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