Carbon dioxide, or CO2, is an end-product of metabolism The body breaks down chemicals such as carbohydrates in food into carbon dioxide to help provide energy for the body. Carbon dioxide combines with water in the blood to make an acid, called carbonic acid. The blood is pumped to the lungs where the carbonic acid is split back into carbon dioxide and water and the carbon dioxide is expelled from the body. Problems with the respiratory system or metabolic problems affecting the acid balance in the body can raise levels of carbon dioxide in the blood.
Respiratory Disorders
Since carbon dioxide is expelled from the lungs with breathing, problems that affect breathing can have an effect on carbon dioxide and the acidity of the blood. According to the text "Clinical Anesthesiology," problems in which the breathing rate or volume of breath expelled per minute are low will raise carbon dioxide. The high carbon dioxide activates sensors in the blood vessels and brain that increase the rate and depth of breathing to lower the CO2 level back into the normal range. An example of diseases that can cause increased CO2 are a stroke in which the respiratory centers in the brain are damaged or asthma. Certain drugs such as morphine and other opiates decrease the respiratory rate.
Metabolic Problems
According to "Harrison's Principles of Internal Medicine," certain metabolic problems in which acid is lost from the body result in an increased level of carbon dioxide. The reason for this is that the increased carbon dioxide increases the level of acid in the blood bringing it back towards normal. Acid can be lost from the kidneys or from the stomach, as with vomiting.
Other metabolic problems can increase the rate of CO2 production, such as during a fever or with high levels of thyroid hormone, but typically respirations will increase to keep level of carbon dioxide in the blood close to normal. (See Reference 2)
Environmental and Iatrogenic Conditions
Certain environmental conditions can increase carbon dioxide as well. One example is during scuba diving, in which the work of breathing increases, making respirations less frequent.
Iatrogenic causes are those induced by a physician. For example, if a person has a breathing tube established and the respiratory rate or the respiratory volume on the ventilator is low, carbon dioxide can build up in the blood. This can be desirable in some cases, however, such as when a person has a chronic condition in which the body is accustomed to high CO2.
References
- "Clinical Anesthesiology"; G. Morgan, Maged Mikhail, and Michael Murray; 4th Ed 2005
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci et al.; 17th Ed 2008
