Nitrous oxide (laughing gas): A gas that can cause general anesthesia. Nitrous oxide is sometimes given in the company of other anesthetic agents but it is not used today as the only anesthetic agent because the concentration of nitrous oxide needed to produce anesthesia is close to the concentration that seriously lowers the blood oxygen level and creates a hazardous hypoxic state.
Nitrous oxide figured in the history of anesthesiology. In 1840 a dentist named Horace Wells had the idea that, with the recently discovered "exhilarating or laughing gas", teeth might be extracted without pain. Under its influence he had one of his own teeth pulled in 1844 and afterwards frequently used it in his practice.