Hypercapnia or hypercapnea (from the Greek hyper = "above" or "too much" and kapnos = "smoke"), also known as hypercarbia, is a condition of poisoning due to abnormally elevated carbon dioxide (CO2) levels in the blood.
Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs. Hypercapnia normally triggers a reflex which increases breathing and access to oxygen, such as arousal and turning the head during sleep. A failure of this reflex can be fatal, as in sudden infant death syndrome. Hypercapnia is the opposite of hypocapnia.