What does low level of CO2 from a blood test mean?

April 13, 2010

The blood is used to transport carbon dioxide out of the body. All the body organs and tissues require oxygen to perform their functions and to stay alive. The waste product of the process of metabolism is carbon dioxide. Some of the carbon dioxide is dissolved in the blood which then forms other compounds that may be waste or useful to the body. The rest of the carbon dioxide is passed into the lungs from where it diffuses into the air and is passed out during breathing. At the same time, oxygen from fresh air is absorbed into the blood. This is the normal process and function of breathing.

A condition where there is a lower than normal quantity of carbon dioxide in the blood is known as hypocapnia. Hypocapnia can be caused by several factors. It may be caused by excessive speed of breathing which is known as hyperventilation and can also be caused by intentional deep breathing or heavy breathing, which is often in the case of divers. Divers wish to extend the period of their dive and thus want extra oxygen in their blood. This makes them breathe harder which lowers the level of carbon dioxide in their blood.

There are also involuntary causes that might lead to a low level of carbon dioxide in the blood. These include kidney failure; heart failure characterized by slow beating and low blood pressure, diabetes, and may be a result of the overdose of drugs.

Hypocapnia can cause some rather serious symptoms. In the case of divers, as mentioned above, it may cause a blackout which can be fatal. This is caused by the brain which controls the level of carbon dioxide in the blood. When the brain detects a low concentration of carbon dioxide, it tends to slow the process of breathing in order to return the carbon dioxide level to equilibrium. In some cases, hypocapnia will cause no outward symptoms. As the body breathes normally, the co2 level will normalize itself. There is a risk that the lack of carbon dioxide might cause a constriction of the blood vessels that feed blood to the brain. This becomes a medical emergency because there is a sudden fall in the level of oxygen in the brain. This situation is known as hypoxia. This can cause dizziness, fainting, and even more severe brain damage problems if not corrected quickly.

Low carbon dioxide is thus a symptom of an underlying problem and a marker for a doctor to investigate the root cause of the hypocapnia.

Submitted by M T on April 13, 2010 at 11:54

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