In 1934 Minnitt 1 introduced an apparatus for the self-administration of nitrous-oxide/air analgesia in labour under the general supervision of the midwife. In 1949 Seward showed that the two main disadvantages of 'gas and air' were firstly, that the 50 % nitrous-oxide given by the apparatus was frequently too weak to provide adequate analgesia and secondly, that after breathing the mixture for a short time, the mother and the baby were likely to become hypoxic, a point recently confirmed by Cole and Nainby-Luxmoorez.Seward3 suggested that more adequate analgesia without hypoxia might be obtained by giving a higher proportion of nitrous-oxide mixed with oxygen instead of air. After finding that a mixture of 85 % nitrous-oxide and 15 % oxygen caused half the mothers inhaling the mixture to become unconscious and partially aniesthetised, he showed that a mixture of 75 % nitrous-oxide with 25 % oxygen gave effective analgesia without loss of consciousness and without affecting the cooperation of the mother. Recently, interest in nitrous-oxide/oxygen analgesia has been revived by the commercial production of machines which are adjustable to give reasonably accurate nitrous-oxide/ oxygen mixtures. The 'Lucy Baldwin' machine, now available, affords the opportunity of assessing the value of self-administered nitrous-oxide/oxygen in labour.This communication reports the result of a trial on over 500 mothers using this machine, with mixtures containing 50%, 60%, 70%,
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.