Hypocapnia is an abnormally low level of carbon dioxide in the blood. It is often linked to pulmonary hyperventilation. A simple blood test can confirm the diagnosis.

The term hypocapnia describes a decrease in carbon dioxide dissolved in blood plasma, where it exists as carbonic acid.

Hypocapnia is generally due to hyperventilation, that is to say an increase in the inflow and outflow of air into the lungs thus causing too rapid elimination of carbon dioxide by the pulmonary alveoli. 

Hypocapnia can cause an inhibition of the respiratory nerve center and be responsible for slowing down or even stopping breathing. This leads to an increase in blood pH, an increase in plasma bicarbonates, a decrease in potassium and blood chlorides. 

Hypocapnia, in case of sudden onset, can possibly lead to respiratory alkalosis also called gas alkalosis, that is to say too much alkalinity of the blood. But the body does not support this modification very well, the acid-base balance is indeed essential for optimal functioning of the body. The kidneys will therefore try to compensate for this phenomenon by eliminating alkaline compounds, bicarbonates, from the blood.

How to recognize the symptom?

Hypocapnia can result in different manifestations:

• dizziness 
• concentration problems 
• visual disturbances 
• headaches 
• the perception of unusual sensations such as numbness or tingling 
• coldness in the feet and hands 
• muscle cramps 
• tetany attacks 
• heart rhythm disturbances.

Risk factors

The “headscarf game” which has been talked about in schoolyards and which consists of a strangulation brings into play the phenomenon of hypocapnia. 

The main causes of hypocapnia are:

• The existence of a respiratory problem such as asthma, the occurrence of pulmonary embolism.
• A metabolic disorder, such as diabetes for example.
• A problem affecting the central nervous system (for example the occurrence of a cerebrovascular accident, meningitis, head trauma, etc.).
• A cardiovascular problem, such as too low blood pressure.
• Other circumstances, such as the hormonal upheavals of pregnancy, the very intense practice of a sport, or a change of environment (altitude, strong heat, etc.), a strong emotivity.
• The massive intake of certain drugs such as aspirin.

Hypocapnia is not inherently dangerous. However, ignoring this symptom carries the risk of missing out on a more important syndrome of which hypocapnia is only a side effect. 

The risks of complications in the event of non-treatment are therefore directly linked to the cause of hypocapnia. 

Treatment for hypocapnia depends on its cause.

In case of transient hypocapnia, the use of re-inspiration (in a paper bag for example) may be effective. 

When hypocapnia is a side effect of a symptom it is necessary to treat this symptom to reduce hypocapnia.