nitrous oxide (N₂O), commonly called ‘laughing gas’, was discovered in 1776 by Priestley. He inhaled the gas and noted that it caused confusion and analgesia. Later, in 1799, Humphry Davy suggested its use in surgical operations. However for the next forty-five years nitrous oxide was used only for entertainment, in which respectable persons were shown to lose their usual demeanour, breaking into laughter, often accompanied by singing and dancing or aggressive behaviour. Unwary persons were encouraged to volunteer for these exhibitions, particularly at fairgrounds. In 1844, Horace Wells, an American dentist, used the gas for tooth extraction, and two years later an American surgeon, William Morton, carried out major surgery under its influence. Nitrous oxide is not a very potent anaesthetic; it was sometimes used at 100% for rapid induction of anaesthesia, with subsequent addition of oxygen to avoid hypoxia.

Nitrous oxide continues to be widely used along with oxygen as a ‘carrier gas’ accompanying other inhalational anaesthetic agents. Its main advantage is that it has an analgesic (pain-relieving) effect, so that less of the main anaesthetic drug needs to be given. As ‘entonox’ it is also used, mixed with air, as an analgesic during labour. The common earlier use for dental extractions has diminished, with new regulations restricting the use of general anaesthesia for this purpose to special centres.

Alan W. Cuthbert

See also anaesthesia, general; analgesia; dentistry; labour.