected.
Health effects associated with carbon dioxide concentration.

Levels between 1000 ppm and 2500 ppm are relatively common in energy-efficient buildings, which may not allow for much exchange with outside air. Smoking and cooking using gas or wood as fuel increases carbon dioxide in air. In the winter, carbon dioxide levels may rise in homes from fireplaces. But, most indoor carbon dioxide comes from people exhaling it. The more people there are in a closed space, the higher the carbon dioxide concentration. Keeping doors open helps air circulate, as does opening a window. During the day (or under lights), houseplants remove excess carbon dioxide, too.

What to Do If You Suspect CO2 Poisoning

It’s important to remove a victim to fresh air as quickly as possible and seek emergency medical aid. Treatment initially includes oxygen administration, but medical personnel also assess effects on the circulatory and respiratory system.

Carbon dioxide toxicity is diagnosed by measuring blood pH and carbon dioxide gas pressure. Low (acidic) serum pH combined with a blood gas concentration over 45 mmHg carbon dioxide indicates hpyercapnia.


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