Carbon dioxide helps maintain the acid-base balance in the body, but an excess of carbon dioxide in the body may cause central nervous system symptoms. Carbon dioxide dissolves in water to form carbonic acid, and the amount of carbon dioxide in the body plays a role in regulating the pH level. When there is an excess of acidic substances in the body, more carbon dioxide can be exhaled, and when there is an excess of alkaline substances in the body, carbon dioxide is exhaled less by regulating the respiratory movement, which plays a role in maintaining the acid-base balance in the body. Certain disease states lead to an increase in carbon dioxide in the body, which cannot be exhaled out of the body, leading to carbon dioxide retention; for example, diseases such as chronic obstructive pulmonary disease and bronchiectasis, which can cause the above condition. As a result of elevated partial pressure of carbon dioxide, neurological symptoms may result, including euphoria, sleep inversion, and even drowsiness and coma.