What condition is indicated by excessive carbon dioxide in the blood?

Hypercapnia is the correct choice as it specifically refers to an excess of carbon dioxide (CO2) in the bloodstream. This condition occurs when the body cannot effectively remove CO2 through respiration, often due to respiratory issues. As CO2 levels rise, they can lead to various physiological effects, including respiratory acidosis, which can impact overall oxygen delivery and usage in the body.

Other conditions mentioned, such as hypoxia, asphyxia, and oxygen toxicity, are related to issues with oxygen or are caused by different mechanisms that do not primarily involve elevated CO2 levels. Hypoxia refers to inadequate oxygen supply to tissues, while asphyxia involves a lack of oxygen leading to cessation of breathing. Oxygen toxicity, on the other hand, arises from prolonged exposure to high levels of oxygen, which can damage the lungs and central nervous system. Understanding hypercapnia is crucial for recognizing the importance of CO2 balance in maintaining respiratory health.