Davies J M, Willis B A, Rosen M
Anaesthesia. 1978 Jun;33(6):545-7. doi: 10.1111/j.1365-2044.1978.tb08395.x.
In a pilot study in six mothers using 50% nitrous oxide and 50% oxygen (Entonox) as an intermittent self-administered analgesic during labour, a significant reduction in the mean times to attain specified end-tidal nitrous oxide concentrations was obtained by a continuous nasal supplement of Entonox. The method proved acceptable in this small number of patients and there were no demonstrable effects upon fetal heart rate.
