Hypercapnia, also known as hypercarbia and CO2 retention, is a condition where there are abnormally elevated levels of carbon dioxide (CO2) in the blood. Carbon dioxide is a gaseous product of the bodys metabolism and is normally expelled through the lungs. Hypercapnia can be acute or chronic, and both forms may be treated with medication, mask-based non-invasive ventilation, or mechanical ventilation. Acute hypercapnia is a medical emergency as it generally occurs in the context of acute illness and can cause neurological symptoms like confusion, disorientation, and paranoia. Chronic hypercapnia, where metabolic compensation is usually present, may cause symptoms but is not generally an emergency. Hypercapnia can be caused by various underlying respiratory conditions, such as chronic obstructive pulmonary disease (COPD), which may prevent a person’s lungs from either taking in enough oxygen or expelling (breathing out) enough CO2.