 Narcosis results from breathing gases under elevated pressure , and may be classified by the principal gas involved . The noble gases , except helium and probably neon , as well as nitrogen , oxygen and hydrogen cause a decrement in mental function , but their effect on psychomotor function ( processes affecting the coordination of sensory or cognitive processes and motor activity ) varies widely . The effects of carbon dioxide consistently result in a diminution of mental and psychomotor function . The noble gases argon , krypton , and xenon are more narcotic than nitrogen at a given pressure , and xenon has so much anesthetic activity that it is a usable anesthetic at 80 % concentration and normal atmospheric pressure . Xenon has historically been too expensive to be used very much in practice , but it has been successfully used for surgical operations , and xenon anesthesia systems are still being proposed and designed . 
